Documentation for the 2008 Update of the United States

National Seismic Hazard Maps

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2008–1128

Documentation for the 2008 Update of the 

United States National Seismic Hazard 

Maps

By Mark D. Petersen, Arthur D. Frankel, Stephen C. Harmsen, Charles S. Mueller, 

Kathleen M. Haller, Russell L. Wheeler, Robert L. Wesson, Yuehua Zeng, Oliver 

S. Boyd, David M. Perkins, Nicolas Luco, Edward H. Field, Chris J. Wills, and 

Kenneth S. Rukstales

Open-File Report 2008–1128

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

Suggested citation:

Petersen, Mark D., Frankel, Arthur D., Harmsen, Stephen C., Mueller, Charles S., Haller, Kathleen M., 

Wheeler, Russell L., Wesson, Robert L., Zeng, Yuehua, Boyd, Oliver S., Perkins, David M., Luco, Nicolas, 

Field, Edward H., Wills, Chris J., and Rukstales, Kenneth S., 2008, Documentation for the 2008 Update of 

the United States National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2008–1128, 61 p. 

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iii

Contents

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

General Methodology....................................................................................................................................4

Seismicity-Derived Hazard Component ............................................................................................5

Fault Sources.........................................................................................................................................5

Attenuation Relations...........................................................................................................................6

Central and Eastern United States..............................................................................................................6

Source Model: Seismicity-Derived Hazard Component.................................................................6

Catalog...........................................................................................................................................6

Maximum Magnitude ..................................................................................................................7

Smoothed-Gridded Seismicity...................................................................................................7

Uniform Background Zones .......................................................................................................8

Special Zones.............................................................................................................................10

Source Model—Faults.......................................................................................................................10

New Madrid Seismic Zone.......................................................................................................10

Rupture Sources ...............................................................................................................10

Magnitudes........................................................................................................................11

Earthquake Recurrence...................................................................................................11

Charleston, South Carolina, Seismic Zone ............................................................................13

Meers Fault, Oklahoma, and Cheraw Fault, Colorado .........................................................13

Ground-Motion Relations ..................................................................................................................13

Western United States................................................................................................................................18

Source Model—Seismicity Derived Hazard Component.............................................................18

Catalog.........................................................................................................................................18

Maximum Magnitude ................................................................................................................20

Smoothed-Gridded Seismicity.................................................................................................20

Uniform Background Zones .....................................................................................................21

Special Zones.............................................................................................................................21

Source Model—Geodetically Derived Areal Source Zones (C Zones) .....................................26

Source Model—Faults.......................................................................................................................26

Magnitudes.................................................................................................................................28

Earthquake Recurrence............................................................................................................28

Intermountain West Fault Sources .........................................................................................29

Pacific Northwest—Cascadia Fault Sources.......................................................................29

California Fault Sources ...........................................................................................................33

Ground-Motion Relations ..................................................................................................................36

Crustal Faults..............................................................................................................................36

Subduction Zone/Plate Interface............................................................................................38

Subduction Zone—In-Slab ......................................................................................................40

Results of the Seismic Hazard Calculations............................................................................................40

Central and Eastern United States Maps .......................................................................................40

Western United States Maps............................................................................................................40
iv

Conclusions and Proposed Future Improvements to Maps .................................................................40

Acknowledgments.......................................................................................................................................55

References....................................................................................................................................................55

Appendixes A–K...........................................................................................................................................61

A. Depth to the Top of Rupture (Ztor) for Western United States Faults

B. Fault Distances to Nonplanar Fault

C. Distance to a Fault with Random Strike

D. Modeling Dip-Slip Background Sources

E. The Gutenberg-Richter Part of the Magnitude-Frequency Distribution for

 Western United States Faults

F. New Madrid Temporal Cluster Model

G. Parameters for Faults in the Intermountain West

H. Parameters for Faults in the Pacific Northwest

I. Parameters for Faults in California

J. Fault-Model Changes in the Western United States

K. Cascadia Subduction Zone

Figures

1. Chart showing process for developing the National Seismic Hazard Maps......................2

2. Seismicity-derived hazard component for the Central and Eastern United States...........8

3. Global data for craton and extended-margin earthquakes ...................................................9

4. Regional zones for the Central and Eastern United States..................................................10

5. Seismicity and finite fault source for New Madrid seismic zone.......................................11

6. New Madrid seismic zone logic tree.......................................................................................12

7. Seismicity and finite fault source for Charleston seismic zone..........................................14

8. Charleston seismic zone logic tree..........................................................................................15

9. Comparison of 0.2-s spectral acceleration attenuation relations ......................................16

10. Comparison of 1-s spectral acceleration attenuation relations .........................................17

11. Effect of the stress-drop alternatives......................................................................................19

12. Western United States background logic tree ......................................................................22

13. Graph comparing earthquake rate in a region surrounding California .............................23

14. Background seismicity model for California ..........................................................................24

15. Background seismicity in regional zones in the Western United States ..........................25

16. Moment estimated from Global Positioning System (GPS) data ........................................27

17. Logic tree for faults in the Intermountain West.....................................................................30

18. Logic tree for the Wasatch fault in Utah.................................................................................31

19. Logic tree for crustal faults in the Pacific Northwest ..........................................................32

20. Logic tree for Cascadia subduction zone ...............................................................................32

21. Casacadia subduction zone rupture models..........................................................................33

22. Magnitude-frequency distribution of the Cascadia subduction zone ...............................34
v

23. Logic tree for crustal faults in California ................................................................................35

24. Pacific Earthquake Engineering Research Center earthquake database ........................37

25. Plots comparing the New Generation Attenuation equations and 

older equations at 0.2-s spectral acceleration......................................................................37

26. Plots comparing the New Generation Attenuation equations and 

older equations at 1-s spectral acceleration.........................................................................38

27. Plots comparing subduction zone interface attenuation relations ....................................39

28–33. Maps of the Central and Eastern United States showing:

 28. 1-hertz spectral acceleration (SA) for 2-percent probability of 

 exceedance in 50 years......................................................................................................41

 29. 5-hertz spectral acceleration (SA) for 2-percent probability of

 exceedance in 50 years......................................................................................................42

 30. Peak ground acceleration (PGA) for 2-percent probability of 

 exceedance in 50 years......................................................................................................43

 31. 1-hertz spectral acceleration (SA) for 10-percent probability of

exceedance in 50 years......................................................................................................44

 32. 5-hertz spectral acceleration (SA) for 10-percent probability of

exceedance in 50 years......................................................................................................45

 33. Peak ground acceleration (PGA) for 10 percent probability of 

exceedance in 50 years......................................................................................................46

34–39. Maps of the Western United States showing:

 34. 1-hertz spectral acceleration (SA) for 2-percent probability of

 exceedance in 50 years......................................................................................................47

 35. 1-hertz spectral acceleration (SA) for 10-percent probability of 

exceedance in 50 years......................................................................................................48

 36. 5-hertz spectral acceleration (SA) for 2-percent probability of

exceedance in 50 years......................................................................................................49

 37. 5-hertz spectral acceleration (SA) for 10-percent probability of 

exceedance in 50 years......................................................................................................50

 38. Peak ground acceleration (PGA) for 2-percent probability of 

exceedance in 50 years......................................................................................................51

 39. Peak ground acceleration (PGA) for 10-percent probability of

exceedance in 50 years......................................................................................................52

40–41. Maps of California showing:

 40. 1-hertz spectral acceleration (SA) for 2-percent probability of

exceedance in 50 years......................................................................................................53

 41. 5-hertz spectral acceleration (SA) for 2-percent probability of

exceedance in 50 years......................................................................................................54

Tables

1. List of significant changes to National Seismic Hazard Maps .............................................3

2. Magnitudes and rupture locations for New Madrid 1811–1812 earthquakes ..................11
vi

3. Weights for Central and Eastern United States attenuation relations ..............................18

4. Source parameters for anisotropically smoothed seismicity sources..............................21

5. Source parameters for geodetic zones of distributed shear ..............................................28

6. Number of earthquakes (N) in each bin for two attenuation relations..............................39

Appendix Figures:

A-1. Plot of probability of surface rupture relative to magnitude

A-2. Plot of depth to top of surface rupture relative to magnitude for 

 earthquakes in Next Generation Attenuation database

B-1. Plot of multisegment fault as defined in 1996 and 2002 maps

B-2. Plot of multisegment fault as defined in 2008 maps

D-1. Diagram of a virtual dipping fault

D-2. Plots showing effect of including hanging-wall term on median ground motion

D-3. Plot showing the increase in Rjb for vertical faults

F-1. Ground motions for two sites in the Central and Eastern United States 

 without cluster model

F-2. Ground motions for two sites in the Central and Eastern United States 

 with cluster model

G-1. Map of fault sources in the Intermountain West

G-2. Slip-rate changes for Intermountain West faults

H-1. Map of fault sources in the Pacific Northwest

J-1. Plot showing increase in characteristic rate due to magnitude rounding

J-2. Plot showing uncertainty in assigned slip rate for selected faults in Utah

Appendix Tables:

A-1. Depth to top of rupture

E-1. Sampling interval details for non-California faults, truncated 

 Gutenberg-Richter distribution

G-1. Updated Intermountain West fault parameters

G-2. Updated fault names for Intermountain West faults

G-3. Intermountain West fault parameters by State

H-1. Pacific Northwest fault parameters by State

I-1. Rupture-model data for California Type-A faults

I-2. List of significant changes to California Type-B faults

I-3. Parameters for California Type-B faults

I-4. Parameters for California Connected-B faults
 1Golden, Colorado

2

Memphis, Tennessee

3

Pasadena, California

4

California Geological Survey, Sacramento, California

Documentation for the 2008 Update of the United States 

National Seismic Hazard Maps

By Mark D. Petersen,1 Arthur D. Frankel,1 Stephen C. Harmsen,1 Charles S. Mueller,1 Kathleen M. Haller,1 

Russell L. Wheeler,1 Robert L. Wesson,1 Yuehua Zeng,1 Oliver S. Boyd,2 David M. Perkins,1 Nicolas Luco,1

Edward H. Field,3 Chris J. Wills,4

 and Kenneth S. Rukstales1

Introduction

The 2008 U.S. Geological Survey (USGS) National 

Seismic Hazard Maps display earthquake ground motions 

for various probability levels across the United States and are 

applied in seismic provisions of building codes, insurance 

rate structures, risk assessments, and other public policy. This 

update of the maps incorporates new findings on earthquake 

ground shaking, faults, seismicity, and geodesy. The resulting maps are derived from seismic hazard curves calculated 

on a grid of sites across the United States that describe the 

frequency of exceeding a set of ground motions. The USGS 

National Seismic Hazard Mapping Project developed these 

maps by incorporating information on potential earthquakes 

and associated ground shaking obtained from interaction in 

science and engineering workshops involving hundreds of 

participants, review by several science organizations and State 

surveys, and advice from two expert panels. The new probabilistic hazard maps represent an update of the 2002 seismic 

hazard maps developed by Frankel and others (2002), which 

used the methodology developed for the 1996 version of the 

maps (Frankel and others, 1996). Algermissen and Perkins 

(1976) published the first probabilistic seismic hazard map 

of the United States which was updated in Algermissen and 

others (1990). The National Seismic Hazard Maps represent 

our assessment of the “best available science” in earthquake 

hazards estimation for the United States (maps of Alaska and 

Hawaii as well as further information on hazard across the 

United States are available on our Web site at http://earthquake.usgs.gov/research/hazmaps/).

USGS probabilistic seismic hazard maps are revised 

every 6 years or so to reflect newly published or thoroughly 

reviewed earthquake science and to keep pace with regular 

updates of the building code. We discussed potential changes 

in the national seismic hazard model and maps at a series of 

topical and regional USGS National Seismic Hazard Mapping 

Project (NSHMP) workshops and committee meetings held 

in 2005 and 2006 (fig. 1). Two workshops were convened in 

Menlo Park, Calif., to discuss ground shaking issues for the 

Central and Eastern United States (CEUS), led by Jack Boatwright, and the Western United States (WUS). In addition, we 

conducted regional seismic hazard workshops for the Pacific 

Northwest in Seattle, Wash., the CEUS in Boston, Mass., the 

Intermountain West in Reno, Nev., and California in San Francisco, Calif. A National User Needs workshop was held in San 

Mateo, Calif., by the Applied Technology Council. Additional 

information regarding our workshops can be found at: http://

earthquake.usgs.gov/research/hazmaps/whats_new/workshops/

index.php and http://www.atcouncil.org/ (The Third ATC-35/

USGS National Earthquake Ground-Motion Mapping Workshop, December 7–8, 2006; CD–ROM available).

