Documentation for the 2014 Update of the

United States National Seismic Hazard Maps

Mark D. Petersen, Morgan P. Moschetti, Peter M. Powers, Charles S. Mueller, Kathleen M. Haller, 

Arthur D. Frankel, Yuehua Zeng, Sanaz Rezaeian, Stephen C. Harmsen, Oliver S. Boyd, Ned Field, 

Rui Chen, Kenneth S. Rukstales, Nico Luco, Russell L. Wheeler, Robert A. Williams, and 

Anna H. Olsen

Open-File Report 2014–1091

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014 

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Suggested citation:

Petersen, M.D., Moschetti, M.P., Powers, P.M., Mueller, C.S., Haller, K.M., Frankel, A.D., Zeng, Yuehua, 

Rezaeian, Sanaz, Harmsen, S.C., Boyd, O.S., Field, Ned, Chen, Rui, Rukstales, K.S., Luco, Nico, Wheeler, R.L.,

Williams, R.A., and Olsen, A.H., 2014, Documentation for the 2014 update of the United States national seismic 

hazard maps: U.S. Geological Survey Open-File Report 2014–1091, 243 p., http://dx.doi.org/10.3 33/ofr20141091. 

ISSN: 2331-1258 (online)

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1
iii

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

Central and Eastern United States Earthquake Source Models .................................................................................. 18

Seismicity-Based Background Source Model........................................................................................................... 18

Earthquake Catalog for the Central and Eastern United States ........................................................................... 19

Seismotectonic Zones .......................................................................................................................................... 23

Calculating a-Grids............................................................................................................................................... 25

Maximum Magnitude for Background Seismicity.................................................................................................. 28

Fault-Based Source Models in the Central and Eastern United States .................................................................... 31

New Madrid Seismic Zone.................................................................................................................................... 32

Faults Near the New Madrid Seismic Zone .......................................................................................................... 36

Charleston Seismic Zone ..................................................................................................................................... 42

Meers Fault .......................................................................................................................................................... 45

Cheraw Fault........................................................................................................................................................ 46

Charlevoix Seismic Zone...................................................................................................................................... 48

Western United States Earthquake Source Models..................................................................................................... 50

Seismicity-Based Background Source Model........................................................................................................... 50

Earthquake Catalog for the Western United States.............................................................................................. 51

Modeling Shallow Crustal Background Seismicity................................................................................................ 53

Maximum Magnitude for Shallow Crustal Background Seismicity ........................................................................ 55

Modeling Deep or Benioff-Zone Seismicity........................................................................................................... 55

Fault-Based Source Model in the Western United States ........................................................................................ 61

Fault-Source Geometry ........................................................................................................................................ 64

Maximum Magnitude for Fault Sources................................................................................................................ 74

Constraining Frequency of Future Events ............................................................................................................ 74

Update of Geologic-Based Fault-Source Parameters........................................................................................... 75

Combined Geodetic- and Geologic-Based Slip-Rate Models................................................................................... 80

Data...................................................................................................................................................................... 81

Combined Geologic and Geodetic Models ........................................................................................................... 83

Implementation of Combined-Inversion Models in Hazard Maps.......................................................................... 87

Hazard Results..................................................................................................................................................... 88

Earthquake Recurrence and Down-Dip Edge of Rupture for the Cascadia Subduction Zone.................................. 91

Logic Trees for Cascadia Subduction Zone Recurrence ...................................................................................... 91

Logic Tree for Down-Dip Edge of Rupture............................................................................................................ 98

Magnitude-Frequency Distribution and Along Strike Earthquake Rate................................................................. 99

California................................................................................................................................................................ 103

Ground Motion Models .............................................................................................................................................. 108

Ground Motion Model Selection Criteria ................................................................................................................ 109

Central and Eastern United States......................................................................................................................... 110

2008 Models and Weights.................................................................................................................................. 111

2014 Models—Major Changes Since 2008 ........................................................................................................ 111

Important Parameters for the Central and Eastern United States Ground Motion Models ................................. 114

Applicability Limits of Models (Magnitude, Distance, Soil Condition).................................................................. 118

Weights .............................................................................................................................................................. 119
iv

Central and Eastern United States Difference and Ratio Maps—Comparing 2014 and 2008 Ground Motion 

Models................................................................................................................................................................ 124

Western United States ........................................................................................................................................... 131

2008 Models and Weights.................................................................................................................................. 131

2014 Model Updates .......................................................................................................................................... 131

Additional Epistemic Uncertainty ........................................................................................................................ 145

Western United States Difference and Ratio Maps—Comparing 2014 and 2008 Ground Motion Models ......... 146

Ground Motion Models for Subduction Interface Earthquakes ........................................................................... 159

Ground Motion Models for Subduction Intraslab Earthquakes (Deep Seismicity)............................................... 169

Results....................................................................................................................................................................... 178

Central and Eastern United States......................................................................................................................... 178

Western United States ........................................................................................................................................... 184

Intermountain West and Pacific Northwest Shallow Crustal Earthquake Hazard ............................................... 185

Cascadia Subduction Interface Contributions..................................................................................................... 193

Cascadia Deep Intraslab Contributions .............................................................................................................. 200

California Shallow Crustal Earthquake Hazard................................................................................................... 206

Changes Caused by UCERF3............................................................................................................................ 219

Conclusions and Future Directions............................................................................................................................ 227

Acknowledgments...................................................................................................................................................... 228

References Cited....................................................................................................................................................... 228

Figures

Figure 1. Maps showing peak ground acceleration for 2-percent probability of exceedance in 50 years and 

VS30 site condition of 760 meters per second............................................................................................................. 6

Figure 2. Maps showing 5-hertz (0.2-second) spectral acceleration for 2-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second ................................................................................... 7

Figure 3. Maps showing 1-hertz (1-second) spectral acceleration for 2-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second ................................................................................... 8

Figure 4. Maps showing peak ground acceleration for 10-percent probability of exceedance in 50 years and 

VS30 site condition of 760 meters per second............................................................................................................. 9

Figure 5. Maps showing 5-hertz (0.2-second) spectral acceleration for 10-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second. .............................................................................. 10

Figure 6. Maps showing 1-hertz (1-second) spectral acceleration for 10-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second ................................................................................. 11

Figure 7. Maps comparing change in peak ground acceleration for 2-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second ................................................................................. 12

Figure 8. Maps comparing change in 5-hertz (0.2-second) spectral acceleration for 2-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second ............................................................. 13

Figure 9. Maps comparing change in 1-hertz (1-second) spectral acceleration for 2-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second ............................................................. 14

Figure 10. Maps comparing change in peak ground acceleration for 10-percent probability of exceedance 

in 50 years and VS30 site condition of 760 meters per second ................................................................................. 15

Figure 11. Maps comparing change in 5-hertz (0.2-second) spectral acceleration for 10-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second ............................................................. 16

Figure 12. Maps comparing change in 1-hertz (1-second) spectral acceleration for 10-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second ............................................................. 17
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Figure 13. Logic tree for the seismicity-based background source model in the Central and 

Eastern United States.............................................................................................................................................. 19

Figure 14. Map showing declustered catalog for the Central and Eastern United States including Mw2.5 

and greater earthquakes occurring since 1700........................................................................................................ 21

Figure 15. Map showing areas of potentially induced seismicity in the Central and Eastern United States. ....... 23

Figure 16. Alternative seismotectonic zonation models used to assign floor a-values and Mmax ...................... 24

Figure 17. Map showing completeness zones for the Central and Eastern United States .................................. 26

Figure 18. Maps showing cumulative seismicity-rate grids from alternative smoothing methods........................ 27

Figure 19. Distribution of large earthquake magnitudes for extended margins in stable continental regions ...... 30

Figure 20. Distribution of large earthquake magnitudes for cratons in stable continental regions....................... 31

Figure 21. Location of fault sources in the Central and Eastern United States ................................................... 32

Figure 22. Representations of fault sources near the New Madrid seismic zone................................................ 33

Figure 23. Logic tree for the New Madrid seismic zone ...................................................................................... 34

Figure 24. Logic tree for the Wabash Valley ....................................................................................................... 37

Figure 25. Logic tree for the Commerce Geophysical Lineament ....................................................................... 38

Figure 26. Logic tree for the north source of the Eastern Rift.............................................................................. 39

Figure 27. Logic tree for the south source of the Eastern Rift ............................................................................. 40

Figure 28. Logic tree for the Marianna ................................................................................................................ 41

Figure 29. Summed a-grid rates for Charleston sources..................................................................................... 43

Figure 30. Logic tree for the Charleston.............................................................................................................. 44

Figure 31. Logic tree for the Meers fault ............................................................................................................. 46

Figure 32. Logic tree for the Cheraw fault........................................................................................................... 47

Figure 33. Logic tree for the Charlevoix .............................................................................................................. 49

Figure 34. Logic tree for the seismicity-based background source model in the Western United States ............ 51

Figure 35. Map showing declustered catalog for the Western United States ...................................................... 52

Figure 36. Maps showing incremental seismicity-rate grids from alternative smoothing methods ...................... 54

Figure 37. Magnitude-frequency distribution of deep seismicity in the Puget Sound region ............................... 58

Figure 38. Distribution of deep seismicity beneath the Cascadia interface at lat 47.3 ̊ N.................................... 60

Figure 39. Distribution of deep seismicity beneath the Cascadia interface in northern California ....................... 61

Figure 40. Logic tree for crustal fault sources in the Intermountain West and Pacific Northwest ........................ 63

Figure 41. Distribution of assigned full-source rupture magnitude for crustal fault sources in the Intermountain 

West and Pacific Northwest by sense of slip ........................................................................................................... 64

Figure 42. Map of Quaternary faults near Salt Lake City, Utah........................................................................... 66

Figure 43. Sketch of spatial relations between the Wasatch and the West Valley fault zones............................ 67

Figure 44. Results of hazard analysis for Roten and others (2011) geometry of the Salt Lake City 

segment of the Wasatch .......................................................................................................................................... 69

Figure 45. Results of hazard analysis for clustered-event model of the Salt Lake City segment 

of the Wasatch......................................................................................................................................................... 71

Figure 46. Plots of probabilistic ground motions for 5-hertz and 1-hertz spectral acceleration ........................... 72

Figure 47. Results of hazard analysis for model 3 of the Salt Lake City segment............................................... 73

Figure 48. Map of crustal fault sources in the Intermountain West and Pacific ................................................... 75

Figure 49. Generic logic tree for Wasatch fault source ....................................................................................... 79

Figure 50. Strain-rate maps of the Western United States based on global positioning system dataset............. 82

Figure 51. Comparison of assigned slip rate in modified 2008 model and fault-based and block models........... 83

Figure 52. Plot of assigned slip rates in the modified 2008 source model and geodetic-based block models..... 84

Figure 53. Map showing location of the zones implemented in the Bird (2013) model....................................... 86

Figure 54. Comparison of cumulative on-fault slip across the Intermountain West and Pacific Northwest ......... 87
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Figure 55. Maps showing difference in 1-hertz (1-second) and 5-hertz (0.2-second) spectral acceleration 

at 2-percent probability of exceedance in 50 years.................................................................................................. 89

Figure 56. Maps showing ratios of 1-hertz (1-second) and 5-hertz (0.2-second) spectral acceleration at 

2-percent probability of exceedance in 50 years...................................................................................................... 90

Figure 57. Distribution of great Cascadia earthquakes and recurrence times..................................................... 92

Figure 58. Logic trees for recurrence of great Cascadia subduction zone earthquakes...................................... 93

Figure 59. Maps of peak ground acceleration for Cascadia subduction zone rupture rates................................ 95

Figure 60. Maps of peak ground acceleration for alternative Cascadia subduction zone models ....................... 96

Figure 61. Alternative locations of down-dip edge of Cascadia rupture .............................................................. 98

Figure 62. Logic tree for down-dip edge of rupture zones of great Cascadia earthquakes ................................. 99

Figure 63. Cascadia subduction zone summary logic tree................................................................................ 100

Figure 64. Total cumulative and binned incremental magnitude-frequency distributions for the Cascadia 

subduction zone..................................................................................................................................................... 101

Figure 65. Variation of earthquake rates for each input model along the Cascadia subduction zone ............... 103

Figure 66. Map of earthquake participation rate for the Uniform California Earthquake Rupture Forecast, 

ver. 3.3 model........................................................................................................................................................ 104

Figure 67. The grand inversion system of equations used in solving for the long-term rate of 

fault-based ruptures. .............................................................................................................................................. 105

Figure 68. Logic tree for the Uniform California Earthquake Rupture Forecast, ver. 3.3 (UCERF3) ................. 107

Figure 69. Comparison of Central and Eastern United States median ground motion models by model type .. 113

Figure 70. Comparison of Central and Eastern United States median ground motion models by category ...... 116

Figure 71. Logic trees for ground motion models in the Central and Eastern United States ............................. 121

Figure 72. Comparison of median spectral acceleration for 2008 and 2014 USGS, and 2013 EPRI ground 

motion models ....................................................................................................................................................... 122

Figure 73. Comparison of combined Central and Eastern United States ground motion models versus 

distance for an earthquake with moment magnitude of 7 ...................................................................................... 123

Figure 74. Maps showing difference in peak ground acceleration from individual ground motion models 

in the Central and Eastern United States............................................................................................................... 125

Figure 75. Maps showing ratio of peak ground acceleration from individual ground motion models in the 

Central and Eastern United States ........................................................................................................................ 126

Figure 76. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground 

motion models in the Central and Eastern United States....................................................................................... 127

Figure 77. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual ground 

motion models in the Central and Eastern United States....................................................................................... 128

Figure 78. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual ground 

motion models in the Central and Eastern United States....................................................................................... 129

Figure 79. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground motion 

models in the Central and Eastern United States .................................................................................................. 130

Figure 80. Magnitude-distance distribution of records in phase 2 of the Next Generation Attenuation project 

(NGA-West2) database ......................................................................................................................................... 132

Figure 81. Comparison of median ground motion versus distance for a strike slip fault.................................... 134

Figure 82. Comparison of median ground motion versus distance on the hanging wall of a normal fault ......... 135

Figure 83. Comparison of median ground motion versus distance on the hanging wall of a reverse fault ........ 136

Figure 84. Standard deviation (sigma) versus magnitude for Central and Eastern United States 

ground motion models ........................................................................................................................................... 137

Figure 85. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration 

versus distance for a strike slip fault in the Western United States........................................................................ 138
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Figure 86. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) 

spectral acceleration versus distance for a strike slip fault in the Western United States...................................... 138

Figure 87. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) 

spectral acceleration versus distance for a strike slip fault in the Western United States...................................... 139

Figure 88. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration 

versus distance for the hanging wall of a normal fault in the Western United States............................................. 139

Figure 89. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) 

spectral acceleration versus distance for the hanging wall of a normal fault in the Western United States ........... 140

Figure 90. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the hanging wall of a normal fault in the Western United States......................... 140

Figure 91. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration 

versus distance for the footwall of a normal fault in the Western United States..................................................... 141

Figure 92. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) 

spectral acceleration versus distance for the footwall of a normal fault in the Western United States................... 141

Figure 93. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) 

spectral acceleration versus distance for the footwall of a normal fault in the Western United States................... 142

Figure 94. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration 

versus distance for the hanging wall of a reverse fault in the Western United States............................................ 142

Figure 95. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral 

acceleration versus distance for the hanging wall of a reverse fault in the Western United States........................ 143

Figure 96. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the hanging wall of a reverse fault in the Western United States........................ 143

Figure 97. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration 

versus distance for the footwall of a reverse fault in the Western United States.................................................... 144

Figure 98. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) 

spectral acceleration versus distance for the footwall of a reverse fault in the Western United States.................. 144

Figure 99. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the footwall of a reverse fault in the Western United States ............................... 145

Figure 100. Maps showing difference in peak ground acceleration from individual ground motion models 

in the Western United States ................................................................................................................................. 147

Figure 101. Maps showing ratio of peak ground acceleration from individual ground motion models in the 

Western United States........................................................................................................................................... 148

Figure 102. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground 

motion models in the Western United States......................................................................................................... 149

Figure 103. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual ground motion 

models in the Western United States..................................................................................................................... 150

Figure 104. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual 

ground motion models in the Western United States............................................................................................. 151

Figure 105. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground motion 

models in the Western United States..................................................................................................................... 152

Figure 106. Maps showing difference in peak ground acceleration from individual ground motion 

models in California ............................................................................................................................................... 154

Figure 107. Maps showing ratio of peak ground acceleration from individual ground motion 

models in California ............................................................................................................................................... 155

Figure 108. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground 

motion models in California.................................................................................................................................... 156
viii

Figure 109. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual 

ground motion models in California ....................................................................................................................... 157

Figure 110. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual 

ground motion models in California ....................................................................................................................... 158

Figure 111. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground 

motion models in California.................................................................................................................................... 159

Figure 112. Plot of subduction-interface ground motion models versus period for an earthquake with 

moment magnitude of 9 at a distance of 110 kilometers........................................................................................ 161

Figure 113. Plot of median 0.2-second spectral acceleration for subduction-interface ground motion 

models versus distance for an earthquake with moment magnitude of 9............................................................... 161

Figure 114. Plot of median 1-second spectral acceleration for subduction-interface ground motion 

models versus distance for an earthquake with moment magnitude of 9............................................................... 162

Figure 115. Maps showing difference in peak ground acceleration from individual subduction-interface 

ground motion models ........................................................................................................................................... 163

Figure 116. Maps showing ratios of peak ground acceleration from individual subduction-interface 

ground motion models ........................................................................................................................................... 164

Figure 117. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual 

subduction-interface ground motion models .......................................................................................................... 165

Figure 118. Maps showing ratios of 0.2-second (5-hertz) spectral acceleration from individual subductioninterface ground motion models............................................................................................................................. 166

Figure 119. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual 

subduction-interface ground motion models .......................................................................................................... 167

Figure 120. Maps showing ratios of 1-second (1-hertz) spectral acceleration from individual subductioninterface ground motion models............................................................................................................................. 168

Figure 121. Plots of subduction intraslab (deep) ground motion models versus.............................................. 170

Figure 122. Maps showing difference in peak ground acceleration from individual deep-intraslab 

ground motion models ........................................................................................................................................... 172

Figure 123. Maps showing ratios of peak ground acceleration from individual deep-intraslab 

ground motion models ........................................................................................................................................... 173

Figure 124. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual deepintraslab ground motion ......................................................................................................................................... 174

Figure 125. Maps showing ratios of 0.2-second (5-hertz) spectral acceleration from individual 

deep-intraslab ground motion models.................................................................................................................... 175

Figure 126. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual 

deep-intraslab ground motion models.................................................................................................................... 176

Figure 127. Maps showing ratios of 1-second (1-hertz) spectral acceleration from individual deep-intraslab 

ground motion models ........................................................................................................................................... 177

Figure 128. Maps showing difference in peak ground acceleration in the Central and 

Eastern United States............................................................................................................................................ 179

Figure 129. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in the Central 

and Eastern United States..................................................................................................................................... 180

Figure 130. Maps showing difference in 1-hertz (1-second) spectral acceleration in the Central 

and Eastern United States..................................................................................................................................... 181

Figure 131. Maps showing ratios of peak ground acceleration in the Central and Eastern United States....... 182

Figure 132. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration in the Central 

and Eastern United States..................................................................................................................................... 183
ix

Figure 133. Maps showing ratios of 1-hertz (1-second) spectral acceleration in the Central and 

Eastern United States............................................................................................................................................ 184

Figure 134. Maps showing difference in peak ground acceleration in the Western United States................... 186

Figure 135. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in the 

Western United States........................................................................................................................................... 187

Figure 136. Maps showing difference in 1-hertz (1-second) spectral acceleration in the 

Western United States........................................................................................................................................... 188

Figure 137. Maps showing ratios of peak ground acceleration in the Western United States ......................... 189

Figure 138. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration in the 

Western United States........................................................................................................................................... 190

Figure 139. Maps showing ratios of 1-hertz (1-second) spectral acceleration in the Western United States... 191

Figure 140. Maps showing difference in peak ground acceleration for the Cascadia subduction zone........... 194

Figure 141. Maps showing ratios of peak ground acceleration for the Cascadia subduction zone.................. 195

Figure 142. Maps showing difference in 5-hertz (0.2-second) spectral acceleration for the Cascadia 

subduction zone..................................................................................................................................................... 196

Figure 143. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration for the Cascadia 

subduction zone..................................................................................................................................................... 197

Figure 144. Maps showing difference in 1-hertz (1-second) spectral acceleration for the Cascadia 

subduction zone..................................................................................................................................................... 198

Figure 145. Maps showing ratios of 1-hertz (1-second) spectral acceleration for the Cascadia 

subduction zone..................................................................................................................................................... 199

Figure 146. Maps showing difference in peak ground acceleration for deep intraslab seismic sources .......... 200

Figure 147. Maps showing ratios of peak ground acceleration for deep intraslab seismic sources ................. 201

Figure 148. Maps showing difference in 5-hertz (0.2-second) spectral acceleration for deep 

intraslab seismic sources....................................................................................................................................... 202

Figure 149. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration for deep 

intraslab seismic sources....................................................................................................................................... 203

Figure 150. Maps showing difference in 1-hertz (1-second) spectral acceleration for deep 

intraslab seismic sources....................................................................................................................................... 204

Figure 151. Maps showing ratios of 1-hertz (1-second) spectral acceleration for deep intraslab 

seismic sources ..................................................................................................................................................... 205

Figure 152. Maps showing changes in peak ground acceleration in California ............................................... 208

Figure 153. Maps showing changes in 5-hertz (0.2-second) spectral acceleration in California...................... 209

Figure 154. Maps showing changes in 1-hertz (1-second) spectral acceleration in California......................... 210

Figure 155. Maps showing changes in peak ground acceleration in California ............................................... 212

Figure 156. Maps showing changes in 5-hertz (0.2-second) spectral acceleration in California...................... 213

Figure 157. Maps showing changes in 1-hertz (1-second) spectral acceleration in California......................... 214

Figure 158. Maps showing difference in peak ground acceleration in California ............................................. 216

Figure 159. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in California ................... 217

Figure 160. Maps showing difference in 1-hertz (1-second) spectral acceleration in California ...................... 218

Figure 161. Maps showing ratios of peak ground acceleration for California .................................................. 220

Figure 162. Maps showing ratios of peak ground acceleration in the San Francisco Bay area....................... 224

Figure 163. Maps showing ratios of peak ground acceleration in the Los Angeles area ................................. 225
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Tables

Table 1. Contributions to the declustered catalog in the Central and Eastern United States ............................... 21

Table 2. Year of catalog completeness in the Central and Eastern United States ............................................... 26

Table 3. Magnitude estimates for the 1811–1812 New Madrid earthquakes. ...................................................... 35

Table 4. Seismic zones in the Charleston area.................................................................................................... 42

Table 5. Magnitude distribution for Charleston source......................................................................................... 44

Table 6. Contributions to the declustered catalog in the Western United States.................................................. 53

Table 7. Global catalog of large deep earthquakes since 1975 ........................................................................... 56

Table 8. Benioff zone earthquake rates ............................................................................................................... 59

Table 9. Changes in Intermountain West and Pacific Northwest crustal fault-source model parameters............. 76

Table 10. Comparison of assigned slip rate in modified 2008 model and combined-inversion models ................. 85

Table 11. Event rates for Cascadia subduction zone........................................................................................... 102

Table 12. Central and Eastern United States 2008 ground motion models and weights ..................................... 111

Table 13. Central and Eastern United States 2014 ground motion models and weights ..................................... 112

Table 14. Frequency-dependent factors to convert NEHRP site class A to NEHRP site class BC...................... 118

Table 15. Western United States 2008 ground motion models and weights........................................................ 131

Table 16. Western United States 2014 ground motion models and weights........................................................ 133

Table 17. Additional epistemic uncertainty in the 2014 hazard maps .................................................................. 146

Table 18. Subduction interface 2008 and 2014 ground motion models and weights........................................... 160

Table 19. Pacific Northwest intraslab 2008 and 2014 ground motion models and weights ................................. 169

Table 20. Intermountain West and Pacific Northwest fault sources that contribute to ground 

motion increases.................................................................................................................................................... 192

Table 21. Intermountain West and Pacific Northwest fault sources that contribute to ground 

motion decreases .................................................................................................................................................. 193

Table 22. California fault sources that contribute to ground motion increases..................................................... 221

Table 23. California fault sources that contribute to ground motion decreases.................................................... 222

Table 24. San Francisco Bay area ground motion changes ................................................................................ 226

Table 25. Los Angeles area ground motion changes........................................................................................... 226

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

mile, nautical (nmi) 1.852 kilometer (km)

yard (yd) 0.9144 meter (m)
xi

Initialisms and Abbreviations

BRPEWG Basin and Range Province Earthquake Working Group

CEUS Central and Eastern United States

CEUS–SSCn Central and Eastern United States Seismic Source Characterization for nuclear facilities

CSZ Cascadia subduction zone

EPRI Electric Power Research Institute

g Gravitational acceleration constant equal to 9.81 meters per second squared

GMM Ground Motion Model

Subduction interface and deep intraslab models: 

AB03—Atkinson and Boore (2003)

AM09—Atkinson and Macias (2009)

BC Hydro—Addo and others (2012) 

ZHAO—Zhao and others (2006) 

Shallow crustal ground motion models for tectonically active regions: 

ASK13 Abrahamson and others (2013, 2014) 

CB08 Campbell and Bozorgnia (2008) 

CB13 Campbell and Bozorgnia (2013, 2014) 

CY08 Chiou and Youngs (2008) 

CY13 Chiou and Youngs (2013, 2014) 

I13 Idriss (2013, 2014)

Shallow crustal ground motion models for stable continental regions: 

A08' Atkinson (2008, 2011) 

AB06 Atkinson and Boore (2006) 

AB06' Atkinson and Boore (2011) 

C03 Campbell (2003) 

F96 Frankel and others (1996) 

S02 Silva and others (2002) 

P11 Pezeshk and others (2011) 

T02 Toro and others (1997, 2002) 

TP05 Tavakoli and Pezeshk (2005) 

S01 Somerville and others (2001)

GPS Global Positioning System, measurements used as geodetic data in this report

GridSrc Background gridded sources

GS Geometric spreading

HAZUS Standardized software program that estimates losses from potential earthquakes

IMW Intermountain West

Kappa Site attenuation of high frequencies

MFD Magnitude frequency distribution

Mmax Maximum magnitude considered in a region—typically limits the earthquake magnitude-frequency 

distribution applied in the seismic source models

Mw Moment magnitude, also M 

mblg Body-wave magnitude based on guided surface waves

NEHRP National Earthquake Hazards Reduction Program

NGA Next Generation Attenuation models, ground motion models

NSHMP National Seismic Hazard Mapping Project

PDF Probability Density Function

PEER Pacific Earthquake Engineering Research center

PNW Pacific Northwest

Q Frequency dependent attenuation term used in ground motion models

RLME Repeated large magnitude earthquake

Rx and Rjb Distances used in ground motion models

R-1 or R-1.3 Geometric spreading parameters used in ground motion models

SCRs Stable continental regions 

SA Spectral acceleration (horizontal) 5% damping
xii

Ground motion intensity measures:

PGA Peak ground acceleration

SA Spectral acceleration 5% damping at 5 hertz (0.2 second) and 1 hertz (1.0 second)

UCERF Uniform California Earthquake Rupture Forecast Model (with 2 or 3 to denote version)

USGS U.S. Geological Survey

UTC Coordinated Universal Time

VS30 Shear wave velocity (time-averaged) in the upper 30 meters—used to define National Earthquake Hazards 

Reduction Program (NEHRP) A,B,C,D soil types, boundary between soil B and C and is defined as 

VS30 = 760 meters/second, which is uniformly applied in maps in this report

WGCEP Working Group on California Earthquake Probabilities

WUS Western United States
1

Documentation for the 2014 Update of the

United States National Seismic Hazard Maps

By Mark D. Petersen, Morgan P. Moschetti, Peter M. Powers, Charles S. Mueller, Kathleen M. Haller, 

Arthur D. Frankel, Yuehua Zeng, Sanaz Rezaeian, Stephen C. Harmsen, Oliver S. Boyd, Ned Field, Rui Chen, 

Kenneth S. Rukstales, Nico Luco, Russell L. Wheeler, Robert A. Williams, and Anna H. Olsen

Abstract

The national seismic hazard maps for the conterminous United States have been updated to 

account for new methods, models, and data that have been obtained since the 2008 maps were released 

(Petersen and others, 2008). The input models are improved from those implemented in 2008 by using 

new ground motion models that have incorporated about twice as many earthquake strong ground 

shaking data and by incorporating many additional scientific studies that indicate broader ranges of 

earthquake source and ground motion models. These time-independent maps are shown for 2-percent

and 10-percent probability of exceedance in 50 years for peak horizontal ground acceleration as well as

5-hertz and 1-hertz spectral accelerations with 5-percent damping on a uniform firm rock site condition 

(760 meters per second shear wave velocity in the upper 30 m, VS30). In this report, the 2014 updated 

maps are compared with the 2008 version of the maps and indicate changes of plus or minus 20 percent

over wide areas, with larger changes locally, caused by the modifications to the seismic source and 

ground motion inputs. 

Introduction

During the past several decades, the U.S. Geological Survey (USGS) national seismic hazard 

maps (NSHM, Algermissen and Perkins, 1976; Frankel and others, 1996, 2002; Petersen and others, 

2008; Petersen and others, 2012) have provided the basis for many public and private policies regarding 

earthquakes, including seismic-design regulations for buildings, bridges, highways, railroads, and other 

structures. The maps are used in building codes (for example, Building Seismic Safety Council, 2009) 

to identify areas where built structures are likely to experience large seismic loads and to allow for 

prudent allocation of resources by reducing waste resulting from over-built structures. In addition, 

structures can be built to a standard that will enable critical activities and resources (such as availability 

of energy resources, accessibility of transportation corridors, and sustainability of medical care) to 

continue with less disruption following an earthquake. Seismic hazard assessments also affect insurance 

rate structures (for example, those based on California Earthquake Authority models; Working Group 

on California Earthquake Probabilities, 2013), governmental disaster management and mitigation 

strategies (such as those based on HAZUS, http://www.fema.gov/hazus/), planning and seismic safety 

applications (for example, the California Seismic Hazards Mapping Act, Nuclear Regulatory 

Commission), and many site-specific engineering analyses by industries and governments (such as those 

applied by the U.S. Department of Defense and the U.S. Bureau of Reclamation). 
2

The USGS updates these time-independent hazard maps to produce the latest science-based 

information on future earthquake ground motions. The hazard models described in this report 

incorporate more than 100 years of global earthquake observations, widely accepted seismology-based 

principles, and a long history of scientific analyses in the science and engineering communities. These 

communities are expanding the geological, geophysical, geodetic, and engineering observational base 

and, in the process, improving our understanding of seismic hazard. Therefore, the National Seismic 

Hazard Mapping Project (NSHMP) maps are updated regularly as new data, methods, and models are 

acquired and analyzed.

The results of this assessment will be considered by structural design communities, including the 

Building Seismic Safety Committee, the American Society of Civil Engineers, and the International 

Code Council, for inclusion in future building codes that generally are adopted by most states and local 

jurisdictions across the United States. In addition, they are applied for risk assessments, and for other 

public policy applications. Because these maps affect public safety and economic vitality, the USGS 

national seismic hazard maps include only earthquake science that is accepted by the science 

community. The maps represent the NSHMP’s assessment of best-available data, models, and methods 

for seismic hazard assessment at the time of this update (Independent Expert Panel, 2011). The USGS 

relies on the science and engineering communities for input to this process. 

To acquire new hazard information, the NSHMP convened workshops and meetings across the 

country to identify models available for consideration, and worked in partnerships with other 

organizations to develop and evaluate the available science and its impact on the seismic hazard. The 

NSHMP held regional workshops in 2012 and 2013 for the Central and Eastern United States (CEUS) 

in Memphis, Tenn.; the Pacific Northwest in Seattle, Wash.; the Intermountain West in Salt Lake City, 

Utah; and in Newark and Menlo Park, California (Calif.). In addition, the NSHMP held topical 

workshops to discuss Cascadia subduction processes (in Eugene and Corvallis, Oregon [Oreg.]), 

geodetic models and their use in the USGS NSHMP maps (in Newark and Menlo Park, Calif., and Hood 

River, Oreg.), Basin and Range hazard (in Salt Lake City, Utah, and Reno, Nev.), and earthquake 

ground-shaking models (in Berkeley, Calif.). Several hundred earthquake scientists and engineers 

participated in these workshops. Many presentations from these workshops are available at 

http://earthquake.usgs.gov/hazmaps/. 

Several organizations provided essential information for this update. The Pacific Earthquake 

Engineering Research Center (PEER) provided new ground motion equations and data across the United 

States, the Central and Eastern United States Seismic Source Characterization for Nuclear Facilities 

(CEUS–SSCn) project provided a new seismic source model, Earthquake Power Research Institute 

(EPRI) provided ground motion weighting information, BC Hydro project (Addo and others, 2012) 

contributed a new subduction zone ground-shaking model, Working Group on California Earthquake 

Probabilities (2013) contributed a new source model for California (UCERF3), and several working 

groups met to discuss other hazard issues for this map update. The USGS external-grants investigators 

provided additional data and models for these maps, as well as new ways to test the results. State and 

Federal agencies as well as participants from academia and industry provided new models and data in 

the published literature. 

The NSHMP steering committee composed of nine seismic hazard experts from academia, industry, 

and government, was assembled to guide the review of the input models and provide advice on the best 

methodologies, data, and input parameter values. This committee met in two separate review periods 

during May (before the release of the draft maps for public review) and August 2013 (following the 

public review and before finalizing the 2014 USGS NSHMP maps). This committee provided critical 
3

advice on developing the final maps and insights on how the model should be revised for this version 

and future updates. 

Inputs to the USGS NSHMP maps are based on time-independent scientific estimates of 

locations and sizes of future earthquakes. These estimates do not consider the time since the last 

earthquake. We model rates of earthquakes on known faults or as seismicity-based background 

earthquakes, which account for unknown faults or the incomplete fault inventory. We assume that 

future, damaging earthquakes generally will occur near past earthquakes or on known faults with 

evidence of past surface rupture; therefore, we model fault ruptures for the hazard assessment to account 

for large earthquakes on such structures. However, we also know that there will be future earthquakes 

that are not associated with mapped Quaternary faults and these earthquakes are modeled using 

historical seismicity (Frankel, 1995) and physics based principles. We model the magnitude-frequency 

distribution for earthquakes with a preferred maximum size (characteristic earthquake model) or with a 

truncated exponential recurrence based on a truncated Gutenberg and Richter (1944) magnitudefrequency distribution. 

In this update, we include many new earthquake sources and ground motion models that are

based on the abundant new data and studies that have been generated since 2008. The NSHMP 

developed some of these models, external organizations (listed below) developed others in coordination 

with the NSHMP for use in this update of the maps, and the NSHMP adopted or adapted other models 

originally developed by external organizations for applications other than the NSHMP. The following 

bullets summarize major changes from the 2008 to the 2014 update of the USGS NSHMP maps.

The NSHMP revised the models for the Central and Eastern United States in the following ways:

• Developed a moment magnitude-based earthquake catalog through 2012, replacing the 2008 body 

wave magnitude that is based on guided surface waves (mblg) based catalog;

• Updated earthquake catalog completeness estimates, catalog of statistical parameters, treatment of 

nontectonic seismicity, and treatment of magnitude uncertainty; 

• Updated the distribution for maximum magnitude (Mmax) for background earthquakes based on a 

new analysis of global earthquakes in stable continental regions; 

• Updated the zonation for Mmax, keeping the two-zone model that distinguishes craton and margin 

zones used in previous maps, and adding a new four-zone model based on the Central and Eastern 

United States seismic source characterization for nuclear facilities project (CEUS–SSCn, 2012) 

delineating the craton, Paleozoic margin, Mesozoic margin, and Gulf Coast; 

• Updated the smoothing algorithms for background seismicity, keeping the previous fixed-length 

Gaussian smoothing model (Petersen and others, 2008), and adding a nearest-neighbor-type adaptive 

smoothing model; 

• Updated the New Madrid source model, including fault geometry, recurrence rates of large 

earthquakes, and alternative magnitudes from Mw6.6 to 8.0 (maintaining the average weighted 

magnitude at about Mw7.5); 

• Adapted seismic sources such as Charleston, Wabash, Charlevoix, Commerce lineament, East Rift 

Margin, and Marianna based on the CEUS–SSCn (2012) model; and 

• Updated the treatment of earthquakes that potentially are induced by underground fluid injection. 

For the Intermountain West and Pacific Northwest crustal sources we made the following changes: 

• Considered suggestions from the Basin and Range Province Earthquake Working Group on 

magnitude-frequency distributions for fault sources, smoothing parameters, comparison of historical 

and modeled seismicity rates, treatment of magnitude uncertainty, assessment of maximum 

magnitude, modeling of antithetic fault pairs, slip rate uncertainties, and dip uncertainty for normal 

faults (Lund, 2012);
4

• Updated the earthquake catalog and treatment of magnitude uncertainty in rate calculations;

• Incorporated dips for normal faults of 35 degrees (°), 50°, and 65° but applied the fault earthquake 

rate using only the 50° dip to the three alternatives; 

• Updated fault parameters for faults in Utah, based on new datasets and models supplied by the Utah 

Geological Survey and the Working Group on Utah Earthquake Probabilities (Lund, 2013), and 

other faults across this part of the country; 

• Introduced new combined geologic and geodetic combined-inversion models for assessing fault slip 

rates on fault sources (Petersen and others, 2013) to account for uncertainty in activity rates on 

faults; 

• Implemented new models for Cascadia earthquake-rupture geometries and rates based on onshore 

(paleotsunami) and offshore (turbidite) studies; 

• Updated the model for deep (intraslab) earthquakes along the coasts of Oregon and Washington, 

including a new depth distribution for intraslab earthquakes;

• Allowed for an Mmax up to Mw8.0 for crustal and intraslab earthquakes; and

• Added the Tacoma fault source and updated the South Whidbey Island fault source in Washington. 