In addition to workshops, the USGS assembled two 

expert panels to provide advice on issues in updating the 

National Seismic Hazard Maps. The NSHMP Next Generation Attenuation Relation Advisory Panel included: Ralph 

Archeleta, John Anderson, Martin Chapman, C.B. Crouse, 

Robert Graves, Tom Heaton, William Holmes, Jonathan Stewart, and David Wald met in Berkeley, Calif. The panel focused 

on implementation of the new Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation 

Relations (NGA) in the national maps. Information from this 

meeting can be found at http://earthquake.usgs.gov/research/

hazmaps/whats_new/workshops/index.php. The NSHM 

Advisory Panel, was composed of seismic hazard experts and 

met in Golden, Colo., to review progress on the maps, hazard 

curves, input data, and procedures used in this update. In addition, they provided final technical review of the 2008 National 

Seismic Hazard Maps. This group included: John Anderson, 

Kenneth Campbell, Allin Cornell, C.B. Crouse, John Ebel, Jeff 

Kimball, William Lettis, Michael Reichle, Paul Somerville, 

and regional coordinators of the USGS earthquake program 

Mike Blanpied, Tom Brocher, Susan Hough, Buddy Schweig, 

and Craig Weaver. 

Additional advice was provided by several science and 

engineering organizations and geological surveys. The Western States Seismic Policy Council convened a 3-day workshop 
2 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Pacific Northwest

Workshop

March 2006

CEUS Workshop

May 2006

Intermountain West

Workshop

June 2006

National User-Needs

Workshop 

December 2006

Advisory Panel

Meeting

May 2007

Comments from 

Outside Community

June–August 2007

Calilfornia Workshop

October 2006

External Review 

Panel on NGA

Meeting

September 2006

Draft Maps

(PROJECT 07)

February 7, 2007

Draft Maps

June 3, 2007

Final Probability Maps

and Design Maps

December 2007

Attenuation Relations

Workshop

August 2005-CEUS

October 2005-WUS

Review by 

Advisory Panel

Dec. 2007–

Feb. 2008

Figure 1. Process for developing the 2008 USGS National Seismic Hazard Maps. CEUS, Central United States; WUS, 

Western United States.

to develop recommendations to the NSHMP on Intermountain 

West hazard issues (March 2006 in Salt Lake City). Their recommendations can be found at http://geology.utah.gov/online/

ofr/ofr-477.pdf (Lund, 2006). The Utah Geological Survey 

convened a working group and held several meetings to recommend recurrence information for Quaternary faults in Utah 

(Lund, 2005). The Working Group on California Earthquake 

Probabilities involving the USGS, California Geological Survey, and Southern California Earthquake Center held several 

meetings and workshops to determine parameters and methodologies in developing a uniform earthquake forecast model 

for California, at http://gravity.usc.edu/WGCEP/. The Pacific 

Earthquake Engineering Research Center (PEER) held several 

meetings to update the Western United States crustal attenuation relations (http://peer.berkeley.edu/products/nga_project.

html). Scientists, engineers, and policy makers from government agencies, academic institutions, and private sector groups 

contributed to the meetings and workshops. As was the case 

for the 1996 and 2002 hazard maps, the California Geological 

Survey (CGS) cooperated in developing the 2008 maps for 

the State (see Field and others, 2008). Further information on 

California hazards can be found at http://www.consrv.ca.gov/

CGS/geologic_hazards/earthquakes/index.htm.

Table 1 outlines the significant changes that were implemented in the 2008 hazard maps. One primary goal of this 

update was to include the best available science including 

information on fault slip rates, paleoseismologic data from 

fault trenching studies, earthquake catalogs, and strong-motion 

recordings from global earthquakes. As much as possible, we 

used consistent methodologies to develop a uniform hazard 

assessment across the country, although we also accounted 

for regional differences where needed. Draft documentation and maps were available for review by State geological 

surveys and the public from June to August 2007 (fig. 1). 

Draft versions of the new maps were delivered on February 

15, 2007, September 30, 2007, and December 21, 2007, to 

the Building Seismic Safety Council (BSSC) for discussions 

of potential implementation in the 2012 building code as part 

of the Federal Emergency Management Agency (FEMA) and 

USGS-sponsored PROJECT 07, a Building Seismic Safety 

Council committee that evaluates potential changes to building 

code design criteria. Draft design maps based on these hazard 

maps (MCE maps) were provided to the BSSC on January 17, 

2008, for their consideration in the 2009 National Earthquake 

Hazard Reduction Program (NEHRP) provisions.

This documentation focuses on the new input parameters 

and output hazard products. The principal methodologies of 

probabilistic seismic hazard analysis can be found in other 

literature (for example, McGuire, 2004). However, it is important to recognize that in this analysis we calculate probabilistic 
Introduction 3

Table 1. Significant changes to National Seismic Hazard Maps.

A. California

a. Revised earthquake catalog and accounted for magnitude round off and uncertainty

b. Constrained model to fit within 2 sigma historical or observed seismicity rates (suggested by WGCEP—

Science review panel) 

i. Reduced moment rate on faults by 10 percent to account for aftershocks, foreshocks, afterslip, and 

smaller earthquakes

ii. Reduced earthquakes M≥6.5 in smoothed gridded seismicity to 1/3 of the rate to account for 

earthquakes already modeled on faults (generally not applied outside California)

iii. Implemented a branch of Gutenberg-Richter model with b=0, which is consistent with modeling of 

several of the large multisegment ruptures on the San Andreas system

iv. Eliminated the epistemic magnitude uncertainty, which is accounted for by implementing the two 

magnitude-area relations

c. Implemented four new recurrence models for southern California Type-A faults from WGCEP (based on 

moment-balanced models, paleoseismic recurrence models, Ellsworth Type-B (Ellsworth, 2003) magnitudearea relations and Hanks and Bakun (2002) magnitude-area relations)

d. Developed new multisegment ruptures for several California Type-B faults

e. Implemented new SCEC CFM model for geometry in southern California

f. Revised slip rates for sections of the San Andreas fault, San Jacinto fault, and nine Type-B faults

g. Developed new zones of distributed shear in southern California and revised geometry in northern California 

(rates considered are about 50 percent of the total strain rate

h. Included new documentation for logic tree (see fig. 23)

B. Intermountain West

a. Updated catalog through 2006 and accounted for magnitude round off and uncertainty 

b. Updated fault parameters on more than 10 percent of faults, added several new faults (see Appendix G)

c. Changed preferred dip for most normal faults from 60° to 50°

d. Allowed for distribution of dips on normal faults (40°, 50°, and 60° with 0.2, 0.6, 0.2 weights, see Appendix 

G) as recommended by Western States Seismic Policy Council

e. Implemented Wasatch fault floating rupture (M7.4) model to account for random multisegment rupture

f. Applied California weights for Gutenberg-Richter and characteristic magnitude-frequency distributions, 1/3 

and 2/3 respectively, as recommended by Western States Seismic Policy Council

g. Revised geometry of zones of distributed shear in Nevada (rates based on 50 percent of the total strain rate)

h. Included new documentation for logic trees (see figs. 12, 17, and 18)

C. Pacific Northwest

a. Updated catalog through 2006 and accounted for magnitude round off and uncertainty

b. Added new recurrence distribution for Cascadia that includes M 8.0–8.7 and M8.8–9.2 models weighted 1/3 

and 2/3, respectively

c. Added new source zone around Portland and the coast to account for potential of large deep earthquakes, 

based on extrapolating the rate of small-magnitude earthquakes (M<4.0)

d. Added new faults (Lake–Creek–Boundary Creek fault, Boulder Creek fault, and Stonewall Anticline structure)

e. Included new documentation for logic trees (see figs. 19 and 20)

f. Modified fault geometry for South Whidbey Island fault to include three hypothetical strands

D. Central and Eastern United States

a. Updated catalog through 2006 and accounted for magnitude uncertainty (see fig. 2)

b. Reduced magnitudes in northern New Madrid seismic zone by 0.2 unit and added logic-tree branch for 

recurrence rate of 1/750 years

c. Added logic-tree branch for 1/1,000-year recurrence rate of earthquakes in New Madrid (recommended by 

advisory panel)

d. Implemented temporal cluster model for New Madrid earthquakes (see Appendix F for example calculation)

e. Modified fault geometry for New Madrid to include five hypothetical strands and increased weight on central 

strand to 0.7

f. Revised dip of Reelfoot fault to 38°

g. Developed maximum magnitude distribution for seismicity-derived hazard sources (see fig. 2)

h. Revised geometry of large Charleston zone, extending it farther offshore to include the Helena Banks fault 
4 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

zone (agreed with members of advisory panel that we would hold workshop to discuss these issues for future 

versions of the maps)

i. Added documentation for logic trees (see figs. 2, 6, and 8)

E. Attenuation relations

a. Applied the three new PEER NGA equations for crustal faults in the Western United States. Accounted for 

additional epistemic uncertainties in ground motions (from ±23 percent to ±50 percent depending the number 

of samples in the particular magnitude-distance bin)

b. Implemented depth to the top of rupture parameter in two NGA equations in the Western United States

c. Implemented new depth to top of rupture for gridded seismicity in the Western United States

d. Implemented virtual dipping faults in the Western United States for seismicity-derived sources

e. Implemented new published equations (see fig. 2, 6, and 8) for Central and Eastern United States (Toro and 

others, 1997; Silva and others, 2002; Atkinson and Boore, 2006; and Tavakoli and Pezeshk, 2005) and revised 

weights

f. Replaced Sadigh and others (1997) ground-motion model with new Zhao and others (2006) model for 

Cascadia subduction interface earthquakes

g. Added the Atkinson and Boore (2003) attenuation relations for interface earthquakes on the Cascadia 

subduction zone

F. General methodology

a. Used two depths to top of rupture values for gridded seismicity hazard calculation for the WUS, 5 kilometers 

for M<6.5 and 1 kilometer for M≥6.5, and different depth to top of rupture for faults (see Appendix A)

b. Applied new magnitude binning scheme to more precisely quantify magnitude distribution and allow for better 

sampling of the distribution

Table 1. Significant changes to National Seismic Hazard Maps.—Continued

hazard curves that depict the annual frequency of exceedance 

at given ground-motion levels (the inverse of the total annual 

frequency of exceedance is the return period of the groundmotion exceedance). To obtain a probability from an annual 

frequency of exceedance we apply the Poisson equation (time 

independent). For example, if the acceptable risk is defined 

as having a 2-percent chance of one or more exceedances in 

50 years then the Poisson equation yields an annual frequency 

of exceedance of 0.000404. We interpolate the hazard curves 

at this annual frequency of exceedance to obtain the hazard 

maps. The maps were developed for 2-percent, 5-percent, and 

10-percent probability of exceedance in 50 years for several 

spectral accelerations. In this documentation we concentrate 

on the 0.2-s and 1-s spectral acceleration and peak horizontal ground acceleration on uniform firm rock site condition 

(760 m/s shear-wave velocity in the upper 30 m of the crust) 

that is applied in current building codes.

The 2008 hazard maps are significantly different from 

the 2002 maps in many parts of the United States. The new 

maps generally show 10- to 15-percent reductions in acceleration across much of the Central and Eastern United States 

for 0.2-s and 1.0-s spectral acceleration and peak horizontal 

ground acceleration for 2-percent probability of exceedance in 

50 years. The new maps for the Western United States indicate 

about 10-percent reductions for 0.2-s spectral acceleration 

and peak horizontal ground acceleration and up to 30-percent 

reductions in 1.0-s spectral acceleration at similar hazard 

levels. Most of the changes in the new maps can be attributed 

to the introduction of new attenuation relations for crustal and 

subduction earthquakes; however, changes to the fault and 

seismicity parameters also can be significant.

General Methodology

In this documentation, we explain the methodology 

and highlight important changes to the procedures and input 

parameters used. Further details of the methodology can be 

found in the earlier documentations (Frankel and others, 1996; 

Frankel and others, 2002; Petersen and others, 1996). Details 

of some of the models can be found in working group reports 

and recent literature (for example, Campbell and Bozorgnia, 

2008; Field and others, 2008; Lund, 2005). Probabilistic hazard is calculated by developing models of seismicity-derived 

hazard sources, models of earthquakes on faults, and models 

of ground shaking resulting from these earthquakes.

As in the 2002 and 1996 maps, we include four different classes of earthquake source models in the 2008 maps: (1) 

smoothed-gridded seismicity, (2) uniform background source 

zones, (3) geodetically derived source zones, and (4) faults. 

The first two models are based on the earthquake catalog and 

characterize the hazard from earthquakes between about M5 

and M6.5–7.0. The geodetically derived source zones are used 

to derive the hazard between M6.5 and the largest potential 

earthquake in a region. In most cases, the faults contribute 

most to the hazard for earthquakes larger than M6.5.
General Methodology 5

Seismicity-Derived Hazard Component

Random seismicity-derived sources account for two types 

of earthquakes: those that occur off known faults, and moderate-size earthquakes that are not modeled on faults. The gridded-seismicity models are based on historical earthquakes and 

account for the observation that larger earthquakes occur at or 

near clusters of previous smaller earthquakes (Frankel, 1995; 

Kafka, 2002; Kafka and Levin, 2000). Uniform background 

zones account for the possibility of future random seismicity in areas without historical seismicity and establish a floor 

to the seismic-hazard calculations. Special zones allow for 

local variability in seismicity characteristics within a zone (for 

example, changes in b-value, changes in maximum magnitude 

Mmax, and uniform seismicity characteristics). These models 

are combined to account for the suite of potential earthquakes 

that can affect a site (see example logic tree in fig. 2).

Seismicity models require a declustered earthquake 

catalog of independent events for calculation of Poissonian 

(time-independent) earthquake rates. The earthquake catalogs 

are constructed by merging catalogs developed by different institutions. Duplicate events and manmade events are 

deleted. The catalog is then declustered to remove dependent 

events such as foreshocks or aftershocks using the routines of 

Gardner and Knopoff (1974). The CEUS catalog includes mbLg

magnitudes, whereas several of the ground-shaking equations 

require moment magnitudes. Therefore, when determining 

the hazard from a bin centered on a certain mbLg, we convert 

this mbLg to a moment magnitude when calculating the ground 

motions from most of the attenuation relations. Completeness 

levels are estimated from the earthquake catalog, and parameters of the magnitude-rate distribution (regional b-values and 

10a-values in cells or zones) are computed using a maximumlikelihood method (Weichert, 1980) that accounts for variable 

completeness. In the 2008 update of the maps, we have taken 

into account the uncertainty in magnitudes represented in the 

catalogs. This tends to reduce the rate of earthquakes in the 

model because magnitudes are more likely to be lower than 

the reported magnitude for a Gutenberg-Richter distribution 

with positive b-value that predicts more small earthquakes.

To calculate the hazard from a particular source, we apply 

a truncated-exponential or Gutenberg-Richter magnitude-frequency distribution (Gutenberg and Richter, 1944). The hazard 

is calculated using a minimum magnitude of 5.0 (moment 

magnitude in the WUS and mbLg in the CEUS). Mmax values are 

determined from paleoseismic information, historical seismicity, or global analogy. Seismicity rate parameters (a- and 

b-values) are obtained from analysis of the catalog. For the 

gridded-seismicity models, the earthquake rates determined 

for the cells (0.1 degree in latitude and longitude) are spatially 

smoothed using a two-dimensional Gaussian smoothing operator (Frankel, 1995).

The hazard is calculated for potential earthquakes at each 

grid cell. Earthquakes smaller than M6.0 are characterized as 

point sources at the center of each cell, whereas earthquakes 

larger than M6 assume hypothetical finite vertical or dipping 

faults centered on the source grid cell (Appendix B). Lengths 

of the finite faults are determined using the Wells and Coppersmith (1994) relations for all faulting styles taken together. 

In 1996 and 2002, the strike of each fault was chosen randomly (except for zones of distributed shear where the strike is 

fixed). In the 2008 update, we precalculate average distances 

from virtual faults with strike directions uniformly distributed 

from 0 to 180° (Appendixes B and C). (The fixed-strike zones 

have the same distance calculation as in previous seismic 

hazard models.) The average-distance calculation ensures that 

no receiver is assigned a biased distance based on an arbitrary 

draw from a random-number generator. This algorithm modification has little visible effect on probabilistic motion at 10–4

or greater probability of exceedance, but it does have an effect 

at smaller probabilities. In addition to the average distance 

calculation, we also apply virtual dipping faults for grids in 

the Western United States to account for hanging-wall terms 

included in the ground-motion prediction equations 

(Appendix D).

Fault Sources

Earthquake recurrence rates for faults are based on geologic measurements, geodesy, and seismicity measurements 

and interpretations. An important consideration in the hazard 

analysis is estimating the sizes of earthquakes that can rupture 

along a fault. We estimate the maximum magnitude along a 

fault by using the mapped surface geology and recorded earthquake location and depth distributions to obtain fault length or 

area. Using the fault dimensions and, in some cases, estimates 

of where earthquake ruptures may initiate and terminate (segmentation models), we can calculate the maximum or characteristic magnitudes from relationships that are dependent 

on fault length or area (for example, Wells and Coppersmith, 

1994; Ellsworth, 2003; and Hanks and Bakun, 2002). These 

parameters, along with the fault slip rate, are needed to define 

the characteristic (Schwartz and Coppersmith, 1984) and 

Gutenberg-Richter (Gutenberg and Richter, 1944) magnitudefrequency distributions (Frankel and others, 1996; Petersen 

and others, 1996). We have sampled the Gutenberg-Richter 

distribution as described in Appendix E. The rates of these 

earthquakes can be inferred from paleoseismic investigations 

(both paleoliquefaction and fault trenching studies) or slip-rate 

estimates (from geodetic or geologic studies).

We develop weighted alternative source models based 

on tectonic, geodetic, and geologic considerations. Alternative models are included to account for epistemic uncertainty 

(the uncertainty between alternative models) in the sizes and 

rates of future earthquakes the sources may generate. We also 

account for aleatory variability (random variability in data 

used to constrain the model) in the locations and magnitudes 

of future earthquakes by including alternative magnitudes and 

fault traces or source areas along which future ruptures may 

occur. This uncertainty is described further in the sections 

below using logic-tree analyses. These analyses indicate the 
6 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

epistemic uncertainty and the associated weights at each decision point in the analysis. Often a given parameter contains 

both epistemic uncertainty and aleatory variability.

Attenuation Relations

Ground-motion prediction equations or attenuation relations relate the source characteristics of the earthquake and 

propagation path of the seismic waves to the ground motion 

at a site. The predicted ground motion is typically quantified in terms of a median value (a function of magnitude, 

distance, style of faulting, and other factors) and a probability 

density function of peak horizontal ground acceleration or 

spectral accelerations. We apply ground-motion equations 

specific to the Central and Eastern United States earthquakes, 

to the Western United States crustal fault earthquakes, and to 

subduction-zone interface and in-slab earthquakes. In the Central and Eastern United States, we generally calculate ground 

motions from sources that are up to 1,000 kilometers from the 

site. In the Western United States, we calculate ground motion 

from crustal sources less than 200 kilometers and subduction 

sources less than 1,000 kilometers from the site.

Central and Eastern United States

As in 1996 and 2002, we include the northern and central 

Rocky Mountains and the Colorado Plateau in the CEUS 

region since earthquake stress drops and the attenuation 

parameter Q are poorly constrained in these areas. The CEUS 

fault model includes four finite fault sources (New Madrid, 

Mo., and adjacent States; Charleston, S.C.; Meers, Okla.; and 

Cheraw, Colo.). These four sources are the only ones in the 

CEUS that have paleoseismic data to constrain large-earthquake recurrence rates.

Source Model: Seismicity-Derived Hazard 

Component

Catalog

The earthquake catalog for central and eastern North 

America (CENA) has been updated through 2006. We include 

earthquakes outside the national border because they influence 

the hazard within the United States. As in the 1996 and 2002 

updates, we combine earthquakes from several (reformatted) 

source catalogs, choose one preferred record for each event 

that is listed more than once and decluster to remove aftershocks and foreshocks (Mueller and others, 1997). As before, 

our goal is to make a CENA catalog that is dominated by the 

well-researched NCEER91 catalog (see below). The final 

declustered catalog used in the hazard analysis (hereinafter 

called emb.cc) lists approximately 3,350 earthquakes from 

1700 through 2006 with magnitude equal to or greater than 

3.0. Most small to moderate-size earthquakes in CENA are 

cataloged using a short-period surface-wave magnitude like 

mbLg or its equivalent. A magnitude mbLg of 5.0 is consistent 

with a Mw of 4.5–4.7 (emb.cc is based on magnitude mbLg).

We use earthquakes from the following original source 

catalogs (listed in order of our preference for choosing 

between multiple listings). The National Center for Earthquake Engineering Research—NCEER91 catalog (Seeber 

and Armbruster, 1991; J. Armbruster, email communication, 

2003) lists about 3,630 events (mbLg2.5 or greater) in the 

Central and Eastern United States and southeastern Canada 

from 1627 to 1985 (~2370 in emb.cc). A major strength of 

NCEER91 is its thorough and consistent treatment of preinstrumental earthquakes. Sanford and others (1995) contribute 

a list of earthquakes in New Mexico from 1963 to 1993 from 

a special study (~20 in emb.cc). Stover and Coffman’s (1993) 

catalog of significant United States earthquakes lists about 

400 CENA events (magnitude ~4.5 or greater and (or) MMI 

VI or greater) from 1774 to 1989 (~30 in emb.cc). Stover and 

others (1984) compiled a series of State-by-State catalogs, listing about 4,280 CENA events (magnitude 2.5 or greater) from 

1752 to 1986 (~240 in emb.cc); they include many smaller 

earthquakes than do Stover and Coffman (1993). The USGS 

Preliminary Determination of Epicenters (PDE) bulletin lists 

about 550 CENA earthquakes (magnitude 3.0 or greater) from 

1960 to 1972 and about 4,000 (magnitude 2.5 or greater) from 

1,973 through 2006 (total ~630 in emb.cc). Finally, the catalog 

compiled by the Decade of North American Geology project 

(Engdahl and Rinehart, 1991) lists about 2,300 CENA events 

(magnitude 3.0 or greater) from 1534 to 1985 (~60 in emb.cc). 

There are two primary changes from the 2002 version of emb.

cc: (1) updates to the NCEER catalog (~220 additions and 

~20 deletions) recommended by J. Armbruster (email communication, 2003) and (2) the addition of about 170 post-2001 

earthquakes from the USGS PDE.

If more than one magnitude is listed in the original 

source-catalog record for an earthquake, a preferred magnitude 

is selected during the reformatting step. Only about 10 percent 

of the earthquakes in emb.cc do not have a listed mbLg or 

mb

; in these cases, the preferred magnitude—of whatever 

type—is assumed to be mbLg for the hazard analysis. The use 

of a preferred magnitude, rather than the previously used 

weighted average, also accounts for some minor differences 

with the 2002 catalog. It should be noted that the choice of 

mbLg for the catalog necessitates conversions between mbLg and 

moment magnitude at several stages in the hazard analysis. 

Foreshocks and aftershocks are deleted using the declustering 

methodology of Gardner and Knopoff (1974); this simple 

algorithm requires no tuning parameters (that is, prejudgments 

about what are or are not aftershocks), and results are easily 

reproducible. Manmade seismic events are deleted if they are 

associated with a transient process that is no longer active 

(for example, earthquakes caused by deep fluid injection at 

the Rocky Mountain Arsenal near Denver), or if the process 

is ongoing but we have no reason to expect that future large, 
Central and Eastern United States 7

hazardous events will be associated with the activity (for 

example, earthquakes caused by fluid injection in the Paradox 

Valley of western Colorado, mining-related events in Colorado 

and Utah, and events related to oil production at the Dagger 

Draw field in New Mexico).

The final declustered catalog lists approximately 3,350 

CENA earthquakes from 1700 through 2006 with magnitude 

equal to or greater than 3.0; about 70 percent and 16 percent 

are contributed by the NCEER and PDE source catalogs, 

respectively. Previously derived catalog completeness levels 

and b-values (0.76 for the high-seismicity zone near Charlevoix, Mich., and 0.95 elsewhere in CENA) are maintained in 

the current model.

Maximum Magnitude

The size of the largest expected earthquake is region 

dependent, and it should be estimated from tectonic or geologic principles rather than from examination of an earthquake 

catalog that spans a time period that is a fraction of the recurrence times of the largest modeled events. The maximummagnitude (Mmax) zonation carries over from 2002, but for 

the 2008 hazard analysis we model uncertainty in maximum 

magnitude using four distributed Mmax values in a weighted 

logic tree (fig. 2).

The maximum magnitude is chosen based on the tectonic 

setting of the region and global analogs (Johnston and others, 

1994). Wheeler (1995) and Wheeler and Frankel (2000) define 

the boundary between the craton and an outboard region of 

crustal extension (fig. 3) as the landward limit of rifting of 

Precambrian crust during the opening of the Iapetan (protoAtlantic) ocean about 500 Ma. Wheeler (1995) argues that 

different maximum magnitudes are appropriate in the two 

regions, and we select values based on analogy with other 

stable continental regions worldwide (Johnston and others, 

1996a; Wheeler and Frankel, 2000; Wheeler and Cramer, 

2002). The histograms of figure 3B show strong peaks at 

moment magnitude 6.7. The stable-continental-region dataset 

includes earthquakes from various continents and tectonic 

histories. This geologic diversity suggests that Mmax could 

exceed 6.7 throughout CENA. The high-magnitude tails of 

the histograms suggest that Mmax could be larger. For the 2008 

model, we use four values of moment magnitude distributed 

between M6.6 and 7.2 for characterizing hazard within the 

craton and four values between M7.1 and 7.7 for the extended 

margin (fig. 2). 

For the extended margin, M7.1 is similar to the magnitudes inferred for the Charleston, S.C., earthquake (Johnston, 

1996b; Bakun and Hopper, 2004), and M7.7 is the magnitude 

calculated for the 2001 Bhuj, India, earthquake (U.S. Geological Survey, http://earthquake.usgs.gov). As in the 1996 and 

2002 models, we use a maximum magnitude of M7.2 for the 

Charleston areal zones, to avoid overlap with the mainshock, 

and M7.0 for the Colorado Plateau and Rocky Mountain 

zones, consistent with the value used for the seismicity models 

in the Western United States (fig. 4). Although the Wabash 

Valley region in southern Indiana and Illinois is part of the 

craton, M7.5 is used for Mmax there, based on the distribution 

of paleoliquefaction features resulting from past large earthquakes (Wheeler and Cramer, 2002). Note that we convert 

Mmax from moment magnitude to mb

 for the hazard calculation, 

using the equations of Johnston (1996a) and Atkinson and 

Boore (1995) with equal weights.)