For California sources we implemented new models: 

• The NSHMP worked in cooperation with the Southern California Earthquake Center and the State of 

California to develop a new seismic source model based on the Uniform California Earthquake 

Rupture Forecast, Version 3 (UCERF3, www.scec.org/ucerf/; Working Group on California 

Earthquake Probabilities, 2013), which include many more multi-segment ruptures than in previous 

versions of the maps (Frankel and others, 1996, 2002; Petersen and others, 2008). These models 

were developed over the past several years and involved a major update of the methodology for 

calculating earthquake recurrence;

For calculating hazard we revised the ground motion models in the following ways: 

• Included new earthquake ground motion models for active shallow crustal earthquakes and 

subduction zone-related interface and intraslab earthquakes; 

• Adjusted the additional epistemic uncertainty model to account for regional variability and data 

availability;

• Updated ground motion prediction equation weights using the Next Generation Attenuation (NGA) 

ground motion database, reevaluated model weights for the Central and Eastern United States in 

light of a preliminary Electric Power Research Institute (EPRI) ground motion study, and included 

newly published ground motion prediction equations for stable continental regions; 

• Incorporated new and evaluated older ground motion models: 5 equations for the applied for the 

Western United States (WUS), 9 for the CEUS, and 4 for the subduction interface and intraslab 

earthquakes; and

• Increased the maximum distance from 200 kilometers (km) to 300 km when calculating ground 

motion from WUS crustal sources. 

In this update of the hazard maps, the NSHMP accounts for broader aleatory variability (random 

variability in a given model) and epistemic uncertainty (uncertainty in which model is most correct) 

than in previous updates. Although the models include the types of earthquakes we would expect in the 

next 50 years, the seismic hazard models probably do not explicitly include all possible earthquakes. 

Extremely rare or low probability events that have not been captured in studies of the historical or 

geologic record may not be represented in this hazard assessment. For this reason, we evaluate the range 

of uncertainty to capture expected, and some unexpected, earthquakes that are consistent with global 

observations as well as earthquake physics and statistics. 
5

The USGS NSHMP maps depict time-independent earthquake ground-shaking exceedance 

levels at specified probabilities over a 50-year time period at several hundred thousand sites across the 

United States. The models only apply time-independent models and do not consider the time since the 

last earthquake in the calculations. The seismic hazard maps for this update and the 2008 maps are 

shown for peak horizontal ground acceleration, 5-hertz (0.2-second) and 1-hertz (1-second) spectral 

accelerations for a 2-percent and 10-percent probability of exceedance in 50 years on a uniform firmrock site condition (VS30=760 meters per second) in figures 1–6. Differences (2014 minus 2008 values 

at each site) and ratios (2014 divided by 2008 values at each site) are shown in figures 7–12. The 2014 

and 2008 USGS NSHMP maps generally have similar appearance; however, the new maps differ from 

the prior maps by plus or minus 20 percent over broad regions and can reach plus or minus 40 percent at 

some sites. 
6

Figure 1. Maps showing peak ground acceleration for 2-percent probability of exceedance in 50 years and VS30

site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps and B, 2014

version.
7

Figure 2. Maps showing 5-hertz (0.2-second) spectral acceleration for 2-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps 

and B, 2014 version.
8

Figure 3. Maps showing 1-hertz (1-second) spectral acceleration for 2-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps 

and B, 2014 version.
9

Figure 4. Maps showing peak ground acceleration for 10-percent probability of exceedance in 50 years and VS30

site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps and B, 2014 

version.
10

Figure 5. Maps showing 5-hertz (0.2-second) spectral acceleration for 10-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps 

and B, 2014 version of the maps.
11

Figure 6. Maps showing 1-hertz (1-second) spectral acceleration for 10-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, 2008 version of the national seismic hazard maps 

and B, 2014 version.
12

Figure 7. Maps comparing change in peak ground acceleration for 2-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 2008 versions of 

the national seismic hazard maps and B, ratio between the 2014 and 2008 versions.
13

Figure 8. Maps comparing change in 5-hertz (0.2-second) spectral acceleration for 2-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 

2008 versions of the national seismic hazard maps and B, ratio between the 2014 and 2008 versions. 
14

Figure 9. Maps comparing change in 1-hertz (1-second) spectral acceleration for 2-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 

2008 versions of the national seismic hazard maps and B, ratio between the 2014 and 2008 versions.
15

Figure 10. Maps comparing change in peak ground acceleration for 10-percent probability of exceedance in 50 

years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 2008 versions of 

the national seismic hazard maps and B, ratio between the 2014 and 2008 versions.
16

Figure 11. Maps comparing change in 5-hertz (0.2-second) spectral acceleration for 10-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 

2008 versions of the national seismic hazard maps and B, ratio between the 2014 and 2008 versions.
17

Figure 12. Maps comparing change in 1-hertz (1-second) spectral acceleration for 10-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second. A, Difference between the 2014 and 

2008 versions of the national seismic hazard maps and B, ratio between the 2014 and 2008 versions.
18

This report describes the changes shown in figures 1–12 and their impacts on hazard for Central 

and Eastern United States sources, Western United States sources (Intermountain West and Pacific 

Northwest crustal sources, Cascadia subduction zone, California sources), combined geologic and 

geodetic inversion sources, and ground motion models (including models for stable crustal, active 

shallow crustal, subduction interface, and subduction in-slab). The “Results” section of this report 

describes details of these differences and quantifies the contributions of the fault models, earthquake 

source models, and ground motion models. 

Central and Eastern United States Earthquake Source Models

We derive the probabilistic seismic hazard for the Central and Eastern United States (CEUS) 

from (1) an earthquake catalog, which records rates and patterns of past earthquakes; (2) geologic 

studies, which identify faults and their associated slip rates capable of generating earthquakes and 

liquefaction features caused by prehistoric earthquakes; and (3) ground motion models for stable 

continental regions (SCRs). This section describes updates of the USGS seismic hazard model (Petersen 

and others, 2008, 2012) for the seismicity-based background source model and the fault-based source 

zones. Ground motion models applied in the CEUS are discussed in a separate section. We discuss the 

impact of these new catalogs and seismic source models in the results section. 

The CEUS Seismic Source Characterization Project recently compiled and reanalyzed 

earthquake catalogs and Quaternary deformation studies in eastern North America to improve 

earthquake hazard assessments for nuclear power plants. This project, hereafter referred to as CEUS–

SSCn (the ‘n’ signifies that this seismic source characterization is intended for use in seismic hazard 

assessments for nuclear power plants), followed the Level-3 guidelines of the Senior Seismic Hazard 

Analysis Committee (Kammerer and Ake, 2012) to develop models that represent the center, body, and 

range of technically defensible interpretations of the available data, models, and methods. The intention 

of these models is to account for broader uncertainties and replace older seismic source models. The 

NSHMP considered the CEUS–SSCn models and adopted some of them in part or with modifications to 

define new source models and broader epistemic uncertainty in the 2014 update. 

Seismicity-Based Background Source Model

The NSHMP has used the seismicity-based background source model, with some variations, 

since 1996 (Frankel and others, 1996, 2002; Petersen and others, 2008). Sources derived from 

seismicity account for two types of earthquakes in the CEUS: seismicity that is distributed randomly 

across the region and large earthquakes that are not associated with identified faults. The seismicitybased background source model assumes that future large earthquakes are more likely to nucleate near 

previous earthquakes with moment magnitude (Mw) greater than or equal to (≥) 2.7. We generate a new 

Mw catalog to produce the seismicity-based background source model. Previous versions of the map 

applied an earthquake catalog based on body-wave magnitude (mblg, from crustal guided surface waves, 

Lg) greater than or equal to 3.0. This body-wave magnitude of 3.0 converts to an Mw of 2.7. The logic 

tree for combining seismic-hazard models is shown in figure 13. The logic tree includes an updated 

earthquake catalog, new tectonic and seismicity-based zonations, alternative smoothing algorithms, and 

nine published ground motion models.

For the hazard calculations, the source geometry associated with the ruptures in the seismicitybased background source model is a virtual fault centered on grid points, which sample latitude and 

longitude at 0.1-degree increments. Earthquakes from Mw4.7 to the maximum magnitude (Mmax) are 

considered, with rates obtained from the smoothed seismicity-based source model. Rupture on a vertical 
19

fault with area, A, are determined from the Somerville relation, A=10M-4.366 square kilometers (km2). The 

virtual fault width is the lesser of 20 km and square root of A divided by 1.618. In contrast to the 

CEUS–SSCn (2012), we do not model uncertainty in seismogenic width. Several alternative ground 

motion models (GMMs) are used to calculate probabilities of ground motion exceedance.

Figure 13. Logic tree for the seismicity-based background source model in the Central and Eastern United States. 

Assigned branch weights shown in parentheses.

Earthquake Catalog for the Central and Eastern United States

The NSHMP developed an earthquake catalog to estimate the rates of future earthquakes across 

the CEUS. A major change from the 2008 to the 2014 catalog is the transition from mblg to Mw. This 

change eliminates uncertain conversions between magnitude scales that formerly were used at several 

stages of the hazard computations. This change is also consistent with recent CEUS ground motion 

equations, which require moment magnitude estimates of earthquake size. 

We developed a uniform seismicity catalog for central and eastern North America through 2012, 

generally following the approach used by the CEUS–SSCn (2012). For each earthquake, the catalog lists 

fields for expected moment magnitude, E[Mw], hypocenter location, and origin time derived from a 

preferred source that is listed in a comment field. Each entry also lists an estimate of magnitude 

uncertainty and a counting factor (a function of the b value and the magnitude uncertainty), which is 

used to compute unbiased seismicity rates. 

We combined published catalogs and characterize them by the method used to assign Mw: 

• Catalogs from the Global CMT (Centroid Moment Tensor) project (Dziewonski and others, 

1981; Ekström and others, 2012), St Louis University (R. Herrmann, written commun., 2013), 

and table B-2 in CEUS–SSCn (2012) list earthquakes with moment magnitudes from inversions 

of long-period waveforms or surface-wave spectra (“observed” or “measured” Mw). We adjust 

magnitudes to E[Mw] and estimate the magnitude uncertainty following CEUS–SSCn (2012). 

• Atkinson (2004a, b), Boatwright (1994), and Macherides (2002) cataloged earthquakes with 

moment magnitudes from analyses of local or regional waveforms or spectra (“approximate” 

Mw). Table B-3 in CEUS–SSCn (2012) lists E[Mw] and magnitude uncertainty for these 

earthquakes, which we adopted without modification. 
20

• Johnston and others (1994), Bakun and others (2003), and Bakun and Hopper (2004a, b) 

cataloged significant historical earthquakes with moment magnitude and magnitude uncertainty 

derived from special studies of intensity data.

• The sources for most earthquakes are published catalogs: 

o National Center for Earthquake Engineering Research (NCEER) (Seeber and

Armbruster, 1991) 

o USGS Preliminary Determination of Epicenters (PDE) online catalog 

(neic.usgs.gov/neis/epic/epic_global.html, accessed April 2007 and January 2013) 

o Geological Survey of Canada (GSC) online catalog (2013) 

o Stover and Coffman (1993) 

o Stover and others (1984) 

o CEUS–SSCn (2012) 

Source catalogs in this group generally list traditional instrumental magnitudes, original intensity 

measures, or both. CEUS–SSCn (2012) developed new empirical conversion relations to Mw from many 

common magnitude and intensity scales, short-period surface-wave magnitude, local magnitude, 

duration and coda magnitudes, epicentral intensity, and felt area. We estimate E[Mw] and magnitude 

uncertainty following the CEUS–SSCn (2012) guidance. 

We also maintain a manually edited, “special-case” catalog of suspected erroneous or 

nontectonic events (explosions, mining-related events, etc.) identified from special studies. For the 2014 

update, nontectonic events compiled by the CEUS–SSCn are added to this file. These special-case 

events are deleted from the final catalog.

The NSHMP combines the source catalogs following the method of Mueller and others (1997). 

The source catalogs overlap in time and space; a preferred entry is selected when an earthquake is listed 

in more than one catalog. Original data sources are preferred over compilations. For consistency, 

observatory magnitudes or original intensities that we can convert to Mw are preferred over published 

magnitudes that have been converted elsewhere. Catalogs with “observed/measured” Mw, 

“approximate” Mw, and Mw derived from special studies (the first three bullets above) rank highest. For 

the remaining sources the preference order is (1) National Center for Earthquake Engineering Research–

NCEER (Seeber and Armbruster, 1991), (2) USGS Preliminary Determination of Epicenters (2013), (3) 

Geological Survey of Canada (2013), (4) Stover and Coffman (1993), (5) Stover and others (1984), and

(6) CEUS–SSCn (2012). Rather than combining all size measures for an earthquake, we instead adopt a 

single estimate of Mw and uncertainty from the preferred catalog; this is done in consideration of catalog 

maintenance and future updates. Comparisons with the CEUS–SSCn (2012) catalog show some Mw

differences, but no obvious systematic biases.

After removing duplicates, the NSHMP declusters the combined catalog (removes events 

considered to be foreshocks or aftershocks) using the Gardner and Knopoff (1974) algorithm. Early 

versions of the declustered catalog contained some events that were, judging by their locations and 

times, probably aftershocks of the 1886 Charleston earthquake. Old, poorly located aftershocks can 

evade the Gardner and Knopoff (1974) distance filter, which was developed from modern data and 

intended for modern applications. We implement a stronger filter pre-1900, a bilinear function of 

distance as compared to magnitude hinged at Mw5 that approximately doubles the Gardner and Knopoff 

(1974) filter radii for all magnitudes. The final declustered catalog includes 6,259 earthquakes from 

1700 through 2012 with Mw greater than or equal to 2.5 (fig. 14). The number of earthquakes that 

contributed to the declustered catalog from each source catalog is listed in table 1. 
21

Table 1. Contributions to the declustered catalog (1700–2012, Mw2.5 and greater). 

[CEUS–SSCn, Central and Eastern United States seismic source characterization for nuclear facilities; Mw, moment 

magnitude]

Source catalog Number of 

earthquakes

Special cases 6 

Mw (observed/measured) 233

Mw (approximate) 332

Mw (intensity special studies) 75

National Center for Earthquake Engineering Research, 

NCEER Seeber and Armbruster (1991) 2,094

USGS Preliminary Determination of Epicenters (2013) 1,311

Geological Survey of Canada (2013) 183

Stover and Coffmann (1993) 10

Stover and others (1984) 446

CEUS–SSCn (2012) 1,569

Total 6,259

Figure 14. Declustered catalog for the Central and Eastern United States including Mw2.5 and greater earthquakes 

occurring since 1700, including potentially induced earthquakes.
22

Some CEUS earthquakes may be causally related to industrial fluid processes such as 

hydrocarbon production or wastewater disposal. This is a well-known phenomenon (McGarr, 2002), and 

previous versions of the maps routinely took out such earthquakes; however, the importance of this 

phenomenon has increased since the 2008 map update because, since that update, there has been a 

dramatic increase in the earthquake count within the CEUS (Ellsworth, 2013). More than 300 

earthquakes with magnitude greater than 3 occurred from 2010 through 2012, compared with an average 

rate of 21 earthquakes per year observed from 1967 to 2000 across the CEUS. Proper treatment of these 

earthquakes in probabilistic seismic-hazard analysis is complicated and a topic of active research. The 

NSHMP is considering several different approaches to account for the hazard from induced earthquakes 

in a consistent way. Based on current literature (Frohlich, 2012; Horton, 2012; Ellsworth, 2013; 

Frohlich and Brunt, 2013) and on unusual patterns of seismicity, we identify and separate localized 

swarms of earthquakes potentially induced by fluid injection from the declustered catalog. These 

swarms, listed with the starting year of their suspect seismic activity, are Rocky Mountain Arsenal, 

Colorado (Colo.) (1962–1979); Rangely, Colo. (1957–present); Fashing, Texas (Tex.) (1973–present); 

Cogdell, Tex. (1976–present); Ashtabula, Ohio (1987–2007); Paradox Valley, Colo. (1991–present); 

Brewton, Alabama (1997–present); Dagger Draw, New Mexico (N. Mex.) (1998–present); Raton Basin, 

Colo.–N. Mex. (2001–present); central Oklahoma (2006–present); Dallas–Ft. Worth Airport, Tex. 

(2008–present); Guy-Greenbrier, Arkansas (Ark.) (2009–present); Youngstown, Ohio (2010–present); 

and Timpson, Tex. (2011–present) (fig. 15). The NSHMP uses the declustered catalog with these 

swarms removed for the hazard analysis. The swarm areas are delineated as zones to show where 

earthquakes have been extracted and where the hazard may vary from what is depicted on the maps

based on various models for activity. We will consider alternative models for including potentially 

induced seismicity in future versions of the map. Users of the current hazard information should 

consider that hazard might be higher in these zones of potentially induced seismicity than are presently 

shown on the map. In addition, we suggest reexamination of hazard in other places with the potential for 

increased rates of earthquakes.
23

Figure 15. Map showing areas of potentially induced seismicity in the Central and Eastern United States.

Seismotectonic Zones

The 2008 NSHMP distinguished four broad seismotectonic zones in the CEUS with distinct 

seismicity and Mmax: craton, extended margin, Colorado Plateau, and Rocky Mountains (Petersen and 

others, 2008). The boundary between the craton and extended-margin zones is based partly on the 

location of the Iapetan rift margin (Wheeler, 1995), which separates the older craton from younger 

Mesozoic and Paleozoic terranes (fig. 16A). CEUS–SSCn (2012) subdivided the CEUS east of longitude 

-105° into 12 seismotectonic zones. We generalize this zonation of the craton and extended margin by 

aggregating the CEUS–SSCn zones into four broader zones (fig. 16B): craton, Mesozoic extended 

terrane, Paleozoic extended terrane, and the Gulf Coast region, which mostly is composed of Paleozoic 

age crust overlain by up to several kilometers of Mesozoic and younger sediments. 
24

Figure 16. Alternative seismotectonic zonation models used to assign floor a-values and Mmax. Map of zonation 

model based on A, 2008 NSHMP model and B, generalized CEUS–SSCn (2012) models. 
25

We use seismicity rate floors within the background seismicity model to account for potential 

activity in areas with very few or no observed earthquakes, as described in the “Calculating a-Grids” 

section below. Only the NSHMP zonation model (not the generalized CEUS–SSCn model) is used for 

this implementation. The NSHMP and generalized CEUS–SSCn zonation models are used to develop 

maximum magnitude models, as described in the “Maximum Magnitude” section below.

Calculating a-Grids

In the 2014 update, the NSHMP has two approaches to calculating seismicity rate grids (a-grids) 

from the declustered catalog. The first approach computes rate grids for three magnitude levels and uses 

a fixed-length smoothing algorithm. The second approach uses a single magnitude level and an adaptive 

smoothing algorithm that allows variable length smoothing depending on the distances to the nearest 

earthquakes. Both approaches assume b=1.0, incorporate variable completeness times, estimate a-values 

over the CEUS grid, and spatially smooth the a-values. Thus, we do not change the overall methodology 

for modeling background seismicity in the CEUS (Frankel, 1995; Frankel and others, 1996), but we add 

the new approach to account for spatially variable smoothing lengths. 

Both approaches share the following components. The NSHMP superimposes a 0.1-degree by 

0.1-degree grid on the CEUS. We assign b=1.0 to each grid cell based on a statistical analysis 

(following Weichert, 1980) of the declustered Mw catalog; however, the analysis of the subcatalog near

Charlevoix yields a smaller b-value, so we use b=0.9 in the hazard analysis for the first approach. The 

historical seismicity rate in each grid cell is compared to the corresponding zone-average rate from the 

NSHMP seismotectonic zonation (defined in the “Seismotectonic Zonation” section), and a rate floor is 

implemented if needed. As in past updates, we assign uniform, average background seismicity rates for

the eastern Tennessee and New Madrid seismic zones (Petersen and others, 2008). Both methods use a 

new magnitude completeness zonation (fig. 17), a generalization of the completeness scheme used by 

the CEUS–SSCn (2012), to account for historical patterns of human settlement and seismic 

instrumentation. Based on discussions with our steering committee, we weight the fixed-smoothing 

model 0.6 and the adaptive-smoothing model 0.4. We assigned the adaptive-smoothing model lower 

weight because it is new and because it tends to tightly smooth some clusters. We describe two methods 

of smoothing the seismicity below.
26

Figure 17. Map of the seven completeness zones for Mw2.7 and greater, Mw3.7 and greater, and Mw4.7 and 

greater in the Central and Eastern United States. See table 2 for years of variable catalog completeness.

Table 2. Year of catalog completeness for Mw2.7 and greater, Mw3.7 and greater, and Mw4.7 and greater for 

zones in the Central and Eastern United States shown in figure 17.

[Mw, moment magnitude]

Zone Mw≥2.7 Mw≥3.7 Mw≥4.7

1 1800 1880 1970

2 1700 1750 1930

3 1800 1885 1975

4 1800 1880 1980

5 1850 1920 1980

6 1850 1900 1960

7 1850 1920 1980

First Approach

In the first approach, separate a-grids are computed for three magnitude levels, accounting for 

variable catalog completeness (table 2). Model 1 counts earthquakes with Mw greater than or equal to 

2.7 (similar to mblg 3 and greater used in previous USGS NSHMP maps updates, Petersen and others, 

2008); Model 2 counts earthquakes with Mw greater than or equal to 3.7 (mblg 4 and greater); and Model 
27

3 counts earthquakes with Mw greater than or equal to 4.7 (mblg 5 and greater). Following CEUS–SSCn

(2012), we use the counting factor N* to adjust rates to account for magnitude uncertainty. Cumulative 

rates are adjusted to incremental rates (Herrmann, 1977). Rate grids are spatially smoothed to account 

for uncertainties in the locations of future earthquakes: we apply a two-dimensional, isotropic, Gaussian 

function with a fixed correlation distance of 50 km for Model 1 or 75 km for Models 2 and 3. This 

spatial smoothing remains unchanged from past NSHMP updates. In addition, a seismicity rate floor, 

Model 4, is implemented to account for future earthquakes in grid cells with little or no historical 

earthquakes. This model consists of a grid with uniform average seismicity rates computed for each 

NSHMP seismotectonic zone (defined in the “Seismotectonic Zonation” section).

The historical seismicity rate in each grid cell is defined as a weighted average of Models 1–3, 

with weights 0.5, 0.25, and 0.25, respectively. If the historical rate exceeds the zone-average rate 

(Model 4), then the final model rate is simply equal to the historical rate. Otherwise, the final model rate 

is a weighted average of Models 1–4 with weights 0.4, 0.2, 0.2, and 0.2, respectively. The final rate in a 

grid cell is never less than the historical rate, and the rate of seismicity in seismically active areas is not 

reduced to make a floor in quiet areas. The total model-seismicity rate across the CEUS exceeds the 

historical rate by about 10 percent using this method (Frankel and others, 1996). 

For this first approach, figure 18A shows the incremental a-grid assuming the NSHMP 

seismotectonic model and fixed smoothing. The incremental a-value represents the annual rate of 

earthquakes with -0.05 less than Mw less than 0.05 in each grid cell. 

Figure 18. Maps showing cumulative seismicity-rate grids from alternative smoothing methods for 5-hertz spectral 

acceleration at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per 

second. A, fixed-correlation-length and B, adaptive-correlation-length smoothing methods.
28

Second Approach

The second approach to estimate the background rate in the 2014 NSHMP update uses an 

adaptive, nearest-neighbor-type smoothing procedure, in which the smoothing distance for each 

epicenter is determined by the distance to the nth nearest epicenter, and the neighbor number (n) is 

optimized by likelihood calculations. Adaptive smoothing techniques were implemented by the USGS 

for a seismic hazard assessment of Afghanistan (Boyd and others, 2007), but have not been used in 

previous versions of the USGS NSHMP model. In this report, we follow the approach of Helmstetter 

and others (2007) and Werner and others (2011). This approach to calculating historical a-grids 

optimizes the neighbor number and completeness level that maximize the likelihood function. 

To calculate the completeness level and neighbor number, the NSHMP uses the likelihood 

testing methods described by previous authors (for example, Helmstetter and others, 2007; Werner and 

others, 2011). For the purposes of optimizing the adaptive smoothing parameters, we divide the CEUS 

earthquake catalog into a “forecasting” subcatalog of older events and a “testing” subcatalog of recent 

events. We smooth seismicity rates calculated from the forecast catalog for all completeness levels 

(Mw2.7–5.2) and neighbor number to produce a set of forecast models and calculate the likelihood of 

observing earthquakes from the testing catalog, assuming a Poisson distribution for earthquake 

occurrence. The completeness levels and lateral variation in completeness investigated for the adaptive 

smoothing are a super-set of those used for the fixed-radius smoothing and were developed by the same 

methods. The completeness level and neighbor number that maximize the likelihood of observing the 

testing catalog are Mw=3.2 and n=4. In other words, assuming a completeness level of Mw=3.2, with 

spatially varying year and a neighbor number of four, best characterizes the recent spatial distribution of 

earthquakes in the CEUS.

We return to the full CEUS declustered earthquake catalog and recalculate the rate for each 

earthquake using a completeness level of Mw=3.2 and smooth this rate geographically over the distance 

to its fourth nearest-neighboring earthquake using a two-dimensional, isotropic, Gaussian function. In 

this way, we smooth the seismicity rates using a unique smoothing distance for the Gaussian function 

and convert from cumulative seismicity rates to incremental seismicity rates using the Herrmann (1977) 

relation.

The differences in the a-grids calculated from the fixed- and adaptive-smoothing approaches 

vary with epicenter density. In regions with high seismicity rates, the adaptive method yields smaller 

smoothing distances (correlation lengths) and locally higher seismicity rates. In regions with sparse 

seismicity, smoothing distances from the adaptive method are larger than those from the fixedsmoothing method, and the corresponding seismicity rates are decreased relative to rates from fixed 

smoothing. A comparison of the historical a-grids from the two approaches, and the differences in 

seismic hazard calculated between the two approaches are shown in figure 18B. 

Maximum Magnitude for Background Seismicity

The background-seismicity model serves a dual purpose in the hazard model—it models 

seismicity from known faults or in places where there is no known fault. Throughout most of the CEUS, 

there is little geological or geodetic information about the presence or absence of active faults; the few 

well-studied seismic zones are areas with documented, unusually large earthquakes. Some areas have 

evidence of paleoearthquakes, but this evidence is insufficient to assign a magnitude or rate to an 

earthquake consistent with the observations. The background-seismicity model accounts for the 

uncertainties in these areas until there is enough evidence to define a more certain fault source.

If we assume (for lack of better evidence) that the Mmax of all possible earthquakes is uniform 

within a seismotectonic zone, then prehistoric and historical earthquakes in each zone provide a lower 
29

bound on Mmax. That is, Mmax must be at least as large as the largest observed earthquake. We cannot 

know, however, if the largest observed earthquake is the largest possible earthquake. Thus, we rely on 

observations from other SCRs to define possible Mmax values for the CEUS. We represent the 

uncertainty in Mmax by assigning weights to four plausible Mmax values. 

The New Madrid and Charleston seismic zones lie in the Mesozoic extended margin. For this 

zone, Mmax must be at least as large as the 1811–1812 New Madrid and 1886 Charleston earthquakes; 

however, the magnitudes of these historical earthquakes are not well constrained. As described later in 

this section, the lowest magnitude estimate among these nineteenth century earthquakes is 6.8 (Hough 

and Page, 2011); it is plausible, but unlikely, that the CEUS cannot produce an earthquake with 

magnitude greater than or equal to 6.8 (we have observed such earthquakes in other analogous regions 

and we have paleoseismic evidence for such earthquakes in the CEUS). Thus, we assign a weight of 0.1 

to this Mmax. Most estimates for the New Madrid and Charleston earthquakes are in the magnitude 

range of 7.1–7.5. Given this current evidence, Mmax is more likely to be greater than 7.1 and possibly 

greater than 7.5. We represent these possibilities with a 0.3 weight at Mmax=7.2 and 0.5 weight at 

Mmax=7.6. Analogous extended margin regions, such as in northeastern India, have ruptured in similar 

size earthquakes (for example, 2001 Mw7.7 Bhuj earthquake, Hough and others, 2002). Earthquakes 

larger than Mw8.0 are not known in the prehistoric and historical SCR record. The low seismicity of 

SCR crust (Johnston and others, 1994; Mueller and others, 1997) indicates, however, that Mw8.0 and 

larger earthquakes have long recurrence intervals and might not appear in the record even if they are 

possible. For this reason, we assign Mmax=8.0 a weight of 0.1. This distribution of uncertainty has a 

weighted average Mmax of 7.44. 

From the 2008 model, we slightly modify the weights of the Mesozoic extended margin to 

define Mmax weights in the Paleozoic extended margin. Johnston (1989) and Johnston and others 

(1994) observed in SCRs worldwide that earthquakes occurred preferentially in areas of young 

extension (Mesozoic or Paleogene, past 252 million years), but the data were insufficient to determine if 

there is a similar correlation for Paleozoic extension (540–252 million years ago). For the Paleozoic 

extension in the four-zone seismotectonic model, we assign equal weight (0.4) to Mmax of 7.2 and 7.6. 

This modification reduces the weighted average to Mw7.40 from Mw7.44 in the Mesozoic extended 

margin.

To inform but not constrain the Mmax distribution, we add prehistoric earthquakes to the catalog 

of large historical SCR earthquakes used in the 2008 update. Figure 19 shows magnitudes for 

prehistoric earthquakes with Mw greater than or equal to 6.0 in the SCRs of North America, Australia, 

and Western Europe. If two or more paleoearthquakes are close enough together geographically to 

possibly have broken the same fault or fault system, then we include only the single largest event. If a

historical earthquake had size and location similar to those of one or more prehistoric earthquakes, then 

the historical earthquake is the best characterized, and is the only earthquake included. Note that, in this 

way, the catalog does not include all observed large-magnitude earthquakes but rather the best single 

estimate of the largest magnitude at a location. The historical catalog has 138 earthquakes with Mw

greater than or equal to 6.0 on their original magnitude scales, which includes earthquakes from all 

continents. There are 78 prehistoric or historical earthquakes in cratons and 51 in extended margins. 

The Mmax distribution for Mesozoic and Paleozoic extended margins is compared to a 

histogram of large earthquakes in SCRs worldwide in figure 19, which also includes the Mmax 

distribution for the extended margin in the 2008 update. Although the observed magnitudes of the 

largest known earthquakes in the CEUS are uncertain, they are consistent with the largest earthquakes 

observed in other SCRs. Note that we assume that Mmax in the CEUS may differ from Mmax in other 

SCRs. If we assumed instead that all SCRs share a common Mmax, then the lower bound for Mmax 
30

would have to be larger than the Mw7.7 earthquake in Bhuj, India, since that is the largest observed 

earthquake in an extended margin (Hough and others, 2002). 

Figure 19. Distribution of large earthquake magnitudes (51 earthquakes) for extended margins in stable 

continental regions, worldwide. Mmax distributions used in the 2008 and 2014 updates shown in inset.

The Mmax distribution for 79 global cratonic earthquakes along with the 2014 and 2008 Mmax 

distributions are shown in figure 20. We broaden the Mmax distribution considerably compared to the 

2008 distribution, extending both to higher and lower magnitudes than applied in the previous model. 

The CEUS–SSCn project also allowed for a similar range of Mmax in their hazard models. The 

prehistoric Cheraw fault earthquake ruptured in the craton of eastern Colorado and was assigned Mw7.0 

based on the Wells and Coppersmith (1994) magnitude-scaling relation (all slip types). This magnitude 

is very uncertain, so we also allow for a possibility that it is an overestimate of the true magnitude. We 

observe dozens of earthquakes with Mw between 6.5 and 7.8 in the global dataset for cratonic regions

(fig 20). Therefore, it is reasonable to expect that such an earthquake could happen in the craton of the 

CEUS. We weight the lower Mmax of 6.5 with a lower weight because most participants at our 

workshops agreed that earthquakes larger than Mw6.5 could be generated in this region. We assign onehalf weight for an Mmax equal to the expected magnitude of the Cheraw fault earthquake, Mw7. The 

observed or inferred magnitude distribution of cratonic earthquakes worldwide extends up to Mw7.8, so 

we also allow for the potential of earthquakes up to Mw7.5 and Mw8.0 (with lower weight) to account 

for these global analogs.
31

Figure 20. Distribution of large earthquake magnitudes (79 earthquakes) for cratons in stable continental regions, 

worldwide. Mmax distributions used in the 2008 and 2014 updates shown in the inset.

Fault-Based Source Models in the Central and Eastern United States

For the 2014 NSHM, we update the fault-based source models in the CEUS, relying heavily on 

the work of the CEUS–SSCn (2012). The 2008 USGS NSHMP maps included four fault-based sources 

in the CEUS: the Meers (Okla.) and Cheraw (Colo.) faults, and the New Madrid (Missouri [Mo.]) and 

Charleston (South Carolina [S.C.]) seismic zones (fig. 21). The 2014 model updates these sources and 

includes an additional six fault-based characteristic or repeating large magnitude earthquake (RLME) 

sources from the CEUS–SSCn (2012): the Wabash Valley (Ill.–Ind.), Commerce Geophysical 

Lineament (Ark.–Ind.), Eastern Rift Margin (western Tennessee), Marianna (east-central Arkansas), and 

Charlevoix (eastern Canada) areal source zones and New Madrid (Ark.–Ky.) fault source (see fig. 22). 

These new sources have characteristic magnitudes ranging from 6.7 to 7.9 and effective return periods 

from less than 400 years in New Madrid to nearly 10,000 years for the Commerce Geophysical 

Lineament and the northern extent of the Eastern Rift Margin. The New Madrid, Charleston, 

Charlevoix, and Meers faults are the main contributors to ground motion hazard, when considering a 2-

percent chance of exceeding defined levels of ground motion in a 50-year time window. Other fault 

sources contribute to ground motion hazard at longer return periods (greater than 2,475 years). 
32

Figure 21. Location of fault sources in the Central and Eastern United States. 

Source geometry associated with fault sources in the CEUS is either characterized as a mapped 

fault or a virtual fault. If the latter, rupture of magnitude, M, on a vertical fault is used to calculate

length, L, from the Wells and Coppersmith (1994) relation, L=10-3.22+0.69M km. The NSHMP models 

faults closely spaced as individual (set of) mapped fault(s) or as a virtual set of faults that span the 

faulted area. Virtual faults are always centered on grid points, which sample latitude and longitude at 

0.1-degree increments.

New Madrid Seismic Zone

The New Madrid seismic zone (NMSZ, fig. 22) contributes significantly to hazard in the CEUS 

(Petersen and others, 2008). In the 2014 USGS NSHMP maps, we update the 2008 NMSZ model and 

add a separate branch for the simplified CEUS–SSCn model (fig. 23). We assign equal weight to these 

alternative models.
33

Figure 22. Representations of fault sources near the New Madrid seismic zone. A, USGS representation from the 

2008 update (dashed lines) and 2014 update (solid lines) and B, CEUS–SSCn (2012) project representation. 
34

Figure 23. Logic tree for the New Madrid seismic zone (NMSZ). A, B, and C in the “Earthquake-recurrence model” 

and “Magnitude-uncertainty model” branches for the USGS representation refer to the northern, central, and 

southern segments of the NMSZ, respectively. Assigned weight for branches shown in parentheses.
35

For the 2014 update of the 2008 NMSZ model, we (1) maintain the five spatially distributed 

faults (fig. 22A), with minor geographic modifications, and their weights; and (2) update the magnitudes 

and earthquake recurrence models with new information. In particular, we update the magnitudes based 

on new estimates for the 1811–1812 sequence and update the rates based on recent geodetic studies. 

Hough and Page (2011) reexamined macroseismic intensity data and estimated magnitudes lower than 

any previously reported (table 3). Hough and Page (2011) also suggested that postglacial rebound is 

sufficient to produce a sequence with a moment release equivalent to one Mw6.8 earthquake in 500 

years, which is different than the magnitude assumed in the 2008 version of the maps, an average Mw7.6 

in 500 years. In contrast, Frankel and others (2012) examined geodetic baselines across the New Madrid 

seismic zone and inferred that the current rate of deformation can support one Mw7.3 earthquake in 500 

years. To account for all published studies, we update the distribution of epistemic uncertainty in the 

magnitude. For the central and southern fault segments (denoted B and C, respectively, in the logic 

tree), the magnitudes (and weights) are Mw6.8 (0.1), Mw7.1 (0.1), Mw7.5 (0.5), Mw7.7 (0.2), and Mw8.0 

(0.1). The range of this distribution (Mw6.8–8.0) is wider than the corresponding distribution in the 2008 

USGS NSHMP model (Mw7.3–8.0, Petersen and others, 2008). The weighted average, Mw7.47, is 

smaller than the previous USGS NSHMP maps, which was Mw7.63. For the northern fault segment (A), 

the magnitudes are 0.2 magnitude units smaller than for the other segments, with the same weights. This 

reduction is consistent with the paleoliquefaction data described in Petersen and others (2008). 

Table 3. Magnitude estimates for the 1811–1812 New Madrid earthquakes.

[Mw, moment magnitude; mb, body-wave magnitude] 

Event Rupture 

segment

Hough and 

Page (2011)

Mw

Hough and 

others (2000) 

Hough and 

Martin (2002)

Mw

Bakun and 

Hopper 

(2004a) 

Mw

Johnston 

(1996)

Mw

Nuttli (1973)

mb

December 16, 1811 southern 6.8 7.2–7.3 7.6 8.1 7.2

December 16, 1811 

aftershock southern 6.6 7.0 Not 

applicable

Not 

applicable

Not 

applicable.