Smoothed-Gridded Seismicity

The gridded-seismicity source model accounts for the 

expectation that future large, damaging earthquakes will 

occur near previous small and moderate-size earthquakes. 

As in 1996 and 2002, we develop three models based on the 

completeness levels observed in the CENA catalog. East of 

about long 105°W., Model 1 counts magnitude 3.0 and larger 

earthquakes since 1924, Model 2 uses 4.0 and larger events 

since 1860, and Model 3 uses 5.0 and larger events since 1700. 

Completeness levels west of long 105°W. are 1976, 1924, 

and 1860 for Models 1–3, respectively. Seismicity rates for 

Models 1–3 are determined by counting earthquakes in each 

grid cell with dimensions 0.1° longitude by 0.1° latitude and 

adjusting for completeness, giving a maximum-likelihood 

estimate of the local rate (Frankel, 1995). Note that in the 

simplest application of the method, a magnitude-5 earthquake 

counts the same as a magnitude-3 earthquake in determining 

the rate. Hence, in contrast to the single model with variable 

completeness used for the Western United States, we apply 

three separate models to better represent the hazard in areas 

like the Nemaha Ridge of eastern Nebraska and Kansas, where 

moderate-size to large earthquakes have occurred but smaller 

events are underrepresented in the catalog.

There are two regions where the spatial patterns of small 

historical earthquakes might not represent the future hazard. 

These are Eastern Tennessee and New Madrid seismic zones 

(fig. 4). For these regions, we implement uniform source 

zones, with average seismicity rates determined from magnitude 3.0 or greater earthquakes since 1976 in each zone. These 

source zones replace the gridded seismicity and are added 

before smoothing (see below).

A two-dimensional spatial Gaussian function is used 

to smooth the gridded rates. We use correlation distances of 

50 kilometers for Model 1 and 75 kilometers for Models 2 and 

3; choices of smoothing parameters are based on judgments 

about earthquake location uncertainties and spatial trends 

observed in historical seismicity (Frankel and others, 1996). 

The resulting “agrid” gives the annual rate of earthquakes with 

magnitude between –0.05 and +0.05 in each grid cell (incremental 10a

 in the Gutenberg-Richter notation, for a magnitude 

bin centered on m=0 with width=0.1 magnitude unit).

For the 2008 model, the seismicity rates are adjusted to 

account for magnitude uncertainty using results published by 

Tinti and Mulargia (1985) and Felzer (2007). As a rough first 

step to account for this effect, we assume standard errors of 

about 0.1 magnitude unit for earthquakes in 1972–2006, 0.2 

for 1932–1971, and 0.3 for 1700–1931 (following guidelines 
8 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Atkinson and Boore (2006)

(0.25)

Toro and others (1997)

(0.25 )

Frankel and others (1996)

(0.125)

Campbell (2003)

(0.125) 140 bar

(0.5)

200 bar

(0.5) Tavakoli and Pezeshk (2005)

(0.125)

Silva and others (2002)

(0.125)

Stress Drop

 ...... as above

CEUS

seismicity

component

Seismicity

catalog

mb(Lg) to M

conversion

uncertainty

models

Johnston (1996a)

(0.5)

Atkinson and Boore (1995)

(0.5)

Johnston (1996a)

(0.5)

Atkinson and Boore (1995)

(0.5)

Catalog M

uncertainty

models 

with magnitude 

correction

(0.333)

without magnitude 

correction

(0.667)

Ground-motion

models

Maximummagnitude

(Mmax)

models

6.6c, 7.1m

(0.1)

6.8c, 7.3m

(0.2)

7.0c, 7.5m

(0.5)

7.2c, 7.7m

(0.2)

M>4 since 1860

(0.25 or 0.2)

M>5 since 1700

(0.25 or 0.2)

uniform backgound zones

(0 or 0.2)

Catalogcompleteness

models

M>3 since 1924

(0.5 or 0.4)

M>4 since 1860

(0.25 or 0.2)

M>5 since 1700

(0.25 or 0.2)

uniform backgound zones

(0 or 0.2)

M>3 since 1924

(0.5 or 0.4)

Figure 2. Logic tree for seismicity-derived hazard component in the Central and Eastern United States (CEUS). Each maximummagnitude branch includes craton (c) and margin (m) estimates. Parameters in this figure include some aleatory variability as well 

as depicted epistemic uncertainty. We treat aleatory variability in ground motion in the hazard code. 

suggested by Felzer for earthquakes in California), and apply 

the Tinti and Mulargia (1985) correction, which reduces modeled rates about 5 to 10 percent depending on the region and 

era. These uncertainty assumptions are untested for CENA. 

Furthermore, rate reductions can be severe near some of the 

old, large earthquakes that we have made a special effort to 

represent in the hazard model (see the above discussion about 

the Nemaha Ridge). For these reasons, gridded-seismicity 

models with and without magnitude-uncertainty corrections 

are combined with respective weights of 1/3 and 2/3. We feel 

it is important to model magnitude uncertainty in a preliminary way, but we do not implement it fully in CENA pending 

more analysis and research. We make no attempt to account 

for possible magnitude rounding effects (see WUS below), 

lacking CENA data.

We recognize that, in an effort to include as many 

earthquakes in the model as possible in the low-seismicity 

CEUS, we may have been somewhat optimistic in our choices 

of catalog completeness levels. To account for this, seismicity 

rates in each grid cell are multiplied by factors (ranging from 

about 1.0 to 2.1, depending on the model and subregion) 

that account for regional differences between modern 

completeness levels, determined from the catalog since 1976, 

and the assumed levels (see Mueller and others, 1997).

Uniform Background Zones

To supplement the gridded-seismicity sources, we also 

implement (as in the 1996 and 2002 models) four nonoverlapping regional uniform background source zones (Model 4); 

these zones are designed to provide a hazard floor to account 

for future random earthquakes in areas with little or no historical seismicity. The four zones cover regions that are geologically and seismologically distinct: the Colorado Plateau 

region, Rocky Mountains, craton, and extended margin (see 

fig. 4 and the previous discussion on maximum-magnitude 

zonation). For example, the largest historical earthquakes in 

CENA have occurred in the extended margin, and the average 

historical seismicity rate there is greater than twice the craton 

rate. An average seismicity rate for each regional zone is 

determined from the catalog since 1976.

As in 1996 and 2002, Model 4 is implemented in a way 

that does not penalize areas of high seismicity in order to 

provide a hazard floor in areas of low seismicity. In each grid 

cell, the historical seismicity rate is computed by combining 

Models 1–3 with respective weights of 0.5, 0.25, and 0.25. If 

this historical rate exceeds the floor value (Model 4), the final 

cell rate simply equals the historical rate. If, however, the floor 

value exceeds the historical rate, Models 1–4 are combined 

with respective weights 0.4, 0.2, 0.2, and 0.2 to give the final 

cell rate. Nowhere is the final cell rate less than the historical 
Central and Eastern United States 9

70°N

80°N

150°W 90°W 90°E

60°N

45°N

30°N

10°N

0°

10°S

30°S

45°S

60°S

70°S

Stable continental region

Craton earthquake

Margin earthquake

0° 150°E

0

2

4

6

8

6.5 6.6 6.7 6.8 6.9 7 7.1 7.2 7.3 7.4 7.5

M

FREQUENCY

B C

A

0

2

4

6

6.5 6.6 6.7 6.8 6.9 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

FREQUENCY

* * * **

*

M 7.5+0.2/-0.4

M max 7.0+0.2/-0.4

w M

max

w

Figure 3. (A) Location of craton and margin worldwide earthquakes used to evaluate Mmax for the area outlined in figure 3 (Wheeler 

and Johnston, 2007) and histograms showing magnitudes for (B) craton (n=17) and (C) margin (n=30) earthquakes. Asterisk indicates 

earthquake located in North America. The New Madrid earthquakes of 1811–1812 are not shown or used because the New Madrid 

seismic zone is treated as a special case (see section “New Madrid Seismic Zone”).
10 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Mmax7.0

110°W 100°W 90°W 80°W 70°W

30°W

40°N

50°N

Extended Margin

Craton

Craton West

Colorado

Plateau

Rocky Mtn

Charlevoix

Charleston

New Madrid

Wabash

Valley

Cheraw fault

Meers fault

Eastern

Tennessee

Mmax7.0

Mmax7.0

Mmax7.0

Mmax7.5

Figure 4. Map of special zones, faults, and regional Mmax zones (shown by colors) in the Central and Eastern United States (see 

text for details). Blue polygons west of long 100°W. denote areas where nontectonic seismic events are removed from the catalog. 

rate, and the total modeled seismicity rate exceeds the total 

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

A special weighting scheme implemented in 2002 for the 

Colorado Front Range region (Frankel and others, 2002) also 

carries over to 2008: the floor rate is given full weight in grid 

cells in the Rocky Mountain zone where the floor rate exceeds 

the historical rate.

Special Zones

As previously described in the gridded seismicity and 

maximum magnitude sections, five special zones are used to 

account for variations in catalog completeness, uniform seismicity, maximum magnitude, and b-value. We implement uniform source zones for the Eastern Tennessee and New Madrid 

seismic zones, with average seismicity rates determined from 

earthquakes in each zone with magnitude 3.0 or greater since 

1976. These zones are smoothed on the edges. The Wabash 

Valley zone incorporates an Mmax of 7.5. The Charlevoix zone 

incorporates a b-value of 0.76. The region west of long 105oW. 

includes different completeness parameters than elsewhere in 

the CEUS. All of these special zones carry over from the 2002 

model and are shown in figure 4.

Source Model—Faults

Figure 4 shows the locations of the four finite fault 

sources included in the CEUS source model (New Madrid, 

Mo., and adjacent States; Charleston, S.C.; Meers, Okla.; and 

Cheraw, Colo.).

New Madrid Seismic Zone

Rupture Sources

Three large earthquakes in 1811–1812 are thought to 

have ruptured the Reelfoot fault and locations to the north 

and south (fig. 5). The locations of these three large events 

are controversial because the only evidence of surface rupture 

for these events is along the Reelfoot fault. Thus, earthquake 

locations are generally constrained only by recorded 
Central and Eastern United States 11

intensities, paleoseismic data, and historical seismicity 

patterns.

In 1996 and 2002, we included three “hypothetical” 

faults to account for uncertainty in future earthquake ruptures 

on the New Madrid fault zone. These rupture sources were 

developed by geological interpretation of the Reelfoot fault, 

mapped geologic structures, and seismicity characteristics. 

Fault traces in 2008 are similar to the 2002 model except we 

have revised the dip of the central segment and have used five 

rather than three subparallel traces to account for the spatial 

variability in future earthquakes (fig. 5). The five traces fill the 

same space as occupied by the previous three traces. Formerly, 

all three arms were modeled as vertical faults, but for 2008 

we have changed the central (Reelfoot) arm from a vertical 

fault to a fault dipping 38° to the southwest. This modification 

was made to reflect the seismicity patterns as seen in cross 

sections perpendicular to the fault (Mueller and Pujol, 2001). 

The central trace, which most closely follows the seismicity, is 

weighted significantly higher than the other traces. The central 

trace is weighted 0.7, the traces just outside of the central trace 

are weighted 0.1 each, and the outer traces are weighted 0.05 

each (fig. 6).

Table 2. Magnitudes and rupture locations for New Madrid 

1811–1812 earthquakes.

Event Rupture 

segment

Hough and 

others (2000) 

Hough and 

Martin (2002)

Bakun 

and 

Hopper 

(2004)

Johnston 

(1996b)

December 16, 1811 southern M7.2–7.3 M7.6 M8.1

December 16, 1811

 (aftershock) southern M7.0

January 23, 1812 northern M7.0 M7.5 M7.8

February 7, 1812 central

(Reelfoot) M7.4–7.5 M7.8 M8.0

Magnitudes

Magnitudes of the 1811–1812 events have been controversial, with suggestions generally ranging from M7.0 up to 

M8.1 (table 2). Of the three largest New Madrid earthquakes, 

the one in January 1812 is the most likely to have ruptured the 

northern arm of the seismic zone. Three widely accepted magnitude estimates for the New Madrid sequence suggest that 

the January 1812 earthquake was about 0.2 magnitude units 

smaller than the December shock (table 2; Johnston, 1996b; 

Hough and others, 2000; Bakun and Hopper, 2004).

In the 2002 model, we applied a distribution of magnitudes for earthquakes on the New Madrid fault. The three arms 

that compose each hypothetical trace ruptured together with 

the following magnitudes and weights: M7.3 (0.15), M7.5 

(0.2), M7.7 (0.5), and M8.0 (0.15). In the 2008 model, we 

assign magnitudes for the northern section that are 0.2 unit 

lower than those assigned to the central and southern sections. 

For the northern arm model, we applied the following weights: 

M7.1 (0.15), M7.3 (0.2), M7.5 (0.5), and M7.8 (0.15). The 

central and southern segments remain the same as in the 2002 

model. The logic-tree branches for magnitude uncertainty are 

shown in figure 6.

Jonesboro

Memphis

Cape Girardeau

Paducah

Tennessee

Missouri

Arkansas

Kentucky

Illinois

91°W 90°W 89°W

35°N

36°N

37°N

Figure 5. Historical seismicity (M≥3) and locations of the 

modeled New Madrid hypothetical faults. Relative weights 

assigned to the hypothetical faults shown by line width. Size of 

red stars indicates relative size of earthquake.

Earthquake Recurrence

Estimated recurrence intervals of large New Madrid 

earthquakes have been refined with additional paleoseismic 

data. In 1996, sparse data loosely constrained recurrence intervals; Frankel and others (1996) estimated an average value of 

1,000 years. By 2002, paleoliquefaction and historical-earthquake data provided evidence for a 500-year recurrence (Cramer, 2001; Frankel and others, 2002; Tuttle and others, 2002). 

At least one large earthquake at about A.D. 300 and three 

sequences of large earthquakes at about A.D. 900, A.D. 1450, 

and A.D. 1811–1812 were recognized from crosscutting relationships and radiometric dating of liquefaction features (Tuttle and others, 2002; Tuttle and others, 2005). The occurrence 

of three sequences between A.D. 300 and A.D. 1811–1812 

(about 1,500 years) implies an average recurrence of about 
12 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Mid West

(0.1)

Mid East

(0.1)

Atkinson and Boore (2006)

(0.2)

Toro and others (1997)

(0.2)

Frankel and others (1996)

(0.1)

Campbell (2003)

(0.1)

Tavakoli and Pezeshk (2005)

(0.1)

Silva and others (2002)

(0.1)

Somerville and others (2001)

(0.2)

1000 years

(0.1)

500 years A, B, C

(0.5)

(0.9)

750 years A, B, C+

1500 years B, C only

(0.5)

M8.0

(0.15)

M7.3

(0.15)

M7.5

(0.2)

M7.7

(0.5)

 ...... as below

 ...... as above

 ...... as below

 ...... as above

 ...... as above

 ...... as above

 ...... as above

NMSZ

1000 years

(0.1)

Locationuncertainty

models

Western

(0.05)

Eastern

(0.05)

Earthquakerecurrence

models

500 years

(0.9)

Central

(0.7)

Fault

models 

Clustered

(0.5)

Unclustered

(0.5)

 . ..... as below

Ground-motion

models

Magnitudeuncertainty

models

Western

(0.05)

Eastern

(0.05)

Central

(0.7)

 ...... as above

 ...... as above

 ...... as above

 ...... as above

Mid West

(0.1)

Mid East

(0.1)

M7.8 (A), M8.0 (B, C)

(0.15)

M7.1 (A), M7.3 (B, C)

(0.15)

M7.3 (A), M7.5 (B, C)

(0.2)

M7.5 (A), M7.7 (B, C)

(0.5)

140 bar

(0.5)

200 bar

(0.5)

Stress Drop

Figure 6. Logic tree for the New Madrid seismic zone (NMSZ). Parameters in this figure include some aleatory variability 

as well as depicted epistemic uncertainty. A, B, and C refer to the northern, central, and southern segments shown in figure 

5. Location and magnitude branches may include aleatory variability and epistemic uncertainty; we have not treated these 

separately. We treat aleatory variability in ground motion in the hazard code. 

500 years. However, it is unclear whether or not the northern 

arm ruptured in the A.D. 1450 sequence. If it did not, then this 

arm has experienced only two events in the past 1,500 years, 

suggesting an average recurrence of about 750 years. We have 

weighted the 500-year and 750-year earthquake recurrence 

alternatives for the northern arm equally (fig. 6).

In addition to these alternative recurrence models, some 

recent research suggests that the New Madrid seismic zone 

may rupture on average every 1,000 years as suggested by 

abrupt changes in meander patterns of the Mississippi River 

that were used to estimate earthquake activity on the Reelfoot 

fault (Holbrook and others, 2006). They infer that large, 

reverse-faulting ruptures are episodic. Within relatively active 

periods, average recurrence intervals are several centuries 

long, but during the less common quiescent periods, average 

recurrence intervals are interpreted to be about 1,000 years. 

Accordingly, we added a 1,000-year branch to the recurrence 

model. At present the meander-pattern methodology cannot 

detect small reverse-slip ruptures of the Reelfoot fault or large 

strike-slip ruptures of other faults in the seismic zone, so we 

assigned the 1,000-year branch a weight of 0.1.

For the 2008 update, we consider temporal clustering in 

modeling large New Madrid earthquakes (Appendix F; Appendix E in Toro and Silva, 2001). As mentioned previously, 

Tuttle and others (2002) provide evidence that large prehistoric earthquakes in the New Madrid seismic zone typically 

occur in sequences of three events, similar to those observed in 

1811–1812. In the 2002 maps, we modeled large New Madrid 

earthquakes with a 500-year recurrence and as single events 

that ruptured across all three arms of the fault source. Modeling three independent events every 500 years would result in 

much higher hazard but would not be a reasonable approach 
Central and Eastern United States 13

since the events are thought to be temporally dependent on 

each other and are on separate arms of the New Madrid source 

zone. Toro and Silva (2001) suggested that these sequences 

should instead be treated as a temporally dependent cluster 

of earthquakes. For hazard calculations, this means that the 

probability of exceeding a ground-motion level at a site will 

be higher when considering three dependent events rather 

than one independent event. Appendix F shows the details of 

the cluster model and some examples illustrating the impact 

of the model on hazard. Figure 6 presents the four clustering scenarios that we consider along with their weights. We 

assign equal weight to the clustered models and to a 2002-type 

unclustered source model.

Charleston, South Carolina, Seismic Zone

The Charleston region (fig. 7) was affected by an earthquake of about M7.3 in 1886. Two areal source zones were 

used in the 2002 hazard maps to account for uncertainty in the 

location of the source of future earthquakes. One was a geographically narrow zone that follows the Woodstock lineament 

and an area of river anomalies; a broader zone encompassed 

many of the known liquefaction features resulting from past 

earthquakes (Frankel and others, 2002; Wheeler and Perkins, 

2000). At the urging of the NSHMP Advisory Panel, we 

extended the southeastern edge of the larger zone offshore to 

enclose the Helena Banks fault zone of Behrendt and others (1981) and Behrendt and Yuan (1987). Marine seismicreflection profiles across strands of the Helena Banks fault 

zone show Miocene strata that are warped in a reverse-faulting 

sense. For the 2008 maps, the two zones were weighted 

equally (fig. 8). For each zone, we combined a characteristic model with magnitudes of 6.8 (wt 0.2), 7.1 (wt 0.2), 7.3 

(wt 0.45), 7.5 (wt 0.15) and a recurrence time of 550 years. 

Additionally, a truncated Gutenberg-Richter model with mbLg

from 5.0 to 7.5 accounts for background events in the extended 

margin, including the Charleston zone. The background seismicity has random fault strike.

Meers Fault, Oklahoma, and Cheraw Fault, 

Colorado

The Meers fault in southwestern Oklahoma and the 

Cheraw fault in eastern Colorado (fig. 4) represent the only 

faults within the stable craton with adequately defined surfacefaulting history constrained by radiometric dating. However, 

like the New Madrid seismic zone, these faults also may 

alternate between periods of relative quiescence and more 

active phases resulting in more frequent surface-rupturing 

earthquakes. This fault model allows for earthquake magnitude 

aleatory variability (2 sigma=0.24) and epistemic uncertainty 

(delta M=±0.2) with 0.2, 0.6, 0.2 weighting for the low, mean, 

and high values.

Two surface-faulting events have occurred on the Meers 

fault in the past 3,000 years (Kelson and Swan, 1990). Middle 

Pleistocene deposits have only been deformed by the late 

Holocene events; thus, surface deformation that preceded 

these two Holocene events occurred more than 100 k.y. earlier 

and possibly many hundreds of thousands of years earlier. As 

in the 2002 maps, the Meers fault is modeled using a characteristic moment magnitude of 7.0 and a recurrence time of 

4,500 years.

The Cheraw fault in eastern Colorado (fig. 4) shows 

evidence of Holocene and earlier faulting based on a study 

by Crone and others (1997). They infer that surface-rupturing events on the fault occurred at about 8 ka, 12 ka, and 

20–25 ka, which may represent an active earthquake phase. 

In contrast, events older than about 25 ka must have occurred 

prior to 100 ka, thus representing a quiescent period of some 

75 k.y. or more. All parameters for the Cheraw fault are 

retained from 2002; the fault was modeled using a slip rate 

of 0.15 mm/yr based on data from the last two events and a 

maximum magnitude of 7.0±0.2 determined from the Wells 

and Coppersmith (1994) fault length for all slip types together 

relation. We use a fixed recurrence time of 17,400 years with 

a truncated Gutenberg-Richter model from M6.5 to 7.0. This 

yields a mean recurrence time of 5,000 years for earthquakes 

with minimum magnitude of 6.5.

Ground-Motion Relations

The 2008 hazard maps include several new attenuation 

relations based on simulated ground motions that were not 

available in 2002 (figs. 9 and 10). In 1996 and 2002, we used 

equations based on a single corner-frequency (source spectrum 

has a single corner similar to a Brune point source model), 

double corner-frequency (source spectrum has two corners 

to account for a finite fault), hybrid (source spectrum from 

empirical sources in WUS are modified to fit CEUS parameters), and finite-source models (full waveform simulations 

considering a finite source and propagation effects). The 

attenuation relations that we retain from the earlier model 

include the Frankel and others (1996) single-corner model, 

Somerville and others (2001) extended-source model, and 

the Campbell (2003) hybrid model. New models that have 

been implemented are Toro and others (1997), a singlecorner extended source model; Atkinson and Boore (2006), 

a dynamic-corner frequency source model; Tavakoli and 

Pezeshk (2005), a hybrid model; and Silva and others (2002), 

a constant stress drop with magnitude saturation model. We 

use the weighting scheme for the attenuation models as shown 

in table 3 and figure 6. The weights are based on the following categories: single-corner finite fault model (accounts for 

magnitude saturation; 0.3), single-corner point-source model 

(accounts for Moho bounce and 1/r geometric spreading; 0.1), 

dynamic-corner-frequency models (account for magnitude 

saturation and variable stress drop; 0.2), full-waveform simulations (account for finite rupture of large earthquakes in CEUS 

crust; 0.2), and hybrid model (translates WUS empirical strong 

motion data for assumed CEUS parameters; 0.2).
14 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

81°W 80°W 79°W

32°N

33°N

34°N

35°N

Columbia

Charleston

Myrtle Beach

Savannah

South Carolina

North Carolina

Figure 7. Historical seismicity (M≥3) and alternative source zones near Charleston, South Carolina. 

Size of red stars indicates relative size of earthquake.
Central and Eastern United States 15

Atkinson and Boore (2006)

(0.2)

Toro and others (1997)

(0.2)

Frankel and others (1996)

(0.1)

Campbell (2003)

(0.1)

Silva and others (2002)

(0.1)

Tavakoli and Pezeshk (2005)

(0.1)

Somerville and others (2001)

(0.2)

 ...... as above

 ...... as above

Charleston

seismic zone

Meanrecurrence

model

550 years

(1.0)

Locationuncertainty

models 

Broad

(0.5)

Narrow

(0.5)

Ground-motion

models

Magnitudeuncertainty

models

Mw7.5

(0.15)

Mw7.3

(0.45)

Mw7.1

(0.2)

Mw6.8

(0.2)

140 bar

(0.5)

200 bar

(0.5)

Stress Drop

Figure 8. Logic tree for the Charleston seismic zone. Parameters in this figure include some aleatory variability as well as 

depicted epistemic uncertainty. Additional aleatory variability may be associated with location and magnitude models. We treat 

aleatory variability in ground motion in the hazard code. 
16 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

F96

AB95

AB05

S01 TP05

C03 T02m

T97

SV02

100 120 140 160 180 200

JOYNER-BOORE DISTANCE, IN KILOMETERS

MEDIAN 0.2-S SPECTRAL ACCELERATION A, IN STANDARD GRAVITY

20 40 60 80

2

4

4

6

8

2

4

6

8

10-1

100

Figure 9. Central and Eastern United States 0.2-s spectral acceleration attenuation relations for M7 earthquake on a vertical 

strike-slip fault and Vs30 760-m/s site conditions: AB95 (Atkinson and Boore, 1995), AB05 (Atkinson and Boore, 2006), F96 

(Frankel and others, 1996), T97 (Toro and others, 1997), T02m (Toro, 2002), C03 (Campbell, 2003), S01 (Somerville, 2001), SV02 

(Silva and others, 2002), and TP05 (Tavakoli and Pezeshk, 2005). Figure provided by Chris H. Cramer. 
Central and Eastern United States 17

S01

AB95

TP05

C03

F96

SV02

T97

T02m AB05

100 120 140 160 180 200

JOYNER-BOORE DISTANCE, IN KILOMETERS

MEDIAN 1.0-S SPECTRAL ACCELERATION, IN STANDARD GRAVITY

20 40 60 80

10-2

2

4

6

8

2

4

6

8

10-1

100

Figure 10. Central and Eastern United States 1-s spectral acceleration (SA) attenuation relations for M7 earthquake on a 

vertical strike-slip fault and Vs30 760-m/s site conditions: AB95 (Atkinson and Boore, 1995), AB05 (Atkinson and Boore, 2006), 

F96 (Frankel and others, 1996), T97 (Toro and others, 1997), T02m (Toro, 2002), C03 (Campbell, 2003), S01 (Somerville, 2001), 

SV02 (Silva and others, 2002), and TP05 (Tavakoli and Pezeshk, 2005). Figure provided by Chris H. Cramer. 
18 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

The National Seismic Hazard Maps use a reference site 

condition that is specified to be the boundary between NEHRP 

site classes B and C, with an average shear-wave velocity in 

the upper 30 m of the crust of 760 m/s. However, some attenuation relations are not developed for this shear-wave velocity. 