January 23, 1812 northern 6.9 7.0 7.5 7.8 7.1

February 7, 1812 central 7.2 7.4–7.5 7.8 8.0 7.4

Several models were developed to account for variation in the recurrence times of large 

earthquakes on the New Madrid Seismic Zone. Calais and Stein (2009) examined available data on 

coseismic slip and geodetic-based strain rates. These data indicate that, in the past couple of decades, 

there have been low surface strain rates across the zone. Calais and Stein (2009) determined that the 

recent Global Positioning System (GPS) based strain rates are consistent with a 10,000- to 100,000-year 

recurrence for large New Madrid earthquakes. We add a logic-tree branch for a recurrence rate of 

50,000 years with a weight of 0.05 to reflect this possibility. From the previous version of the maps 

(Petersen and others, 2008), we maintain the logic-tree branch for the 500-year recurrence interval, 

which is obtained from paleoseismic data and includes the possibility that the northern fault branch 

ruptures with either a 500-year or 750-year recurrence interval, with a weight of 0.9, and reduces the 

weight on the 1,000-year recurrence branch, obtained from sedimentary studies (Holbrook and others, 
36

2006), to 0.05. This new weighting model gives most weight to the possibility that ruptures will 

continue with about a 500 year recurrence (based on feedback from our CEUS workshop) but accounts 

for ruptures with longer recurrences that are consistent with the GPS data and sedimentary studies that 

have been proposed in the literature. 

CEUS–SSCn (2012) developed a new model for the NMSZ that consists of several alternative 

magnitude and earthquake rates on individual fault strands. We have simplified this model by removing 

the branches of the CEUS–SSCn logic tree that account for alternative time-dependent and depth-ofrupture distributions. 

Faults Near the New Madrid Seismic Zone

The CEUS–SSCn Project comprehensively reviewed the existing literature on paleoseismic 

studies and paleoliquefaction features near the New Madrid seismic zone. The CEUS–SSCn defined 

four areal source zones: Wabash Valley, Commerce Geophysical Lineament or Commerce fault zone, 

Eastern Rift Margin, and Marianna (fig. 22B). The NSHMP adopts the CEUS–SSCn sources with the 

modifications described in the following sections. For example, we assume a single value for the depth 

of rupture, and we do not include the low-weighted time-dependent branches. The CEUS–SSCn (2012) 

documentation provides a detailed discussion of the research supporting these sources and logic-tree 

branches.

Wabash Valley

The 2008 update of the USGS NSHMP maps defined a separate seismicity zone for the Wabash 

region (fig. 22B). The NSHMP used the background seismicity model with a single Mmax value of 

Mw7.5 to account for the rates and magnitudes of paleoearthquakes identified before 2008. For the 2014 

update, we maintain this model for fixed smoothing only, as well as adopt the CEUS–SSCn Wabash 

Valley RLME source. The CEUS–SSCn (2012) project collected studies of paleoearthquakes in this 

area, which indicate that there were at least eight Holocene and latest Pleistocene earthquakes with Mw

between 6 and 7.8. The CEUS–SSCn seismic zone explicitly models RLMEs, as opposed to assuming a 

larger Mmax than the surrounding region as was implemented in the 2008 NSHMP maps (Petersen and 

others, 2008). The CEUS–SSCn project defined a polygonal zone oriented northeast to southwest as a 

leaky source of earthquakes with possible Mw between 6.7 and 7.5 (fig. 24). In leaky sources, the 

rupture centroid is constrained to lie within the areal source zone, but the rupture may extend outside the 

zone. They modeled this source as vertical strike-slip and dipping thrust faults with three distinct 

orientations. We simplify their model by defining vertical strike-slip faults oriented parallel to the long 

axis of the zone and do not account for potential dipping structures.
37

Figure 24. Logic tree for the Wabash Valley source. Value given in “Earthquake-recurrence model” branch is 

number of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 

Although eight large-magnitude earthquakes occurred in this region since latest Pleistocene 

(Obermeier, 1998), the CEUS–SSCn associated only two with the Wabash Valley source and treated the 

rest as background seismicity. The two earthquakes considered for this source happened in the last 11 to 

13 thousand years ago (Hajic and others, 1995; Obermeier, 1998). After accounting for the uncertainty 

in these dates, the return periods consistent with this observation range from 2,300 to 42,000 years, with 

an effective return period of 5,900 years. We use the effective return period in our updated model. 

Commerce Geophysical Lineament

The Commerce Geophysical Lineament (CGL), or Commerce Fault zone, is a northeasterly 

trending geophysical anomaly that is located west of and roughly parallel to the southern and northern 

arms of the New Madrid seismic zone (fig. 22B). The CEUS–SSCn (2012) compiled observations and 

reports that indicate the CGL is seismically active. Along the CGL in southeast Missouri, these 

observations include anomalously flowing drainages, displaced Tertiary and Pleistocene to Holcene 

deposits, and paleoliquefaction features.

Following the CEUS–SSCn (2012) Project, we model this seismic source with leaky, vertical 

strike-slip fault sources oriented parallel to the long axis of the zone, though we implement a single 

depth to the top of rupture (5 km). The length of the Commerce Geophysical Lineament allows a broad 

range of possible magnitudes; we adopt, without modification, the CEUS–SSCn’s set of magnitudes 

from 6.7 to 7.7. The CEUS–SSCn presented evidence for two or three earthquakes in the past 20 

thousand years. Return periods from 3,000 to 72,000 years are consistent with this observation; the 

effective return period is 9,300 years (fig. 25).
38

Figure 25. Logic tree for the Commerce Geophysical Lineament source. Value given in “Earthquake-recurrence 

model” branch is number of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 

Eastern Rift Margin

The CEUS–SSCn (2012) reviewed studies in the areas of the Eastern Rift Margin (ERM). 

Seismic imaging along the margin and paleoseismic trenching (fig. 22B) revealed repeated movement 

on Quaternary faults. These studies reported several meters of right-lateral and vertical offset in the 

north, which increased to the south, and reported evidence that the offsets occurred in the past 20 to 60 

thousand years. Following the CEUS–SSCn, we model the ERM source as leaky, vertical strike-slip 

ruptures parallel to the long axis of the zone. 

The CEUS–SSCn divided the ERM into northern and southern zones (fig. 22B) to account for 

the higher rates of deformation in the south. In the northern zone, the CEUS–SSCn assumed magnitudes 

of 6.7 to 7.4 based on the potential fault length and observations in paleoseismic trenches. The 

paleoseismic observations also indicated that one or two earthquakes may have happened in the past 12–

35 thousand years. This information gives a range of return periods from 2,500 to 71,000 years, with an 

effective return period of 9,300 years. We adopt the CEUS–SSCn model for the northern zone but use a 

single depth to the top of rupture (5 km) (fig. 26). 
39

Figure 26. Logic tree for the north source of the Eastern Rift Margin. Value given in “Earthquake-recurrence 

model” branch is number of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 

The CEUS–SSCn (2012) further divided the southern zone to account for recent deformation in 

the along the Mississippi River just west of Memphis, Tenn. (fig 22). Using observations in the south 

like those in the north, the CEUS–SSCn assumed that a set of magnitudes ranging from 6.7 to 7.7 are 

possible. The CEUS–SSCn (2012) project conclude that 2–4 earthquakes may have occurred over the 

past 20 thousand years. This uncertainty yields a range of return periods from 2,000 to 30,000 years 

with an effective return period of 4,900 years (fig. 27).
40

Figure 27. Logic tree for the south source of the Eastern Rift Margin. Value given in “Earthquake-recurrence 

model” branch is number of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses.
41

Marianna

Marianna, Ark., is about 80 km southwest of Memphis, Tenn. (fig. 22B). The CEUS–SSCn

(2012) reviewed studies in this region, which document several very large sand blows, and they define a 

seismic zone with two fault orientations parallel to the zone’s boundaries. We adopt a N. 45° E. 

orientation of leaky (faults extend outside of zone), vertical strike-slip faults. The size of the Marianna 

source zone and the size of the sand blows suggest that it could produce earthquakes with magnitudes 

between 6.7 and 7.7. We adopt magnitudes and assigned weights based on the CEUS-SSC model (fig. 

28). Paleoliquefaction studies collected in the CEUS–SSCn (2012) suggest that the sand blows in the 

Marianna region were associated with three or four events and formed about 5 to 10 thousand years ago, 

predating those in the New Madrid seismic zone. These observations are consistent with return periods 

from 1,200 to 14,000 years, with an effective return period of 2,800 years. The CEUS–SSCn (2012) 

acknowledged that this source zone may be inactive and gave 0.5 weight to an out-of-cluster, inactive, 

branch, which we adopt. 

Figure 28. Logic tree for the Marianna source. Value given in “Earthquake-recurrence model” branch is number of 

earthquakes per year (eq/yr). Assigned branch weight shown in parentheses.
42

Charleston Seismic Zone

Like the New Madrid seismic zone in the central United States, the Charleston, S. C., seismic 

zone (fig. 21) contributes significantly to hazard in the Southeast. In 2008, the NSHMP defined two 

regions within the Charleston seismic zone. A narrow zone was entirely onshore, following the 

Woodstock lineament and an area of river anomalies. The second zone was broader and extended 

offshore, encompassing known liquefaction features and offshore faults (Petersen and others, 2008). 

The scientists at the CEUS regional workshop (Memphis, Tenn., 2012) identified needed modifications 

in the narrow zone for the 2014 update and the NSHMP steering committee suggested we consider the 

CEUS–SSCn (2012) results. As a consequence, we adopt the regional, local, and narrow seismic zones, 

and the wider range of epistemic uncertainty in earthquake magnitudes and rates defined by the CEUS–

SSCn (2012; table 4) for the 2014 update of the USGS NSHMP maps (fig. 29).

Table 4. Seismic zones in the Charleston area (see fig. 29).

Zone Mapped faults Virtual fault strike Recurrence model Weight

Narrow Woodstock N. 17.5 ̊ E. Poisson 0.3

Local Various onshore N. 50 ̊ E. Poisson 0.5

Regional Various, including 

Helena Banks

N. 50 ̊ E. Poisson 0.2
43

Figure 29. Summed a-grid rates for the local, narrow, and regional Charleston sources. The rate shown is per 0.1- 

by 0.1-degree cell per year, and is scaled by 105. 

The southwestern edge of the 2014 regional Charleston zone extends farther southwest than the 

southwest edge of the 2008 broad zone. Five or more paleoearthquake-liquefaction features near the 

South Carolina–Georgia border supported the extension of the southwestern edge (CEUS–SSCn, 2012). 

In our current implementation, finite faults can extend outside the zone boundary in the strike direction 

but not in the perpendicular direction. In contrast, the CEUS–SSCn (2012) constrained the virtual faults 

to rupture entirely within the zone boundaries of the regional and local zones, whereas they 

implemented leaky boundaries along the northeast and southwest edges of the narrow zone. Some of the 

virtual faults in the 2014 USGS NSHMP model are now very close to Savannah, Ga., which impacts 

hazard in Savannah and elsewhere in eastern Georgia.

We adopt, without modification, the CEUS–SSCn set of five magnitudes and weights (fig. 30). 

The new distribution of magnitudes is compared to that in the 2008 update in table 5; the weighted 

average magnitude was 7.19 in 2008 and is now 7.1. Within each of the 3 zones, the mean return period 

is 529 years, which is the average of the in-cluster (0.9 weight) and out-of-cluster branches (0.1). 
44

Figure 30. Logic tree for the Charleston source. Value given in “Earthquake-recurrence model” branch is number 

of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 

Table 5. Magnitude distribution for Charleston source. 

[CEUS–SSCn, Central and Eastern United States seismic source characterization for nuclear facilities; NSHMP, National 

Seismic Hazard Mapping Project; Mw, moment magnitude]

CEUS–SSCn Mw CEUS–SSCn weight 2008 NSHMP Mw 2008 NSHMP weight

6.7 0.10

6.9 0.25 6.8 0.20

7.1 0.30 7.1 0.20

7.3 0.25 7.3 0.45

7.5 0.10 7.5 0.15

The CEUS–SSCn defined time-dependent branches in the narrow zone, but the NSHMP does 

not adopt these models because the recurrence models for all zones in the 2014 NSHMP maps are time 

independent (as advocated by workshop participants). In the CEUS–SSCn (2012) time-dependent 

model, the relatively recent 1886 Charleston earthquake (compared to the mean return period of 500 to 

550 years) results in a slightly lower probability of a similar event in the next 50 years relative to the 

time-independent model. The CEUS–SSCn assigns a total weight of 0.1 to these time-dependent 

branches.
45

Meers Fault

Previous updates of the USGS NSHMP maps include the Meers fault in southwestern Oklahoma 

(fig. 21). In the 2008 update, the NSHMP assigned a characteristic Mw7.0 and a return period of 4,500 

years, based on 2 surface-faulting events in the past 3,000 years (Crone and Luza, 1990; Kelson and 

Swan, 1990) and a lack of evidence of additional surface-rupturing events over the past 100,000 or more 

years.

The CEUS–SSCn (2012) developed a set of alternative models that account for a much broader 

range of earthquake magnitudes and rates than the single magnitude and rate assumed in the 2008 

NSHMP model. For example, the CEUS–SSCn model includes return periods from 476 to 500,000 

years. The CEUS–SSCn model also gives 10-percent weight to the possibility of an extended fault 

length, but we do not adopt this branch in the 2014 update. We weight the modified CEUS–SSCn model 

0.5 and the 2008 NSHMP model 0.5, because they are alternatives based on different interpretations of 

the same published data (fig. 31). 
46

Figure 31. Logic tree for the Meers fault source. Value given in “Earthquake-recurrence model” branch is number 

of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 

Cheraw Fault

Previous USGS NSHMP map updates defined the Cheraw fault in eastern Colorado (fig. 21) 

based on existing information (Petersen and others, 2008). Crone and others (1997) showed evidence of 

Holocene and earlier faulting, and inferred surface ruptures about 8, 12, and 20–25 thousand years ago. 

The NSHMP modeled the fault using a slip rate of 0.15 millimeters per year (mm/yr) based on data 

from the last two events and a maximum magnitude of Mw7.0 plus or minus (±) 0.2 determined from the 

Wells and Coppersmith (1994) fault length relation for all slip types combined. 
47

The CEUS–SSCn (2012) defined a set of alternative magnitudes, rates, and fault lengths, and we 

include some of the important alternatives in the 2014 update. For example, the CEUS–SSCn model 

accounted for a broader range of magnitudes and rates, which we adopt (fig. 32). We do not adopt the 

extended fault alternative that the CEUS–SSCn considers because these models are not well constrained 

and further research is needed to verify the new model. 

Figure 32. Logic tree for the Cheraw fault source. Value given in “Earthquake-recurrence model” branch is number 

of earthquakes per year (eq/yr). Assigned branch weight shown in parentheses.
48

Charlevoix Seismic Zone

The 2008 USGS NSHMP maps included the Charlevoix seismic zone, an area in Canada (fig. 

21) that contributes to seismic hazard in the northeastern United States. The NSHMP modeled this zone 

with the background-seismicity model having a spatially uniform seismicity rate and a b value of 0.76. 

We continue to include the Charlevoix background source zone in the 2014 update; however, because of 

the new implementation of moment magnitudes, the b value is now 0.9 for the fixed-smoothing model 

and the b value is 1.0 for the adaptive smoothing model (accounting for additional epistemic 

uncertainty). In addition to our model of the source zone, we also include the CEUS–SSCn (2012) 

model for the Charlevoix seismic zone. We recognize that there is some overlap between the 

magnitudes in the two models; however, the rates of the seismicity-based background source are much 

lower than the rates associated with the RLME so this overlap may not be important. 

Of the five Mw5.5 and larger earthquakes in the Charlevoix region over the last 350 years, the 

CEUS–SSCn considers the two largest, the 1963 Mw7.00 and 1870 Mw6.55, to be in the source zone. 

The remaining events are considered part of the background source zone. Paleoseismic investigations 

reveal at least three Holocene paleoearthquakes of Mw6.2 and larger (Tuttle and Atkinson, 2010); 

therefore, the CEUS–SSCn (2012) considers a range of return periods from 100 to 5,600 years with an 

effective return period of 730 years. The CEUS–SSCn assigns a range of moment magnitudes from 6.75 

to 7.5 with greatest weight given to Mw7.0 because of the estimates and uncertainty in the size of the 

historical and paleoseismic events and the potential size earthquakes within the source zone (fig. 33). 

We simplify the CEUS–SSCn (2012) model by modeling sources within this zone as vertical 

strike-slip ruptures with random strike having a constant depth to the top of rupture (5 km). The CEUS–

SSCn modeled these sources as random strike thrust events dipping between 40° and 60° in crust with a 

seismogenic thickness of 25 or 30 km. 
49

Figure 33. Logic tree for the Charlevoix source. Value given in “Earthquake-recurrence model” branch is number of 

earthquakes per year (eq/yr). Assigned branch weight shown in parentheses. 
50

Western United States Earthquake Source Models

The overall approach to modeling seismic hazard in the Western United States (WUS) is similar 

to past USGS NSHMP maps, documented in Frankel and others (1996, 2002) and Petersen and others 

(2008) that is based on seismicity-based background models and fault models. The models, data, and 

methods can also be accessed at http://earthquake.usgs.gov/hazmaps/. As in previous models, we use 

historical seismicity (gridded and smoothed spatially) to estimate the hazard from earthquakes on 

unidentified or uncharacterized faults (seismicity-based background sources). These models account for 

random earthquakes by using the rate and distances of nearby historical earthquakes above a certain size 

threshold to estimate the rate of future events. In addition, we apply geologic and geodetic data to 

estimate slip rates on faults. This additional fault input allows for broader uncertainty in the activity 

rates on faults. Fault-based models are dependent on a slip rate that is based on a dated offset feature or 

on multiple measurements of geodetic strain rates across the region. In past models, the geologic data 

were mostly used exclusively to estimate slip rates and annual recurrence rates on faults; geodetic (GPS) 

data were used primarily to constrain the regional slip rates or to define rates within designated zones. 

However, in this update, we include combined geologic and geodetic inversion methods to estimate slip 

rates on faults (see the section “Combined Geodetic- and Geologic-Based Slip-Rate Models” for more 

details). These models were incorporated in the 2014 hazard assessment for sites across the WUS. 

Earthquake-rate data are used with an earthquake magnitude-frequency distribution (with a 

defined slope or b-value) to estimate the rate of earthquakes at any particular place. As in previous 

models we apply an exponential magnitude-frequency distribution with a doubly truncated exponential 

recurrence based on a Gutenberg-Richter curve (Gutenberg and Richter, 1944) to estimate hazard from 

random sizes of earthquakes on faults as well as in background seismic source models. For the 

background seismicity, we consider earthquakes from Mw5.0 to the maximum magnitude obtained from 

global and regional analogs (the Mmax distribution allows for the highest weight at about Mw7.5). For 

most of the fault sources, we consider earthquakes from Mw6.5 up to the maximum magnitude expected 

for the fault, which is obtained from published magnitude scaling relations that predict magnitude from 

fault area or length constraints. We also consider a preferred earthquake magnitude distribution that 

ruptures the entire source (Schwartz and Coppersmith, 1984). These two distributions form the basis for 

defining the different sizes of earthquakes on faults. 

This update of the USGS NSHMP maps includes several new seismic source and ground motion 

models. The California fault sources are addressed separately in this report, with sources defined by the 

Uniform California Earthquake Rupture Forecast Model (UCERF ver. 3.3; Working Group on 

California Earthquake Probabilities, 2013). The Pacific Northwest update is focused on new information 

concerning the sizes and rupture sources of earthquakes along the Cascadia subduction zone, the 

addition of the Tacoma fault source, and modifications to some other fault sources in the region. The 

Intermountain West update is based on new recommendations on fault modeling from the Basin and 

Range Province Earthquake Working Group (BRPEWG, Lund, 2012) and the Utah Geological Survey. 

Both regions incorporate a new earthquake catalog and background seismicity models as well as 

combined new geologic and geodetic inversion slip-rate models. Several new ground motion models 

have also been included to account for uncertainty (epistemic) in this analysis.

Seismicity-Based Background Source Model

The logic tree for the seismicity-based background source model, which accounts for the hazard 

from earthquakes that are located away from modeled faults, is shown in figure 34. Statistical 

parameters of the seismicity model are derived from the earthquake catalog (Frankel, 1995). A catalog 
51

for the Western United States is updated for this analysis. This analysis defines a truncated-exponential

magnitude-frequency distribution for the estimation of rates of different sized earthquakes. The 

epicenters are spatially smoothed using both fixed length (50 km correlation length) and adaptive 

smoothing methods (described below). Models for estimating background earthquake rates from (1) 

shallow crustal background seismicity and (2) deep background seismicity are discussed in this section.

Figure 34. Logic tree for the seismicity-based background source model in the Western United States. Assigned 

branch weight shown in parentheses. 

Earthquake Catalog for the Western United States

Several published source catalogs are combined (Mueller and others, 1997) to develop a 

composite, uniform seismicity catalog for western North America through 2012. The updated catalog is 

a 6-year extension of the 2006 catalog used for the 2008 hazard maps. The catalog lists each earthquake 

with Mw, hypocenter, and origin time derived from a preferred source catalog. A comment field 

summarizes information from the original source catalog for each entry. We consider magnitude 

uncertainty in deriving an expected Mw value (E[Mw]) for each earthquake after many discussions with 

seismic hazard experts. In this analysis we distinguish earthquakes that have (1) “observed” Mw

(typically from inversions of long-period waveforms or surface-wave spectra), (2) magnitudes that are 

assumed to be equivalent to Mw (for example, local magnitude mL and duration magnitude md), and (3) 

Mw formally converted from another magnitude or intensity measure, generally following the formalism 

described by CEUS–SSCn (2012). Magnitudes are adjusted for saturation and scaling effects using 

empirical relations from Sipkin (2003) for body-wave magnitude (mb) and Utsu (2002) for local 

magnitude (mL) and surface-wave magnitude (MS). Magnitude uncertainty is either taken from the 

original source catalog or estimated following Felzer (2008). Each entry in the catalog lists E[Mw], 
52

magnitude uncertainty, and a counting factor (a function of b and magnitude uncertainty) that is used to 

compute unbiased rates (see below). 

Sources contributing to the 2006 catalog included Stover and others (1984), Engdahl and 

Rinehart (1991), Stover and Coffman (1993), Engdahl and Villaseñor (2002), Pancha and others (2006), 

California Geological Survey–UCERF2 Project (Felzer and Cao, 2008), USGS Preliminary 

Determination of Epicenters (2013), and Petersen and others (2008). Information concerning new 

earthquakes since 2006 comes from several sources. The Global Centroid Moment Tensor Project 

catalog (2013) and the St. Louis University catalog (Herrmann, 2013) list earthquakes with “observed” 

moment magnitudes. Catalogs from the UCERF3 project (K. Felzer, written commun., 2013) and the 

USGS Comprehensive Catalog (2013) contribute earthquakes with various types of size measures. We 

also maintain a hand-edited “special-case” catalog from special studies and personal communications, 

including suspected erroneous events and nontectonic events. 

Source catalogs are reformatted, concatenated, and sorted chronologically. They overlap in time 

and space, and when an earthquake is listed in more than one catalog a preferred source is chosen based 

on our best judgment. In the case of duplicates, entries from new catalogs generally supersede old 

entries. Known explosions, mining-related events, and erroneous events are deleted. The catalog with 

duplicates removed is declustered using the algorithm from Gardner and Knopoff (1974). The 

declustered catalog lists 5,622 earthquakes between 1850 and 2012 with Mw greater than or equal to 3.5 

(fig. 35). The contributions from individual source catalogs are listed in table 6. 

Figure 35. Declustered catalog for outlined region of the Western United States with earthquakes Mw3.5 and 

greater since 1850.
53

Table 6. Contributions to the declustered catalog, Mw3.5 and greater, 1850–2012.

[PDE, Preliminary determination of epicenters; UCERF2, Uniform California Earthquake Rupture Forecast version 2;

UCERF3, Uniform California Earthquake Rupture Forecast version 3]

Source catalog Number of earthquakes

Special Cases 16

UCERF2 100

Engdahl and Villaseñor (2002) 27

USGS Preliminary Determination of Epicenters—PDE (2013) 419 

Stover and Coffman (1993) 198 

Stover and others (1984) 235

Pancha and others (2006) 76 

Engdahl and Rinehart (1991) 33

Mw from Centroid Moment Tensor Project (2013) and St. Louis 

University (Herrmann, 2013) 163

UCERF3 2,867

USGS Comprehensive Catalog (2013) 1,488

Total 5,622

Modeling Shallow Crustal Background Seismicity

The overall approach to modeling background seismicity in the WUS was not changed from 

Petersen and others (2008), but we incorporated a new catalog and adaptive smoothing methods in this 

version. Magnitude-dependent catalog completeness levels are the same as 2008. Statistical analysis 

(Weichert, 1980) of the declustered Mw catalog yields a b value of about 0.8, and b=0.8 is adopted for 

the hazard analysis. A grid 0.1 degree in latitude by 0.1 degree in longitude is superimposed on the 

region. Earthquakes with Mw greater than or equal to 4.0 that pass a completeness test are counted in 

each grid cell, and rates are adjusted for variable completeness (Weichert, 1980). Counting is adjusted 

for magnitude uncertainty to give unbiased rates (CEUS–SSCn, 2012). To account for future random 

earthquakes in places with little or no historical seismicity, a seismicity-rate floor is implemented based 

on average seismicity rates computed from the catalog for several broad regions. The historical rate is 

compared with the regional average rate for each grid cell. If the historical rate exceeds the regional 

average, the final modeled rate simply equals the historical rate; however, if the regional average 

exceeds the historical rate, the models are combined with branch weights of 0.667 (historical) and 0.333 

(regional). The final cell rate is never smaller than the historical rate, and active areas are not penalized 

to compensate for the rate floor in quiet areas. Incremental 10a (Herrmann, 1977) is computed from the 

cumulative count. The resulting “a-grid” represents the annual rate of earthquakes with Mw plus or 

minus 0.05 magnitude units in each grid cell.

As in past models, a two-dimensional spatial Gaussian function with a fixed, uniform correlation 

distance of 50 km is implemented to smooth the a-grid to account for uncertainties in the locations of 

future earthquakes. For the 2014 update, a procedure that adaptively derives smoothing lengths using a 

nearest-neighbor algorithm also has been implemented based on work by Helmstetter and others (2007) 

and Werner and others (2011). The smoothing distance is unique to each earthquake and is set equal to 
54

the distance to the nth nearest neighboring epicenter (neighbor-number). We use established likelihood 

testing methods (Helmstetter and others, 2007; Werner and others, 2011) to optimize the neighbornumber, and find that the fourth nearest neighbor produces the optimal smoothed model to match recent 

spatial patterns of seismicity. The adaptive smoothing is implemented for a single completeness level 

that maximizes the likelihood parameter. For the WUS catalog, we find that the completeness level 

giving the highest likelihood is Mw4.0 (since 1963). Differences in the a-grids from the fixed- and 

adaptive-smoothing methods result from the spatial variation in epicenter density. In more active 

regions, the adaptive method yields smaller correlation lengths and higher local seismicity rates. 

Comparisons of the a-grids from the different smoothing methods and the resulting hazard differences 

are given in figure 36. In the final hazard model, a-grids using fixed and adaptive smoothing are 

combined with branch weights of 0.60 and 0.40, respectively. 

Figure 36. Maps showing incremental seismicity-rate grids from alternative smoothing methods for 5-hertz spectral 

acceleration. Costal California and Central and Eastern United States seismicity is not included in the grids. A, 

Map of fixed-correlation-length smoothing method and B, adaptive-correlation-length smoothing method. 

As in past models, separate a-grids are developed from subcatalogs for regions where 

extensional or nonextensional ground motion relations are used to compute hazard. For the extensional 

zone, we apply ground motion models with branch weights of 0.667 on normal faulting mechanisms and 

0.333 on strike-slip faulting mechanisms to account for variability in future Intermountain West 
55

earthquakes. For the nonextensional zone, we apply branch weights of 0.667 on reverse faulting 

mechanisms and 0.333 on strike-slip faulting mechanisms to account for the compression and shear in 

the Pacific Northwest region. These ratios were determined from the geodetic data and are described in 

section “Combined Geodetic- and Geologic-Based Slip-Rate Models.” 

Maximum Magnitude for Shallow Crustal Background Seismicity

The 2008 and previous USGS NSHMP maps modeled Mmax 7.0 for background seismicity in 

most places in the WUS, except in the Central Nevada Seismic Zone (Mmax 7.5) and in geodetic-based 

shear zones (Mmax 7.6). General consensus in the scientific community is that Mmax should be greater 

than that assumed in previous models because (1) our inventory of potential sources is incomplete, (2) 

we have not considered possible linkage of short faults into a long rupture, and (3) we cannot identify 

locations where possible future rupture on a fault is not or is poorly expressed at the surface, such as the 

causative fault of the September 2010, Mw7.1, Darfield, New Zealand, earthquake (Quigley and others, 

2011). In addition, hazard studies in California and the CEUS have considered magnitudes of Mw7.9 

and greater, which is much larger than we have considered in previous models. All known faults are not 

included in our source model because nearly three-fourths of all known Quaternary faults have 

insufficient information to characterize recurrence rates of moderate to large earthquakes. The historical

record clearly demonstrates that faults that might be considered independent sources (segments) could 

link up to form larger earthquakes than we have modeled in the past. The longest historical normal 

surface rupture in North America happened in 1887 in northern Mexico. The Sonora earthquake had an 

estimated magnitude between Mw7.2 and Mw7.6 and ruptured four distinct faults (Suter, 2006, 2008a, 

b). Because we are increasing Mmax in surrounding regions and for other reasons previously stated in 

this section, we cannot identify defensible reasons to exclude them from the Intermountain West or the 

Pacific Northwest model. Therefore, we selected two Mmax alternatives: one with Mw7.45 (branch 

weight 0.9), similar to the Sonora, Mexico, earthquake; and one with Mw7.95 (branch weight 0.1), 

which is consistent with the moment of the geodetic-based velocity data. On the Mw7.45 maximummagnitude branch the magnitude-frequency distribution is modeled as truncated exponential. On the 

Mw7.95 maximum-magnitude branch, the magnitude-frequency distribution is modeled with a tapered 

Kagan (2002) magnitude-frequency distribution, with a corner magnitude of Mw7.5. The maximum 

magnitude Mw7.45 branch also defines Mmax at a value below the minimum characteristic magnitude 

of nearby faults; however, the maximum magnitude Mw7.95 branch does not apply this constraint. On 

this branch, we assume that earthquake ruptures may link up parts of mapped faults and unknown 

structures in the vicinity. In regions with relatively dense mapped faults, we expect big earthquakes 

would be associated with significant coseismic slip on several of these neighboring faults. The Wells 

and Coppersmith (1994) scaling relation for average displacement on normal faults suggests 

displacements of less than 3.5 meters (m) for Mw7.9 earthquakes. 

Modeling Deep or Benioff-Zone Seismicity

In this section we describe the modeling of deep intraslab seismicity. We discuss earthquake 

rates, maximum magnitude, and a new depth distribution. 

Earthquake Rates and Maximum Magnitude

In this update, hazard from deep earthquakes is computed in three separate regions: Washington, 

Oregon, and northern California. Deep earthquakes (greater than 40 km deep) are modeled with a 

truncated Gutenberg-Richter magnitude-frequency distribution. The minimum magnitude is Mw5.0 in 
56

California and Washington and is Mw6.5 in Oregon, and the maximum magnitude is Mw7.45 or Mw7.95. 

In Washington and Oregon, the b value is 0.4 up to Mw7.2, whereas in northern California, the b value 

is 0.8. 

For deep seismicity with magnitude greater than Mw7.2, the rates are based on a GutenbergRichter magnitude-frequency distribution with slope 0.8 in all three regions. Based on steering 

committee recommendations, we increased the Mmax associated with deep seismicity to Mw7.45 with 

branch weight 0.5 and to Mw8.0 with branch weight 0.5 from Mw7.2 used in previous USGS NSHMP 

maps. The current Mmax values are more consistent with worldwide data; a search of the Global 

Centroid Moment Tensor Project catalog (2013) using a minimum magnitude of Mw7.4, a hypocenter 

depth range of 40–80 km, and a starting date of 1973 yields the hypocenter set shown in table 7. 

Table 7. Global catalog search for large deep earthquakes since 1975. The depth range is 40–80 kilometers. 

[°, degrees; km, kilometers; Mb, body-wave magnitude; MS, surface-wave magnitude; Mw, moment magnitude; UTC, 

Coordinated Universal Time] 

Origin time (UTC) Latitude

(°)

Longitude

(°)

Depth

(km) Magnitude Magnitude type and source

2011-03-11 

06:15:40.28 36.281 141.111 42.6 7.9 Mw USGS Preliminary Determination of Epicenters. 

2009-10-07 

22:03:14.47 ‒13.006 166.510 45.0 7.7 Mw USGS Preliminary Determination of Epicenters. 

2007-11-14 

15:40:50.53 ‒22.247 ‒69.890 40.0 7.7 Mw USGS Preliminary Determination of Epicenters. 

2006-05-03 

15:26:40.00 ‒20.150 ‒174.100 55.0 8.0 Mw Engdahl, and Villaseñor, 2002.

1999-09-30 

16:31:14.00 16.045 ‒96.869 40.0 7.5 MS Engdahl, and Villaseñor, 2002.

1995-07-30 

05:11:24.00 ‒23.336 ‒70.265 40.5 8.0 MS Engdahl, and Villaseñor, 2002.

1993-08-08 

08:34:25.00 12.999 144.872 57.1 7.8 MS Engdahl, and Villaseñor, 2002.

1993-06-08 

13:03:36.00 51.195 157.755 60.5 7.5 MS Engdahl, and Villaseñor, 2002.

1987-03-05 

09:17:05.00 ‒24.396 ‒70.099 46.4 7.6 MS Engdahl, and Villaseñor, 2002.

1985-03-04 

00:32:24.00 ‒33.236 ‒71.740 40.0 7.4 MS Engdahl, and Villaseñor, 2002.

1983-04-03 

02:50:04.00 8.716 ‒83.129 57.0 7.5 MS Engdahl, and Villaseñor, 2002.

1980-07-08 

23:19:24.00 ‒12.485 166.482 55.7 7.5 MS Engdahl, and Villaseñor, 2002.

1978-06-12 

08:14:29.00 38.223 142.022 52.7 7.7 MS Engdahl, and Villaseñor, 2002. 
57

Table 7. Global catalog search for large deep earthquakes since 1975. The depth range is 40–80 kilometers.—

Continued

Origin time (UTC) Latitude

(°)

Longitude

(°)

Depth

(km) Magnitude Magnitude type and source

1977-06-22 

12:08:34.00 ‒22.908 ‒175.749 64.2 8.1 MS Engdahl, and Villaseñor, 2002.

1977-04-21 

04:24:12.00 ‒10.007 160.811 43.4 7.4 MS Engdahl, and Villaseñor, 2002.

1976-11-30 

00:40:58.00 ‒20.548 ‒68.874 74.4 7.6 MS Engdahl, and Villaseñor, 2002.

1976-08-16 

16:11:11.00 6.292 124.091 58.5 8.0 MS Engdahl, and Villaseñor, 2002.

1976-01-14 

15:56:34.00 ‒29.212 ‒177.635 42.2 7.8 MS Engdahl, and Villaseñor, 2002.

1975-10-31 

08:28:04.00 12.537 125.999 51.1 7.5 Mw Engdahl, and Villaseñor, 2002.

1975-07-20 

14:37:42.00 ‒6.612 155.095 61.1 7.5 Mb Engdahl, and Villaseñor, 2002.

In our model, we do not want to overpredict the rate of large deep earthquakes, since we have 

seen none with magnitude greater than Mw7 in the historical record of the WUS coastal region (an 

earlier estimate of the 1949 Olympia deep-source earthquake is Mw7.1; however, more recent estimates 

are lower, Ichinose and others, 2006). To obtain a reasonable rate of large deep earthquakes, we assume 

the historical rate of Mw4–7 earthquakes, and we constrain the model to have that same cumulative rate. 

The deep-source (magnitude-rate) distribution in the Puget Sound area is shown in figure 37. The 

cumulative rate under the black line from Mw4 to 7 equals the cumulative rate under the dashed red line 

from Mw4 to 7. In Oregon, we used the same approach as is shown in figure 37. That is, we conserved 

the observed rate of Mw4–7, and used two branches both with truncated Gutenberg-Richter rates, with

b=0.8, and with maximum magnitude of Mw7.45 and Mw7.95, respectively. In northern California, we 

simply increased Mmax; the parameter b was set to 0.8 for all magnitudes in California.
58

Figure 37. Magnitude-frequency distribution of deep seismicity in the Puget Sound region. Black curve shows the 

incremental rate of earthquakes up to Mw7.2; bin size equals 0.1-magnitude unit. Two logic-tree branches are 

used for earthquakes with magnitudes greater than Mw7.2, one having maximum magnitude of Mw7.5 (green 

curve), the other having maximum magnitude of Mw8.0 (blue curve), each branch weight 0.5.

The deep-focus (Benioff zone) earthquake rates in the 2008 and current models are summarized 

in table 8. The final two columns show the rates of larger earthquakes not previously considered. For 

example, the mean annual rate of Mw7.2–7.5 in western Washington is 6.4E-04 for a recurrence time of 

1,562 years (branch weight 0.5) or a mean annual rate of 9.9E-04 for a recurrence time of 1,010 years 

for Mw7.2–8.0 (branch weight 0.5). Similar estimates of deep earthquake rates in Washington and 

Oregon for the 2014 model compared to that of 2008 are shown in table 8, but a significant decrease of 

this rate in northern California. The decrease in estimated rate of deep earthquakes in northern 

California is attributed to two factors: (1) a reclassification of some deep earthquakes as aftershocks that 

were previously treated as independent earthquakes, and (2) a reclassification of several hypocenters as 

shallow that previously were listed as deep but were poorly constrained. In the 2014 update, the 

Washington and California Benioff zone boundaries remain the same as in previous USGS NSHMP 

maps, but the Oregon Benioff zone has been expanded to cover the entire western part of the State. In 

2008, this zone only covered the northwest part of the State. In Oregon, because of the sparseness of 

deep earthquakes in the catalog, two logic-tree branches on earthquake location are considered for the 

2014 update. The first uses Gaussian smoothing with a 50-km smoothing radius around catalog 

epicenters and the second uses a uniform zone (keeping the rate of deep events per unit area constant). 