Therefore, we have typically converted hard-rock attenuation 

relations to approximate ground motions for a site with shear 

velocity on the NEHRP B-C boundary. Kappa is a key parameter in this conversion that defines the high-frequency nearsurface site attenuation of the ground motion. For this and 

past versions of the maps, we applied a kappa of 0.01 for the 

CEUS to convert from hard rock to firm rock site conditions 

(see Frankel and others, 1996). The new Atkinson and Boore 

(2006) attenuation relations apply a kappa of 0.02 for a class 

BC site condition, which brings additional epistemic uncertainty into the 2008 maps. We use their attenuation relations 

for B/C sites directly in the hazard calculation. For several of 

these models, we used frequency-dependent factors to convert 

from hard rock (NEHRP site class A) to firm rock (NEHRP 

site class BC). These factors are: 1.52 for peak ground acceleration, 1.74 for 0.1-s, 1.76 for 0.2-s, 1.72 for 0.3-s, 1.58 for 

0.5-s, 1.34 for 1.0-s, and 1.20 for 2.0-s spectral acceleration 

(see Frankel and others, 1996).

Another parameter that is important in ground-motion 

simulations for CEUS attenuation relations is stress drop. 

We have applied two alternative stress drops of 140 bars and 

200 bars for the Atkinson and Boore (2006) model to account 

for epistemic uncertainty in that parameter. The effect of the 

stress drop alternatives is seen in figure 11.

To apply the background seismicity models, we assume 

a 5-kilometer source depth. For calculating ground motions, 

we convert mb-values to moment magnitude using the Johnston 

(1994, 1996a) factors. We cap or truncate calculated 

ground-motion values to avoid unacceptably large ground 

motions. Capping and truncation do not significantly affect 

the results at probability levels of 2 percent in 50 years and 

greater. Median ground motions are capped at 1.5 g for 

peak ground acceleration and at 3.0 g for the 0.2-s spectral 

acceleration. In addition, we truncate the distribution of 

ground motions at three standard deviations above the median 

for peak ground acceleration and spectral accelerations. The 

ground-motion distribution for peak ground acceleration is 

truncated at 3 g and for 0.2-s spectral acceleration at 6 g, when 

these values are less than the 3-sigma cutoff.

Western United States

Source Model—Seismicity Derived Hazard 

Component

The background seismicity model, which accounts for 

random moderate-size earthquakes, is based on historical 

seismicity patterns (gridded), uniform broad regional zones 

(regional zones), and local seismicity variations (special 

zones). This background seismicity model requires a declustered earthquake catalog (consisting of independent events) for 

calculation of Poissonian earthquake rates.

Catalog

The earthquake catalog for western North America 

(WNA) has been updated through 2006. As in the 1996 and 

2002 updates, we combine earthquakes from several (reformatted) source catalogs, choose one preferred record for each 

event that is listed more than once, and decluster to remove 

aftershocks and foreshocks (Mueller and others, 1997). Our 

goal is to make a WNA catalog that is dominated by wellresearched source catalogs like the CGS/WGCEP catalog in 

California and the UNR/Pancha catalog in the Intermountain 

West. The final declustered catalog used in the hazard analysis 

(hereinafter called wmm.cc) lists approximately 3,260 earthquakes from 1850 through 2006 with magnitude equal to or 

greater than 4.0. Moment magnitude (Mw) has been determined for many moderate-size to large earthquakes in the 

WUS, and Mw is used in all the WUS ground-motion relations, 

so the WNA catalog is based on Mw.

We use earthquakes from the following original source 

catalogs (listed in order of our preference for choosing 

between multiple listings). Pancha and others (2006) at the 

University of Nevada, Reno developed a catalog (designed 

for studies of crustal deformation) that lists about 800 WNA 

events (Mw equal to or greater than about 4.8) from 1855 to 

1999 (~200 in wmm.cc). The UNR/Pancha catalog provides 

new moment-magnitude estimates for many older earthquakes. 

The catalog originally developed and maintained by the 

California Geological Survey (CGS) has been updated and 

extended through 2006 (Felzer and Cao, 2007). The CGS/

WGCEP catalog lists about 5,390 events (Mw or mL 4.0 or 

greater) from 1769 through 2006 (~2070 in wmm.cc), and 

dominates the hazard from the seismicity models in California. 

Geological Survey of Canada provided a catalog of deep 

Table 3. Weights for CEUS attenuation relations.

Single corner—finite fault Weight

Toro and others (1997) 0.2

Silva and others (2002)—constant stress drop 

w/ saturation 0.1

Single corner—point source with Moho bounce

Frankel and others (1996) 0.1

Dynamic corner frequency

Atkinson and Boore (2006) 140 bar stress drop 0.1

Atkinson and Boore (2006) 200 bar stress drop 0.1

Full waveform simulation

Somerville and others (2001) for large earthquakes 0.2

Hybrid empirical model

Campbell (2003) 0.1

Tavakoli and Pezeshk (2005) 0.1
Western United States 19

Figure 11. Comparison of Atkinson and Boore (2006) attenuation relations for peak ground acceleration 

and 1-hertz and 5-hertz spectral acceleration with 140-bar and 200-bar stress drop.

10 100 1,000

FAULT DISTANCE, IN KILOMETERS (Rcd)

0.1

1

10

100

1,000

PSA , IN CENTIMETERS/SECOND/SECOND

Peak ground acceleration

1-hertz spectral acceleration

5-hertz spectral acceleration

140 bar 200 bar 

earthquakes beneath the Georgia Strait–Puget Sound region 

(magnitude 4.0 or greater) from 1909 to 1989 (15 in wmm.

cc). Engdahl and Villaseñor (2002) compiled a global catalog 

that contributes 18 earthquakes (magnitude ~5.5 or greater, 

1900–1999) to wmm.cc. Stover and Coffman’s (1993) catalog 

of significant United States earthquakes lists about 2,050 

WNA events (magnitude ~4.5 or greater and (or) MMI VI or 

greater) from 1769 to 1989 (~110 in wmm.cc). Stover and 

others (1984) compiled a series of State-by-State catalogs 

(excluding California, Oregon, and Washington), listing 

about 4,790 WNA events (magnitude 3.0 or greater) from 

1857 to 1986 (~150 in wmm.cc); they include many smaller 

earthquakes than do Stover and Coffman (1993). The USGS 

Preliminary Determination of Epicenters (PDE) bulletin lists 

about 17,700 WNA events (magnitude ~3.2 or greater) from 

1960 through 2006 (~550 in wmm.cc). Finally, the catalog 

compiled by the Decade of North American Geology project 

(Engdahl and Rinehart, 1991) lists ~6,220 WNA events 

(magnitude 4.0 or greater) from 1808 to 1985 (~150 in wmm.

cc). Primary changes from the 2002 version of emb.cc are due 

to: (1) updates to the CGS/WGCEP catalog, (2) a decision to 

extend the predominance of the CGS/WGCEP catalog well 

beyond the California border (a region much larger than was 

used in 1996 and 2002), and (3) the addition of the UNR/

Pancha catalog.

If more than one magnitude is listed in the original source 

catalog record for an earthquake, a preferred magnitude is 

selected during the reformatting step. Mw, mb

, Ms, or mL is 

the preferred magnitude type for about 95 percent of the 

earthquakes in wmm.cc. These are all assumed to be Mw

as listed for the hazard analysis, except in about 20 cases 

where magnitude is adjusted to Mw using published relations 

to account for saturation or other scaling effects. We use 

Sipkin (2003) for mb

 and bilinear or trilinear approximations 

to the curves plotted by Utsu (2002) for Ms

 and mL. All 

other magnitude types (the other 5 percent including ~80 

cases of “unknown” type—most from the DNAG catalog) 

are also assumed to be Mw as listed for the hazard analysis. 

Foreshocks and aftershocks are deleted using the declustering 

methodology of Gardner and Knopoff (1974); this simple 

algorithm requires no tuning parameters (that is, prejudgments 

about what are or are not aftershocks), and results are easily 

reproducible. Manmade seismic events are deleted from the 

catalog if they are associated with a transient process that is no 

longer active (for example, nuclear explosions at the Nevada 

Test Site), or if the process is ongoing but we have no reason 
20 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

to expect that future large, hazardous events will be associated 

with the activity (for example, mining-related events in Utah).

The final declustered catalog lists approximately 

3,260 earthquakes from 1850 through 2006 with moment 

magnitude equal to or greater than 4.0; about 64 percent, 

6 percent, and 17 percent are contributed by the CGS/WGCEP, 

UNR/Pancha, and PDE source catalogs, respectively. Previously derived catalog completeness levels and b-values are 

maintained in the current WUS seismicity model.

Deep earthquakes have caused considerable damage 

in the Puget Sound region (major events in 1949, 1965, and 

2001), and these earthquakes have different ground-motion 

properties than shallow earthquakes. Earthquakes deeper 

than 35 kilometers occur beneath the Pacific Northwest and 

northern California. We maintain the two hazard models for 

deep seismicity from 2002 (Frankel and others, 2002). (1) For 

the Puget Sound region we apply completeness levels of M4.0 

or greater since 1963 and M5.0 or greater since 1940, and a 

b-value of 0.40. (2) For northern California we use completeness levels of M4.0 or greater since 1963, and M5.0 or greater 

since 1930, and M6.0 or greater since 1950, and a b-value of 

0.8. Based on recent seismicity near Portland, we add a new 

zone in northeastern Oregon for deep earthquakes using a 

b-value of 0.8 (described below in section “Special Zones”).

Maximum Magnitude

We maintain the maximum-magnitude (Mmax) models for 

the WUS seismicity hazard calculations from 2002 but have 

updated the input files where needed. For shallow seismicity 

we use Mmax 7.0 in most regions. Exceptions include areas near 

modeled faults (see below), and the Central Nevada seismic 

zone and Puget Lowland regions where Mmax is increased as 

a proxy to account for deficits between geodetic and seismic 

deformation rates (see section “Special Zones”). We use Mmax

7.2 for deep seismicity (the commonly reported moment magnitude for the 1949 Puget Sound earthquake is 7.1).

In developing the 2002 hazard maps, we recognized that 

our methodology for combining hazard from gridded seismicity and faults potentially double-counts earthquakes in the 

magnitude range 6.5 to 7.0 where the models overlap (Petersen 

and others, 2000; Frankel and others, 2002). Although it has 

only a minor effect on the computed hazard, we resolved 

this issue in 2002 by decreasing Mmax over dipping faults and 

within 10 kilometers of vertical faults so that there was no 

magnitude overlap. When the hazard from gridded seismicity is calculated, computer runs are performed using the Mmax

grids that correspond to the characteristic and GutenbergRichter fault cases. The hazard curves from these runs are then 

added with the appropriate weights used for the characteristic 

and Gutenberg-Richter models for faults in that area. For the 

Gutenberg-Richter epistemic branch, Mmax for the griddedseismicity model is set to M6.5, the Mmin of the GutenbergRichter relation for each fault. For the characteristic branch, 

Mmax is the same as Mchar or 7.0, whichever is smaller. Mmax is 

set to 7.0 for the gridded-seismicity calculation for areas away 

from faults. For 2008, we update this model using the new 

magnitude data for faults in the WUS.

Smoothed-Gridded Seismicity

Gridded-seismicity models include earthquakes that are 

not on faults or in zones of distributed shear and are calculated 

by smoothing the earthquake recurrence rates across a grid 

of points. The gridded-seismicity models are based on the 

assumption that future large, damaging earthquakes will occur 

near past small and moderate-size events.

Seismicity rates for the gridded-seismicity model (Model 

1) are determined by counting earthquakes in each grid cell 

with dimensions 0.1° longitude by 0.1° latitude, accounting 

for variable catalog completeness using Weichert’s (1980) 

maximum-likelihood method. For shallow seismicity (depth 

≤35 kilometers) in a zone covering most of California (including the most seismically active regions near the coast), we use 

completeness levels of 4.0≤Mw<5.0 since 1933, 5.0≤Mw<6.0 

since 1900, and Mw≥6.0 since 1850. For the rest of the WUS, 

we use 4.0≤Mw<5.0 since 1963, 5.0≤Mw<6.0 since 1930, and 

Mw≥6.0 since 1850. For deep seismicity (depth >35 kilometers), we use 4.0≤Mw<5.0 since 1963 and Mw≥5.0 since 

1940 for the Puget Sound region, and 4.0≤Mw<5.0 since 

1963, 5.0≤Mw<6.0 since 1930, and Mw≥6.0 since 1850 for the 

northern California region. (These completeness levels are the 

same as 2002). Unlike the CEUS (above), we feel that a single 

model is sufficient to capture the hazard from the historical 

seismicity in the WUS, since virtually all earthquakes with 

magnitude 5 or greater have occurred near clusters of smaller 

events. It is important to note that the maximum-likelihood 

scheme counts one large earthquake the same as one magnitude 4 event in determining the rate. The resulting “agrid” 

gives the annual rate of earthquakes in each grid cell as an 

incremental 10a

 in the Gutenberg-Richter notation, between 

M–0.05 and M+0.05, or a 0.1 bin width centered on M=0. 

For the WUS, we apply a b-value of 0.8, which was calculated from a magnitude-frequency analysis of the declustered 

catalog.

Based on seismic observatory data and historical practice, Felzer (2007) and Frankel and Mueller (2008) provided 

estimates of magnitude uncertainties and rounding errors for 

earthquakes in the CGS/WGCEP catalog, and we extend the 

guidelines given in her work to estimate magnitude uncertainty and rounding errors for earthquakes in the rest of 

the WNA catalog. As rough first steps to account for these 

effects, we assume standard errors of about 0.1 magnitude 

unit for earthquakes in 1972–2006, 0.2 for 1932–1971, and 

0.3 for 1850–1931. We also assume that for earthquakes from 

1900–1941 a magnitude listed as x.0 or x.5 has been rounded 

to the nearest 0.5, and that otherwise magnitudes have been 

rounded to the nearest 0.1 or 0.01 as reported. Magnitude 

uncertainty is accounted for following Tinti and Mulargia 

(1985). Each rounded magnitude is “unrounded” into a binned 

distribution of possible “true” magnitudes, and counted following the completeness rules. Both effects tend to reduce 
Western United States 21

modeled seismicity rates, generally in the neighborhood of 2 

to 15 percent depending on the region and time period.

In the 1996 and 2002 maps, we computed separate agrids 

from shallow seismicity in extensional and nonextensional 

regions of the WUS and used corresponding combinations of 

ground motion relations to compute the hazard (fig. 12). This 

overall scheme is maintained for the current update, although 

it is implemented somewhat differently using the NGA relations (below). The nonextensional region covers most of 

California, the Pacific Northwest, and the northwest part of the 

Basin and Range source zone (the “Yakima” zone described in 

the 2002 documentation); the rest of the WUS is modeled as 

extensional.

A two-dimensional spatial Gaussian function with a 

correlation distance of 50 kilometers is used to smooth the 

gridded rates in most of the WUS (for both shallow and deep 

seismicity). Smoothing parameters are based on earthquake 

location uncertainties and spatial trends seen in historical 

seismicity (Frankel and others, 1996). One problem with the 

smoothing method is apparent in some parts of California 

where seismicity that occurs in narrow linear zones is oversmoothed into nearby aseismic regions. We follow the 2002 

methodology by implementing an anisotropic smoothing 

scheme that provides some smoothing but generally keeps 

the modeled hazard closer to the original seismicity. Using 

respective correlation distances of 75 and 10 kilometers for 

directions parallel and normal to dominant seismicity trends, 

we apply this method (table 4) to earthquakes within 10 kilometers of the Brawley seismic zone in southern California, 

within 20 kilometers of the creeping section of the San 

Andreas fault in central California, and within 25 kilometers 

of the Mendocino fracture zone in offshore northern California 

(also removing the Mendocino fault source that was used in 

previous models).

The gridded-seismicity model is based on analysis of 

the historical earthquake catalog and should predict the total 

number of earthquakes observed in California from Mw5 to 

7. But in addition to this model we also allow earthquakes 

between Mw6.5 and 7.0 to occur on modeled faults. In this 

case, we expect the total modeled rate of Mw6.5 to 7.0 earthquakes to exceed the total historical rate. To achieve a match, 

we need to reduce the rate of modeled earthquakes, either 

on faults or in the gridded seismicity. Our preliminary studies indicate that about two-thirds of the large earthquakes in 

California are associated with modeled faults (this percentage 

was confirmed in the research by the Working Group on California Earthquake Probabilities reported by Field and others, 

2008). For the 2008 model, we have simply reduced the rate of 

earthquakes with Mw≥ 6.5 in the gridded model by a factor of 

two-thirds in an effort to match the historical rate in a region 

surrounding California (fig. 13). We recognize that additional 

research is needed to provide a more satisfactory long-term 

solution and to address this problem outside of California.

Uniform Background Zones

In contrast to the gridded-(smoothed-) seismicity model, 

regional background zones account for earthquake potential 

spread uniformly across tectonic or geologic regions with 

constant geologic or strain characteristics. These zones are 

designed to provide a hazard floor and account for future random earthquakes in areas with little or no historical seismicity. The earthquake rate for each WUS background zone is 

determined by counting earthquakes with Mw≥4 since 1963, 

computing an annualized rate, and prorating this rate uniformly across the entire zone.

As in the 1996 and 2002 maps, we model background 

seismicity (WUS Model 2) in five nonoverlapping regional 

zones: the Basin and Range Province extended to include the 

Rio Grande rift, parts of Arizona and New Mexico, western 

Texas, eastern Washington, and northern Montana and Idaho; 

the Cascade volcanic province; the Snake River Plain province; the Yellowstone seismicity parabola province; and a 

region of southeastern California and southwestern Arizona 

(figs. 14 and 15). These regions are geologically and seismologically distinct, and the reasoning behind the zonation is 

discussed in detail in the 1996 documentation.

As in 1996 and 2002, the regional zone model (Model 2) 

is implemented in a way that does not penalize areas of high 

seismicity in order to provide a hazard floor in areas of low 

seismicity. In each grid cell, the historical gridded-seismicity 

rate (Model 1) is compared with the floor value from Model 2. 

If the historical rate exceeds the floor value, the final cell rate 

simply equals the historical rate. If, however, the floor value 

exceeds the historical rate, Models 1 and 2 are combined with 

respective weights 0.67 and 0.33 to calculate the final cell rate. 

Nowhere is the final cell rate less than the historical rate, and 

the total modeled seismicity rate in the WUS exceeds the total 

historical rate by about 16 percent.

Special Zones

Models 1 and 2 do not account for all of the local variations in earthquake potential that we would like to include in 

the hazard analysis. Special zones can be used to account for 

variations in catalog completeness, magnitude-rate distribution, maximum magnitude, depth, and b-value.

Table 4. Source parameters for anisotropically smoothed 

seismicity sources.

[SAF, San Andreas Fault]

Zone Mmin Mmax

Virtual 

fault 

strike (°)

bvalue

Ratio of 

strike slip: 

Reverse: Normal

Brawley zone 5.0 6.5 157 0.8 0.5: 0: 0.5

Creeping 

section 

of SAF

5.0 6.0 –42.5 0.9 1.0: 0: 0

Mendocino 

fracture zone 5.0 7.0 90 0.8 0.5: 0.5: 0
22 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Gridded- Magnitude range

seismicity

region

Coastal California 

catalog

Ground-motion

models

 Boore and Atkinson (2008)

(0.333)

Chiou and Youngs (2008)

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

 Boore and Atkinson (2008)

(0.333)

Chiou and Youngs (2008)

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

 Boore and Atkinson (2008)

(0.333)

Chiou and Youngs (2008)

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

Characteristic

(0.667)

Gutenberg-Richter

(0.333)

Magnitude from 

Fault Model 2.1

(0.5)

Fault Model 2.4

(0.5)

M5–Mmax*

M5–Mmax*

M5–Mmax*

*Mmax is 7 unless gridded value 

 is over a fault (see Mmax grid 

 and text for Mmax over faults) 

Strike slip

(0.5)

Reverse

(0.5)

Extensional WUS

catalog

Characteristic

(0.667)

Gutenberg-Richter

(0.333)

Strike slip

(0.5)

Normal

(0.5)

Washington–Oregon

fault model

(0.5)

Puget + no Puget

fault model

(0.5)

 ...... as above

Nonextensional WUS

catalog 

Characteristic

(0.5)

Gutenberg-Richter

(0.5)

Strike slip

(0.5)

Reverse

(0.5)

 ...... as above

 ...... as below

 ...... as below

 ...... as below

Figure 12. Logic tree for seismicity-derived hazard component in the Western United States (WUS). Parameters in this figure 

include some aleatory variability as well as depicted epistemic uncertainty. We treat aleatory variability in ground motion in 

the hazard code. NGA, Next Generation Attenuation; gnd is the logarithm of median spectral acceleration or peak ground 

acceleration; dgnd is uncertainty in median spectral acceleration or peak ground acceleration at a given distance (R) and 

magnitude (M). See table 6.
Western United States 23

5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00

MAGNITUDE

1 01

1 00

1 0–1

1 0–2

1 0–3

1 0–4

CUMULATIVE ANNUAL RATE OF EARTHQUAKES

Type-A faults

Characteristic Type-B faults

Gutenberg-Richter Type-B faults

Non-California Type-B faults

Background seismicity

C zones

Total WGCEP (2007) model

Total observed

California sources

Figure 13. The total, cumulative magnitude-frequency distribution implied by the Working Group on California Earthquake 

Probability (Field and others, 2008) source model (black) as well as from the contributions from various types of sources in the 

model. The cumulative rates inferred from the historical earthquake catalog are shown in red; the outer red crosses represent 

the 95-percent confidence bounds described in Appendix I of Field and others (2008).
24 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

125°W 120°W 115°W

35°N

40°N

WGCEP

CSTCAL

BSNRNG

CASCAD

SCARIZ

B

C

M

EC

SG

I

N

Z1

Z2

Z3

Z4

Figure 14. Historical seismicity patterns (gridded seismicity), uniform broad regional zones (regional zones), 

and local seismicity variations (special zones) used in California background seismicity model. Regions include: 

BSNRNG, Basin and Range; CASCAD, Cascadia; CSTCAL, Coastal California; SCARIZ, Southern California and 

Arizona; WGCEP, Working Group on California Earthquake Probabilities. Anisotropically smoothed seismicity 

sources: B, Brawley zone; C, creeping section of the San Andreas fault; M, Mendocino fracture zone. EC, Eastern 

California; N, Central Nevada seismic zone; SG, San Gorgonio; Z1–Z4 are zones of distributed shear discussed in 

text.
Western United States 25

120°W 110°W 100°W

30°N

40°N

50°N

N

P

BSNRNG

BSNRNG

CASCAD

CSTCAL

SCARIZ

SNAKRP

YSPARA

CSTPNW

MEXICO

YAKIMA

Figure 15. Historical seismicity patterns (gridded seismicity), uniform broad regional zones (regional zones), and local 

seismicity variations (special zones) used in Western United States background seismicity model. Regions include: 

BSNRNG, Basin and Range; CASCAD, Cascadia; CSTCAL, Coastal California; SCARIZ, Southern California and Arizona; 

SNAKRP, Snake River Plain; YSPARA, Yellowstone parabola; YAKIMA, Yakima; CSTPNW, coastal Pacific Northwest; 

MEXICO, Mexico; WGCEP, Working Group on California Earthquake Probabilities. Other regions: P, Puget Lowlands; see 

figure 14 for explanation.
26 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

We model a seismicity-based source zone for the Puget 

Lowland region to account for an observed deficit between 

geodetic and seismic deformation rates. An average seismicity 

rate is determined from the number of earthquakes in the zone 

with Mw≥5.0 since 1928, and Mmax is increased from 7.0 to 7.3 

as a proxy to account for 2.7 mm/yr of north-south contraction 

across the zone. We create two agrids for modeling the WUS 

gridded seismicity; one agrid is developed with the Puget 

zone earthquakes removed and the other a-grid includes those 

events. These two agrids are each weighted 50 percent. The 

Puget zone is a uniform zone that is added with 50 percent 

weight and fills in the hole remaining in the first agrid. This 

model allows for weight on the two models (1) earthquakes 

across the Puget region occur uniformly across the zone of 

high deformation and (2) future earthquakes occur close to 

past earthquakes.

Similar to the Puget Sound region, the Mmax is increased 

from 7.0 to 7.5 in the background gridded-seismicity model in 

central Nevada as a proxy to account for part of the 2.0 mm/

yr rate of geodetic extension observed in the region. Several 

large earthquakes occurred in this region during the early 20th

century: 1915 Pleasant Valley, 1954 Dixie Valley, and 1954 

Fairview Peak events. Treatment of these zones carries over 

from 2002, and further details can be found in the documentation (Frankel and others, 2002).

Gridded-seismicity models were included near the Cascadia subduction zone to account for potential deep earthquakes 

such as the 2001 Nisqually earthquake that caused damage 

near Seattle and Olympia, Wash. These zones are discussed 

in the gridded seismicity section since they are based on 

spatially smoothed earthquakes and include regions near the 

Puget Sound and in northern California. USGS/NEIC seismicity data indicate that since 1990 several deep, magnitude-2.5 

earthquakes have occurred beneath Portland, Ore., at a rate 

of about 0.38/yr—about a factor of 10 less than the rate of 

magnitude-2.5 events beneath the Puget Lowland region. We 

included a new source zone for deep earthquakes near coastal 

Oregon. The new model is consistent with a Gutenberg-Richter distribution and a b-value of 0.8 that would predict a low 

rate of M6.5 events of about 0.003–0.005/yr.