These two logic-tree branches are assigned equal weight.
59

Table 8. Benioff zone earthquake rates. 

[yr, years; Mw, moment magnitude] 

Region 2008 mean 

annual rate

2008 mean 

return time

(yr)

2014 mean 

annual rate

Mean annual 

rate Mw7.2–7.5

Mean annual 

rate Mw7.2–8 

N.W. California 4.41E-02 22.7 0.0273 2.1E-04 3.7E-04

W. Oregon 4.0E-03 250 0.00374 1.3E-04 1.6E-04

W. Washington 1.153E-01 8.8 0.1357 6.4E-04 9.9E-04

The Staircase Distribution of Benioff Hypocenters

When computing hazard from deep earthquakes, GMMs are sensitive to depth of the earthquake 

rupture. This depth parameter not only affects the hypocentral depth, and therefore distance from site, 

but also affects the ground motion models since the increase of median response increases with focal 

depth (at the depths considered in this analysis). Intraplate (deep) earthquakes in the Pacific Northwest 

tend to be confined to a depth band of about 35 to 70 km. In other regions, Benioff zone seismicity 

extends to greater depths, as much as 600 km or more, but is limited in this study area because of the 

relative youthfulness of the Juan de Fuca slab (McCrory and others, 2012), which is warmer than other 

convergent margin slabs. 

In all previous NSHMP products, deep seismicity in the Pacific Northwest and California was 

assigned a fixed depth of 50 km. Although 50 km is a reasonable average depth, an improved model 

would account for an increasing average depth of focus as the Juan de Fuca slab descends into the 

Earth’s mantle. In the 2014 update, we improve the hazard model by increasing the slab depth towards 

the east as a set of three steps, with discrete jumps at specific longitudes. Hypocenter data and 

information about the interface location are used to build the focal-depth model. The two sets of 

hypocenter data (USGS Advanced National Seismic System, 2014, and the declustered catalog from this 

study), the Cascadia interface at the latitude of Seattle, and the proposed depths for Benioff seismicity 

(the “staircase”) are shown in figure 38. Longitudes of some cities are shown. Seattle, Wash., is over the 

deepest step (60 km), Portland, Oreg., is over the middle step (50 km), and Astoria, Oreg., is over the 

shallowest step (41 km). The shallowest depth on the interface with episodic tremor and slip is at the 

intersection of the red and green lines, about 35 km depth in figure 38. This location is the deepest 

interface-event rupture depth on any logic-tree branch. Deep intraplate seismicity, however, extends 

much farther east. The blue squares in figure 38 are the reported hypocenters of the deep seismicity used 

to compute the activity grid (C. Mueller, written commun., 2013). The black squares are event 

hypocenters from the USGS Advanced National Seismic System (2014) catalog, for Mw2.6 and greater 

sources with depth greater than 35 km and origin times in the period 1990–2013, when hypocenter 

estimates are believed to be reasonably accurate. The catalog of deep Oregon seismicity is too sparse to 

provide guidance for defining a staircase depth distribution. The depth distribution shown in figure 38

also is used in Oregon in the 2014 update. 
60

Figure 38. Distribution of deep seismicity beneath the Cascadia interface at lat 47.3 ̊ N. and modeled depth used 

for Washington deep seismicity.

The northern California distribution of deep hypocenters, the proposed staircase for modeling 

these hypocenters, and Cascadia interface projected onto a plane at the lat 41.3°N. are shown on figure 

39. Eureka, Calif., is over the shallowest step, at a depth of 39 km, and Redding, Calif., is over the 

deepest step, at depth –60 km. The top of the zone of episodic tremor and slip is at –30 km in northern 

California, shown in figure 39 as the point where the red Cascadia (seismically active) interface meets 

the green (aseismic) Cascadia interface. The shallow step extends farther east, to long 123.05°W., than 

the corresponding step in Washington and Oregon. 
61

Figure 39. Distribution of deep seismicity beneath the Cascadia interface in northern California and modeled depth 

used for northern California deep seismicity hazard.

Fault-Based Source Model in the Western United States

Many fault studies show clear evidence of repeated earthquakes of sufficient magnitude to 

rupture the surface of the Earth. Thus, it is standard practice to include explicit fault sources to augment 

background sources defined by seismicity, thereby extending the historical record back thousands of 

years. For each update of the USGS NSHMP maps, we adjust our source characterization to incorporate 

new published studies in the region. Paleoseismic and geologic data inform the fault-source model 

regarding the timing, amount of slip per earthquake, and slip rate. 

Source characterization improves through better understanding of the region’s seismic sources. 

There are over 2,000 known faults in the WUS that are oriented such that they could relieve regional 

stress in future earthquakes. Most are poorly understood and characterized only by their location. The 

NSHMP models include a fault as a source of future earthquakes when the paleoseismic history has 

been studied sufficiently. These studies provide not only fault location but also evidence of the size, 

extent of surface rupture, and timing of earthquakes. These site-specific details are required to 

characterize a source for the purpose of this fault-source model. As a consequence, the fault-source 

inventory in this model, as in previous models, remains incomplete. Nearly 75 percent of the known 

faults with Quaternary surface rupture in the region are poorly characterized. Many of these 
62

uncharacterized faults are tens of kilometers to more than 100 km in length and could generate 

significant earthquakes.

We model potential future earthquakes on the explicit fault sources as those that could rupture 

the entire fault (full-source rupture) and more numerous smaller magnitude earthquakes (floating 

partial-source ruptures) that range in magnitude from Mw6.5 to the magnitude of the full-source rupture. 

The full-source rupture magnitude branch is assigned a branch weight of 0.667 in the Intermountain 

West and 0.5 in the Pacific Northwest; the partial-source rupture magnitude branch is assigned either 

0.333 or 0.5 in the respective regions (fig. 40). Most faults in the WUS are normal fault with possible 

maximum magnitudes of Mw6.15–7.75 (fig. 41); however, we characterize the longest sources (longer 

than about 100 km) by floating partial-source ruptures with magnitudes of Mw6.5–7.5. The mode of the 

maximum magnitude for all normal sources is Mw6.95–7.05. The region contains many fewer strike-slip 

and thrust sources. Strike-slip fault sources are assigned maximum magnitudes of Mw6.00–7.34 and 

thrust and reverse fault sources are assigned maximum magnitudes from Mw6.15 to 7.5. Partial-source 

ruptures allow for smaller earthquakes on a fault. 
63

Figure 40. Logic tree for crustal fault sources in the Intermountain West (IMW) and Pacific Northwest (PNW). 

Assigned branch weight shown in parentheses.
64

Figure 41. Distribution of assigned full-source rupture magnitude for crustal fault sources in the Intermountain 

West and Pacific Northwest by sense of slip.

Fault sources in this model are constrained by 40 years of published geologic and paleoseismic 

studies that characterize activity rate and fault geometry throughout the United States. The model is 

based on simplified fault geometry that defines its three-dimensional plane in the Earth’s crust and one 

or more parameter(s) to constrain how active the fault is in the model. Typically, the assigned parameter 

is slip rate; slip rate is the measure of displacement on the fault resolved to the three-dimensional fault 

plane divided by the appropriate time period. For some fault sources, we constrain the rate of future 

earthquakes based on the known geologic record when that record does not support the predicted return 

time of full-source ruptures that would be derived from the assigned slip rate. The dimensions of the 

fault source constrain its potential maximum magnitude, which along with slip rate determines the 

frequency of future earthquakes as an annualized rate.

Fault-Source Geometry

The location of fault sources is simplified from the USGS Quaternary fault and fold database 

(http://earthquake.usgs.gov/hazards/qfaults/); faults in this compilation are mapped at scales of either 

1:250,000 or 1:100,000. However, the fault sources are accurately located at a scale of 1:1,000,000. 

Each fault source projects from the Earth’s surface to a depth of 15 km, and is assigned a nominal dip 

based on its sense of slip: strike-slip fault sources dip 90°, thrust fault sources dip 45°, and reverse fault 

sources dip 60°. 

In early versions of the NSHMP maps, normal faults in the WUS were modeled using a single 

assigned dip of 60° (Frankel and others, 1996, 2002), based on the theory of maximum principal stress 

for extensional environments (Anderson, 1951) and Byerlee’s (1978) law. The previous version of the 

NSHMP model included dip uncertainty (Petersen and others, 2008). In 2008, normal faults were 

assigned dips of 40°, 50°, and 60° based on recommendations from the Basin and Range Province 

Earthquake Working Group (Lund, 2006). In 2012, the working group determined that dip uncertainty 

was underrepresented based on a global dataset of normal earthquakes. The Basin and Range Province 

Earthquake Working Group suggested using a default dip of 50±15° for normal faults (Lund, 2012). 

Implications for hazard are significant: sources with gentler dips are closer to the Earth’s surface at 
65

greater distances, the bottom of a 35°-dipping source extends horizontally up to three times the 

horizontal distance from the surface trace than a 65°-dipping source, and the conversion of vertical 

displacement to fault-parallel slip is proportional to (1/sin(dip))2

. These effects all contribute to 

increased hazard over the shallow-dipping source alternative. Fault-specific dip data are sparse for 

normal faults in the WUS, but the studies cited below conclude that normal faults dip between 45° and 

55°. Locally, the Salt Lake City segment of the Wasatch fault, Utah, may dip 35° (see figure 8 in Bruhn 

and others, 1992); however, the preferred model for the Wasatch and other nearby faults for analytic 

stress modeling was pure normal slip on planar rectangular faults dipping 55° (Chang and Smith, 2002; 

Chang and others, 2006). Historically, normal crustal earthquakes have been shown to nucleate on 

moderate-to-steeply dipping structures, with a mode of 45° (Molnar and Chen, 1982; Jackson and 

White, 1989; Thatcher and Hill, 1991; Collettini and Sibson, 2001; Jackson, 2002). Recent data suggest 

that low-angle normal faults may be located in Papua New Guinea, Greece (the Gulf of Corinth), and 

Italy (the Apennines) (Collettini, 2011), but the debate regarding the potential of low-angle faults is 

ongoing (Abers, 2009). Whether or not these recent findings are relevant to the extensional WUS is 

unknown. This update assigns a default dip to normal sources of 50±15° (fig. 40). No dip uncertainty is 

assigned to strike-slip, thrust, or reverse fault sources. 

We recognized in past models (Frankel and others, 1996, 2002; Petersen and others, 2008) that 

our results predicted somewhat more full-source ruptures than is represented in the paleoseismic record. 

The segmentation paradigm in the WUS is based on the observation that long faults do not rupture in 

their entirety in large-magnitude earthquakes and when they rupture they typically have a similar 

displacement at any given site. These models often identify changes in fault geometry and timing of past 

earthquakes to prescribe segments; however, historically geometrical boundaries often are not 

diagnostic in defining the limits of the surface rupture. The 1887 Sonora earthquake (Suter, 2006, 

2008a, b), the 1915 Pleasant Valley earthquake (Wallace, 1984), the 1985 Borah Peak earthquake 

(Crone and others, 1987), and the 1959 Hebgen Lake earthquake (Witkind, 1964) ruptured through at 

least one geometrical boundary. To account for this uncertainty in defining segments, we model both 

full-rupture sources as well as partial segment ruptures to account for a broad range of alternatives. For 

fault sources longer than about 100 km, we float ruptures along the source with Mw6.5 to Mw7.5. 

We model fault segments for only a few fault sources in this model; the remaining faults in the 

model are allowed to rupture their entire length or rupture shorter parts of the fault (floating ruptures) 

that do not exaggerate hazard at segment boundaries. The source model is informed both by reported 

single-event displacement, where large displacement is the best evidence for past large magnitude 

earthquakes, and earthquake recurrence from the USGS Quaternary fault and fold database and 

supplemental sources. For most WUS sources, larger magnitudes are calculated from magnitudelength/area scaling relations than is supported by large single-event displacements reported in the 

literature. We have only used the Wells and Coppersmith (1994) equations for calculating magnitudes 

and it may be useful to include other scaling relations in the future versions of the map. 

Wasatch Fault Zone—Fault Geometry Under Salt Lake City

The Salt Lake City segment of the Wasatch fault zone presents challenges because of uncertainty 

in the location of the fault plane, especially beneath metropolitan Salt Lake City, Utah. Salt Lake City 

occupies a large re-entrant in the Wasatch Mountains range front that is bounded on the north by the Salt 

Lake salient and on the south by the Traverse Mountains. Complex surface faulting is recognized at the 

latitude of Salt Lake City (fig. 42). Three-dimensional relations between the faults that define the eastdipping West Valley fault zone and the west-dipping Wasatch fault zone are not known but may be 

illustrated as depicted in figure 43, from right to left: the Wasatch range-front fault, and the East Bench 
66

fault, the Taylorsville scarp and the Granger scarp of the West Valley fault zone. An alternative to this 

assumption is that the Wasatch range-front fault and the East Bench fault do not merge at depth and 

independently project to seismogenic depths (15 km), with the West Valley fault(s) truncating at the 

East Bench fault; however, several alternative models can represent the bifurcation and gap in surface 

expression of faulting. Geophysical data do not provide conclusive evidence of the location or dip of the 

fault.

Figure 42. Map of Quaternary faults near Salt Lake City, Utah. The predominantly west-dipping faults with 

evidence of Holocene activity associated with the Wasatch fault zone are differentiated from those without 

evidence of Holocene surface rupture. The Holocene West Valley fault zone is antithetic to the Wasatch fault 

and dips to the east.
67

Figure 43. Sketch of spatial relations between a primary fault zone and antithetic fault zone that may reflect the 

relations between the northern part of the Salt Lake City segment of the Wasatch fault zone and the West 

Valley fault zone (modified from Bruhn and Schultz, 1996).

The location of the Wasatch fault near Salt Lake City is constrained by nearly continuous, 

prominent fault scarps at or near the range front from the Traverse Mountains to the Salt Lake salient. 

Details of surface rupture are further defined at four trench sites: the two southernmost trench sites at 

South Fork of Dry Creek (Black and others, 1996) and Little Cottonwood Canyon (Swan and others, 

1980; McCalpin, 2002), and the northern two on the East Bench fault at Dresdan Place (Machette and 

others, 1992) and Penrose Drive (DuRoss and Hylland, 2010). Trenches on the Warm Spring fault at 

Warm Springs Park did not reveal the Wasatch fault (DuRoss and Hylland, 2010); however, evidence of 

surface rupture was present in a trench in northern Salt Lake City (Robison and Burr, 1991). Thus, the 

absence of fault scarps between the northern end of the East Bench fault and the Warm Springs fault 

permits a number of viable options, not all of which are explored here. All the models we present vary 

in location north of Big Cottonwood Canyon. The magnitude of the full-source rupture is defined by 

surface-trace length to magnitude-scaling (all) relations of Wells and Coppersmith (1994). 

We adopted alternative rupture models in the update of the USGS NSHMP maps: two 

alternatives break the entire length of the Salt Lake City segment and one alternative breaks two parts of 

the fault in a short period of time. The mean recurrence interval for full-source ruptures is constrained to 

1,300 years (Lund, 2013). Along with the full-source rupture, we model partial rupture of the source 

with magnitudes Mw6.5–7. The rate of floating partial-source ruptures is constrained by an assigned slip 

rate of 1.7 mm/yr (based on throw rate of 1.3 mm/yr in Lund, 2013), a dip of 50±15° (Lund, 2012), and

b=0.8. Weights assigned to the three dip branches are 0.6, 0.2, and 0.2, respectively. The mean annual 

slip rate on the fault is constrained to 1.3/sin(50 ̊) on all three dip branches.

In addition, a floating Mw7.4±0.2 rupture of the Wasatch fault zone from its southern to its 

northern extremity is included in the model. The floating Mw7.4±0.2 is modified from its 

characterization in the previous version of the national seismic hazard maps (Petersen and others, 2008). 
68

The modification places a discontinuity in the fault at the north end of the East Bench location and uses 

a 3-km step when moving this rupture along the fault trace. In the 2008 model, we used a 1-km step. 

Model 1 

The full-source magnitude for the Salt Lake City segment of the Wasatch Fault source in this 

alternative model is Mw7.03±0.2. The northern part of this source is constrained by the easternmost 

branch of the East Bench fault; the source passes through both the Dresdan Place trench site and the 

Penrose Drive site. The Penrose Drive location is joined to the southern end of the eastern trace of the 

Warm Springs fault. J. Pechmann (written commun., 2010) provided this two-dimensional geometry 

based on Roten and others (2011). This model differs from the Roten and others (2011) model by 

defining a uniform dip along the entire source instead of using variable dip along strike as defined by 

Bruhn and others (1992). The 5-hertz and 1-hertz spectral acceleration associated with this model (fig. 

44) results in maximum ground motion of 1.465 g (acceleration of gravity) and 0.455 g, respectively, at 

lat 40.705°N., long 111.90°W.
69

Figure 44. Results of hazard analysis for model 1 based on Roten and others (2011) geometry of the Salt Lake 

City segment of the Wasatch and the West Valley sources for 5-hertz (0.2-second) and 1-hertz (1-second) 

spectral acceleration for 2-percent probability of exceedance in 50 years and VS30 site condition of 760 meters 

per second. Maps compare A, 5-hertz and B, 1-hertz spectral acceleration results; and ratios of the alternative 

model compared to 2008 source model for C, 5-hertz and D, 1-hertz spectral acceleration. Locations of the

Warm Springs fault, hypothetical tear fault, and East Bench fault are shown.
70

Model 2 

In this alternative model, we retain the geometry in model 1 and replace the single rupture with 

three temporally clustered ruptures: an Mw6.9±0.2 rupture on the Cottonwood-East Bench fault, an 

Mw5.4±0.2 rupture on a hypothetical tear fault (Roten and others, 2011), and an Mw6.7±0.2 rupture on 

the Warm Springs fault. The sum of moment rates for these three events approximates an Mw7 source 

on the entire Salt Lake City segment. The clustered-event approach allows us to associate different 

rupture styles, different fault top and bottom depths, and different fault dips on the three subsources, a 

degree of flexibility that is not possible if we assume a full-source rupture. In the temporally clustered

model, the tear fault is shallow with the top of rupture at 1-km depth and bottom of rupture at 6-km 

depth; the sense of movement on the tear fault is strike slip. Presumably, the hypothetical strike-slip 

fault is truncated at depth by the East Bench fault. The partial-source (but nonclustered) rupture 

branches are the same as those in model 1. In the other models, software limitations require that the 

same normal-slip fault extends from the surface to 15-km depth everywhere. This model also 

accommodates the potential west-trending tear fault. The probabilistic motions are shown in figure 45. 

The maximum 5-hertz and 1-hertz ground motions are 1.57 g and 0.476 g, respectively, at lat 40.765°N. 

and long 111.90°W. 
71

Figure 45. Results of hazard analysis for model 2, the clustered-event model of the Salt Lake City segment of the 

Wasatch and the West Valley sources for 5-hertz (0.2-second) and 1-hertz (1-second) spectral acceleration for 

2-percent probability of exceedance in 50 years and VS30 site condition of 760 meters per second. Maps 

compare A, 5-hertz and B, 1-hertz spectral acceleration results; and ratios of the alternative model compared to 

2008 source model for C, 5-hertz and D, 1-hertz spectral acceleration. Locations of the Warm Springs fault, 

hypothetical tear fault, and East Bench fault are shown.
72

The temporally clustered-event model produces slightly larger probabilistic motion than several 

of the other models at sites near the three faults (fig. 46) (that is, parts of downtown Salt Lake City). 

This is because any of the three ruptures can produce the maximum motion. Although not specified 

exactly when these three earthquakes would rupture, it is generally assumed that they would happen 

within minutes to months of one another. Little guidance is available from the limited historical Basin 

and Range earthquake sequences, but one could consider analogies with the 1954 ruptures in the Central 

Nevada seismic zone including July, Stillwater; August, Rainbow Mountain; and December, Dixie 

Valley-Fairview Peak earthquakes or the 1959 Hebgen Lake doublet (Doser, 1985). 

Figure 46. Plots of probabilistic ground motions for 5-hertz and 1-hertz spectral acceleration at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second along profiles A, at lat 

40.75°N. and B, at lat 40.60°N.

Model 3 

The full-source rupture magnitude for the Salt Lake City source in this alternative model is 

Mw7.05±0.2. The northern part of this source is constrained by the easternmost branch of the East 

Bench fault; the source passes through the Dresdan Place trench site and the Penrose Drive site. The 

Penrose Drive locality is joined to the Warm Springs fault following the Virginia Street fault, which is 

in the footwall of the Warm Springs fault. The part of the Warm Springs fault nearest to and possibly 

extending into downtown Salt Lake City is not included in this source. The 5-hertz and 1-hertz spectral 

acceleration associated with this model (fig. 47) results in maximum ground motion of 1.387 g and 

0.431 g, respectively, at lat 40.7°N, long 111.90°W. 
73

Figure 47. Results of hazard analysis for model 3 of the Salt Lake City segment of the Wasatch and the West 

Valley sources for 5-hertz (0.2-second) and 1-hertz (1-second) spectral acceleration for 2-percent probability of 

exceedance in 50 years and VS30 site condition of 760 meters per second. Maps compare A, 5-hertz and B, 1-

hertz spectral acceleration results; and ratios of the alternative model compared to 2008 source model for C, 5-

hertz and D, 1-hertz spectral acceleration. Locations of the Warm Springs fault, hypothetical tear fault, and 

East Bench fault are shown.
74

These three models represent epistemic alternatives on the fault geometry and the nature of fault 

rupture. We assign equal weight (0.24 weight) to each alternative in the final hazard model for fullsource ruptures and floating partial-source ruptures of only alternative model 1 (0.18 weight).

Maximum Magnitude for Fault Sources

Regression relations based on the seminal compilation of Wells and Coppersmith (1994) have 

been used to assign the magnitude of full-source ruptures (Mw with two-sigma uncertainty of ±0.24 

magnitude units) for the hundreds of fault sources in the Intermountain West and the Pacific Northwest 

in the NSHMP model. It typically has been the standard of practice in the industry to apply this scaling 

equation to estimate magnitude from fault dimensions; the previous versions of the maps used this 

scaling equation as well. Nevertheless, when these modeled annual frequencies are compared to the 

paleoseismic record, the modeled rates often are larger than the frequency of paleoseismic earthquakes.

A consequence of underestimating magnitudes for full-source ruptures is that higher annual frequencies

for all magnitudes are implied. Further studies are required to determine the most appropriate scaling 

equations for this region. For this update, we continue to apply the Wells and Coppersmith (1994) 

equations as in previous versions of the maps. We plan to study this effect and determine if alternative 

magnitude-scaling equations should be applied in future versions of the map. 

Constraining Frequency of Future Events

Typically, what is reported as a slip rate is in fact a throw or heave rate that is not resolved to the 

fault plane at depth. This limited information is reported because the dip of the fault is unknown and, 

with few exceptions, the dip of the fault at the surface is a poor proxy of its dip at depth. Trenching of 

historical, normal surface ruptures clearly shows faults at much steeper dips in the near-surface 

exposure than the modeled fault based on seismological constraints. Therefore, most geologic and 

paleoseismologic studies report only the horizontal or vertical component of displacement at one or a 

few point locations along the fault. Few, if any, faults in the WUS are characterized by a sufficient 

number of randomly distributed sites to yield statistically significant models of earthquake recurrence

(Hemphill-Haley and Weldon, 1999). Furthermore, it is rare that investigators describe whether offset at 

the selected site represents an average displacement or not; however, if the actual extent of the ruptures 

were known, a general statement of representativeness could be made (for example, Biasi and Weldon, 

2006; Wesnousky, 2008). The current methodology accepts these limitations in the data, but there 

remains considerable uncertainty in the fault-source model. Slip rate as assigned in this model may 

represent many or all published data or it may reflect only the best-documented data. 

Scaling slip rate with dip uncertainty increases the rate of earthquakes modeled on shallowdipping alternatives and reduces the number of earthquakes at steeper dips; however, the shallowdipping alternative would contribute most to the hazard if slip rate was scaled to the assigned dip of the 

source. An unintended consequence of incorporating dip uncertainty into the model is that rates of 

future earthquakes exceed those observed from the prehistoric record. In order to minimize this effect, 

we constrain event rate for the alternative dips by the rate from the preferred dip of the source. This 

method is preferred because calculated event rate then can be compared directly to the known geologic 

record. 
75

Update of Geologic-Based Fault-Source Parameters

We update the fault-source model based on new literature published since the previous maps 

(Petersen and others, 2008), which includes our comprehensive review of the key input data for the 

model. 

Faults across the United States were discussed at several of our workshops and we have updated 

parameters and models (fig. 48, table 9).

• All normal faults have updated three-dimensional geometry

• New sources were added based on recent studies 

• Nine sources are modified with additional geologic information

• Fourteen sources have updated slip rate 

Figure 48. Map of crustal fault sources in the Intermountain West and Pacific Northwest. Fault sources in 

California are not shown.
76

Table 9. Changes in Intermountain West and Pacific Northwest crustal fault-source model parameters. 

Name State Updated parameter 2008 value 2014 value Reference

Algodones fault 

zone

Arizona extend length of source 19.17 26.57 U.S. Bureau of Reclamation (2009).

Big Chino-Little 

Chino fault

Arizona extend length of source 

to include Little Chino 

fault

64.61 Gootee and others (2010); Ferguson 

and others (2012); Pearthree and 

Ferguson (2012).

Gore Range 

frontal fault

Colorado new source in 2014 Derouin and others (2010).

Williams Fork 

Mountains fault

Colorado new source in 2014 Kirkham (2004).

Sawtooth fault Idaho new source in 2014 Thackray and others (2009, 2013); 

Johnson (2010).

Centennial fault Montana throw rate 0.9 0.7 Petrik (2008).

Benton Spring 

fault

Nevada heave rate 0.27 0.5 Bell (1995); Wesnousky (2005).

Bettles WellPetrified Springs 

fault

Nevada heave rate 1.3 Wesnousky (2010).

Desatoya 

Mountains fault 

zone

Nevada throw rate 0.1 0.04 Koehler and Wesnousky (2011).

Eglington fault Nevada constrain annual rate 0.000066 0.00044 C. dePolo (written commun., 2013).

Lone Mountain 

fault zone

Nevada throw rate 0.13 0.2 Hoeft and Frankel (2010).

Rainbow 

Mountain fault 

zone

Nevada heave rate 0.15 0.2 Caskey and others (2004).

Sand Springs 

Range fault

Nevada throw rate 0.1 0.2 Bell and others (2004).

Schell Creek 

Range fault 

system

Nevada throw rate 0.01 0.1 Koehler and Wesnousky (2011).

Smith Valley fault Nevada throw rate 0.38 0.25 Hayes (1985); Wesnousky and 

Caffee (2011).

Toiyabe Range 

fault zone

Nevada throw rate 0.22 0.06 Koehler and Wesnousky (2011).

Wassuk Range 

fault zone

Nevada throw rate 0.55 0.7 Bormann and others (2012).

Western Toiyabe 

Range fault zone

Nevada throw rate 0.2 0.07 Koehler and Wesnousky (2011).

Embudo fault New 

Mexico

heave rate 0.09 0.13 Bauer and Kelson (2004).

Steens fault zone Oregon throw rate 0.3 0.27 Personius and others (2007).
77

Table 9. Changes in Intermountain West and Pacific Northwest crustal fault-source model parameters.—Continued

Name State Updated parameter 2008 value 2014 value Reference

Great Salt Lake 

fault zone, 

Antelope Island 

section

Utah constrain annual rate 0.000651 0.000238 Lund (2005, 2013).

Great Salt Lake 

fault zone, 

Fremont Island 

section

Utah constrain annual rate 0.000746 0.000238 Lund (2005, 2013).

Great Salt Lake 

fault zone, 

Promontory 

section

Utah constrain annual rate 0.000511 0.000238 Lund (2005, 2013).

Sevier/Toroweap 

fault zone 

(northern)

Utah throw rate 0.36 0.04 Lund and others (2008).

Wasatch fault 

zone, Nephi 

section

Utah constrain annual rate 4.00E-04 1.11E-03 Lund (2013).

Wasatch fault 

zone, Provo 

section

Utah constrain annual rate 4.17E-04 7.69E-04 Lund (2013).

Wasatch fault 

zone, Salt Lake 

City section

Utah location modified Roten and others (2011).

Wasatch fault 

zone, Weber 

section

Utah constrain annual rate 7.14E-04 7.69E-04 Lund (2013).

West Cache 

fault, Junction 

Hills section

Utah new source in 2014 Lund (2005).

Saddle Mountain 

fault

Washington Added 0.25 branch 

weight to Holocene 

slip rate

0.5 mm/yr West and others (1996); West 

(1997). 

Southern 

Whidbey Island

Washington extend length of 

source

Dragovich and others (2007, 2009, 

2010); Sherrod and others (2008).

Tacoma fault Washington new source in 2014

maps

Sherrod and others (2004).

Bear River fault Wyoming constrain annual rate Not 

applicable

0.00043 Lund (2013).

Grand Valley 

fault

Wyoming throw rate 1.1 0.8 reevaluation of original data.

Rock Creek fault Wyoming throw rate 1.7 0.62 Lund (2013).

Teton fault Wyoming throw rate 1.3 0.7 O’Connell and others (2003); 

Hampel and others (2007); White 

and others (2009).
78

Wasatch Fault Zone

The Wasatch fault, bounding the eastern side of the Utah urban corridor, is one of the few faults 

with explicit segmentation in the NSHMP model. The source geometry includes the same dip 

uncertainty as other Intermountain West normal faults (50±15°), and characteristic magnitudes are

based on the surface-rupture length for all styles of faulting (Wells and Coppersmith, 1994). 

Much of the model is similar to that in the 2008 USGS NSHMP maps, which is based on a rich 

paleoseismic record. The Wasatch fault zone is the most studied of any fault in the region; most of the 

trenches, which are distributed along the central 300 km of the Wasatch fault zone, have evidence of 

multiple late Quaternary surface ruptures that are constrained by radiometric dating. In this update of the 

USGS NSHMP maps, we assign a low branch weight (0.1) to floating Mw6.5–7.4 ruptures that are 

permitted to break through segment boundaries. The rate of these modeled earthquakes is defined by the 

mean slip rates for each segment in Lund (2013). 

The geometry used in the 2008 fault-source model for all segments of the Wasatch fault zone is 

retained in this update except for the Salt Lake City segment, which is described above. The geometry 

of the central six fault sources constrains the extent of independent rupture in future earthquakes. The 

rupture of entire segments is defined by the preferred recurrence interval in Lund (2013); the basis of 

the recommendation is a reevaluation of radiometric ages from trenching studies that are OxCal 

calibrated (refer to table 9 for results). The frequency of partial-segment ruptures (Mw6.5 up to the 

assigned segment magnitude) is constrained by the slip rates in Lund (2013). This 2014 model retains 

the branch weights used in previous models (fig. 49).
79

Figure 49. Generic logic tree for Wasatch fault source, Utah. Assigned weight for branches shown in parentheses. 

Seattle Fault Zone

For the Seattle fault zone, the recurrence parameters are the same as those used in the 2008 

NSHMP maps, the recurrence rates are constrained by paleoseismic studies (Petersen and others, 2008). 

For the characteristic model, we use a recurrence time of 5,000 years. This is based on the lack of 

paleoseismologic evidence for coastal uplift comparable to that of the 900 A.D. earthquake for the 5,000 

years before 900 A.D. (B. Sherrod, oral commun., 2013). The partial-source rupture model has a 

recurrence time of 1,000 years for earthquakes greater than or equal to Mw6.5 in the Seattle fault zone. 
80

This rate is similar to the long-term rate of back-thrust earthquakes observed in trenches on Bainbridge 

Island and the Kitsap Peninsula (Nelson and others, 2003a, b).

Combined Geodetic- and Geologic-Based Slip-Rate Models

An important observation for seismic hazard assessment is that the geologic slip rates, the 

smoothed seismicity, and the geodetic strain rates are highly correlated. This observation points out the 

importance of using each of these datasets in assessing seismic hazard; however, these datasets all have 

limitations and the maturity of the available methodologies for applying these data in hazard 

assessments varies considerably. For example, the geologic slip rate estimation methods, paleoseismic 

trenching studies and seismicity studies have been developed extensively over the past century, whereas

the geodetic strain rate data and combined geologic and geodetic inversion methods are only recently 

beginning to be used for hazard assessment. The geodetic data are an important source of information 

on the activity rates of earthquakes and should be considered in hazard assessments.

In developing previous versions of the maps, we held workshops to determine if there was 

sufficient GPS strain rate data to apply in the seismic hazard analysis; participants generally decided

that the timespan of GPS observations was insufficient for this purpose. Therefore, in developing the 

2008 NSHMP maps for the WUS, we relied on geologic slip rates and earthquake recurrence rates from 

studies of correlated offset Quaternary landforms or deposits. We used the geodetic data for 

constraining fault slip rates over a broad region and in specific zones located near the eastern California 

border. These specific zones are known as “shear zones” and are modeled to account for high geodetic 

strain observations in places where there are few or no fault data to constrain slip rates. Geodetic-based 

zones were imposed in eastern California and western Nevada to account for earthquakes on faults that 

are not explicitly included in the model (Frankel and others, 1996, 2002; Petersen and others, 1996, 

2008). For these source models, we used 50 percent of the geodetic slip rate and modeled Mw6.5–7.6 

earthquakes on evenly spaced line sources that fill the zone. Only 50 percent of the geodetic slip rate 

was applied because some slip likely does not result in earthquakes and some slip is released in smaller 

earthquakes or aftershocks that are not considered in the hazard analysis. The geodetic-based models 

were updated in the 2008 version of the maps by using regional GPS strain-rate models to identify 

boundaries of regions characterized with high strain rates.

To determine how to use geodetic data in the 2014 NSHMP update, we held two open 

workshops to discuss new geodetic models and their utility in hazard maps, convened one meeting with 

modeling teams to coordinate efforts, and formed an expert panel to provide advice on whether or not 

the models are sufficiently mature for this update. In addition, the UCERF model (ver. 3, Working 

Group on California Earthquake Probabilities, 2013) convened multiple meetings to discuss how to use 

combined-inversion slip-rate data for California and issues on the geodetic data, models, and resulting 

seismic hazard. The participants generally agreed that geodetic data and models would be useful for the 

2014 update. In this section, we review the basic information needed for applying geodetic and geologic 

information in the hazard calculations. For more details on the models and their implications, refer to 

Petersen and others (2013).

Several new geodetic- and geologic-based kinematic models (combined-inversion models) have 

been developed over the past few years that can provide new information on locations and rates of 

future earthquakes, which are discussed in appendixes of Petersen and others (2013). For the 2014 

version of the maps, we incorporate new fault-based combined-inversion models with a 20-percent 

branch weight in the Western United States (WUS) and 70-percent branch weight in California 

(http://www.scec.org/ucerf2/). Three steps were important in constructing the final geodetic- and 

geologic-based models for the maps: (1) compiling and processing GPS-based velocity data and 
81

entering these data into a new database available for use by all model developers, (2) computing new 

combined-inversion slip-rate models, and (3) implementing the new models in the hazard analysis. 

Data

We use both geologic and geodetic data in assessing seismic hazard in the 2014 update. In this 

section, we discuss the geologic and geodetic data and their strengths and limitations for use in seismic 

hazard.

Geologic displacements record long-term average rates (typically over several hundreds or 

thousands of years) that are essential for assessing the activity rates needed for seismic-hazard analyses. 

Observations are converted to average slip rates, which are used to forecast the rate of earthquakes on 

the modeled fault; higher slip rates imply higher activity rates and lower slip rates imply lower activity 

rates for sources having the same length and width. Paleoseismic trenching studies provide further 

details that identify earthquake displacements and timing of surface-rupturing earthquakes on faults, so 

they are direct evidence for past earthquake activity. 

Unfortunately, there are several limitations in applying geologic data. First, the slip rates on 

faults vary from site to site and over different time spans. Therefore, it is difficult to assess which of 

these rates is most appropriate for a 50-year period for which the maps are made. We typically give 

more consideration to slip rates that span several of the most recent seismic cycles to assess the future 

hazard, but this practice may not account for slip rates that vary through time. Second, fault slip rate has 

substantial uncertainties associated with the measurement of fault displacements and the timing of those 

displacements, and these uncertainties rarely are documented. Thus, geologically informed slip rate 

uncertainties can extend over more than a factor of two on poorly studied faults. Third, many faults in 

the WUS are characterized at only a few sites along the entire length of the fault; in other words, 

measurements are not a representative sampling of the fault. Fourth, although the paleoseismic data are 

our most direct estimate of earthquake rates, it is difficult to know if the record of past earthquakes is 

complete at the site, and this uncertainty can lead to an inaccurate estimate of earthquake rates. Finally, 

the dip of the fault is required data for calculating slip rate; this input is uncertain and carries with it the 

greatest impact. These factors are all critical elements in defining the slip-rate uncertainty.

Modern GPS data provide more spatially complete observations on ground deformation, cover a 

period of 25 years (from 1987–2012), and record the most recent plate-loading rates with submillimeter 

per year precision, which is more precise than data provided by geologic studies. Geodetic data, in 

general, are consistent with geologic data but with exceptions that may be important for assessing 

hazard. These data also have their own limitations for use in hazard analysis. For example, these data do 

not record the long-term slip rates that we generally need for hazard assessments and the data may 

include transient strains or aseismic deformation, which are difficult to remove for use in hazard 

assessment. 

The geodetic database, which supported the combined-inversion modeling, was developed by 

McCaffrey and others (2013) using a variety of sources and by correcting for Cascadia subduction-zone 

motion. The geologic-based slip-rate model is updated compared to the model applied in the 2008 

USGS NSHMP maps (Haller and Wheeler, 2008a, b) and represents expert opinion assessment of all 

pertinent geologic and paleoseismologic data to inform a single slip rate for each fault source. Geodeticbased models also cannot resolve differences among fault slip rates where faults are closely spaced; 

resolution of individual fault slip rates in such regions can be poor. In addition, uncertainties are 

particularly large for the block-type models, which focus deformation only on block boundaries. All of 

these models consider off-fault or off-block deformation; however, it is unclear how to distribute the 
82

strain rates across the inner parts of the block even though we know that there are many faults 

distributed within the defined blocks. 

We developed strain rate maps using these GPS data, but in these plots we do not eliminate the 

back-slip motion of the Cascadia subduction zone so that we can view this important component of the 

hazard. The distribution of maximum shear and dilatation strain rates is shown on figure 50. The 

maximum shear strain rate map can be considered a proxy for the maximum strain rate. The maps seem

similar to the fault slip rate map, the seismicity map, and the previous hazard maps that did not use the 

geodetic information directly. The dilatation strain rate, on the other hand, provides crucial supporting 

information on earthquake faulting style in the Western United States. For example, in the Pacific 

Northwest region, the compressional strain rate dominates the shear strain rate, suggesting higher rate of 

earthquakes with thrusting mechanisms compared to strike slip mechanisms. In the extensional 

Intermountain West region, the dilatational strain rate dominates the shear, indicating a higher rate of 

earthquakes with extensional normal faulting than of strike slip faulting.

Figure 50. Strain-rate maps of the Western United States calculated using the global positioning system (GPS) 

dataset collected for the combined-inversion models showing A, maximum shear and B, dilatational strain. 

Fault sources are shown (black lines).
83

Combined Geologic and Geodetic Models

Four modeling teams participated in developing combined geodetic and geologic slip-rate 

models, and these are described in Petersen and others (2013). The USGS considered combinedinversion slip-rate models for faults in the WUS, including two block models (McCaffrey and others, 

2013; Hammond and Bormann, 2013) and two fault-based models (Bird, 2013; and Zeng and Shen, 

2013). Each modeling group developed horizontal slip rates using their own inversion methods and 

these slip rates were then projected onto the preferred fault dip assigned in the NSHMP model by 

dividing by the cosine of the dip angle. 

To implement the geodetic-based models in the hazard analysis, we compared the geologic and 

the combined-inversion slip rates to identify similarities and differences between the data. Comparisons 

between the geologic model and combined geologic and geodetic inversion models are shown in figure 

51. Some combined-inversion models suggest slip rates that are significantly different from the geologic 

slip rates. For this analysis, we consider factors of two and one-half of the mean down-dip slip rate (fig. 

51) to encompass the 95-percent confidence range for geologic slip rates (Petersen and others, 1996). 

Figure 51. Comparison between the fault-based combined-inversion slip-rate models and the modified 2008 

NSHMP assigned slip rates (see Petersen and others, 2013, for modifications to the 2008 model). Solid line 
84

represents equality between the geology and geodesy slip rates, dashed lines represent factors of 2 and 1⁄2 

compared to the equality line. A, Slip rates from McCaffrey and others (2013) and B, Hammond and Bormann 

(2013) block models. C, Slip rates from Bird (2013) and D, Zeng and Shen (2013) fault-based models. Red 

symbols on the Bird (2013) graph represent slip rates that were modified in the hazard assessment.

The combined-inversion slip rates of McCaffrey and others (2013) and Hammond and Bormann 

(2013) generally are higher than the modified 2008 source slip rates (fig. 51). It is important to point out 

that this comparison does not imply that the slip rates derived from block modeling are right or wrong; 

we can only conclude that the rates differ from the assigned geologic rates assigned in past hazard maps. 

The block models use block boundaries that are interpreted from the earthquake data, fault data, and 

strain rate orientations. Therefore, slip rates in these models are constrained only on the block 

boundaries, and faults within the blocks are modeled as uniform. The block models only include about 

one-third of the faults that are in the modified 2008 source model. The modified 2008 source slip rates 

for the faults included and excluded from the block models are shown in figure 52. About half of the 

faults that are not included in the block models have slip rates less than 0.3 mm/yr; however, a few of 

the geologically faster slipping faults also are excluded from the block models because of their locations 

compared to the block boundaries. For this hazard map implementation, we used slip rates derived from 

block modeling to assess the general geodetic trends, but did not arrive at consensus on an appropriate 

method to distribute slip rate within blocks.

Figure 52. Plot of assigned slip rates in the modified 2008 source model and geodetic-based block models.

The Bird (2013) and the Zeng and Shen (2013) slip-rate models also differ from the modified 

2008 source slip rates (fig. 51), though the differences are not as large as they are for the block models. 

Generally, these two models are more compatible with the modified 2008 source slip rates (fig. 51), 
85

which again does not suggest that they are more correct, but only that they are more similar to the 

previous slip rates applied in the USGS NSHMP maps.

The Bird (2013) slip-rate model differs significantly (by a factor of two or more) from the 

modified 2008 source slip rates for some faults (table 10) in western and central Nevada. The modified 

2008 source slip rates on these faults are low (about 0.1 mm/yr) and the combined-inversion rates are 

higher by factors of 10 or more. We model these higher rates in our hazard analysis by using 50 percent 

of the slip rate indicated by the Bird model and by spreading the reduced slip rate over a region 

extending about 10 km around the group of faults modeled with high slip rates (fig. 53). We reduce the 

slip rates on these central Nevada faults because of the first-order differences between the slip rates 

assigned in the modified 2008 source model and combined geologic-geodetic slip rates, which could be 

influenced by transient strain or other effects. Further research is required to define the range of 

acceptable rates before we implement such a major change in the maps that will cause a significant 

hazard hotspot in the hazard. These faults mostly are located in central Nevada in the vicinity of some 

past large earthquakes. The region may be influenced by transient deformation (Hammond and others, 

2009), groundwater withdrawal, or other nontectonic effects. In addition, the combined-inversion slip 

rates may not be well resolved and may have large uncertainties. Another possibility is that poorly dated 

offset features are not reliable and that the geodetic data are more appropriate for hazard in the next 50 

years. Additional combined-inversion slip rates in northwestern Oregon also are higher than the 

modified 2008 source slip rates (fig. 53). Therefore, we also have spread the slip rates for these faults 

over a zone to account for our uncertainty in the location of future earthquakes in this region. 

Table 10. Comparison of assigned slip rate in modified 2008 model and Bird (2013) slip rates where Bird slip 

rates are greater than two times the slip rate in modified 2008 model. 

[km, kilometers ; mm/yr, millimeters per year] 

Fault name State

Modified 2008 

assigned slip 

rate (mm/yr)

Bird (2013) 

mean slip rate

Predominate 

sense of slip Length (km) Dip (degrees)

Benton Spring 

fault

Nevada 0.26 1.76 Strike slip 85 90

Bettles WellPetrified SpringsNevada 0.1 11.6 Strike slip 71 90

Buffalo Valley 

fault

Nevada 0.13 0.483 Normal 41 50

Coaldale fault 1 Nevada 0.1 4.33 Strike slip 66 90

Coaldale fault 2 Nevada 0.1 4.33 Strike slip 17 90

Fairview fault Nevada 0.13 0.0981 Normal 34 50

Faults in 

Excelsior Mtns

Nevada 0.1 Strike slip 27 90

Hot Springs fault Nevada 0.13 0.25 Normal 24 50

Huntoon Valley 

fault

Nevada 0.1 Strike slip 38 90

Rattlesnake fault Nevada 0.1 Strike slip 15 90

Sand Springs 

fault

Nevada 0.13 0.25 Normal 42 50

Spanish Springs 

Peak fault

Nevada 0.1 4.33 Strike slip 5 90

Unnamed faults Nevada 0.1 Strike slip 40 90
86

Figure 53. Map showing location of the zones placed around ten fault sources in the Bird (2013) model to smooth 

the effects of high slip rates on individual fault sources. Slip rates in the two southern Nevada zones are 

reduced by 50 percent in the hazard model.

A comparison of the on-fault cumulative geologic slip rates and fault-based combined-inversion 

slip rates of Bird, and Zeng and Shen models along east-west oriented profiles is shown in figure 54, 

located at 0.1° intervals from 35° to 45° latitude for east (extension, fig. 54A) and north (strike slip, fig. 

54B) motion. Hanging-wall displacements were separated into two components (north and east) and 

summed along transects to show variability from north to south across the study area; total slip is shown 

in millimeters per year. The transects show variation of total slip up to 5 mm/yr extension (fig. 54A) and 

less than 4 mm/yr strike-slip component (fig. 54B), which is more than a factor of 20 lower than the 

UCERF3 model for California (Working Group on California Earthquake Probabilities, 2013). For the 

extensional rates (east), the three models track each other very well in the north, but the Bird (2013) 

model deviates from the other two near the southern end of the central Nevada seismic zone (latitudes 

between 38° and 39.5°). This area encompasses the faults for which we have reduced the slip rates. For 

the strike-slip rates (north), the three models again track each other in the north but deviate from each 

other near the southern central Nevada seismic zone. The Zeng and Shen (2013) model shows 

particularly high strike-slip motion in this zone compared to the other two models. 
87

Figure 54. Plot of cumulative on-fault total slip summed along east-west oriented profiles for the 2008 modified 

source model (Petersen and others, 2013), Bird (2013) model, and Zeng and Shen (2013) model slip rates at 

0.1° intervals from lat 32°–48N. for A, east (extension) and B, north (strike slip) motion. On-fault total slip in 

California is not included in the sum.

We also considered applying a new off-fault, geodetic-based strain rate as an alternative to the 

smoothed seismicity model for forecasting Mw5–7 events; however, participants at our workshops and 

members of our steering committee who reviewed the maps decided that the transient strains and overall 

off-fault strain rates were not well constrained. In addition, they decided that more work is needed to 

focus on comparisons between geodetic strain rate tensors and seismicity-based moment tensors before 

these off-fault models are introduced into the NSHMP maps. 

Implementation of Combined-Inversion Models in Hazard Maps

To implement the models in the NSHMP maps, we first examined the combined-inversion 

model outputs to determine how they differ from the geologic-based slip rates. The Zeng and Shen 

(2013) model is most similar to the geologic model. Some of our workshop participants have criticized 
88

that the similarity adds little additional information; however, we found important differences between 

the purely geologic and the Zeng and Shen (2013) models. The differences call attention to high or low 

slip rates in regions where the geologic data are not well constrained. The Zeng and Shen (2013) model 

fits the geodetic data equally well as any other geodetic models. The Bird (2013) fault-based, combinedinversion model differs from the geologic model more than the Zeng and Shen model, but in many 

places the patterns are similar. We modified some of the high slip rates in western and central Nevada in 

the Bird (2013) model. This modification provides a model that dampens and spreads the hazard in 

southwestern and central Nevada more than the original Bird model. The block models in the WUS 

often were significantly different from the geologic-based model as well as the fault-based combined 

geologic and geodetic inversion models. In addition, the block models did not account for slip rates on 

all of the faults included in the hazard model. Therefore, these models were not applied directly in the 

final hazard maps. Further studies will help us understand these discrepancies and determine how to use 

these models in future applications. 

We introduce the combined-inversion fault-based models for the first time into the hazard maps 

with a low weight (0.2) in the Intermountain West and Pacific Northwest. Project members, the steering 

committee, and workshop participants recommended low weights for the combined-inversion models 

since they are new studies that will improve with more research. A higher weight (0.7) is applied in 

California where the data are more spatially and temporally abundant (http://www.scec.org/ucerf). The 

two fault-based models are weighted equally because we do not favor any particular model. The 

remaining weight (0.8) is given to the model constrained by expert analysis of geologic data. It should 

be pointed out that although the geologic-based model receives most of the weight, it also considers the 

geodetic data implicitly in that the cumulative slip rates across the region are modeled to be consistent 

with the regional geodetic rates.

In addition, we maintain the geodetic-based shear zones outside of California (from Petersen and 

others, 2008) to account for additional earthquakes in areas of observed high strain rates (Moschetti and 

others, 2013). We also include a geodetic zone near Puget Sound (from Petersen and others, 2008) to 

account for earthquakes located off of the modeled faults. We use the same zones as were applied in the 

2008 USGS NSHMP maps. These zones correspond with high off-fault velocities.

Hazard Results

The two fault-based, combined-inversion models for the WUS are similar in many ways, 

showing similar high- and low-strain rate areas with respect to the purely geologic model. Difference 

and ratio maps (figs 55, 56, respectively) display changes in hazard assuming the weighted two faultbased, combined-inversion models and the geologic model. Adding the combined-inversion models (0.2 

weight) typically elevates the hazard in areas with higher than expected strain rates compared to the 

hazard resulting from applying only the geologic model. The effect of applying these new models is 

highest in Nevada, near the southern portion of the Wasatch fault (Utah), near the Rio Grande Rift 

(Colorado and New Mexico), near the borders between Oregon and Washington, and in Wyoming. The 

weighted combination of fault-based combined-inversion and geologic models results in about 15–20 

percent increases (or about 0.02–0.05 g) compared to the geologic-based model alone in places with 

observations of high strain rates. The final weighted model results in a hazard map that is similar to 

previous hazard maps but allows for additional earthquakes in places where higher strain rates have 

been observed over the past two decades.
89

Figure 55. Maps showing difference in 1-hertz (1-second) and 5-hertz (0.2-second) spectral acceleration at 2-

percent probability of exceedance in 50 years and VS30 site conditions of 760 meters per second. Maps of 1-

hertz (1-second) spectral acceleration difference of A, fault-based models by Bird (2013) and B, Zeng and 

Shen (2013) and the 2008 modified source model and 5-hertz (0.2-second) spectral acceleration difference of 

C, fault-based models by Bird (2013) and D, Zeng and Shen (2013) and the 2008 modified source model 

respectively. California data not shown.
90

Figure 56. Maps showing ratios of 1-hertz (1-second) and 5-hertz (0.2-second) spectral acceleration at 2-percent 

probability of exceedance in 50 years and VS30 site conditions of 760 meters per second. Ratios of 1-hertz (1-

second) spectral acceleration of A, fault-based models by Bird (2013) and B, Zeng and Shen (2013) and the 

2008 modified source model and 5-hertz (0.2-second) spectral acceleration of C, fault-based models by Bird 

(2013) and D, Zeng and Shen (2013) and the 2008 modified source model respectively. California data not 

shown.
91

The inclusion of these models in this version of the maps demonstrates our recognition that there 

are advantages to using both the geologic and combined-inversion slip rates. Both datasets have benefits 

and limitations in constraining the hazard maps. These combined-inversion slip-rate models will 

continue to evolve and will be more useful in future hazard assessments. 

Earthquake Recurrence and Down-Dip Edge of Rupture for the Cascadia Subduction Zone

Logic trees for the recurrence of great earthquakes on the Cascadia subduction zone have been 

developed from discussions at the November 2010 and March 2012 workshops (Frankel, 2011), which 

were held for the update of the USGS national seismic hazard maps and for the UCERF3. The location 

of the down-dip edge of the rupture zones of great Cascadia subduction zone earthquakes was debated 

in workshops in December 2011 and March 2012 (Frankel, 2011). A logic tree for the position of the 

down-dip edge also has been developed from these deliberations. For this 2014 update of the NSHMP 

maps, we considered a broad range of alternative models for the Cascadia subduction zone; however, 

for this update we did not implement a model based on a proposed temporal correlation of turbidite 

sediments in marine sediment cores that suggests that the northern San Andreas Fault and Cascadia 

subduction zone could fail together in north-to-south propagating ruptures (Goldfinger and others, 

2008). 

Logic Trees for Cascadia Subduction Zone Recurrence

The November 2010 workshop focused on evaluating the analysis and interpretation of turbidites 

in deep-ocean cores by Goldfinger and others (2012), to constrain the recurrence time and magnitudes 

of great earthquakes on the Cascadia subduction zone. This workshop is summarized in Frankel (2011). 

Figure 57 (modified from Goldfinger and others, 2012) shows the great earthquake rupture zones 

estimated from the 10,000-year turbidite record. During this workshop, the participants accepted the 

idea of Mw8 earthquakes that rupture only the southern portion of the Cascadia subduction zone. 

Evidence for these earthquakes is manifested in turbidites (Goldfinger and others, 2008, 2012) and in 

tsunami deposits found on land at Sixes River (Kelsey and others, 2002) and Bradley Lake (Kelsey and 

others, 2005; Nelson and others, 2006) in southwestern Oregon. Brian Atwater also presented evidence 

regarding the possibility of Mw8 earthquakes that only rupture the northern portion of the Cascadia 

subduction zone, mainly inferred from tsunami deposits at Discovery Bay (Williams and others, 2005). 
92

Figure 57. Figure modified from Goldfinger and others (2012) showing rupture zones of great Cascadia 

earthquakes determined from the turbidite record over the past 10,000 years. Yellow dots are locations of 

cores. Designation of great earthquakes for each rupture scenario is given on left side of each panel (for 

example, T1, T5b). Location of Cape Blanco (CB), Heceta Bank (HB), and Nehalem Bank (NB) is shown. The 

preferred magnitude range and recurrence time used for each rupture scenario in our implementation is shown 

below each panel. Recurrence times are determined by dividing 10,000 yr by the number of earthquakes in that 

scenario.

These partial Cascadia subduction zone rupture earthquakes (fig. 57B, C, D) supplement the 

whole Cascadia subduction zone ruptures with moment magnitudes inferred to be about 9.0 (fig. 57A), 

based on observations and modeling of the tsunami in Japan inferred to have been generated by the 

1700 Cascadia earthquake (Satake and others, 1996, 2003). These whole Cascadia subduction zone 

rupture earthquakes have been well documented from about 5,000 years of evidence of coastal 

subsidence, tsunami deposits, and liquefaction at numerous sites near the coast of Washington, Oregon, 

and northern California (Atwater, 1987, 1992; Nelson and others, 1996; Atwater and Hemphill-Haley, 

1997; Kelsey and others, 2002, 2005; Witter and others, 2003), as well as from 7,500–10,000 years of 

turbidites (Adams, 1990; Goldfinger and others, 2003, 2008). Workshop participants agreed that a mean 

recurrence time of about 500–550 years was appropriate for these whole Cascadia subduction zone 

ruptures, with an important caveat. They also thought that some of these 500–550-year scenarios may 

have been a series of Mw8 earthquakes that ruptured the whole Cascadia subduction zone over several 

years or a couple of decades, similar to what has been observed for the Nankai Trough in Japan (1944 

and 1946, Ando, 1975) and along the Columbia-Ecuador coast of South America (1942–1979, 

Kanamori and McNally, 1982).

The participants of the November 2010 workshop also came to a consensus that the 2014 USGS 

NSHMP maps and UCERF3 should use a mean recurrence rate of 0.001 per year for Mw8 earthquakes 

that only rupture the southern portion of the Cascadia subduction zone. This rate is about half the rate 

for these earthquakes determined by Goldfinger and others (2012). One motivation for this choice was 

that this rate of partial Cascadia subduction zone ruptures is similar to that observed over certain periods 
93

of time at Sixes River and Bradley Lake (Nelson and others, 1996, 2006). This mean rate was regarded

by some workshop participants as a compromise position, pending future research. As new work on the 

turbidites and other evidence is accomplished, the mean rate for the hazard maps should be reassessed. 

No consensus on the rate of partial Cascadia subduction zone ruptures in the northern Cascadia 

subduction zone was reached at the November 2010 workshop. It should be stressed that there is still 

active debate about the interpretation of the turbidite data (for example, Atwater and Griggs, 2012). 

Figure 58 shows the two proposed logic trees for Cascadia subduction zone recurrence. The 

hazard (frequency of exceeding a specified ground motion) from these two logic trees is additive. For 

the whole rupture of the Cascadia subduction zone (fig. 58), we consider aleatory uncertainty by having 

Mw8.8–9.3 earthquakes that rupture the whole Cascadia subduction zone and the possibility of serial 

Mw8 earthquakes that rupture the entire Cascadia subduction zone over a period of a few decades or less 

(would be given 20 percent of sequences if implemented). The average recurrence time is 526 years, 

either for the whole-rupture earthquakes or the series of Mw8s. For the current update of the NSHMP 

maps, however, we have not implemented the serial Mw8 possibility.

Figure 58. Logic trees for recurrence of great Cascadia subduction zone earthquakes. Note that the hazard 

(frequency of exceeding any given ground motion) from whole Cascadia subduction zone ruptures (fig. 57A) 

and partial ruptures (fig. 57 B, C, and D) is additive. Goldfinger and others (2012, GEA) rupture rate shown in 

figure 57. Assigned branch weight shown in parentheses.
94

The lower probability (would be 20 percent of sequences) for the serial Mw8 rupture reflects 

many factors. Having an Mw8 earthquake rupture at any location every 500 years, as part of a rupture 

sequence, would obviously produce less average slip than an Mw9 earthquake rupturing the whole zone 

every 500 years. The overall plate motion of about 40 mm/yr can be accommodated with Mw9 

earthquakes every 500 years with average slip of 20 m per event. This plate rate cannot be 

accommodated by Mw8.3–8.5 earthquakes with a 500-year recurrence time at any one rupture location. 

This would be a problem if the shallow (less than 30 km depth) part of the subduction interface is highly 

coupled. Bird and Kagan (2004) found a high coupling factor for a global collection of subduction 

zones, using a Gutenberg-Richter recurrence model with parameters derived from the observed 

seismicity; however, it does not seem that earthquakes on the Cascadia subduction zone follow a 

Gutenberg-Richter magnitude-frequency distribution, given the lack of historically observed 

earthquakes with magnitudes less than 7 on most of the zone. Pacheco and others (1993) found low 

coupling factors in many subduction zones, although their results were based on only a 90-year catalog 

of seismicity. Goldfinger and others (2012) did not indicate evidence of Mw8 serial ruptures in the 

Cascadia turbidite data. A time-independent hazard calculation for the serial ruptures could be done 

using the procedure in Toro and Silva (2001), similar to the approach used in the 2008 USGS NSHMP 

maps for clustering of 1811–1812 type New Madrid earthquakes (Petersen and others, 2008). 

To determine the magnitudes of the whole and partial Cascadia subduction zone ruptures, we 

first calculate the rupture area using a logic tree involving the three down-dip edges of rupture described 

below. Then we use three global magnitude area relations developed for subduction zone interface 

earthquakes: Papazachos and others (2004), Murotani and others (2008), and Strasser and others (2010), 

each with equal weight. Therefore, for each rupture scenario there are nine different values of 

magnitude used in the hazard calculation. For the whole Cascadia subduction zone ruptures, the 

magnitudes range from 8.6 to 9.3. 

The logic tree shown in the top part of figure 58 characterizes the hazard from individual 

earthquakes that rupture only a portion of the Cascadia subduction zone. The first node of the partial 

Cascadia subduction zone rupture logic tree is for segmented as opposed to the unsegmented rupture 

models, which are given equal weight. Goldfinger and others (2012) presented a rupture model with 

rupture boundaries approximately chosen at Cape Blanco, Heceta Bank, and Nehalem Bank (fig. 57). 

This model is used in the “segmented” branch of the logic tree. Participants in the November 2010 

workshop decided that Cape Blanco represented a likely segment boundary, for multiple reasons. The 

age of the incoming subducting plate varies from north to south at that location. Although there is a 

marked difference in age for the incoming plate at the trench at this latitude, Wilson (2002) found that 

the age difference is less pronounced in the portion of the plate beneath the coast (P. McCrory, written 

commun., 2013). Cape Blanco also is near the latitude of the southern edge of the mafic Siletz block on 

the overriding plate (Burgette and others, 2009). There is more disagreement on whether or not Heceta 

Bank and Nehalem Bank represent possible segment boundaries. The turbidite data are from a limited 

number of coring sites and can be interpreted with either segmented or unsegmented rupture models. 

An earlier version of these logic trees was described and discussed at a workshop for the update 

of the Pacific Northwest portion of the USGS NSHMP maps. Some participants suggested that a more 

formal treatment of the logic tree describing the rate for partial Cascadia subduction zone ruptures 

should be used. This model has been adopted in the revised logic tree in figure 58. The consensus rate of 

0.001 per year for southern Cascadia subduction zone partial ruptures was still advocated by most of the 

people who expressed an opinion at the workshop. 

For the logic tree node for the overall recurrence rate of southern ruptures, we use three 

branches: (1) the rate from onshore geologic observations (about 0.001 per year), (2) the rate from 
95

Goldfinger and others (2012; about 0.0023 per year), and (3) a rate of 0.0005 per year. The last rate 

reflects the possibility that some of the onshore and offshore observations may not reflect great 

earthquakes on the Cascadia subduction zone and also recognizes that there are periods of time in the 

geologic records at Sixes River and Bradley Lake when the annual rate of inferred partial Cascadia 

subduction zone rupture events is less than 0.001. Based on the workshop discussion, most participants 

would assign higher weight to the onshore geologic observations. Assigning weights of 0.5, 0.25, and 

0.25, respectively, to these three branches yields a mean rate of 0.0012 per year, very close to the 0.001 

rate recommended in the November 2010 workshop. 

Figure 59 shows the effect on a seismic hazard map when the Goldfinger and others (2012) 

rupture model is used full weight, compared to applying the inputs of the 2008 NSHMP model. The 

magnitudes of the earthquakes were determined from rupture lengths. Peak ground acceleration with 

2-percent probability of exceedance in 50 years increase substantially along the Oregon and northern 

California coasts when the Goldfinger and others (2012) model is used. Figure 60 shows a hazard map 

with the Goldfinger and others (2012) model for partial Cascadia subduction zone-rupturing earthquakes 

applied at half weight, but retaining the hazard from whole Cascadia subduction zone ruptures. 

Applying this half weight is equivalent to using the 0.001 rate reported from the onshore geologic data 

(Nelson and others, 1996). The hazard values along the southern Oregon and northern California coasts 

are still significantly higher than those in the 2008 NSHMP model (compare maps left fig. 59B and 

fig. 60B).

Figure 59. Peak ground acceleration (in percent gravity) at 2-percent probability of exceedance in 50 years and 

VS30 site conditions of 760 meters per second maps for A, model that assigns half weight to the partial 
96

Cascadia subduction zone rupture rates from Goldfinger and others (2012) and B, adding a northern zone 

(recurrence rate of 0.001) suggested by Atwater and Griggs (2012). The northern zone extends from the 

northernmost edge of Goldfinger’s zones (Heceta Bank) to the northern end of the Cascadia subduction 

zone. Hazard from whole Cascadia subduction zone rupture events (about Mw9.0) was included in each 

figure. Other hazard sources (gridded shallow and deep seismicity, background zones, and crustal faults) 

included in both maps.

Figure 60. Peak ground acceleration (in percent gravity) at 2-percent probability of exceedance in 50 years and 

VS30 site conditions of 760 meters per second maps for A, model that assigns half weight to the partial 

Cascadia subduction zone rupture rates from Goldfinger and others (2012) and B, adding a northern zone 

(recurrence rate of 0.001) suggested by Atwater and Griggs (2012). The northern zone extends from the 

northernmost edge of Goldfinger’s zones (Heceta Bank) to the northern end of the Cascadia subduction zone. 

Hazard from whole Cascadia subduction zone rupture events (about Mw9.0) included in each figure. Other 

hazard sources (gridded shallow and deep seismicity, background zones, and crustal faults) also included in 

both maps.

The next node of the logic tree (fig. 58) on the segmented model branch is for a northern 

Cascadia subduction zone rupture, a possibility suggested by Atwater and Griggs (2012), largely from 

tsunami evidence from Discovery Bay, Wash. (Williams and others, 2005). They argue that the 

additional tsunamis observed at this location that do not correspond in time with Pacific coastal 
97

evidence of whole Cascadia subduction zone rupture events may indicate Mw8 ruptures on a northern 

portion of the Cascadia subduction zone. Others at the workshop argue that these deposits may be from 

local earthquakes under the Strait of Juan de Fuca or the Georgia Straight. One branch is given a 

recurrence rate of 0.001 per year (Atwater and Griggs, 2012), the other zero. Weights are 0.25 and 0.75, 

respectively. Note that this possible northern rupture zone is in addition to the more southerly rupture 

zones specified in Goldfinger and others (2012) that are shown in figure 57. Figure 60B shows a hazard 

map that uses a northern rupture zone along with the southerly rupture zones specified by Goldfinger 

and others (2012) and whole Cascadia subduction zone ruptures. Note the increase in hazard for 

northwest Washington and Vancouver Island when a northern rupture zone is added. 

The unsegmented branch of the logic tree (fig. 58) entails the use of floating rupture zones. That 

is, the hazard for each earthquake magnitude is calculated by moving the rupture zone incrementally 

along the strike of the Cascadia subduction zone until it reaches the other end. The rate of any particular 

rupture scenario is just the total rate for that magnitude divided by the number of rupture zones for that 

magnitude. We consider two possibilities for the portion of the Cascadia subduction zone to use for the 

floating ruptures. The first is for ruptures that cover the area from Cape Mendocino to approximately the 

latitude of the Washington–Oregon state line. This is the approximate location of the northernmost cores 

(Astoria) where Goldfinger and others (2012) report evidence of turbidites from southern Cascadia 

subduction zone earthquakes. The other option is to have floating ruptures over the entire extent of the 

Cascadia subduction zone, similar to what was used as a scenario for the 1996, 2002, and 2008 USGS 

NSHMP maps (Frankel and others, 1996, 2002; Petersen and others, 2008). 

Trial hazard maps for 2-percent probability of exceedance in 50 years indicate that the 

segmented rupture model of Goldfinger and others (2012) and models with floating ruptures produce 

very similar hazard maps for onshore locations, if the models are based on the same total rate of partial 

rupture earthquakes. Thus, the mean rate of 0.0012 per year is the controlling factor in the hazard maps, 

rather than the details of the segmentation. The first node of the unsegmented branch describes different 

models that satisfy the 0.0012 mean annual rate. In this report, we use a Gutenberg-Richter frequencymagnitude distribution from Mw8.0 to 8.7. We choose branches with b=1 and b=0. The former 

represents an average global b value for the Gutenberg-Richter relation. The b=0 branch reflects the 

unusual nature of the Cascadia subduction zone. Overall, the Cascadia subduction zone does not seem to 

follow the typical Gutenberg-Richter relation with a b value of one. Given Mw9 earthquakes with a 526-

year recurrence time, we do not see Mw7 earthquakes with 5-year recurrence time, at least over the past 

150 years of observations. A b value of zero implies equal likelihood of having an Mw8.0 or an Mw8.7 

earthquake. The 2008 USGS NSHMP maps essentially used a b value of about zero for Mw8.0–8.7 

earthquakes (Petersen and others, 2008); however this scenario represented the hazard from a series of 

Mw8 earthquakes that fill the Cascadia subduction zone, as an alternative to whole rupture Mw9 

earthquakes. In any case, using a b value of one or zero, with an overall rate of Mw8.0–8.7 earthquakes 

of 0.0012 per year, yields very similar seismic hazard maps.

The input models apply alternatives for floating ruptures over the entire Cascadia subduction 

zone reflect the idea that there could be an Mw8.0–8.7 earthquake at any location on the Cascadia 

subduction zone. This is a reasonable model, given the uncertainties and the possibility that onshore 

sites and offshore cores may not have recorded all of the Mw8 earthquakes on the Cascadia subduction 

zone. It is problematic to choose a rate for these branches with floating rupture over the entire Cascadia 

subduction zone. We use the logic tree of rates applied only to the southern ruptures (fig. 58), multiplied 

by the length ratio of the whole Cascadia subduction zone to the southern rupture zone (fig. 57B), to 

maintain the logic tree rate in the southern Cascadia subduction zone (relative to the case with only 

southern ruptures) and to account for the possibility of ruptures in the northern portion. 
98

A time-dependent hazard calculation would be straightforward for the whole Cascadia 

subduction zone rupture scenarios (Mw8.6–9.3 or a series of Mw8s), given a 526-year average recurrence 

time and the time since the 1700 earthquake (Petersen and others, 2002). Calculating time-dependent 

hazard maps for the Mw8.0–8.7 partial rupture scenarios would be problematic given the variability of 

the rupture scenarios. 

Logic Tree for Down-Dip Edge of Rupture

The location of the down-dip edge of the rupture zones of great Cascadia earthquakes (fig. 61) 

can have substantial effect on the seismic hazard estimates for certain areas. This location is used to 

determine the closest distance of rupture to a site for the GMMs used in the seismic hazard calculation. 

One important issue is how the developers of GMMs use empirical data to identify the edge of a rupture 

zone. This edge often is determined by slip distributions derived from inversions of strong motion data 

or teleseismic data. Thus, it corresponds to the location where the coseismic slip is a small fraction of 

the peak slip on the plate interface during a great earthquake. 

Figure 61. Alternative locations of down-dip edge of Cascadia rupture. We use the midpoint of the updated version 

of the fully locked zone from Flück and others (1997) and the average of the 1-cm/yr locking contours as the 

seaward branch in the logic tree.
99

In the December 2011 workshop, participants had favorable views of procedures that used 

modeling of GPS and uplift data to constrain the interseismic locking on the Cascadia subduction zone. 

Participants also wanted to use the top of the tremor zone as one model for the location of the down-dip 

edge of rupture. There were suggestions from participants to give low weight to a model with the downdip edge at the midpoint of the tremor zone. We have not implemented this suggestion. 

For the March 2012 workshop, we presented a logic tree based on three branches (fig. 62): (1) 

the average of the 1 centimeter per year (cm/yr) locking contours from McCaffrey and others (written 

commun., 2012) and Schmidt and others (written commun., 2012), based on modeling GPS and uplift 

data and applying a down-dip tapering function derived in Wang and others (2003); (2) the top of 

tremor zone based on the compilation of Gomberg and others (2010) and Aaron Wech from 

http://tunk.ess.washington.edu/map_display/ (Pat McCrory and Luke Blair, written commun., 2012), 

and (3) the base of the locked zone from Flück and others (1997), based on thermal modeling and uplift 

data. Figure 61 shows a map with these possibilities.

Figure 62. Logic tree for down-dip edge of rupture zones of great Cascadia earthquakes. Assigned branch weight 

shown in parentheses.

The March 2012 workshop participants clearly stated that the 1-cm/yr locking contour was a 

reasonable center of mass of opinion for the location of the down-dip edge. This depth corresponds to 

the location on the fault plane with a coupling factor of approximately 0.25. Given the observation that 

the down-dip portion of the rupture zone of the 2011 Mw9.0 Tohoku earthquake that generated 

significant strong ground motions had a coseismic slip much lower than the peak slip determined for the 

rupture (Frankel, 2013), workshop participants thought that using the 1-cm/yr locking contour (about 25 

percent locking) for the consensus estimate of the downdip edge was a reasonable strategy.

The March 2012 workshop participants did not have a consensus on the model to use for the 

most seaward logic-tree branch. Participants did express the view that applying the base of the Flück 

and others (1997) locked zone was too far seaward. As an interim solution, we propose the seaward 

branch to be located at the midpoint of the base of the locked zone from the updated equivalent of Flück 

and others (1997) and the 1-cm/yr locking contour from the recent GPS and uplift modeling. 

The logic tree for the down-dip edge is shown in figure 62. We assigned weights of 0.5, 0.3, and 

0.2, respectively, to the 1-cm/yr locking contour determined from GPS and uplift modeling, the top of 

nonvolcanic tremor, and the midpoint between the base of the fully locked zone and the 1-cm/yr contour 

(fig. 61). 

Magnitude-Frequency Distribution and Along Strike Earthquake Rate

Figure 63 presents a summary logic tree that combines the rate logic trees (fig. 58), the down-dip 

edge logic tree (fig. 62), and magnitude scaling and ground motion model choices. Note that the three 
100

magnitude-area scaling relations are applied to full Cascadia subduction zone ruptures and the 

segmented model of partial Cascadia subduction-zone ruptures. The three down-dip edge options 

combined with three magnitude-area scaling relations yield a total of nine magnitudes for the full 

Cascadia subduction-zone rupture and for each of the four partial rupture scenarios in the segmented 

model. The magnitude ranges for these scenarios are given in table 11, along with logic tree mean rate 

for individual rupture scenarios and model weights. Table 11 also lists magnitude range and rate for the 

unsegmented model. Figure 64 shows the total cumulative and incremental rates for all ruptures for the 

entire Cascadia subduction zone. The incremental magnitude-frequency distributions are for binned 

magnitudes with a bin width of 0.1 magnitude units and rates are given at the center of each bin. The 

Cascadia subduction zone cumulative magnitude-frequency distribution implies an effective recurrence 

time of about 300 years for earthquakes with Mw8.0 and greater. 

Figure 63. Cascadia subduction zone (CSZ) summary logic tree. Note that the hazard (frequency of exceeding any 

given ground motion) from full Cascadia subduction zone ruptures and partial ruptures is additive. Assigned 

weight for branches shown in parentheses. The magnitude scaling branches apply to all three rupture-depth 

branches. Ground motion model branches apply to all magnitude-scaling branches as well as all branches in 

the unsegmented model. GEA denotes the Goldfinger and others (2012) rupture rate (fig. 57).
101

Figure 64. Total cumulative and binned incremental magnitude-frequency distributions for all rupture scenarios for 

the Cascadia subduction zone.
102

Table 11. Event rates for Cascadia subduction zone.

Rupture cases Mw

Mean rate for 

individual 

rupture

(per year) 

Weight

Characteristic 

(segmented)

Full Cascadia subduction zone 1

(all four segments) 8.6–9.3 0.00190 1.0

Partial rupture Case B2

(southern three

segments)

8.4–9.1 0.00021

0.5

Case C2

(southern two

segments)

8.3–8.9 0.00047

Case D2

(southernmost 

segment)

8.1–8.8 0.00052

Northern zone 8.3–8.9 0.001 0.1

Gutenberg-Richter 

(floating rupture)

Full Cascadia 

subduction 

zone3

8.0–8.7 0.0012 0.1

Southern zone4 8.0–8.7 0.0012 0.4

1

Full Cascadia subduction zone, southern three segments, southern two segments, and southernmost segment rupture cases 

correspond to Goldfinger and others (2012), cases A, B, C, and D (fig. 57), respectively. The northern zone extends from the 

northernmost edge of Case B to the northern end of Cascadia subduction zone. 

2

Rates were determined in a way that maintains the relative rates observed by Goldfinger and others (2012) while honoring 

the logic tree mean rate of 0.0012 per year (along the southernmost segment). Goldfinger and others (2012) rates for Cases 

B, C, and D were obtained by dividing the number of events for each case by 10,000 years. Hazard from these events is 

additive.

3

Rate is scaled from logic tree mean rate of 0.0012 per year by the ratio of full Cascadia subduction zone length to the length 

of the southern zone.

4

Rupture floats over the southern part of Cascadia subduction zone only, identical to the extent of Case B (fig. 57B).

Earthquake rates along the Cascadia subduction zone are dominated by the full characteristic 

Cascadia subduction zone ruptures, with 1 event in 526 years. We also added additional partial Cascadia 

subduction zone ruptures that are more numerous in the south. Figure 65 shows the contributions to the 

earthquake rates from each of the models and how the rates vary along the fault. For example, in the far 

south (adjacent to California) the large earthquake rate is about 1 event in 315 years, whereas in the far 

north (adjacent to Washington) the rate is lower, about 1 event in 460 years. 
103

Figure 65. Variation of earthquake rates for each of the input model along the Cascadia subduction zone.

California

The California portion of the 2014 USGS NSHMP maps is based on the long-term, timeindependent component of the UCERF3 developed by the Working Group on California Earthquake 

Probabilities (2013). The two primary goals of this earthquake-rate model are to relax faultsegmentation assumptions and include multifault ruptures, both of which were limitations of the 

previous model (UCERF2). To accomplish this, UCERF3 leverages a newly developed “grand 

inversion” platform, which solves for the rate of all earthquakes simultaneously (fig. 66), while also 

using a broader range of data constraints (fig. 67). This approach eliminates the apparent UCERF2 

overprediction of Mw6.5–Mw7 earthquake rates and permits inclusion of multifault ruptures similar to 

those recently observed in nature (for example, the 2002 Mw7.9 Denali, Alaska earthquake rupture, 

Schwartz and others, 2012).
104

Figure 66. Map of earthquake participation rate for the Uniform California Earthquake Rupture Forecast, ver. 3.3

(UCERF3) model. For the purpose of this illustration, faults are projected above the earth’s surface.
105

Figure 67. The grand inversion system of equations used in solving for the long-term rate of fault-based ruptures. 

The inversion approach conceptually is simple and extensible with respect to adding other 

constraints. Without invoking segmentation, however, the problem inherently is underdetermined in 

terms of solving for the rate of every possible rupture (solutions are nonunique). The inversion 

calculation therefore uses a multithreaded simulated-annealing algorithm, which samples the null space 

efficiently and samples a range of models given overall data uncertainties. This approach is more 

derivative than the prescriptive nature of previous models (magnitude-frequency distributions are now 

derived rather than assumed). Individual solutions are more difficult to understand, necessitating the 

development of a variety of analysis tools. 

While building UCERF3, the WGCEP updated almost all datasets from UCERF2 and developed 

a number of new key components. These include four new deformation models, which provide fault slip 

rates: one based on pure geologic data, and three kinematically consistent models that also incorporate 

geodetic data. These models provide slip rates on faults where none previously existed, thereby 

producing some of the largest hazard changes relative to UCERF2. The deformation models also 

constitute one of the largest epistemic uncertainties, with the other important contributors being a new 

smoothed-seismicity algorithm, two new scaling equations, and alternative values for the total regional 

rate of Mw5 and larger events. All of these influential options are new, so UCERF3 represents a 
106

considerable broadening of epistemic uncertainties, with the complete set yielding 1,440 alternative 

models (logic-tree branches; fig. 68). The large number of models, coupled with a need to sample the 

null space of each, required the use of supercomputers. Extensive hazard calculations not only quantify 

the influence of each epistemic uncertainty, but also show that those associated with model 

nonuniqueness are negligible in comparison. 
107

Figure 68. Logic tree for the Uniform California Earthquake Rupture Forecast, ver. 3.3 (UCERF3) model. Assigned 

branch weights shown in parentheses. Fault models (FM) version 3.1 and 3.2 are assigned equal weight. PDF 

refers to probability density function, MFD to magnitude-frequency distribution, and UCERF2 to version 2 of the 

Uniform California Earthquake Rupture Forecast. 
108

Before inverting for fault-based earthquake rates, UCERF3 faults are discretized into 

approximately 7-km subsections. Each subsection is allowed to rupture with any other subsection 

located within 5 km, subject to static-stress based geometric compatibility rules, and ruptures must span 

at least two subsections. These constraints allow approximately 250,000 unique fault ruptures across 

California, some that are much larger than previously considered. Geodetic and geologic slip rates, as 

well as paleoseismic recurrence data, are then inverted to solve for the rate of each unique rupture, 

subject to a variety of additional constraints, including along fault (rate) smoothness, regional and faultspecific magnitude-frequency distributions (MFDs), and a-priori rates (for example, at Parkfield; see 

Working Group on California Earthquake Probabilities (2013) for more details. Once fault-based rates 

have been computed, the total fault-based MFD is subtracted from the statewide MFD, and the 

remainder is distributed across the state using spatial probability density functions (PDFs) derived from 

models of smoothed seismicity. Two spatial PDFs are considered, one based on the fixed radius 

Gaussian smoothing kernel of UCERF2, and a second that uses adaptive smoothing (where the 

smoothing radius is a function of the density of Mw greater than 2.6 earthquakes). In this way, faultbased and gridded, or background, earthquake rates are coupled across all branches of the UCERF3 

logic tree, and do not exceed the historical statewide rate dictated by the “Mw greater than or equal to 5 

rate” branch of the logic tree.

As with prior California earthquake rate models, UCERF3 is an approximation of the system and 

represents a limited range of models. For example, inversions are explicitly constrained to stay as close 

as possible to UCERF2, and rules are applied with respect to whether ruptures can jump between faults. 

This means that, although UCERF3 is demonstrably better than UCERF2 overall, there may be areas 

that warrant further site-specific investigations. To this end, the entire framework is available on an 

open-source platform. The grand inversion is not free of expert judgment; it provides a system-level 

framework for testing hypotheses and formally balancing the influence of different experts. For 

example, significant challenges are posed by the inversion when applying the Gutenberg-Richter 

hypothesis to individual faults, which may indicate that the hypothesis should be rejected. A timedependent UCERF3 model also is under development and will be published separately in the near 

future. Please refer to the Working Group on California Earthquake Probabilities (2013) documentation 

for a comprehensive description of UCERF3 methodology, key assumptions, and potential 

improvements. 

Ground Motion Models

Ground motion models (GMMs) are equations that express the ground motion intensity in terms 

of characteristics of the earthquake source, propagation path of the seismic waves, and the site 

conditions. The ground motion intensity is quantified by the mean and standard deviation of an assumed 

normal probability density function for the horizontal spectral acceleration (SA) in the logarithmic scale. 

Median and logarithmic standard deviations typically are expressed as functions of spectral period, 

earthquake magnitude, source-to-site distance, and other parameters characterizing the earthquake 

source, path, and site conditions. 

Ground motion models used in the USGS NSHMP maps are categorized into three groups based 

on their tectonic settings: (1) those developed for earthquakes in stable continental regions, which are 

used in the Central and Eastern United States (CEUS) region; (2) those for shallow crustal earthquakes 

in active tectonic regions, which are used in the Western United States (WUS) region; and (3) those for 

earthquakes in subduction zones (including both interface and intraslab), which are used in the Pacific 

Northwest region. 
109

In the CEUS and for subduction interface earthquakes, we calculate ground motions from 

sources that are up to 1,000 km from the site. In the WUS and for deep intraslab earthquakes, ground 

motions are calculated for distances less than 300 km from the site. For CEUS sources, we cap and 

truncate ground motions to avoid unacceptably large values. Capping and truncation do not significantly 

affect the results at probability levels of 2-percent probability or greater of exceedance in 50 years. 

Median ground motions are capped at 1.5 g for peak ground acceleration (PGA) and at 3.0 g for the 0.2-

second (5-hertz) spectral acceleration. The ground motion distribution for PGA is truncated at 3 g and 

for 0.2-second spectral acceleration at 6 g when these values are less than the 3-sigma cutoff, where 

sigma represents the logarithmic standard deviation of the ground motion model (GMM). In addition, 

we truncate the distribution of ground motions at three standard deviations above the median for PGA

and SA for all GMMs.

Ground Motion Model Selection Criteria

For the 2014 update of the USGS NSHMP maps, the steering committee suggested that the 

USGS produce a set of criteria for selecting GMMs from the collection of all available GMMs. 

Although these criteria have been considered in the past updates of the USGS NSHMP maps in a 

general sense, they have not been formally introduced. Using Bommer and others (2010) as a guideline 

and based on the expertise and advice of the steering committee members and the NSHMP members, 

USGS has developed the following set of criteria. As advised in Cotton and others (2006), the following 

criteria are designed not to be excessively specific at the time of writing, but rather sufficiently flexible 

to be adaptable to the continuing growth of the global strong motion database and the continued 

evolution of GMMs. 

General Requirements

1. Basic—The GMM must provide, as a minimum, equations for the median and aleatory 

uncertainty of the horizontal component for peak ground acceleration and spectral acceleration at

0.2- and 1-second spectral periods (5-hertz and 1-hertz frequencies). The GMM must be 

applicable to one of the tectonic regions relevant to the United States. 

2. Publication—The GMM must be published in the form of a journal paper, open-file report, or 

similar publicly accessible publication. The publication should summarize the database, 

reasonably describe the modeling procedure, demonstrate the scaling characteristics with 

parameters in the model over the parameter ranges of applicability, and provide justification for 

the fit of the model to data. The database used in development of the model must be accessible 

to the public as to allow the work to be reproduced and validated by others. 

3. Implementation—GMM modelers are required to provide source codes (currently in Fortran 

language), verification tables, or validation plots to the USGS NSHMP team members, and be 

available to discuss and provide guidance on the implementation of their models. 

4. Uniqueness—Because USGS uses a weighted combination of published GMMs, each GMM 

should be a statistically independent model. If a GMM is a combination of other GMMs, it 

should include models not already used in the USGS weighted combination to avoid double 

counting. 

Ground Motion Model Database

5. Data—A recorded or simulated database should be processed using uniform criteria and 

procedures that account for noise. Database also must be accessible to the public.

Ground Motion Model Parameters and Applicability Range
110

6. Magnitude—The GMM must have magnitude dependence (also see items 11–13 on functional 

form). The magnitude applied must be based on moment magnitude. The model must be 

applicable or reasonably extrapolated to a magnitude range of 5.0 to 8.2 for shallow crustal 

earthquakes in the WUS and 4.7 to 8.2 for stable continental earthquakes in the CEUS. The 

GMMs for subduction earthquakes should be applicable or reasonably extrapolated to a 

magnitude range of 5.0 to 8.0 for intraslab and 8.0 to 9.3 for interface earthquakes.

7. Distance—The GMM must have distance dependence (also see items 12–13 on functional 

form). Distance should be measured from the rupture source or from the surface projection of the 

rupture source. The GMM should be applicable or reasonably extrapolated to a distance of 300

km for shallow crustal and intraslab subduction earthquakes, and 1,000 km for stable continental 

and interface subduction earthquakes. 

8. Faulting style—Shallow crustal GMMs for the WUS need to account for strike-slip, reverse, 

and normal faulting mechanisms.

9. Hanging wall—Shallow crustal GMMs for the WUS need to have physically reasonable 

behavior in close proximity of faults over the hanging wall and footwall.

10. Site conditions—GMMs must include a term for VS30 (currently for WUS GMMs), or be 

accompanied by other relations that transfer their equations to a VS30 of 760 meters per second 

(m/s) (currently for CEUS and subduction interface and deep intraslab GMMs). For use in softer 

soil hazard maps, GMMs should account for nonlinear soil effects. 

Ground Motion Model Functional Form and Modeling Procedure

11. The GMM should have nonlinear magnitude dependence and a source corner frequency or 

source spectral shape that is magnitude dependent.

12. The GMM should include magnitude saturation for close distances through the use of an 

appropriate finite-fault distance measure or fictitious depth term or both. The GMM should have 

a magnitude-dependent distance decay to reasonably extrapolate across the magnitude and 

distance range of interest.

13. The GMM should include an exponential decay with distance term to account for frequency 

dependent attenuation (that is, Q). 

14. GMMs should balance model complexity and either data constraints or constraints based on 

ground motion simulation as decided by the NSHMP team and Steering Committee.

15. GMMs should not display any substantial biases or trends in the between-event (inter-event) or 

within-event (intra-event) residuals with respect to distance, magnitude, soil conditions such as 

VS30, and other parameters included in the model.

16. When applicable, standard deviations should distinguish between within-event (intra-event) and 

between-event (inter-event) components of variability.

Central and Eastern United States

For the CEUS, ground motion models and their weights are updated. In this section we discuss 

the changes that contribute to the new weighting scheme, including the important parameters and 

applicability limits of each model.
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2008 Models and Weights

The 2008 hazard maps (Petersen and others, 2008) used seven GMMs with two different 

weighting schemes, one for RLMEs such as the New Madrid seismic zone and the Charleston seismic 

zone, and the other for background-gridded sources (GridSrc). These GMMs and their corresponding 

weights are listed in table 12. Most GMMs developed for the CEUS are based on simulated ground 

motions because of the scarcity of recordings for large magnitude events in this region. In 2008, we 

categorized the models based on the type of their simulated databases, which is shown as the model 

“Type” in table 12 and was the basis for assigning weights. 

Models by Frankel and others (1996), Toro (2002) for the midcontinent region, and Silva and 

others (2002) with constant stress drop and magnitude saturation are categorized as single-corner 

frequency models, with the first representing a point source model and the last two representing finite 

fault models. Two versions of the model by Atkinson and Boore (2006) are dynamic-corner frequency 

models, one with a stress drop of 140 bars and the other with a stress drop of 200 bars. Models by 

Campbell (2003) and Tavakoli and Pezeshk (2005) are categorized as hybrid models, translating WUS 

empirical data and models to the CEUS for assumed parameter ratios between the two regions. Finally, 

the model by Somerville and others (2001) for nonrift regions is based on full-waveform simulations. 

Weight assignments were based on model types and will be discussed later in the Weight section below 

in more detail.

Table 12. Central and Eastern United States ground motion models and weights in the 2008 hazard maps. 

[GMM, ground motion model; GridSrc, background-gridded sources; RLME, regional large-magnitude earthquake] 

2008 GMM Abbreviation Type Weight

RLME GridSrc

1. Frankel and others (1996) F96 Single corner–point source 0.1 0.125

2. Toro and others (1997), Toro (2002) T02 Single corner–finite fault 0.2 0.25

3. Silva and others (2002) S02 Single corner–finite fault 0.1 0.125

4. Atkinson and Boore (2006)

• 140 bar stress drop

• 200 bar stress drop

AB06 Dynamic corner 0.1

0.1

0.125

0.125

5. Campbell (2003) C03 Hybrid 0.1 0.125

6. Tavakoli and Pezeshk (2005) TP05 Hybrid 0.1 0.125

7. Somerville and others (2001) S01 Full-waveform simulation 0.2 0 

2014 Models—Major Changes Since 2008

The 2014 hazard maps include two new models that were not available in 2008: Atkinson 

(2008’), which refers to the Atkinson (2008) model as updated in Atkinson and Boore (2011), and 

Pezeshk and others (2011). Both of these models use WUS empirical strong motion models and adjust 

them for use in the CEUS by assuming certain differences between the ground motion characteristics in 

the two regions. Pezeshk and others (2011) is similar in methodology to the models by Campbell (2003) 

and Tavakoli and Pezeshk (2005) and is categorized as a hybrid model. Atkinson (2008’) is placed 

under a separate category in the logic tree, namely the “reference empirical” branch, because it uses a 

slightly different approach in modeling than hybrid GMMs (that is, it uses regional ground motion 
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observations to develop scaling factors for a WUS GMM and does not use a stochastic or seismological 

model). Due to this modeling approach, Atkinson (2008’) follows a different geometric spreading (GS) 

than the hybrid models mentioned above, which will be discussed in more detail in the next section. In 

the 2014 update, we also replace the dynamic corner frequency model by Atkinson and Boore (2006) 

with their 2011 update, referred to as the Atkinson and Boore (2006’). This updated model has a 

magnitude-dependent stress drop and therefore covers only one branch of the logic tree. The final list of 

GMMs used in the 2014 hazard maps is given in table 13. 

Table 13. Central and Eastern United States ground motion models and weights in the 2014 hazard maps.

[GMM, ground motion model; GS, geometric spreading; km, kilometers; NA, not applicable; RLME, regional largemagnitude earthquake; >, greater than] 

2014 GMM Abbreviation Type

Kappa* 

(hard to 

firm rock) 

GS Weight** 

RLME GridSrc >500 km

1. Frankel and others (1996) F96 Single corner 0.01 R-1 0.06 0.06 0.16

2. Toro and others (1997), Toro 

(2002) T02 Single corner 0.01 R-1 0.11 0.13 0 

3. Silva and others (2002) S02 Single corner 0.01 R-1 0.06 0.06 0 

4. Campbell (2003) C03 Hybrid 0.01 R-1 0.11 0.13 0.17

5. Tavakoli and Pezeshk (2005) TP05 Hybrid 0.01 R-1 0.11 0.13 0.17

6. Atkinson and Boore (2006’) AB06’ Dynamic corner 0.02 R-1.3 0.22 0.25 0.3

7. Pezeshk and others (2011) P11 Hybrid 0.02 R-1.3 0.15 0.16 0.2

8. Atkinson (2008’) A08’ Reference Empirical 0.02 NA 0.08 0.08 0 

9. Somerville and others (2001) S01 Full waveform 0.01 NA 0.10 0 0 

* Hard rock and firm rock, respectively, refer to VS30 greater than about 1500 and about 760 meters per second

** Rounded to two decimal places

In previous USGS NSHMP maps, all CEUS GMMs were used up to a 1,000 km distance. In the 

2014 update, we use two weighting schemes, one for distances shorter than 500 km and one for 

distances between 500 and 1,000 km, to improve the maps. Table 13 shows the weights for selected 

GMMs. For distances longer than 500 km, we remove the models that are not applicable at very large 

distances and redistribute the weights among the remaining models. The median ground motions for the 

selected models for distances shorter than 500 km are shown in figure 69 at peak ground acceleration, 

0.2-second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral acceleration for a moment 

magnitude of 7. In these figures, GMMs are color coded by the model type. In the 2014 update, weight 

assignments are not only based on the model type, but also on the CEUS parameters, which are 

discussed below. 
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Figure 69. Comparison of Central and Eastern United States median ground motion models by model type. 

Graphs show ground motion versus distance for A, peak ground acceleration; B, 0.2-second spectral 

acceleration; and C, 1-second spectral acceleration for an earthquake with moment magnitude of 7 and 

VS30 site conditions of 760 meters per second. Ground motion model abbreviations are defined in 

table 13. 
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Figure 69. Comparison of Central and Eastern United States median ground motion models by model type. Graphs 

show ground motion versus distance for A, peak ground acceleration; B, 0.2-second spectral acceleration; and 

C, 1-second spectral acceleration for an earthquake with moment magnitude of 7 and 

VS30 site conditions of 760 meters per second. Ground motion model abbreviations are defined in 

table 13.—Continued

Important Parameters for the Central and Eastern United States Ground Motion Models 

Two important parameters in modeling of ground motions for the CEUS are Kappa and 

geometric spreading (GS). Assumptions for these parameters are listed in table 13 for each model. 

Kappa defines the high-frequency, near-surface site attenuation of the ground motion. Geometric 

spreading usually has been represented by the inverse of distance from the source (R-1) but in some 
115

recent models developers have preferred R-1.3 for distances out to 70 km. In December 2012, the USGS 

held a workshop on ground motion models where valid reasons/ranges for both R-1 and R-1.3 were 

presented. Empirical validation is difficult because of the scarcity of large magnitude events in the 

region; therefore, we use both types of models for representing epistemic uncertainty. These parameters 

are considered in addition to the model type to assign our weights in 2014. Figure 70 shows the median 

ground motions for selected models coded by color based on their geometric spreading. 
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Figure 70. Comparison of Central and Eastern United States median ground motion models by category. Graphs 

show ground motion versus distance for A, peak ground acceleration; B, 0.2-second spectral acceleration; and 

C, 1-second spectral acceleration for an earthquake with moment magnitude of 7 and VS30 site conditions of 

760 meters per second. Ground motion model abbreviations are defined in table 13. 
117

Figure 70. Comparison of Central and Eastern United States median ground motion models by category. Graphs 

show ground motion versus distance for A, peak ground acceleration; B, 0.2-second spectral acceleration; and 

C, 1-second spectral acceleration for an earthquake with moment magnitude of 7 and VS30 site conditions of 

760 meters per second. Ground motion model abbreviations are defined in table 13.—Continued

In the 2014 update, even though Pezeshk and others (2011) is considered an update of Tavakoli 

and Pezeshk (2005), we do not remove Tavakoli and Pezeshk (2005) based on our discussions with the 

developer. This decision was made because the two models use two different assumptions on the CEUS 

parameters, Kappa and GS. Including both models in the hazard maps represents epistemic uncertainty; 

however, the Tavakoli and Pezeshk (2005) model is given lower weight because of its use of outdated 

empirical data and models.
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Applicability Limits of Models (Magnitude, Distance, Soil Condition)

The applicable range of each model considered for the CEUS varies. The model by Somerville 

and others (2001) is applicable only for earthquakes with magnitudes greater than 6.0. Therefore, this 

model is used only for RLME sources. For background seismicity (that is, GridSrc in table 13), this 

model is removed and the weights for other models are re-normalized. 

Recommendations on the applicable distance range varies from modeler to modeler; however, as 

previously mentioned, for simplicity, in the past USGS NSHMP maps used all CEUS models up to a 

distance of 1,000 km. In the 2014 update, we improve the maps by removing Toro and others (1997), 

Toro (2002), Silva and others (2002), Atkinson (2008’), and Somerville and others (2001) for distances 

between 500 and 1,000 km. The maximum distance recommended by the authors of the mentioned 

GMMs were 500, 400, 700, and 500 km, respectively.

The CEUS GMMs typically are developed for hard rock conditions (National Earthquake 

Hazards Reduction Program, NEHRP; Building Seismic Safety Council 2009, site class A, with timeaveraged shear wave velocity in the upper 30 m of the crust of VS30≥1,500 m/s); however, the national 

seismic hazard maps are prepared for a reference site condition on firm rock representing the boundary 

between NEHRP site classes B and C and specified by VS30=760 m/s. Therefore, a conversion from hard 

to firm rock (NEHRP site class A to BC) is required. Two models provide frequency-dependent 

conversion factors (table 14). Frankel and others (1996) developed factors using a Kappa of 0.01 for BC 

site class and 0.006 for A site class. Atkinson and Boore (2011) developed their factors using a Kappa 

of 0.02 for BC site class and 0.005 for A site class. The factors by Atkinson and Boore (2011) are 

applied to models with geometric spreading of R-1.3 (that is, Atkinson and Boore, 2006’; Pezeshk and 

others, 2011), Atkinson (2008’) is based on a WUS GMM and uses VS30 directly as an input parameter, 

and factors by Frankel and others (1996) are applied to all other models for conversion to firm rock. As 

can be seen in table 14, differences between the two models are greater at lower spectral periods and 

smaller at longer periods. As noted in Atkinson and Boore (2011), there is considerable uncertainty in 

these crude correction factors, and they may greatly underestimate the actual amplifications for CEUS 

sites, because of the prevalence of soils overlying very hard rock, which sets up resonance conditions in 

this region. 

Table 14. Frequency-dependent factors to convert from hard rock (NEHRP site class A) to firm rock (NEHRP 

site class BC).

[PGA, peak ground acceleration]

Spectral period Frankel and 

others (1996) 

Atkinson and 

Boore (2011) 

PGA 1.52 1.04*

0.1 second 1.74 1.04

0.2 second 1.76 1.31

0.3 second 1.72 1.41

0.5 second 1.58 1.40

1.0 second 1.34 1.27

2.0 second 1.20 1.26

*The amplification factor at PGA can be distance dependent as noted in Atkinson (2008). The value listed is from Atkinson 

and Boore (2011) and is applicable to distances near 10 kilometers. 
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Weights

The weighting scheme for the GMMs in 2008 was based on their model types. The single-corner

models received a weight of 0.4, with finite-fault models and point-source models each receiving

weights of 0.3 and 0.1, respectively. Dynamic-corner models, hybrid models, and full-waveform

simulation based models each received a weight of 0.2. Each type of model has certain advantages and 

takes into account ground motion features that others do not; therefore, this kind of weighting accounts 

for epistemic uncertainty in modeling. Figure 69 shows the models grouped by type. In 2008, most 

GMMs incorporated R-1 geometric spreading; however, the Atkinson and Boore (2006) models received 

20-percent weight and applied alternative stress drops of 140 and 200 bars and R-1.3 geometric 

spreading.

In 2014, in addition to the model type, we also consider geometric spreading and Kappa to 

distribute the weights. Weights are developed based on the logic tree shown in figure 71. Based on 

workshop discussions and the results of some external studies (that is, residual analysis and EPRI study 

described below), the group of models with R-1.3 geometric spreading receive a larger weight relative to 

2008. Consequently, proportional weights are assigned to the two alternative Kappa models. Figure 70 

shows the models grouped by their geometric spreading. In general, R-1.3 models have lower median

ground motions than R-1 models. Therefore, the combined median model for 2014 is lower than that in 

2008, as shown in figure 72, for moment magnitudes of 6.5, 7.0, and 7.5, and distances of 20 and 100 

km on hard rock site conditions. Figure 73 shows the attenuation of the combined median model with 

distance at a moment magnitude of 7.0 on firm rock site conditions for peak ground acceleration, 0.2-

second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral acceleration. Although it is not 

shown on figure 73, in general, the 2014 combination is closer to the 2008 combination for smaller 

magnitudes (see fig. 72). 
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Figure 71. Logic trees for ground motion models in the Central and Eastern United States (CEUS GMM) at 

distances A, less than or equal to 500 kilometers and B, greater than 500 kilometers. Assigned branch weight 

shown in parentheses.
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Figure 71. Logic trees for ground motion models in the Central and Eastern United States (CEUS GMM) at 

distances A, less than or equal to 500 kilometers and B, greater than 500 kilometers. Assigned branch weight 

shown in parentheses.—Continued
122

Figure 72. Comparison of median spectral acceleration for 2008 and 2014 USGS, and 2013 EPRI ground motion 

models. Graphs show results of combined median ground motion models for three magnitudes at two 

distances and VS30 site conditions of 760 meters per second.
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Figure 73. Comparison of combined Central and Eastern United States ground motion models versus distance for 

VS30 site conditions of 760 meters per second for an earthquake with moment magnitude of 7. Graphs show A, 

peak ground acceleration, B, 0.2-second (5-hertz) spectral acceleration, and C, 1-second (5-hertz) spectral 

acceleration for Central and Eastern United States sources using ground motion models for the 2008 and 2014 

version of the maps.

Additional considerations in assigning the weights came from external studies comparing GMM 

equations to CEUS earthquake data (written commun., Christine Goulet and Chris Cramer; Electrical 

Power Research Institute, 2013). We did not use these studies directly, but rather considered their results 

as additional guidelines and tools. Two external studies (personal commun., Christine Goulet and Chris 

Cramer; Electrical Power Research Institute, 2013) utilized the NGA-East preliminary database of 

ground motions for the CEUS to perform residual analyses for each of the GMMs. One study examined 

total residuals and, by averaging over various scenarios and over the three spectral periods used by the 

USGS, proposed bias factors to rank the fit of individual models to data. Another study used mixedeffects residuals, separating residuals into between-event and within-event terms and looking at patterns 
124

with magnitude and distance separately. This study qualitatively evaluated each model within and 

outside its applicability range. Both studies offer useful comparisons, but suffer from the disadvantage 

of data scarcity for moderate to large magnitudes that have significant contribution to hazard. Therefore, 

we use these residual studies only as guidelines in our decision making but not as direct ranking tools. 

Another external study that we considered was that of the Electric Power Research Institute 

(EPRI) project on assessing CEUS ground motions (Electrical Power Research Institute, 2013). The 

EPRI model categorizes the CEUS GMMs into different classes, and assigns weights to each class 

based on the confidence in models and their fit to available data. Their classes are also based on the R-1

and R-1.3 geometric spreading models. The EPRI model was not available in final form by May 2013 for 

this update; however, the steering committee encouraged the use of the EPRI model in establishing 

GMM weights. We compared our weighted combination of GMMs to that of Electrical Power Research 

Institute (2013). Figure 72 shows examples of this comparison at magnitudes 6.5, 7, and 7.5, for two 

distance measures of 20 and 100 km, on hard rock conditions. In general, even though our 2014 model 

is lower than our 2008 model, it is closer to that of Electrical Power Research Institute (2013). At 0.2 

and 1 second, the model by Electrical Power Research Institute (2013) is slightly lower than our 2014 

weighted combination. 

To show the difference in median ground motion since 2008, the ground motion combinations 

according to the 2008 USGS model (table 12) and the 2014 USGS model (table 13) are plotted versus 

distance in figure 73 for peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-

second (1-hertz) spectral acceleration, for a magnitude of 7.0 on firm rock site conditions. The subplots 

in this figure are for distances up to 200 km where ground motions are of significant amplitudes. In 

general, at short to moderate distance ranges the new 2014 combination is lower than the 2008 

combination (lower at 1-second and 0.2-second spectral acceleration than at PGA). Although not shown 

in figure 73, at longer distances (greater than 500 km), the 2014 combination is a little higher than that 

of 2008 because of changes mentioned previously; however, these ground motions at such long 

distances are very small, around 0.01 g, and consequently their contribution to hazard is minimal. 

Central and Eastern United States Difference and Ratio Maps—Comparing 2014 and 2008 Ground Motion 

Models 

In this section, we discuss the changes in the 2014 hazard maps caused by GMMs for the CEUS 

by showing difference and ratio maps for 2-percent probability of exceedance in 50 years on a uniform 

firm rock site condition at peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-

second (1-hertz) spectral acceleration with 5-percent damping. These maps illustrate a deaggregation of 

the hazard and show the relative contribution of an individual GMM to the overall hazard. The 

difference maps demonstrate the difference between the probabilistic ground motions obtained using the 

2014 seismic source model and an individual 2014 GMM, and the probabilistic ground motions 

obtained using the 2014 seismic source model and the weighted combination of all nine 2014 GMMs. 

The ratios also use the 2014 source model and are made by dividing the probabilistic ground motions 

from an individual GMM by the probabilistic ground motions from the weighted combination of all nine 

GMMs.

Probabilistic seismic hazard difference and ratio maps for Frankel and others (1996, F96), Toro 

(2002, T02), Silva and others (2002, S02), Atkinson and Boore (2006, AB06’), Atkinson (2008, A08’), 

Campbell (2003, C03), Tavakoli and Pezeshk (2005, TP05), Pezeshk and others (2011, P11), and 

Somerville and others (2001, S01) GMMs are shown in figures 74–79. Earthquakes on faults and within 

background sources in the CEUS are modeled with magnitudes ranging from Mw4.7 to 8.0 and the 

mechanisms are not specified CEUS earthquakes.
125

Ratio maps show variability among the 2014 GMMs ranging from below 0.5 up to a factor of 2, 

and the differences range within about ±0.5 g. Note that most significant differences between GMMs 

shown in figures 74–79 are seen at very close proximity of the faults in regions with higher activity 

rates. Models with R-1.3 attenuation have lower ground motions than models with R-1 attenuation. The 

Somerville and others (2001) and the Atkinson (2008’) models are more variable, sometimes higher 

than average and sometimes lower.

Figure 74. Maps showing difference in peak ground acceleration from individual ground motion models in the 

Central and Eastern United States compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, AB06’ (Atkinson 

and Boore, 2006); C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 (Pezeshk and others, 

2011); F, S02 (Silva and others, 2002); G, S01 (Somerville and others, 2001); H, T02 (Toro, 2002); and I, TP05 

(Tavakoli and Pezeshk, 2005). Western United States sources are not included.
126

Figure 75. Maps showing ratio of peak ground acceleration from individual ground motion models in the Central 

and Eastern United States compared to the 2008 model at 2-percent in 50 years probability of exceedance and 

VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, AB06’ (Atkinson and Boore, 2006); 

C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 (Pezeshk and others, 2011); F, S02 (Silva 

and others, 2002); G, S01 (Somerville and others, 2001); H, T02 (Toro and others, 2002); and I, TP05 (Tavakoli 

and Pezeshk, 2005). Western United States sources are not included.
127

Figure 76. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground motion 

models in the Central and Eastern United States compared to the 2008 model at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, 

AB06’ (Atkinson and Boore, 2006); C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 

(Pezeshk and others, 2011); F, S02 (Silva and others, 2002); G, S01 (Somerville and others, 2001); H, T02 

(Toro and others, 2002); and I, TP05 (Tavakoli and Pezeshk, 2005). Western United States sources are not 

included.
128

Figure 77. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual ground motion models 

in the Central and Eastern United States compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, AB06’ (Atkinson 

and Boore, 2006); C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 (Pezeshk and others, 

2011); F, S02 (Silva and others, 2002); G, S01 (Somerville and others, 2001); H, T02 (Toro and others, 2002); 

and I, TP05 (Tavakoli and Pezeshk, 2005). Western United States sources are not included.
129

Figure 78. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual ground motion 

models in the Central and Eastern United States compared to the 2008 model at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, 

AB06’ (Atkinson and Boore, 2006); C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 

(Pezeshk and others, 2011); F, S02 (Silva and others, 2002); G, S01 (Somerville and others, 2001); H, T02 

(Toro and others, 2002); and I, TP05 (Tavakoli and Pezeshk, 2005). Western United States sources are not 

included.
130

Figure 79. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground motion models in 

the Central and Eastern United States compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, A08’ (Atkinson, 2008); B, AB06’ (Atkinson 

and Boore, 2006); C, C03 (Campbell, 2003); D, F96 (Frankel and others, 1996); E, P11 (Pezeshk and others, 

2011); F, S02 (Silva and others, 2002); G, S01 (Somerville and others, 2001); H, T02 (Toro and others, 2002); 

and I, TP05 (Tavakoli and Pezeshk, 2005). Western United States sources are not included.
131

Western United States

For the WUS, all ground motion models are updated. In this section we discuss the new models 

and their assigned weights. 

2008 Models and Weights

In 2008, three of the NGA relations (Power and others, 2008) were implemented in the national 

seismic hazard maps. The NGA project was coordinated by the PEER center and developed a global 

strong motion database containing 173 earthquakes and 5 new GMMs for shallow crustal earthquakes in 

active tectonic regions. For 2008, the USGS selected three of the NGA models and used VS30 as an input 

parameter to generate the maps for reference site conditions. Each of the modelers used a different 

subset of the global database to develop and constrain their models. The models were weighted equally 

and additional epistemic uncertainty was added based on the database used by two of the GMMs to 

account for the close interactions between modelers. The models used in 2008 are listed in table 15. 

Table 15. Western United States ground motion models and weights in the 2008 hazard maps.

[GMM, ground motion model; NGA, Next Generation Attenuation project]

2008 GMM Abbreviation Source Weight

1. Boore and Atkinson (2008) BA08 NGA 1/3

2. Campbell and Bozorgnia (2008) CB08 NGA 1/3

3. Chiou and Youngs (2008) CY08 NGA 1/3

2014 Model Updates

In 2010, PEER started phase 2 of the NGA project (NGA-West2). Tasks related to the horizontal 

component of ground motion concluded in 2013, with final PEER reports published and posted on May 

15, 2013 (Bozorgnia and others, 2014). We started interactions with NGA-West2 modelers in 2012, 

implementing preliminary models in stages, looking at their individual effects on the hazard maps, and 

providing feedback to the developers. The NGA-West2 project updated the NGA (hereafter referred to 

as “NGA-West1”) database for small, moderate, and large magnitude events, as well as the five GMMs 

for horizontal component of ground motion. Thousands of ground motions recorded worldwide since 

2003 have been uniformly processed and added, resulting in the NGA-West2 database (see figure 80 for 

magnitude-distance distribution), which is more than a factor of two larger than that of the NGA-West1. 

The new database includes ground motions recorded during the 2003 Bam (Iran), 2004 Parkfield 

(Calif.), 2007 Niigata Chuetsu-oki (Japan), 2008 magnitude 7.9 Wenchuan (China), 2009 L’Aquila 

(Italy), 2010 Darfield (New Zealand), 2011 Christchurch (New Zealand), and more small-magnitude 

data from California (Bozorgnia and others, 2014). 
132

Figure 80. Magnitude-distance distribution of records in phase 2 of the Next Generation Attenuation project (NGAWest2) database.

Changes in the five NGA-West2 GMMs are not only due to the extended database, but also 

caused by other modeling features that represent significant advances compared to NGA-West1 models. 

We also show the changes in the median and standard deviations of each model for certain scenarios

(see figs. 81–84). In general, compared to the 2008 models, NGA-West2 models have lower median

ground motions for small magnitude events, significant changes in hanging wall terms due to better 

modeling of this feature using additional simulations, and higher standard deviations, especially at 

smaller magnitudes caused by the extended database. All five NGA-West2 models are included in the 

2014 USGS NSHMP maps for the reference firm site conditions of VS30=760 m/s. 

All GMMs used for the WUS and their assigned weights are shown in table 16. In addition to the 

NGA-West2 models, other GMMs (for example, an updated version of Graizer and Kalkan, 2011) also 

were considered; however, due to late publication or failure to satisfy our GMM selection criteria, they 

were not incorporated in the 2014 update of the USGS NSHMP maps. The model by Idriss (2013) lacks 

nonlinear soil modeling and cannot be used for maps of soft soil conditions, but inclusion of this model 

for the reference firm rock site condition maps provides epistemic uncertainty. The weights are 

distributed evenly between all GMMs with the exception of the Idriss (2013) model, which is assigned a 
133

lower weight because it does not have as many detailed modeling features (for example, the lack of 

distinction between normal and strike-slip fault mechanisms, hanging wall term, and basin depth term). 

Table 16. Western United States ground motion models and weights in the 2014 hazard maps. 

[GMM, ground motion model; NGA, Next Generation Attenuation project]

2014 GMM* Abbreviation Source Weight

1. Abrahamson and others (2013, 2014) ASK13 NGA-West2 0.22

2. Boore and others (2013, 2014) BSSA13 NGA-West2 0.22

3. Campbell and Bozorgnia (2013, 2014) CB13 NGA-West2 0.22

4. Chiou and Youngs (2013, 2014) CY13 NGA-West2 0.22

5. Idriss (2013, 2014) I13 NGA-West2 0.12

*References are based on May 2013 PEER reports, but the final models implemented in the USGS NSHMP maps are based 

on the modelers’ Earthquake Spectra publications appearing in 2014, listed in the references.

Figures 81–83 show the median values of the GMMs used in 2008 and 2014 hazard maps at 

peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral 

acceleration. Two magnitudes, 5.0 (left subplots) and 7.0 (right subplots), are displayed. Figure 81 is for 

an example of a strike-slip fault, whereas figures 82 and 83 show an example over the hanging wall side 

of a normal fault and a reverse fault, respectively. Figure 84 shows how standard deviation (commonly 

known as “sigma”) varies with magnitude for the selected GMMs at 0.2-second and 1-second spectral 

acceleration. More detailed comparison of NGA-West2 models can be found in Gregor and others 

(2014).
134

Figure 81. Comparison of median ground motion versus distance for a strike slip fault at three periods and two 

magnitudes and VS30 site conditions of 760 meters per second. A, Peak ground acceleration for moment 

magnitude 5 earthquake; B, peak ground acceleration for moment magnitude 7 earthquake; C, 0.2-second (5-

hertz) spectral acceleration for moment magnitude 5 earthquake; D, 0.2-second (5-hertz) spectral acceleration

for moment magnitude 7 earthquake; E, 1-second (1-hertz) spectral acceleration for moment magnitude 5 

earthquake; and F, 1-second (1-hertz) spectral acceleration for moment magnitude 7 earthquake. 
135

Figure 82. Comparison of median ground motion versus distance on the hanging wall of a normal fault at three 

periods and two magnitudes and VS30 site conditions of 760 meters per second. A, Peak ground acceleration

for moment magnitude 5 earthquake; B, peak ground acceleration for moment magnitude 7 earthquake; C, 0.2-

second (5-hertz) spectral acceleration for moment magnitude 5 earthquake; D, 0.2-second (5-hertz) spectral 

acceleration for moment magnitude 7 earthquake; E, 1-second (1-hertz) spectral acceleration for moment 

magnitude 5 earthquake; and F, 1-second (1-hertz) spectral acceleration for moment magnitude 7 earthquake. 
136

Figure 83. Comparison of median ground motion versus distance on the hanging wall of a reverse fault at three 

periods and two magnitudes and VS30 site conditions of 760 meters per second. A, Peak ground acceleration

for moment magnitude 5 earthquake; B, peak ground acceleration for moment magnitude 7 earthquake; C, 0.2-

second (5-hertz) spectral acceleration for moment magnitude 5 earthquake; D, 0.2-second (5-hertz) spectral 
137

acceleration for moment magnitude 7 earthquake; E, 1-second (1-hertz) spectral acceleration for moment 

magnitude 5 earthquake; and F, 1-second (1-hertz) spectral acceleration for moment magnitude 7 earthquake. 

Figure 84. Standard deviation (sigma) versus magnitude for Central and Eastern United States ground motion 

models for A, 0.2-second (5-hertz) and B, 1-second (1-hertz) spectral acceleration.

Figures 85–99 show weighted combinations of WUS GMMs for five different faulting 

scenarios: strike slip fault (figs. 85–87), normal fault over the hanging wall (figs. 88–90), normal fault 

over the footwall (figs. 91–93), reverse fault over the hanging wall (figs. 94–96), and reverse fault over 

the footwall (figs. 97–99). In each group of figures, the first, second and third figures, respectively, 

correspond to peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-second (1-

hertz) spectral acceleration. In each figure, weighted combinations of the median and 84th-percentile 

ground motions (that is, plus one sigma) are given for magnitudes 6.5, 7.0, and 7.5. Black dashed lines 

labeled “combo-08” are based on table 15 with three GMMs and solid red lines labeled “combo-13” 

correspond to table 16 with five GMMs. 

At large distances, the 2014 combination attenuates at a faster rate than the 2008 combination in 

almost all the figures. This effect can be observed in the ratio maps of 2014 hazard to 2008 hazard 

presented in the Results section. 
138

Figure 85. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration versus 

distance for a strike slip fault in the Western United States at three magnitudes and VS30 site conditions of 760 

meters per second. Graphs show A, median and B, 84th percentile.

Figure 86. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral 

acceleration versus distance for a strike slip fault in the Western United States at three magnitudes and VS30

site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
139

Figure 87. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for a strike slip fault in the Western United States at three magnitudes and VS30

site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 88. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration versus 

distance for the hanging wall of a normal fault in the Western United States at three magnitudes and VS30 site 

conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
140

Figure 89. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral 

acceleration versus distance for the hanging wall of a normal fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 90. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the hanging wall of a normal fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
141

Figure 91. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration versus 

distance for the footwall of a normal fault in the Western United States at three magnitudes and VS30 site 

conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 92. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral 

acceleration versus distance for the footwall of a normal fault in the Western United States at three magnitudes

and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
142

Figure 93. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the footwall of a normal fault in the Western United States at three magnitudes

and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 94. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration versus 

distance for the hanging wall of a reverse fault in the Western United States at three magnitudes and VS30 site 

conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
143

Figure 95. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral 

acceleration versus distance for the hanging wall of a reverse fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 96. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the hanging wall of a reverse fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
144

Figure 97. Comparison of 2008 and 2014 combined ground motion models for peak ground acceleration versus 

distance for the footwall of a reverse fault in the Western United States at three magnitudes and VS30 site 

conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Figure 98. Comparison of 2008 and 2014 combined ground motion models for 0.2-second (5-hertz) spectral

acceleration versus distance for the footwall of a reverse fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.
145

Figure 99. Comparison of 2008 and 2014 combined ground motion models for 1-second (1-hertz) spectral 

acceleration versus distance for the footwall of a reverse fault in the Western United States at three 

magnitudes and VS30 site conditions of 760 meters per second. Graphs show A, median and B, 84th percentile.

Additional Epistemic Uncertainty

We acknowledge that inclusion of all five NGA-West2 models in the maps has increased the 

epistemic uncertainty in the WUS; however, we still follow the square-root rule used in 2008 to estimate 

the additional epistemic uncertainty based on the number of earthquakes used in modeling. In 2008, the 

ground motion uncertainty was assumed to be 50 percent for Mw7 and larger events, and Rrup less than

10 km, where Rrup represents the closest distance to rupture. This assumption remains unchanged in 

2014, which translates to an additive factor of 0.4 in the log-space (90-percent confidence limits). 

Epistemic uncertainty for other magnitude-distance bins (table 17) was calculated based on 

Dgnd=0.4×√(n/N), where N is the number of earthquakes recorded in the given magnitude-distance bin, 

and n is the number of earthquakes in the Mw7 and larger and Rrup less than 10 km bin. Two databases 

were used in 2008 (those of CB08 and CY08) and the results were averaged. In 2014, we use databases 

from ASK13, BSSA13, CB13, and CY13 to update the 2008 values. The results are shown in table 17. 

Similar to 2008, this uncertainty (that is, Avg Dgnd, which stands for the average difference in ground 

motion) is applied symmetrically, with the unmodified model (that is, gnd, which stands for the ground 

motion prediction) weighting 0.63, and the “gnd±Avg Dgnd” models weighting 0.185. 
146

Table 17. Additional epistemic uncertainty for use in the 2014 hazard maps. N is the number of earthquakes 

recorded in the given magnitude-distance bin used by the given ground motion model. Dgnd=0.4×√(n/N). 

[M, moment magnitude, Rrup, distance measure used in ground motion models; ≤, less than or equal to] 

M and Rrup range

N 

ASK13

Dgnd 

ASK13

N 

BSSA13

Dgnd

BSSA13

N 

CB13

Dgnd

CB13

N 

CY13

Dgnd

CY13

Avg Dgnd 

2013

5≤M<6, Rrup<10 km 19 0.29 13 0.33 7 0.48 10 0.38 0.37

5≤M<6, 10≤Rrup<30 49 0.18 32 0.21 24 0.26 27 0.23 0.22

5≤M<6, 30≤Rrup 43 0.19 69 0.14 29 0.23 14 0.32 0.22

6≤M<7, Rrup<10 29 0.23 19 0.28 26 0.25 24 0.24 0.25

6≤M<7,10≤Rrup<30 33 0.22 25 0.24 32 0.22 26 0.24 0.23

6≤M<7, 30≤Rrup 32 0.22 31 0.22 34 0.22 19 0.28 0.23

M≥7, Rrup<10 10 0.40 9 0.40 10 0.40 9 0.40 0.40

M≥7, 10≤Rrup<30 12 0.37 10 0.38 13 0.35 11 0.36 0.36

M≥7, 30≤Rrup 12 0.37 13 0.33 18 0.30 13 0.33 0.33

Western United States Difference and Ratio Maps—Comparing 2014 and 2008 Ground Motion Models 

In this section, we discuss changes in the 2014 hazard maps for the WUS by showing difference 

and ratio maps for 2-percent probability of exceedance in 50 years on a uniform firm rock site condition 

for peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral 

acceleration with 5-percent damping. 

Intermountain West and Crustal Sources in the Pacific Northwest

Here we discuss changes to the seismic hazard compared to the 2008 maps for the Western 

United States outside of California. These maps illustrate a deaggregation of the hazard showing the 

relative contribution of an individual GMM to the overall hazard. The difference maps demonstrate the 

difference between the probabilistic ground motions obtained using the 2014 source model and one 

2014 GMM, and the probabilistic ground motion obtained using the 2014 source model and the 

weighted combination of all five 2014 GMMs. The ratios also use the 2014 source model and are made 

by dividing the probabilistic ground motions from one GMM by the probabilistic ground motion from 

the weighted combination of all five GMMs.

Figures 100–105 show probabilistic seismic hazard difference maps and ratio maps for the 

Abrahamson and others (2013 and 2014, ASK13), Boore and others (2013 and 2014, BSSA13), 

Campbell and Bozorgnia (2013 and 2014, CB13), Chiou and Youngs (2013 and 2014, CY13), and Idriss 

(2013 and 2014, I13) GMMs. Most faults contained in the Intermountain West region have normal, or in 

a few cases strike slip mechanisms, with magnitudes ranging from around 6.5 to 7.5. Crustal faults in 

the Pacific Northwest region typically are reverse faults with some strike-slip motion and are 

characterized with magnitudes ranging from about 6.5 to 7.5. Background earthquakes included in the 

2014 model are combinations of strike slip and normal (Intermountain West region) or strike slip and 

reverse (Pacific Northwest region) and range from Mw5 to 7.95. 

Observe that most significant differences in these figures are seen at very close proximity to the 

faults, which likely is due to the differences in modeling of hanging wall and footwall effects in various 

GMMs. There is complexity for individual GMMs because of effects of fault mechanism and 

earthquake rate.
147

Figure 100. Maps showing difference in peak ground acceleration from individual ground motion models in the 

Western United States compared to the 2008 model at 2-percent in 50 years probability of exceedance and 

VS30 site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 

(Boore and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 

2013, 2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models. Central and Eastern 

United States sources are not shown.
148

Figure 101. Maps showing ratio of peak ground acceleration from individual ground motion models in the Western 

United States compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site 

conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore and 

others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 

2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models. Central and Eastern United 

States sources are not shown.
149

Figure 102. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground motion 

models in the Western United States compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 

2014); B, BSSA13 (Boore and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 

(Chiou and Youngs, 2013, 2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models.

Central and Eastern United States sources are not shown.
150

Figure 103. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual ground motion models 

in the Western United States compared to the 2008 model at 2-percent in 50 years probability of exceedance 

and VS30 site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, 

BSSA13 (Boore and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou 

and Youngs, 2013, 2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models. Central 

and Eastern United States sources are not shown.
151

Figure 104. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual ground motion 

models in the Western United States compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 

2014); B, BSSA13 (Boore and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 

(Chiou and Youngs, 2013, 2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models.

Central and Eastern United States sources are not shown.
152

Figure 105. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground motion models in 

the Western United States compared to the 2008 model at 2-percent in 50 years probability of exceedance and 

VS30 site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 

(Boore and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 

2013, 2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models. Central and Eastern 

United States sources are not shown.

California

Difference and ratio maps for California are shown for similar hazard levels as were applied for 

the rest of the WUS in figures 106–111. These maps illustrate the relative contribution of each 

individual GMM to the overall hazard. The difference maps demonstrate the difference between the 

probabilistic ground motions obtained using the 2014 source model and one GMM, and the probabilistic 

ground motion obtained using the 2014 source model and the weighted combination of all five GMMs. 
153

The ratios also use the 2014 source model and are made by dividing the ground motion from one GMM 

by the ground motion from the weighted combination of all five GMMs: Abrahamson and others (2013 

and 2014, ASK13), Boore and others (2013 and 2014, BSSA13), Campbell and Bozorgnia (2013 and 

2014, CB13), Chiou and Youngs (2013 and 2014, CY13), and Idriss (2013 and 2014, I13). Each plot 

also includes a comparison of the 2014 and 2008 combined GMMs (ratio: 2014/2008 or difference: 

2014–2008) using the 2014 source model. Note that in these latter maps (2014 compared to 2008), the 

2014 source model does not include gridded seismicity sources outside the state. 

Most faults in California are strike slip but the eastern part of California also contains normal 

faults, and the Transverse Ranges and northwest portions contain reverse faults. Magnitudes on faults 

range from 6 to higher than 8 and on background sources range from 5 to 7.9. Ground motions for PGA 

are lower when applying the Chiou and Youngs (2013, 2014) compared to the others, but they are lower 

for 0.2-second and 1-second spectral acceleration when applying the Idriss (2013, 2014) model, 

especially over the San Andreas fault system. The California ground motions from Abrahamson and 

others (2013, 2014) and Chiou and Youngs (2013, 2014) are higher than average at 0.2-second and 1-

second spectral acceleration over the active faults. Individual GMMs show complexity due to variable 

magnitude scaling and mechanism. Because activity rates are higher in California than in the rest of the 

WUS, higher epsilons often are observed (that is, difference between ground motion at 2-percent 

probability of exceedance in 50 years often are higher than the median ground motion for a particular 

magnitude and distance). 
154

Figure 106. Maps showing difference in peak ground acceleration from individual ground motion models in 

California compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site 

conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore and 

others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 

2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models.
155

Figure 107. Maps showing ratio of peak ground acceleration from individual ground motion models in California and 

the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per 

second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore and others, 2013, 2014); C, 

CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 2014); E, I13, Idriss (2013, 

2014); and F, 2014 combined ground motion models.
156

Figure 108. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual ground motion 

models in California compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30

site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore 

and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 

2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models.
157

Figure 109. Maps showing ratio of 0.2-second (5-hertz) spectral acceleration from individual ground motion models 

in California and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions of 

760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore and others, 2013, 

2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 2014); E, I13, 

Idriss (2013, 2014); and F, 2014 combined ground motion models.
158

Figure 110. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual ground motion 

models in California compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30

site conditions of 760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore 

and others, 2013, 2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 

2014); E, I13, Idriss (2013, 2014); and F, 2014 combined ground motion models.
159

Figure 111. Maps showing ratio of 1-second (1-hertz) spectral acceleration from individual ground motion models in 

California and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions of 

760 meters per second. A, ASK13 (Abrahamson and others, 2013, 2014); B, BSSA13 (Boore and others, 2013, 

2014); C, CB13 (Campbell and Bozorgnia, 2013, 2014); D, CY13 (Chiou and Youngs, 2013, 2014); E, I13, 

Idriss (2013, 2014); and F, 2014 combined ground motion models.

Ground Motion Models for Subduction Interface Earthquakes

The 2008 and 2014 GMMs for subduction interface earthquakes and their weights are given in 

table 18. Figure 112 displays the spectral acceleration from the models used in 2014 at a site 110 km 

from the nearest point on the rupture surface from an interface earthquake of magnitude 9. Figures 113 

and 114 display the decay with distance of median 0.2-second and 1-second spectral acceleration, 

respectively, from a magnitude 9 subduction source. These figures include the Youngs and others 
160

(1997) model that was used in the 2008 hazard maps for reference. The Youngs and others (1997) 

model was removed from the 2014 hazard maps per the authors’ request. 

The Atkinson and Boore (2003) global model is retained with a lower weight because the 

possibility of gentle decay with distance of the intermediate- to long-period motion cannot be rejected. 

This model may need some modifications for periods beyond 1 hertz (1 second). The other models 

exhibit steeper decay with distance but are influenced strongly by Tohoku, Japan, data, which may not 

be representative of behavior in the Pacific Northwest region. Beyond the distance of 400 km 

recommended by the authors, this model is simply extrapolated with distance for spectral periods below 

and including 1-second. For longer periods, however, extrapolation to larger distances (beyond 400 km) 

results in unlikely high ground motion values. This is due to the zero anelastic attenuation at spectral 

periods greater than 1-second, which is built in the model regardless of the distance. Based on 

communications with the authors and comparisons with the available long-period data from large 

earthquakes at long distances (for example, earthquakes in Tohoku, Japan, and Maule, Chile), the model 

is modified slightly to include an anelastic attenuation term for distances beyond 400 km and periods 

greater than 1 second (s). For 2-second and 3-second spectral acceleration maps, the term 

­0.001×(R­400) is added to account for the anelastic attenuation beyond 400 km, where R represents 

the distance in km. For 1.5-second spectral acceleration maps, the cut-off distance is reduced to 200 km 

and the term ­0.001×(R­200) is used instead to ensure that the anelastic attenuation is less than that of 

1 second, but more than what is used at 2 second. 

Table 18. Subduction interface ground motion models and weights in 2008 and 2014 hazard maps.

Interface GMM 2008 weights 2014 weights

1. Geomatrix (Youngs and others, 1997) 0.25 0 

2. Atkinson and Boore (2003) global model 0.25 0.10

3. Zhao and others (2006) 0.5 0.30

4. Atkinson and Macias (2009) 0 0.30

5. BC Hydro (Addo and others, 2012) 0 0.30
161

Figure 112. Plot of subduction-interface ground motion models versus period for an earthquake with moment 

magnitude of 9 at a distance of 110 kilometers for VS30 site conditions of 760 meters per second.

Figure 113. Plot of median 0.2-second spectral acceleration for subduction-interface ground motion models versus 

distance for an earthquake with moment magnitude of 9 and VS30 site conditions of 760 meters per second.
162

Figure 114. Plot of median 1-second spectral acceleration for subduction-interface ground motion models versus 

distance for an earthquake with moment magnitude of 9 and VS30 site conditions of 760 meters per second.

Figures 115–120 show comparisons of the individual subduction interface GMMs and the 

weighted average of the suite of GMMs used in the 2014 maps. These comparisons are made for peak 

ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral 

acceleration; AB03-GL, which represents the Atkinson and Boore (2003) global model; AM09, which 

represents the Atkinson and Macias (2009) model; BCHYDRO, which represents the Addo and others 

(2012) model; and ZHAO, which represents the Zhao and others (2006) model. The individual GMM is 

subtracted with or divided by the 2014 weighted average to obtain the difference and ration maps. Hot 

colors (red, yellow) represent ground motions higher than average, whereas cold colors (blues) represent 

motions lower than average. 

For sites located near the Cascadia subduction zone, the BC Hydro and Zhao and others (2006) 

models typically are higher than the others, whereas for sites located farther away, the Atkinson and 

Boore (2003) model typically is higher than the others. The Atkinson and Macias (2009) model 

typically is lower than the others for all three periods. 
163

Figure 115. Maps showing difference in peak ground acceleration from individual subduction-interface ground 

motion models compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site 

conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AM09

(Atkinson and Macias, 2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 2006)

models.
164

Figure 116. Maps showing ratios of peak ground acceleration from individual subduction-interface ground motion 

models and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 

meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AM09 (Atkinson and Macias, 

2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 2006) models.
165

Figure 117. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual subductioninterface ground motion models compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global 

model; B, AM09 (Atkinson and Macias, 2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao 

and others, 2006) models.
166

Figure 118. Maps showing ratios of 0.2-second (5-hertz) spectral acceleration from individual subduction-interface 

ground motion models and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site 

conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AM09

(Atkinson and Macias, 2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 2006)

models.
167

Figure 119. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual subductioninterface ground motion models compared to the 2008 model at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global 

model; B, AM09 (Atkinson and Macias, 2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao 

and others, 2006) models.
168

Figure 120. Maps showing ratios of 1-second (1-hertz) spectral acceleration from individual subduction-interface 

ground motion models and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site 

conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AM09

(Atkinson and Macias, 2009); C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 2006)

models.
169

Ground Motion Models for Subduction Intraslab Earthquakes (Deep Seismicity) 

In the 2008 hazard maps, we used three GMMs to model ground vibration from deep-focus 

earthquakes: the Youngs and others (1997) model with 0.5 weight, and two Atkinson and Boore (2003) 

models, one for global source (0.25 weight) and one for the Cascadia source (0.25 weight). By depth 

and location, most of these are associated with the Benioff zone of the subducting slab. The 

modifications to the GMMs from 2008 to 2014 maps are listed in table 19 with inclusion of two new 

models, Zhao and others (2006) and BC Hydro (Addo and others, 2012). The Atkinson and Boore 

equations have been retained to sample epistemic uncertainty in ground motion from deep earthquakes. 

The Youngs and others (1997) equation was dropped in the 2014 update per developers’ 

recommendation. 

Zhao and others (2006) was truncated to saturate the ground motions above Mw7.8. The effect of 

capping magnitude at 7.8 is to limit the median ground motion to the following values: (1) truncation 

for 0.2-second spectral acceleration and 50-km distance (closest distance to rupture, Rcd) at 1.5 g and 

100-km distance at 0.52 g, (2) truncation is applied for 1-second spectral acceleration and 50-km 

distance at 0.4 g and 100-km distance at 0.14 g, and (3) truncation is applied for PGA and 50-km 

distance at 0.7 g and 100-km distance at 0.22 g. The probabilistic ground motion is limited to the 

median plus three sigma. 

Figures 121A and B show median GMMs for deep sources associated with table 19 for 0.2-

second spectral acceleration (5 hertz frequency) and 1 second spectral acceleration (1 hertz frequency), 

respectively. Figure 121B shows the four 2014 GMMs and figure 121A also includes Youngs and others 

(1997) for comparison. The medians are shown for sources of magnitudes of 6.2 and 7.2 with a depth of 

50 km. The newer GMMs tend to predict larger short period motion and lower long period motion than 

the earlier models.

Table 19. Pacific Northwest intraslab (deep) ground motion models and weights in 2008 and 2014 hazard maps.

[GMM, ground motion model]

Intraslab (deep) GMM 2008 weights 2014 weights

1. Geomatrix (Youngs and others, 1997) 0.5 0 

2. Atkinson and Boore (2003) global model 0.25 0.1667

3. Atkinson and Boore (2003) Cascadia model 0.25 0.1667

4. Zhao and others (2006) 0 0.33

5. BC Hydro (Addo and others, 2012) 0 0.33
170

Figure 121. Plots of subduction intraslab (deep) ground motion models versus distance for A, 0.2-second spectral 

acceleration, and B, 1-second spectral acceleration. 
171

Figures 122–127 show comparisons of the individual deep intraslab GMMs and the weighted 

average of the suite of GMMs used in the 2014 maps. These comparisons are made for peak ground 

acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-second (1-hertz) spectral acceleration; 

AB03-GL, which represents the Atkinson and Boore (2003) global and Cascadia models; BCHYDRO, 

which represents the Addo and others (2012) model; AM09, which represents the Atkinson and Macias 

(2009) model, and ZHAO, which represents the Zhao and others (2006) model. The individual GMM is 

subtracted from or divided by the 2014 weighted average to obtain the difference and ration maps. Hot 

colors (red, yellow) represent ground motions higher than average, whereas cold colors (blues) represent 

motions lower than average. 

For sites located near deep seismicity in the Pacific Northwest, the BC Hydro and Zhao and 

others (2006) models for peak ground acceleration and 0.2-second (5-hertz) spectral acceleration are 

typically higher than the others whereas the Atkinson and Boore (2003) models are both typically lower 

than average. The trend is opposite for 1-second (1-hertz) spectral acceleration with the Atkinson and 

Boore models having a little higher ground motions than average. 
172

Figure 122. Maps showing difference in peak ground acceleration from individual deep-intraslab ground motion 

models compared to the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions 

of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-Cascadia (Atkinson 

and Boore, 2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 

2006) models. Changes in the Zhao and others (2006) model is close to the mean; differences are close to 

zero. 
173

Figure 123. Maps showing ratios of peak ground acceleration from individual deep-intraslab ground motion models 

and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters 

per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-Cascadia (Atkinson and Boore, 

2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 2006)

models.
174

Figure 124. Maps showing difference in 0.2-second (5-hertz) spectral acceleration from individual deep-intraslab 

ground motion models compared to the 2008 model at 2-percent in 50 years probability of exceedance and 

VS30 site conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-

Cascadia (Atkinson and Boore, 2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO 

(Zhao and others, 2006) models.
175

Figure 125. Maps showing ratios of 0.2-second (5-hertz) spectral acceleration from individual deep-intraslab ground 

motion models and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions 

of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-Cascadia (Atkinson 

and Boore, 2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 

2006) models.
176

Figure 126. Maps showing difference in 1-second (1-hertz) spectral acceleration from individual deep-intraslab 

ground motion models compared to the 2008 model at 2-percent in 50 years probability of exceedance and 

VS30 site conditions of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-

Cascadia (Atkinson and Boore, 2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO 

(Zhao and others, 2006) models. Changes in the Zhao and others (2006) model is close to the mean; 

differences are close to zero.
177

Figure 127. Maps showing ratios of 1-second (1-hertz) spectral acceleration from individual deep-intraslab ground 

motion models and the 2008 model at 2-percent in 50 years probability of exceedance and VS30 site conditions 

of 760 meters per second. A, AB03-GL (Atkinson and Boore, 2003) global model; B, AB03-Cascadia (Atkinson 

and Boore, 2003) Cascadia model; C, BCHYDRO (Addo and others, 2012); and D, ZHAO (Zhao and others, 

2006) models.
178

Results

The 2014 USGS NSHMP maps incorporate significant source and ground motion modifications 

that create complex patterns of hazard changes across the United States. Updates of the earthquake 

catalog, rates, and smoothed seismicity methods; fault rupture models using geologic and geodetic 

information; and ground motion models have resulted in changes to ground motions in nearly all of the 

conterminous United States. In this section we concentrate our discussion on the building code type 

hazard maps that are computed for 2-percent probability of exceedance in 50 years and a uniform firm 

rock (VS30=760 m/s) site condition for PGA and spectral response acceleration at 1-hertz (1-second 

spectral acceleration) and 5-hertz (0.2-second spectral acceleration) for 5-percent damping. We have 

examined other ground shaking types such as for longer periods that will be considered in future reports.

In the following sections, we present the changes to the USGS NSHMP maps, relative to the 

2008 USGS NSHMP maps, and discuss the contributing factors that result in probabilistic ground 

motion differences. To examine the causes of the differences between the 2014 and 2008 USGS 

NSHMP maps, we show difference (2014 probabilistic ground motions minus 2008 ground motions) 

and ratio maps (2014 probabilistic ground motions divided by 2008 ground motions) for the WUS, 

CEUS, California, and subduction related earthquakes. In addition to the total changes in ground 

motions at PGA and 1-hertz and 5-hertz spectral acceleration between the 2014 and 2008 USGS 

NSHMP maps, we show separately the influence of changes caused by updated fault-source models, 

seismicity-based background-source models, and ground motion models. 

Central and Eastern United States

Differences between the 2008 NSHMP maps and the 2014 NSHMP maps are complex across 

the CEUS with hazard varying locally (figs. 128–133). These changes mainly are caused by (1) updated 

GMMs; (2) updated seismicity rate calculations and smoothing methods; and (3) modified fault models 

for New Madrid (Missouri) seismic zone and surrounding area, Charleston (S.C.) seismic zone, new 

Charlevoix (eastern Canada) fault and areal source zones, and the Meers (Oklahoma) and Cheraw

(Colo.) faults (fig. 21). 

The updated GMMs and their weights have the overall effect of reducing ground motions for all 

sources and at all ground motion spectral periods. The reason for this is that the 2014 models are 

weighted more heavily with the equations that decay more quickly with distance than the models 

applied in 2008. These hazard decreases, in general, are more significant for moderate distances and 

larger magnitudes. 

Earthquake catalog and rate changes in the gridded-seismicity model cause many of the local 

differences across the CEUS (especially for shorter periods). Regional changes in hazard across the 

CEUS are caused by a new catalog and newly adopted treatment of the seismicity rates; the 2014 

NSHMP model incorporates seismicity-rate adjustments for observed and converted magnitudes 

following the CEUS–SSCn (2013), applies a new catalog with modified completeness criteria, and 

applies partial weight to seismicity rate distributions calculated from new adaptive-smoothing 

techniques. As in 2008, we have omitted earthquakes suspected to be related to mining or industrial 

fluid injection/extraction processes. Some changes in the seismicity rate and treatment of these events

cause local differences in the maps (such as Fashing, Tex., central Oklahoma, and the Raton Basin, 

Colo. and N. Mex.). Methods to account for the hazard from these deleted events in a consistent manner 

are under development in the seismological community. 

Fault sources affect ground shaking hazard at a large range of distances; for example, changes in 

the model near New Madrid, Mo., and Charleston, S. C., are clear on both the difference and ratio maps. 
179

Ground motions have changed near Charlevoix due to the addition of a new fault source. The ground 

motion maps clearly show the influence of the New Madrid seismic zone out to 1,000 km where 

concentric patterns are observed (figs. 128–133).

Figure 128. Maps showing difference in peak ground acceleration in the Central and Eastern United States at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Differences in 

ground motion due to A, updates to the 2014 model compared to the 2008 model; B, changes in fault-source 

model; C, changes in background seismicity rates; and D, changes in ground motion models. A includes 

Western United States sources and the other panels do not.
180

Figure 129. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in the Central and Eastern United 

States at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion due to A, updates to the 2014 model compared to the 2008 model; B, changes in 

fault-source model; C, changes in background seismicity rates; and D, changes in ground motion models. A

includes Western United States sources and the other panels do not.
181

Figure 130. Maps showing difference in 1-hertz (1-second) spectral acceleration in the Central and Eastern United 

States at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion due to A, updates to the 2014 model versus the 2008 model; B, changes in faultsource model; C, changes in background seismicity rates; and D, changes in ground motion models. A

includes Western United States sources and the other panels do not.
182

Figure 131. Maps showing ratios of peak ground acceleration in the Central and Eastern United States at 2-percent 

in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in ground 

motion shown include A, updates to the 2014 model versus the 2008 model; B, changes in fault-source model; 

C, changes in background seismicity rates; and D, changes in ground motion models. A includes Western 

United States sources and the other panels do not.
183

Figure 132. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration in the Central and Eastern United 

States at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Changes in ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, 

changes in fault-source model; C, changes in background seismicity rates; and D, changes in ground motion 

models. A includes Western United States sources and the other panels do not.
184

Figure 133. Maps showing ratios of 1-hertz (1-second) spectral acceleration in the Central and Eastern United 

States at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Changes in ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, 

changes in fault-source model; C, changes in background seismicity rates; and D, changes in ground motion 

models. A includes Western United States sources and the other panels do not.

Western United States

In this section we discuss the hazard sensitivity from the shallow crustal earthquakes, subduction 

interface earthquakes, deep intraslab earthquakes, and California earthquakes. We look at the effects of 

seismicity-based models, fault-based models, and ground motion models on the total hazard. 
185

Intermountain West and Pacific Northwest Shallow Crustal Earthquake Hazard

Figures 134–139 show difference and ratio maps comparing 2014 to 2008 probabilistic ground 

motions in the WUS for PGA (figs. 134 and 137), 5-hertz (0.2-second; figs. 135 and 138) and 1-hertz

(1-second; figs. 136 and 139) spectral acceleration with a 2-percent probability of exceedance in 50-year 

level on firm rock site condition. The 2014 maps in the WUS depict a complicated hazard pattern across 

a broad area compared to the 2008 maps. Changes in hazard are due to (1) changes in the GMMs, (2) 

changes in the earthquake catalog and seismicity rate changes for shallow crustal earthquakes, and (3) 

changes in the crustal fault models. 

The shallow crustal GMMs are composed of the NGA-West2 updated equations (Bozorgnia and 

others, 2014). The GMMs for shallow crustal faults cause increases in hazard over several major faults 

for peak ground acceleration, decreases for 0.2-second (5-hertz) spectral acceleration, and minor 

changes for 1-hertz spectral acceleration. Strike-slip ground motions and aleatory uncertainties for large 

earthquakes with high recurrence rates typically are higher than in 2008, whereas dip slip ground 

motions vary with period. This partially is accounted for by a reduced hanging-wall effect for normal 

faulting earthquakes. The ratio maps (figs. 137–139) show that with respect to distance, GMMs fall off 

faster than in older models. This is consistent with the attenuation with distance shown in the previous 

section. Ratios show changes up to ±30 percent; nevertheless, the differences can be very small and only 

range within about ±0.05 g away from faults and about ±0.15 g over faults. 

Earthquake catalog and rate changes as well as smoothing algorithms cause changes in hazard 

across the WUS. Due to the addition of the adaptive smoothing model, ground motions often increase 

over a seismicity cluster but decrease at larger distances.
186

Figure 134. Maps showing difference in peak ground acceleration in the Western United States at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Differences in ground 

motion are due to A, updates to the 2014 model compared to the 2008 model; B, changes in fault-source 

model; C, changes in background seismicity rates; and D, changes in ground motion models. A includes 

Central and Eastern United States sources and the other panels do not.
187

Figure 135. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in the Western United States at 

2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Differences 

in ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; C, changes in background seismicity rates; and D, changes in ground motion models. A

includes Central and Eastern United States sources and the other panels do not.
188

Figure 136. Maps showing difference in 1-hertz (1-second) spectral acceleration in the Western United States at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Differences in 

ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; C, changes in background seismicity rates; and D, changes in ground motion models. A

includes Central and Eastern United States sources and the other panels do not.
189

Figure 137. Maps showing ratios of peak ground acceleration in the Western United States at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second. Changes in ground motion shown 

include A, updates to the 2014 model compared to the 2008 model; B, changes in fault-source model; C, 

changes in background seismicity rates; and D, changes in ground motion models. A includes Central and 

Eastern United States sources and the other panels do not.
190

Figure 138. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration in the Western United States at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; C, changes in background seismicity rates; and D, changes in ground motion models. A includes 

Central and Eastern United States sources and the other panels do not.
191

Figure 139. Maps showing ratios of 1-hertz (1-second) spectral acceleration in the Western United States at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; C, changes in background seismicity rates; and D, changes in ground motion models. A includes 

Central and Eastern United States sources and the other panels do not.
192

Fault model changes are due to using geodetic/geologic combined-inversion models, adding new 

or modifying existing fault sources, and calculating rates based on the 50° dip on normal faults. In 

particular, several new faults have been added or modified in the 2014 NSHMP maps.

Important changes near Salt Lake City, Utah; Reno, Nev.; Las Vegas, Nev.; and Seattle, Wash., 

are described below. Hazard near the Salt Lake City segment of the Wasatch fault zone has changed due 

to a new logic tree on fault geometry beneath Salt Lake City. The hazard on the southern Wasatch fault 

has increased due to changes in the geologic and geodetic fault models. Sites in Salt Lake City have 

reduced hazard for several reasons: (1) Great Salt Lake fault is characterized by reduced event rates 

(Lund, 2013), (2) lower partial-source rupture rates due to lower event rates on shallow-dipping source, 

(3) lower ground motions on the hanging-wall of the fault. Hazard near Reno, Nev., has decreased due 

to lower event rates on shallow dipping Carson Range and Kings Canyon fault system. Ground motions 

have increased near Las Vegas, Nev. because of the modification of the slip rate on the Eglington fault. 

Important changes in Washington are related to the addition of the Tacoma fault and changes to the 

South Whidbey Island fault. The Seattle region hazard has not changed significantly because we use a 

very similar model for the Seattle fault as was applied in 2008. We have not modified this fault using 

the geodetic model. 

Changes to probabilistic ground motion at 2-percent probability of exceedance in 50 years for 

Intermountain West and Pacific Northwest crustal fault sources are apparent only for the most active 

faults in the region. Tables 20 and 21 identify maximum ground motion changes at 5-hertz spectral 

acceleration (figs. 135B and 138B) due to the 2014 update to fault-source parameters.

Table 20. Intermountain West and Pacific Northwest fault sources that contribute to ground motion increases at 

5-hertz (0.2-second) spectral acceleration.

[g, gravitational acceleration constant equal to 9.81 meters per second squared; GM, ground motion; <, less than] 

Fault source State Notes

Gore Range frontal fault Colorado new source increases GM <0.05 g.

Williams Fork Mountains fault Colorado new source increases GM <0.05 g. 

Sawtooth fault Idaho new source increases GM <0.5 g.

Benton Spring fault Nevada slip rate change increases GM <0.5 g. 

Bettles Well-Petrified Springs fault Nevada slip rate change increases GM <0.5 g.

Eglington fault Nevada annual rate and slip rate change increases GM <0.5 g.

Lone Mountain fault zone Nevada slip rate change increases GM <0.25 g. 

Smith Valley fault Nevada slip rate change increases GM <0.25 g.

Wassuk Range fault zone Nevada slip rate change increases GM <0.25 g. 

Steens fault zone Oregon slip rate change increases GM <0.1 g.

Wasatch fault zone, Nephi section Utah annual rate and slip rate change increases GM <0.5 g.

Wasatch fault zone, Provo section Utah annual rate and slip rate change increases GM <0.5 g. 

Wasatch fault zone, Salt Lake City section Utah location modified locally increases GM.

Wasatch fault zone, Weber section Utah annual rate and slip rate change increases GM <0.1 g. 

West Cache fault, Junction Hills section Utah new source increases GM <0.1 g.

Saddle Mountain fault Washington added 0.25 branch weight to Holocene slip rate increases 

GM <0.05 g.

Southern Whidbey Island Washington length of source extended, which locally increases GM.

Tacoma fault Washington new source increases GM <0.5 g. 
193

Table 21. Intermountain West and Pacific Northwest fault sources that contribute to ground motion decreases at 

5-hertz (0.2-second) spectral acceleration.

[g, gravitational acceleration constant equal to 9.81 meters per second squared; GM, ground motion; <, less than] 

Fault source State Notes

Centennial fault Montana slip rate change decreases GM <0.1 g. 

Desatoya Mountains fault zone Nevada slip rate change decreases GM <0.05 g. 

Sand Springs Range fault Nevada slip rate change decreases GM <0.25 g. 

Toiyabe Range fault zone Nevada slip rate change decreases GM <0.25 g. 

Western Toiyabe Range fault zone Nevada slip rate change decreases GM <0.25 g. 

Steens fault zone Oregon slip rate. 

Great Salt Lake fault zone, Antelope 

Island section Utah constrained annual rate change decreases GM <0.5 g. 

Great Salt Lake fault zone, Fremont 

Island section Utah constrained annual rate change decreases GM <0.5 g. 

Great Salt Lake fault zone, 

Promontory section Utah constrained annual rate change decreases GM <0.5 g. 

Sevier/Toroweap fault zone (northern) Utah slip rate change decreases GM <0.25 g.

Wasatch fault zone, Salt Lake City 

section Utah location modified locally decreases GM. 

Bear River fault Wyoming constrained annual rate change decreases GM <0.5 g.

Grand Valley fault Wyoming slip rate change decreases GM <0.25 g.

Rock Creek fault Wyoming slip rate change decreases GM <0.5 g. 

Teton fault Wyoming slip rate change decreases GM <0.5 g. 

Southern Whidbey Island Washington length of source extended, which locally decreases GM. 

Cascadia Subduction Interface Contributions

Figures 140–145 show difference and ratio maps for the total 2014 model with respect to the 

2008 model, the contribution from the 2014 Cascadia subduction interface sources compared to the 

2008 seismic sources, and the contribution from the 2014 compared to the 2008 subduction interface 

GMMs. These comparisons are made for peak ground acceleration, 0.2-second (5-hertz) spectral 

acceleration, and 1-second (1-hertz) spectral acceleration for 760 m/s VS30. 
194

Figure 140. Maps showing difference in peak ground acceleration for the Cascadia subduction zone at 2-percent in 

50 years probability of exceedance and VS30 site conditions of 760 meters per second. Differences in ground 

motion are due to A, updates to the 2014 model compared to the 2008 model; B, changes in fault-source 

model; and C, changes in ground motion models.
195

Figure 141. Maps showing ratios of peak ground acceleration for the Cascadia subduction zone at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in ground motion 

shown include A, updates to the 2014 model compared to the 2008 model; B, changes in fault-source model; 

and C, changes in ground motion models. 
196

Figure 142. Maps showing difference in 5-hertz (0.2-second) spectral acceleration for the Cascadia subduction 

zone at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, 

changes in fault-source model; and C, changes in ground motion models. 
197

Figure 143. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration for the Cascadia subduction zone at 

2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; and C, changes in ground motion models. 
198

Figure 144. Maps showing difference in 1-hertz (1-second) spectral acceleration for the Cascadia subduction zone 

at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, 

changes in fault-source model; and C, changes in ground motion models. 
199

Figure 145. Maps showing ratios of 1-hertz (1-second) spectral acceleration for the Cascadia subduction zone at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in faultsource model; and C, changes in ground motion models. 

The 2014 maps along the Cascadia subduction zone depict a complicated hazard pattern across a 

broad area compared to the 2008 maps. Changes in hazard are due to (1) changes in the ground motion 

models and (2) changes in the Cascadia subduction zone source models. 

For the 2014 NSHMP maps, two new GMMs for subduction interface earthquakes were added 

and the weights were redistributed. The new subduction-interface ground motions are higher close to the 

source and decay faster with greater distances than in the 2008 models. The updated ground motion 

models mostly affect coastal Washington, Oregon, and California. 

The Cascadia source model contains a higher rate of earthquakes in the south based on new data 

described in “Earthquake Recurrence and Down-Dip Edge of Rupture for the Cascadia Subduction 

Zone” section which increases hazard in the southern half of the zone. The Cascadia subduction source 

and GMM changes have caused an increase in ground shaking hazard along northwestern Washington 

and California and along the southwestern Oregon coastlines for all three periods. Ground shaking 

hazard generally is lower in northwestern Oregon due to changes in the rate of large subduction 

interface earthquakes on the northern Cascadia. Ground shaking tends to be a little lower at sites farther 

from the subduction zone because the ground motion models generally fall off faster than in previous 

models. 
200

Cascadia Deep Intraslab Contributions

Figures 146–151 show difference and ratio maps for the total 2014 model with respect to the 

2008 model, the contribution from the 2014 deep intraslab sources compared to the 2008 seismic 

sources, and the contribution from the 2014 deep intraslab GMMs compared to the 2008 GMMs. These 

comparisons are made for peak ground acceleration, 0.2-second (5-hertz) spectral acceleration, and 1-

second (1-hertz) spectral acceleration for 760 m/s VS30. 

Figure 146. Maps showing difference in peak ground acceleration for deep intraslab seismic sources at 2-percent in 

50 years probability of exceedance and VS30 site conditions of 760 meters per second. Differences in ground 

motion are due to A, updates to the 2014 model compared to the 2008 model; B, changes in deep-seismicity 

model; and C, changes in ground motion models. 
201

Figure 147. Maps showing ratios of peak ground acceleration for deep intraslab seismic sources at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in ground motion 

shown include A, updates to the 2014 model compared to the 2008 model; B, changes in deep-seismicity 

model; and C, changes in ground motion models. 
202

Figure 148. Maps showing difference in 5-hertz (0.2-second) spectral acceleration for deep intraslab seismic 

sources at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, 

changes in deep-seismicity model; and C, changes in ground motion models. 
203

Figure 149. Maps showing ratios of 5-hertz (0.2-second) spectral acceleration for deep intraslab seismic sources at 

2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in deepseismicity model; and C, changes in ground motion models. 
204

Figure 150. Maps showing difference in 1-hertz (1-second) spectral acceleration for deep intraslab seismic sources 

at 2-percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. 

Differences in ground motion are due to A, updates to the 2014 model compared to the 2008 model; B, 

changes in deep-seismicity model; and C, changes in ground motion models. 
205

Figure 151. Maps showing ratios of 1-hertz (1-second) spectral acceleration for deep intraslab seismic sources at 2-

percent in 50 years probability of exceedance and VS30 site conditions of 760 meters per second. Changes in 

ground motion shown include A, updates to the 2014 model compared to the 2008 model; B, changes in deepseismicity model; and C, changes in ground motion models. 

The 2014 maps for deep intraslab earthquakes are quite different from the 2008 maps. Changes 

in hazard are due to (1) changes in the GMMs and (2) changes in the earthquake catalog and seismicity 

rate changes for deep intraslab earthquakes, (3) the Mmax distribution, the depth distribution (staircase), 

and (4) the deep source zone beneath Washington and Oregon. Figures 146–151 show sensitivity of the 

hazard model to proposed changes in the seismic sources and ground motion models. 

The GMMs for deep intraslab earthquakes cause large increases to the hazard for 5-hertz and 

lower hazard at 1-hertz spectral acceleration in the Puget Sound region, Wash. Figures 146C and 147C

show the effect on probabilistic peak ground acceleration in western Washington, Oregon, and 

northwest California of changing ground motion models, using the 2014 source model in the numerator 

and denominator. Near the Washington and Oregon source, peak ground acceleration increases about 10 

percent. At greater distances, peak ground acceleration decreases. In California, however, peak ground 

acceleration decreases over 20 percent near the source. The difference between source characterizations 

explains this behavior. In California, the mean magnitude is relatively small due to a larger b value 

(0.8), whereas in Washington and Oregon, the mean magnitude is relatively large due to a smaller b 

value (0.4). The updated GMMs tend to reduce the median peak ground acceleration for smaller 

intraplate sources but tend to raise the median peak ground acceleration for larger intraplate sources. 

Figures 148C and 149C show the effect on probabilistic 0.2-second (5-hertz) spectral acceleration in the 

same region. The 0.2-second (5-hertz) spectral acceleration increases about 20 percent near the 

Washington and Oregon source, but decreases 10 percent near the California source. Again, this 
206

different behavior is attributed to lower mean magnitude of deep sources in the California part of the 

hazard model. At greater distances from the deep source, the 5-hertz spectral acceleration decreases 

everywhere in the 2014 model. Figures 150C and 151C show the effect on probabilistic 1-hertz spectral 

acceleration in the same region. The 1-hertz spectral acceleration decreases everywhere. This change is 

larger in California, up to 50 percent lower than in the 2008 model; in Washington and Oregon, up to a 

30-percent decrease is more typical. Newer GMMs tend to greatly reduce the median 1-hertz spectral 

acceleration for smaller sources but tend to only slightly reduce the median 1-hertz spectral acceleration

for larger sources, compared to the 2008 suite of GMMs.

The combined effects of source model, including new activity grids, higher Mmax, and the use 

of a staircase depth distribution, are shown in figures 146B–151B. Effects of the SSC and GMMs are 

shown in the left panel. In Washington, the new ground motions at 5-hertz frequency are slightly larger 

(fig. 148A), due to combined effects of increased Mmax (fig. 148B) and ground motions (fig. 148C). 

The new ground motions at 1-hertz frequency are slightly lower (fig. 150A) at Washington sites because 

the decrease in median motion (fig. 150C) dominates the increase due to larger Mmax (fig. 150B). In 

northern Oregon, probabilistic ground motion decreases for peak ground acceleration, 5-hertz, and 1-

hertz frequency (fig. 146A‒151A), but in southern Oregon it increases due to the new seismic source 

model, which spreads out hazard over the entire western one-half of the state in the 2014 NSHMP maps. 

In northern California, the overall hazard is dominated by the subduction interface ground motions. 

Lower activity rates and ground motions from intraslab GMMs decrease the hazard relative to the 2008 

model. At coastal sites, the decrease is less pronounced because the depth of seismicity has been 

reduced from 50 km (the default value in 2008) to 39 km. The shallower focal depth tends to increase 

predicted motion at sites directly over these events.

California Shallow Crustal Earthquake Hazard

Proposed changes to probabilistic ground motions in California arise from the adoption of the 

new UCERF3 developed by the WGCEP (Working Group on California Earthquake Probabilities, 

2013) and the use of new GMMs for shallow crustal seismic sources (see “Ground Motion Models” 

section). The following figures and text summarize the significant changes in hazard implied by these 

new models, relative to the 2008 USGS NSHMP maps by (1) examining changes due broadly to the 

earthquake source models and GMMs, and (2) examining source model specific changes at the 

statewide and local levels (that is, San Francisco and Los Angeles) and explaining all the areas where 

calculated ground motions are expected to change more than 10 percent. The probabilistic seismic 

hazard, difference, and ratio maps presented in this section are for 2-percent probability of exceedance 

in 50 years on firm rock (VS30=760 m/s) uniform site condition for PGA and spectral acceleration at 0.2 

second (5 hertz) and 1.0 second (1 hertz). Note that the figures and explanatory text do not identify 

every change; however, the largest changes are identified and addressed, and the many numerous small 

changes (such as those spanning a few pixels in the accompanying statewide maps) fall into the broad 

categories identified herein. The higher resolution local maps offer insight as to the causes of smaller 

changes.

Earthquake Source and Ground Motion Model Changes

In this section we present the total model and the contributions of the source and ground motion 

models. 
207

Total Model

Figures 152–154 (peak ground acceleration, 1-hertz spectral acceleration, and 5-hertz spectral 

acceleration, respectively) show comparisons of the 2008 USGS NSHMP maps (A in each figure) to the 

new 2014 maps (B in each figure). Note that these maps include Cascadia subduction interface events 

and deep subduction intraslab events in the northwest part of the State that mask contributions from 

some shallow crustal sources present in the UCERF3 earthquake rate model. Broadly speaking, the 

hazard maps at each period are similar, but the accompanying ratio (C in each figure) and difference (D

in each figure) maps reveal significant variation between the two. Across the three periods examined, 

the spatial distribution of differences is similar; causes of changes that exceed ±10 percent are detailed 

in the following section. 
208

Figure 152. Maps showing changes in peak ground acceleration in California at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. A, 2008 map of peak ground acceleration in 

California, and B, 2014 map. These maps include Cascadia subduction interface and intraslab sources in the 

northwest part of the state. C, shows the ratio of and D, the difference between the results shown in A and B. 

Note that the ratio scale spans a factor of two and that light gray masks changes within ±5 percent. Sources 

entirely outside of California are not included.
209

Figure 153. Maps showing changes in 5-hertz (0.2-second) spectral acceleration in California at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. A, 2008 map of peak 

ground acceleration in California, and B, 2014 map. These maps include Cascadia subduction interface and 

intraslab sources in the northwest part of the state. C, shows the ratio of and D, the difference between the 

results shown in A and B. Note that the ratio scale spans a factor of two and that light gray masks changes 

within ±5 percent. Sources entirely outside of California are not included.
210

Figure 154. Maps showing changes in 1-hertz (1-second) spectral acceleration in California at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second. A, 2008 map of peak ground 

acceleration in California, and B, 2014 map. These maps include Cascadia subduction interface and intraslab 

sources in the northwest part of the state. C, shows the ratio of and D, the difference between the results 

shown in A and B. Note that the ratio scale spans a factor of two and that light gray masks changes within ±5 

percent. Sources entirely outside of California are not included.
211

Contributions From Fault and Gridded Seismicity Sources

Figures 155–157 (peak ground acceleration, and 5-hertz and 1-hertz spectral acceleration, 

respectively) show ratios (A and B in each figure) and differences (C and D in each figure) between the 

2008 and 2014 USGS NSHMP maps decomposed into contributions from fault (A in each figure) and 

background (or gridded seismicity) sources (B in each figure). Note that these maps do not include 

subduction interface and intraslab sources as in figures 152–154. Comparison with figures 152–154 

shows that most of the changes in probabilistic ground motions at all periods of interest are due to the 

UCERF3 fault-source model, which is examined in more detail in the following section. The UCERF3 

logic tree includes two gridded seismicity source branches, one that approximates the 2008 USGS 

NSHMP model and another that uses a tighter smoothing kernel, each receiving 50-percent weight. The 

branch with the tighter smoothing kernel concentrates grid sources in areas of high instrumental 

seismicity, resulting in spikes (orange dots) of increased probabilistic ground motions across the State. 

The complementary effects of these increases are light blue halos of decreased ground motion around 

the spikes (see for example, fig. 157D, along the California–Nevada border). It is also worth noting that 

the branch with the tighter smoothing kernel was generated using a declustered catalog that included 

events down to Mw2.5, giving rise to additional spatial variations in modeled earthquake rates. Again, 

although the amplitude of the differences between 2008 and 2014 vary, the spatial distribution of 

changes implied by fault and grid sources is similar across the periods examined.
212

Figure 155. Maps showing changes in peak ground acceleration in California at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. Maps do not include subduction interface and 

intraslab sources in the northwest part of the state. Changes in ground motion shown include A, ratio of the 

2014 fault-source model compared to the 2008 model; B, ratio of the 2014 background seismicity rates 

compared to that in the 2008 model; C, difference between the 2014 fault-source model and the 2008 model; 

and D, difference between the 2014 background seismicity rates and the 2008 model. Sources entirely outside 

of California are not included.
213

Figure 156. Maps showing changes in 5-hertz (0.2-second) spectral acceleration in California at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Maps do not include 

subduction interface and intraslab sources in the northwest part of the state. Changes in ground motion shown 

include A, ratio of the 2014 fault-source model compared to the 2008 model; B, ratio of the 2014 background 

seismicity rates compared to that in the 2008 model; C, difference between the 2014 fault-source model and 

the 2008 model; and D, difference between the 2014 background seismicity rates and the 2008 model. 

Sources entirely outside of California are not included.
214

Figure 157. Maps showing changes in 1-hertz (1-second) spectral acceleration in California at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second. Maps do not include subduction 

interface and intraslab sources in the northwest part of the state. Changes in ground motion shown include A, 

ratio of the 2014 fault-source model compared to the 2008 model; B, ratio of the 2014 background seismicity 

rates compared to that in the 2008 model; C, difference between the 2014 fault-source model and the 2008 

model; and D, difference between the 2014 background seismicity rates and the 2008 model. Sources entirely 

outside of California are not included.
215

E arthquake - Source Model Versus Ground Motion Model

Figures 158–160 (peak ground acceleration, and 5-hertz and 1-hertz spectral acceleration, 

respectively) show the total difference (D in each figure) between the 2008 and 2014 USGS NSHMP 

maps (considering only crustal fault and gridded seismicity sources), and its decomposition into 

contributions from UCERF3 (B in each figure) and the new ground motion models (A and C in each 

figure). These figures show that across the three periods of interest, most of the proposed ground motion 

changes arise from adoption of UCERF3 as the source model of the USGS NSHMP maps. Only where 

increases implied by the 2014 ground motion models are highest (for instance, along the San Andreas 

corridor) do ground motions further increase above that implied by the change in source model. 
216

Figure 158. Maps showing difference in peak ground acceleration in California at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. Differences are due to changes in the ground 

motion models using the A, 2008 source models; and C, 2014 source model; and B, changes in the faultsource model; and D, the total difference between the 2014 model compared to the 2008 model. Sources 

entirely outside of California are not included.
217

Figure 159. Maps showing difference in 5-hertz (0.2-second) spectral acceleration in California at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Differences are due to 

changes in the ground motion models using the A, 2008 source models; and C, 2014 source model; and B, 

changes in the fault-source model; and D, the total difference between the 2014 model compared to the 2008 

model. Sources entirely outside of California are not included.
218

Figure 160. Maps showing difference in 1-hertz (1-second) spectral acceleration in California at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second. Differences are due to 

changes in the ground motion models using the A, 2008 source models; and C, 2014 source model; and B, 

changes in the fault-source model; and D, the total difference between the 2014 model compared to the 2008 

model. Sources entirely outside of California are not included.
219

To compute the source model differences the 2008 USGS NSHMP ground motions were 

subtracted from those computed using the UCERF3 source model with the 2008 GMMs. The GMM

differences were computed by subtracting the ground motions implied by the 2008 GMMs from those 

implied by the 2014 GMMs using both the 2008 (top-left) and 2014 (bottom-left) source models. In 

these latter maps, it is interesting to note the sensitivity of the 2014 GMMs to source model rate changes 

at different magnitudes and for specific focal mechanisms. In both cases, the 2014 GMMs further 

increase computed ground motions along the strike-slip faults of the San Andreas corridor; however, 

when using the 2014 source model, the increase at peak ground acceleration and 5-hertz spectral 

acceleration extends across most faults in the State. Using the 2008 source model implies we would 

expect broad decreases in ground motions in the vicinity of normal and reverse faults; however, the 

inclusion of multifault ruptures with much larger magnitudes in UCERF3 indicates the opposite is true. 

Changes Caused by UCERF3

The following section outlines the specific ±10-percent changes in ground motion in the 2014 

USGS NSHMP maps that arise from adoption of UCERF3 as the NSHMP earthquake source model. 

The previous section showed that the spatial distribution of changes are consistent across the three 

spectral periods of interest, and so only peak ground acceleration with a 2-percent probability of 

exceedance in 50 years is examined in detail. Note that the ground motion maps used to derive the 

figures accompanying this section do not include Cascadia subduction interface and intraslab sources, 

which tend to dominate hazard in the northwest part of the State.

Gridded Source Contributions

Many changes (mostly increases) in probabilistic ground motion are due to the use of the 

“UCERF3 smoothed seismicity” model for background sources. Although this background source 

model only receives 50-percent weight (a model based on UCERF2 smoothed seismicity receives the 

other half), it uses a tighter, adaptive smoothing kernel, which gives rise to spikes in ground motion 

over small areas. The locations of the most significant grid source contributions to hazard are circled in 

figure 161B. Comparison with figures 155–157 show that there are numerous locations where it is 

difficult to resolve if a ground motion increase is due exclusively to changes in the 2014 smoothed 

seismicity model.
220

Figure 161. Maps showing ratios of peak ground acceleration for California at 2-percent in 50 years probability of 

exceedance and VS30 site conditions of 760 meters per second. Maps do not include Cascadia subduction 

sources. Changes in ground motion include A, updates to the 2014 model compared to the 2008 model; B, 

changes in background seismicity rates; and maps that highlight C and D, increases and decreases arising 

from changes to the fault-source model, respectively (numbers correspond to descriptions in tables 22 and 23).

Sources entirely outside of California are not included.
221

Fault-Source Contributions

The remaining changes to probabilistic ground motion arise from (1) slip- or moment-rate 

changes on existing 2008 USGS NSHMP faults, (2) geometric changes to existing faults, (3) the 

introduction of new faults, and (4) fault participation in multifault ruptures. Although the rates of large 

multifault events generally are quite low, they consume a significant portion of the statewide moment 

budget and do not contribute significantly to 2-percent probability of exceedance in 50 years PGA 

ground motions, resulting in a general decrease in ground motion along the major California fault zones. 

Figure 161C and D highlight the significant increases and decreases, respectively, in ground motion 

implied by UCERF3; see tables 22 and 23 for explanations of each numbered item in figure 161. 

Table 22. California fault sources that contribute to ground motion increases (see fig. 161C). 

[ABM, average block model; UCERF2, Uniform California Earthquake Rupture Forecast, ver. 2]

ID Fault source Notes

1 Big Lagoon–Bald Mountain fault Extended north approximately 60 km and has 8x moment rate 

for ABM deformation model.

2 South Klamath Lake West fault New fault. 

3 Goose Lake, Fitzhugh Creek, Jess 

Valley, and Davis Creek faults

New faults.

4 Likely fault Moment rate doubled.

5 Pittville fault New fault.

6 Honey Lake fault Fault extended to west.

7 Almanor, Walker Spring, Keddie 

Ridge, Skinner Flat, Mohawk Valley, 

Dog Valley, Polaris, and Incline 

Village faults

Seven new faults.

8 West Tahoe and Antelope Valley 

faults

New fault and southern extension of West Tahoe fault.

9 Maacama fault 20-percent increase in moment rate.

10 West Napa fault 3.5x increase in moment rate, mostly due to ABM deformation 

model.

11 Great Valley 03, 05, and 06, and Los 

Medanos–Roe Island faults

New and alternate fault models.

12 Greenville South and Ortigalita faults Ortigalita: geometric and moment-rate changes; Greenville 

South extended further south.

13 Silver Creek, Monte Vista–Shannon, 

and Sargent faults

New or extension of existing (Monte Vista–Shannon) faults.

Zayante–Vergeles fault Moment-rate increase (x9 increase for reverse fault 

representation)

14 Oceanic–West Hausna faults New fault with high moment rate.

15 Los Alamos, Santa Ynez River, Santa 

Ynez West, and Hosgri Extension 

faults

New faults.
222

Table 22. California fault sources that contribute to ground motion increases (see fig. 161C).—Continued

ID Fault source Notes

16 Lost Hills fault New fault.

17 Fish Slough, Independence, and 

Owens Valley faults

Fault geometry change (Fish Slough) and moment-rate increases 

on all three faults.

18 Sierra Nevada (N. extension) and 

White Wolf Extension Faults; Scodie 

and Lake Isabella Seismicity 

lineaments

New faults commingled with gridded seismicity sources.

19 15+ new faults Many new faults added in the eastern Mojave desert; some were 

present in UCERF2 with 0 zero slip rate; others are entirely new 

(for example, Cleghorn Pass and Lake Faults). 

20 San Clemente, San Diego Trough, 

Santa Cruz Catalina Ridge, 

Oceanside, and San Pedro Basin faults

Multiple new offshore faults.

21 Elmore Ranch fault Moment-rate increase.

22 Cerro Prieto fault New fault.

Table 23. California fault sources that contribute to ground motion decreases (see fig. 161D) 

ID Fault Source Notes

1 Gillem–Big Crack & Cedar Mtn.–

Mahogany Mtn. faults

Lower slip rates.

2 Surprise Valley Fault Moment-rate decrease.

3 Hat Creek–McArthur–Mayfield fault Moment-rate decrease.

4 Maacama fault High slip-rate fault shortened at northern end.

5 Bartlett Springs fault Trace geometry changes.

6 Great Valley 03, 04 faults Moment-rate decrease.

7 Great Valley 08 (Orestimba) fault 60-percent decrease in moment rate; participation in multifault 

ruptures.

8 Mono Lake fault Moment-rate decrease.

9 Death Valley North, South, and Black 

Mtn. Frontal faults

40-percent decrease in moment rate; participation in multifault 

ruptures.

10 San Gregorio South Fault geometry and slip/event rate change.

11 Hosgri fault Down dip width increase and participation in multifault ruptures 

contributes to lower hazard although total moment rate has 

changed little.

12 San Cayetano, Anacapa–Dume, Oak 

Ridge Offshore, and Channel Islands 

Deep Ramp faults 

New faults and moment-rate increases on existing.

13 Cucamonga fault Methodological difference; Cucamonga participates in 

multifault ruptures rather than by itself in high-rate 

“characteristic” events. Down dip width also increased.

14 North Frontal and Cleghorn faults Moment-rate decreases.
223

Local Changes

Comparisons of local changes in probabilistic ground motion for the San Francisco Bay and Los 

Angeles areas implied by the use of UCERF3 as the USGS NSHMP earthquake source model are 

shown in figures 162 and 163, respectively. These comparisons are improved by using higher resolution 

computational grids (0.02 and 0.05 degrees per pixel, as opposed to 0.1 degree per pixel in the statewide 

comparisons). As with the statewide comparisons, most changes in ground motion arise from updates to 

existing faults (slip- or moment-rate, or geometry) or the introduction of new faults. A number of such 

changes are identified in figures 162 and 156, and explanations of each are provided in tables 24 and 25. 

The higher resolution map and scale reveal how sensitive hazard is to slight changes in geometry (for 

example, a once vertical fault that now has a slight dip picks up a hanging-wall effect). Another 

contribution to changes in hazard that stands out at the local scale is the presence of segment boundaries 

in the 2008 USGS NSHMP fault model, across which slip-rate changes are common. As with the 

previous section, these comparisons are all for 2-percent probability of exceedance in 50-year PGA 

ground motion. 
224

Figure 162. Maps showing ratios of peak ground acceleration in the San Francisco Bay area at 2-percent in 50 

years probability of exceedance and VS30 site conditions of 760 meters per second implied by the Uniform 

California Earthquake Rupture Forecast, ver. 3 (UCERF3) source model to that of the 2008 fault-source model

(maps do not consider new ground motion models). A, 2008 version of the fault-source model (black dots mark 

significant 2008 modeled segment boundaries); B, shows UCERF3 faults (all fault models, refer to table 24 for 

explanations of ground motion variation at the numbered locations); and C, ratio of 2014 model compared to 

the 2008 model. 
225

Figure 163. Maps showing ratios of peak ground acceleration in the Los Angeles area at 2-percent in 50 years

probability of exceedance and VS30 site conditions of 760 meters per second implied by the Uniform California 

Earthquake Rupture Forecast, ver. 3 (UCERF3) source model to that of the 2008 fault-source model (maps do 

not consider new ground motion models). A, 2008 USGS NSHMP faults (black dots mark significant 2008 

modeled segment boundaries); B, shows UCERF3 faults (all fault models, refer to table 25 for explanations of 

ground motion variation at the numbered locations); and C, ratio of 2014 model compared to the 2008 model. 
226

Table 24. San Francisco Bay area ground motion changes (see fig. 162). 

[mm/yr, millimeters per year] 

ID Notes

1 Oakland—Hazard decrease due to the Hayward fault as a whole participating in multifault 

ruptures and the presence of the Hayward N.–Hayward S. segment (slip-rate change) boundary in 

the 2008 USGS NSHMP source model (UCERF2).

2 Numerous new fault and updated fault geometries

Monte Vista–Shannon extension

Hayward S. Extension addition

Silver Creek addition.

3 New fault: Greenville S.

4 Numerous Contra Costa Faults connecting Calaveras N. and West Napa. 

5 Increased hazard between Calaveras N. and Hayward South due to change in fault geometry. Both 

faults dip towards each other, whereas they were both vertical in UCERF2, thereby increasing 

hanging-wall effects.

6 Green Valley relocated slightly to west but also now dipping to the west thereby significantly 

reducing hazard on what is now the footwall (east) side of the fault trace.

7 Increased hazard in vicinity of Zayante–Vergeles (ZV) and San Andreas (at Santa Cruz; SAF). To 

the west of ZV, the broad area of increased hazard is due to one fault model (3.1) representing ZV 

as a west-dipping reverse fault. The area of high increase between ZV and SAF is due to the Santa 

Cruz section having a 79-degree west dip, whereas it was vertical in UCERF2. High hazard to the 

east of the SAF is due to the inclusion of the Sargent fault in UCERF3.

8 The large drop in hazard on the southern part of the central Calaveras primarily is due to the drop 

in slip rate on the central Calaveras (15 mm/yr to approximately 11.5 mm/yr). On the northern 

one-half of the fault, this drop is overwhelmed by the rapidly slipping, east dipping south Hayward 

Extension. The loss of the south-central Calaveras segment boundary also contributes to lower 

hazard.

Table 25. Los Angeles area ground motion changes (see fig. 163). 

ID Notes

1 Conversion from independent overlapping faults to “stepovers” on both the San Jacinto and 

Elsinore faults.

2 (Note: there are two number 2 markers in figure.) Decreased hazard due to presence of segment 

boundaries in 2008 model (UCERF2).

3 Multiple new faults considered that had 0 mm/yr slip rates in the 2008 USGS NSHMP maps. 

Although rates generally are low (approximately 1 mm/yr) (for example, Compton, San Pedro 

escarpment), these significantly increase 2 percent in 50-year ground motions.

4 Anacapa-Dume; 7-percent reduction in moment.

5 Cucamonga methodological change; now participates with other faults.

6 San Cayetano; 10-percent reduction in moment.
227

Considering the 2014 GMMs in conjunction with UCERF3, probabilistic ground motions 

generally increase in a manner consistent with what was observed at the statewide scale. In the case of 

PGA, probabilistic ground motions increase most dramatically along strike-slip faults of the San 

Andreas corridor and exhibit little or no change in the vicinity of reverse faults. For example, in the Bay 

Area (fig. 162C), there is a marked increase in probabilistic ground motion along the San Andreas Fault 

and broader areas of increased ground motion about the faults of the East Bay (such as the CalaverasHayward system among others). Near Los Angeles (fig. 163C), probabilistic ground motion along the 

Mojave section of the San Andreas Fault is increased, whereas when considering the UCERF3 source 

model alone, ground motion had decreased. 

Conclusions and Future Directions

The 2014 national seismic hazard maps apply the best available science as determined by project 

scientists, workshop participants, and the National Seismic Hazard Mapping Project (NSHMP) steering 

committee that provided critical review and guidance. Many new input datasets, models, and methods 

were implemented in this update, including the following: the Central and Eastern U.S. Seismic Source 

Characterization for Nuclear Facilities (CEUS–SSCn, 2012) project developed a new Central and 

Eastern U.S. (CEUS) source model; Electric Power Research Institute reevaluated weights for CEUS 

ground motion models; the Basin and Range Province Earthquake Working Group and the Working 

Group on Utah Earthquake Probabilities models provided new information for the Intermountain West 

region faults; a working group combined geologic and geodetic inversion slip rates to update the fault 

sources across the Western United States (WUS); the Cascadia working groups developed new models 

for fault geometry and earthquake recurrence; the Uniform California Earthquake Rupture Forecast 

model provided new multisegment rupture models; and the Next Generation Attenuation group (Pacific 

Earthquake Engineering Research Center, PEER) provided new ground motion models for WUS crustal 

earthquakes. In addition, many other scientists and engineers participated in workshops, a Tiger Team 

committee, and numerous meetings and discussions of earthquake sources and ground motions that were 

implemented in this analysis. The new seismic hazard models benefitted from the advice of many 

hundreds of experts across the country.

The 2014 updated hazard maps differ from the 2008 maps in complex ways. The new ground 

motions vary locally depending on complicated changes in the underlying models. In the CEUS, the 

new earthquake catalog, completeness models, smoothing algorithms, magnitude uncertainty 

adjustments, and fault models change the hazard, and the new ground motion model-weighting scheme 

generally lowers the ground motions. The resulting maps for the CEUS can differ by ±20 percent over 

broad areas, with larger changes locally, compared to the 2008 maps due to complicated interactions 

between the various parts of the models. In the Intermountain West region, the combined geologic and 

geodetic inversion models increase the hazard along the Wasatch fault and central Nevada region, but 

the new NGA-West2 ground motions tend to lower the hazard on the hanging walls of normal faults 

with respect to the 2008 USGS NSHMP maps. These counteracting effects can result in complicated 

patterns of changes which are about ± 20 percent over broad portions of the region compared to the 

previous hazard maps. In the Pacific Northwest, the new Cascadia source model causes the hazard to 

increase by up to 40 percent in the southern Cascadia subduction zone due to the addition of possible 

Mw8 and greater earthquakes, but causes the hazard to decrease slightly along the northern Cascadia 

subduction zone because of reduced earthquake rates relative to the 2008 NSHMP model. Subduction 

ground motions from the new models fall off faster with distance than motions in previous models, but 

they also tend to be higher near fault ruptures. In California, the new UCERF3 model accounts for 

earthquakes that rupture multiple faults yielding larger magnitudes than applied in the previous model; 
228

however, the new maps also include new ground motion models, new slip rates from combined 

geodetic-geologic inversions, new faults, and an adaptive smoothing seismicity model that can locally 

increase the hazard compared to the previous model. The overall changes are often less than ±20 percent 

across most of California. At a specific site, it is important to examine all model changes to determine 

why the ground motions may have increased or decreased. 

Several issues still need to be addressed in future versions of the maps. For example, we have 

not finalized a model for the treatment of hazard from earthquakes suspected of being caused by fluid 

injection (potentially induced earthquakes). This is a very complex problem and alternatives will, most 

likely, be considered as a series of logic-tree branches in future models. The users of the hazard maps 

should consider additional hazard from potentially induced events. Another issue involves the timedependence of hazard displayed in these maps. The current hazard model is a time-independent model 

and does not consider the elapsed time since the last earthquakes on faults. These maps do not vary in 

time, which is a desirable feature in building code maps; however, other users want to consider time

dependence. As source models are updated and new ground motion models are developed for the CEUS 

(NGA-East project) and for subduction zones (NGA-Subduction project), such models will better define 

the potential ground motions and associated uncertainty for these earthquakes. We will continue to 

examine the sensitivity and uncertainty in ground motions from all logic-tree branches included in this 

2014 NSHMP model. Maps for alternative site conditions, alternative probabilities, and alternative 

ground motion parameters and frequencies are also important products that will have many uses. 

Scenario hazard maps and urban seismic hazard maps will help guide urban planning and development. 

In addition, new updates for Alaska, Hawaii, and Puerto Rico seismic hazard are currently under 

revision. We welcome comments on these maps and encourage discussions on how to improve future 

updates of the USGS NSHMP maps.

Acknowledgments

We wish to thank the hundreds of workshop, working group, review, and other participants who 

made valuable suggestions for revising the 2014 USGS national seismic hazard maps and models. We 

especially thank members of the National Seismic Hazard Mapping Project steering committee (John 

Anderson (chair), Norm Abrahamson, Ken Campbell, Martin Chapman, Michael Hamburger, William 

Lettis, Nilesh Shome, Ray Weldon, Chris Wills), who reviewed the documentation, data, methods, and 

models, and provided excellent feedback that helped us to improve the quality of this product. We thank 

the National Earthquake Hazard Reduction Program (NEHRP) for funding the development of the 

maps. Many groups and organizations are discussed in the documentation and we appreciate all of their 

cooperation in working on strict timelines to make the maps available to the Building Seismic Safety 

Council for their consideration in the building code process. In addition we appreciate the efforts of 

Stephanee R. Walker who served as editor of this report and Janet L. Slate who reviewed the document 

for content and policy issues. 

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http://dx.doi.org/10.3133/ofr20141091