Source Model—Geodetically Derived Areal 

Source Zones (C Zones)

Earthquake rates in zones of distributed shear are 

estimated from the geodetically determined rate of deformation across an area of high strain rate in areas where geologic 

strain rates are not well known. One outstanding issue in the 

Intermountain West region is that for several areas of the Basin 

and Range Province, the moment estimated from geology is 

about one-half the moment estimated from Global Positioning System (GPS) data (Pancha and others, 2006). Zones of 

distributed shear account for earthquakes in these areas where 

faults are poorly defined and geodetic or seismic data indicate 

a higher level of shear strain. These zones are implemented 

using geodetic data and Kostrov’s formula (Kostrov, 1974) that 

converts strain rate to moment rate.

The 1996 and 2002 maps included four zones of distributed shear in northern California and Nevada. Similar zones 

were used in the 2008 maps but the geometries of the zones in 

northern California and Nevada were slightly modified to be 

consistent with recent geodetic strain-rate data. The shape of 

the updated C-zones was based on the shape of the maximum 

geodetic shear strain rate distribution in the area. We did not 

include the high shear strain rate in the central Nevada seismic 

belt because of significant post-seismic influences from the 

Pleasant Valley, Fairview Peak, and Dixie Valley earthquake 

sequences (Hammond and Thatcher, 2005). GPS velocities 

in and around those C-zones are modeled using a broadly 

distributed shear deformation belt (fig. 16, bottom panel) to 

obtain the shear rates in those zones. The shear rate of the 

eastern California Foothills fault system (zone 1) is based on 

fault slip-rate studies (for example, Clark and others, 1984). 

The rates of shear in zone 2 (northeastern California), zone 

3 (Mohawk–Honey Lake), and zone 4 (western Nevada) are 

based on a composite of geodetic, geologic, and seismicity 

strain rates. We found average geodetic shear rates of 7, 7, 

and 10 mm/yr for zones 2, 3, and 4, respectively (fig. 16). The 

corresponding geologic shear rates in the same zones are 2.3, 

2, and 0 mm/yr. The corresponding seismicity shear rates are 

0.6, 1.0, and 1.5 mm/yr. We used 50 percent of the residual 

shear rate between the geodetic and the combined geologic 

and seismic shear rates as our final shear rates for those zones.

Rates for each zone are shown in table 5.

Additionally, two new zones of distributed shear were 

added to the 2008 model in southern California based on 

research presented in the Working Group on California Earthquake Probabilities report (Field and others, 2008): the Mojave 

(eastern California) and San Gorgonio zones. Each of these 

zones was modeled using a shear strain rate of 2 mm/yr, which 

is about half of the geodetic strain rate leftover after considering known fault strain rates. Parameters used to define the 

zones are outlined in table 5.

These zones are characterized using a preferred strike 

and a Gutenberg-Richter magnitude-frequency distribution 

between M6.5 and 7.6. For the 2008 maps, we have selected 

M7.6 as the maximum magnitude for these zones based on the 

magnitude of the 1872 Owens Valley earthquake.

Source Model—Faults

Fault sources are based on published fault studies and 

recommendations from State geological surveys. We only 

include mapped structures for which we can estimate a mean 

slip rate or mean recurrence interval. Fault models applied 

to the WUS are described in Appendixes G (Intermountain 

West), H (Pacific Northwest), and I (California). Fault models 

depend on the fault geometry (segmentation) and slip rate or 

paleoseismic recurrence rates to establish the locations, sizes, 

and rates of future earthquakes. To model each rupture we 
Western United States 27

50°N Shear Strain Rate (1.0e9)

46°N

42°N

42°N

38°N

38°N

34°N

48°N

44°N

40°N

40°N

36°N

32°N

124°W 120°W 116°W 112°W 108°W 122°W 120°W 118°W

3

4

2

3

4

2

1

A

B

C

A 

7 mm/yr

B

7 mm/yr

C

10 mm/yr

0

200 100 100 200

10

20

GPS VELOCITY 

(MM/YR)

DISTANCE (KM)

0

0

200 100 100 200

10

20

GPS VELOCITY 

(MM/YR)

DISTANCE (KM)

0

0

200 100 100 200

10

20

GPS VELOCITY 

(MM/YR)

DISTANCE (KM)

0

Figure 16. Moment estimated from Global Positioning System (GPS) data. mm/yr, millimeters per year; 

km, kilometers.
28 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

estimate a fault rupture length and width. These parameters are 

obtained from geologic mapping (fault geometry and length) 

and seismicity characteristics (fault dip and rupture depth). To 

model the rate of each size of earthquake along crustal faults, 

we use weighted combinations of characteristic and Gutenberg-Richter magnitude-frequency distributions to characterize 

the sources.

Magnitudes

In the source model, we either use historical magnitudes 

or estimate magnitude based on fault area (California) or 

surface-rupture length (Intermountain West and Pacific Northwest regions). The equations of Ellsworth—type B equation 

(Ellsworth, 2003)—and Hanks and Bakun (2002) were applied 

for California; surface-rupture length relative to magnitude 

relations of Wells and Coppersmith—all fault types (Wells and 

Coppersmith, 1994) were applied to faults in the WUS outside 

of California.

A change in detail compared to 2002 fault-hazard modeling is that we now round derived magnitude estimates to 

two decimal places, compared to one decimal place in 2002 

(see Appendix F4 for further discussion). One reason for this 

change is that epistemic uncertainty in the magnitude-area 

relation frequently is lost when we round to nearest tenth but 

is retained when rounding to nearest hundredth. This change 

alters earthquake recurrence rate estimates because larger 

events produce more slip per event. Changes in probabilistic 

ground motion that are associated with this change in rounding 

procedure change are apparent particularly in the new spectral 

acceleration (SA) ratio maps, even when the geology model 

for a given fault has not changed.

We include an epistemic uncertainty of ±0.2 magnitude 

units for the characteristic earthquake magnitude and the 

maximum magnitude of the Gutenberg-Richter distribution 

for most regions of the WUS. The uncertainty is applied with 

weights of 0.2 for the lower, 0.6 for the median, and 0.2 for the 

upper branches. However, no additional epistemic uncertainty 

in magnitude is applied within California; the two rupture 

area-magnitude relations that are used in that region account 

for some epistemic uncertainty.

In addition to the epistemic uncertainty, we also include 

aleatory uncertainty for characteristic earthquakes using a normal distribution with standard deviation of 0.12. For the 2008 

maps we extend the value at which the distribution is truncated 

from ±0.15 magnitude units used in 2002 to a-value of 2 sigma 

or ±0.24 that was applied in the Working Group on California 

Earthquake Probabilities (2003) report. Most of the magnitude-frequency models are moment balanced using different 

characteristic magnitudes. Exceptions include the California 

Type-A fault a priori model and the Wasatch model. We do 

not apply any additional aleatory uncertainty for the models 

that use Gutenberg-Richter magnitude-frequency distributions 

(including the California Type-A fault unsegmented model) 

because these models are thought to already account for aleatory uncertainty in the size of earthquakes on a fault.

Earthquake Recurrence

The characteristic rate of earthquakes on a fault is determined by the ratio of the slip rate (vertical or horizontal) to the 

slip of the characteristic earthquake determined by the length 

or area of the fault. For Gutenberg-Richter relations, we use 

standard equations that relate slip rate and magnitude to the 

rate of earthquakes in each magnitude bin (Frankel and others, 

2002; Petersen and others, 1996). In the 2002 source models, 

we applied a ratio of 67-percent characteristic and 33-percent 

Gutenberg-Richter magnitude-frequency distribution for faults 

in coastal California and have applied equal weighting for the 

rest of the WUS (including eastern California).

The Western State Seismic Policy Council (WSSPC) 

held a workshop to discuss issues for the Intermountain West 

region. One of their recommendations was to change the ratio 

of characteristic and Gutenberg-Richter magnitude-frequency 

distributions in the Intermountain West region to reflect 

similar event weighting to that used in coastal California, 

67-percent characteristic and 33-percent Gutenberg-Richter 

(see Appendix J for discussion). Scientists in the Pacific 

Table 5. Source parameters for geodetic zones of distributed shear.

[°, degree; mm/yr, millimeters per year; km, kilometers]

Zone Mmin Mmax

Virtual 

fault 

strike (°)

bvalue

Ratio 

SS:Rev:

Normal

Slip 

rate 

(mm/yr)

Length 

(km)

Width 

(km)

S. Calif.–Mojave 6.5 7.6 –47 0.8 1: 0: 0 2.0 219 15

S. Calif.–San Gorgonio 6.5 7.6 –67 0.8 1: 0: 0 2.0 102 18

Shear1–Calif. Foothills 

fault 6.5 7.6 –35 0.8 1: 0: 0 0.05 360 12

Shear2–NE Calif. 6.5 7.6 –25 0.8 1: 0: 0 2.0 230 15

Shear3–Mohawk-Honey 

Lake 6.5 7.6 –45 0.8 1: 0: 0 2.0 88 15

Shear4–W. Nev. 6.5 7.6 –45 0.8 1: 0: 0 4.0 245 15
Western United States 29

Northwest, however, did not accept this recommendation; 

they felt that uncertainties in recurrence are large in that 

region. Therefore, we have implemented the 2/3-characteristic 

1/3-Gutenberg-Richter magnitude-frequency distribution for 

faults in the Intermountain West region but not in the Pacific 

Northwest region.

Intermountain West Fault Sources

Nearly 300 faults in the Intermountain West are included 

as sources in the 2008 model (fig. 17, Appendix G). We 

updated input parameters for more than 10 percent of those 

faults based on a literature review of parameters such as slip 

rate and recurrence. The majority of changes in our model 

resulted from the comprehensive reevaluation of all published 

paleoseismic studies by the Utah Quaternary Fault Working 

Group (Lund, 2005).

The WSSPC recommended that the USGS model allow 

for multisegment ruptures along the Wasatch fault (fig. 18). 

Therefore, in addition to a segmented model, similar to that 

applied in the 2002 maps, we include a floating M7.4 earthquake rupture model that assumes a 1.2 mm/yr mean slip rate 

for the Wasatch fault and that is weighted 0.1 in the model. 

This model allows for earthquakes that cross segment boundaries and was agreed on by the Utah Fault Working Group.

Another WSSPC recommendation was to change the 

default dip for normal faults from 60° to 50°. The WSSPC 

group and our own studies indicate that a default dip of 50° 

may be more consistent with global normal faulting seismic 

data (focal mechanisms). Therefore, we have modified the preferred dips of faults in the Basin and Range Province to adhere 

to their recommendation. The Lost River fault preferred dip 

was not modified; it was determined from the focal mechanism of the Borah Peak earthquake and the aftershock distribution. This change to the fault dips across the Intermountain 

West region generally increases the hazard by changing the 

distance from the source to the site and also increasing the 

fault-parallel slip rate (see Appendix J for further discussion).

Several WSSPC recommendations (Lund, 2006) were 

not adopted in this update of the maps, one of which was to 

promote all characteristic earthquakes on fault sources with 

M less than 6.5 to M6.5. This recommendation was based on 

the observation that earthquakes with M less than 6.5 often 

do not have well-defined surface ruptures. We applied this 

promotion in earlier versions of the map but reverted back 

to the calculated magnitudes in the final version because 

establishing a default minimum magnitude caused a higher 

rate of M6.5 events than have been observed in the historical 

earthquake catalog. Even though this recommendation was 

not implemented in this version of the maps, we agree that the 

suggestion needs further review. Another recommendation was 

to incorporate slip rate uncertainties in the models. Slip-rate 

uncertainties are not available for all the faults in the model, so 

it is premature to implement this recommendation (see Appendix J for the consensus uncertainty data). We plan to work 

with other State geological surveys to produce this information 

for the next version of the maps.

Pacific Northwest—Cascadia Fault Sources

The Pacific Northwest fault sources (fig. 19) are 

described in Appendix H, and the Cascadia subduction zone is 

described in Appendix K. The primary changes to the Pacific 

Northwest model are to the Cascadia subduction zone, which 

includes a broader magnitude-frequency distribution. In addition, one fault was modified (the South Whidbey Island fault) 

and three new faults have been added for 2008 maps (the Lake 

Creek–Boundary Creek fault, Stonewall anticline, and Boundary Creek fault—see Appendix H for further details).

The Cascadia subduction zone extends about 1,200 kilometers from Vancouver Island in British Columbia to Cape 

Mendocino in California. Adjacent to northern California the 

Gorda plate is consumed eastward beneath North America at a 

rate of about 40 mm/yr (Nishimura and others, 1984). The last 

great Cascadia rupture is thought to have occurred in January 1700, based on analysis of tsunami records in Japan, trees 

along the Pacific coast, study of onshore tsunami deposits, and 

other geophysical data (Satake and others, 2003).

We include the same Cascadia subduction-zone geometry 

and weighting scheme (fig. 20) as used in the 2002 model. 

Thermal models of Flück and others (1997) and global analogs 

of shallow-dipping subduction zones were used to develop 

alternative rupture models. These models include ruptures 

that extend (1) through various depth ranges thought to be 

related to the elastic and transitional properties of the crust 

and (2) down to a depth of about 30 kilometers similar to other 

large subduction earthquakes (fig. 21).

The primary constraint on the recurrence of Cascadia 

earthquakes is that great earthquakes occur on average every 

500 years beneath all sites on the coast of the Cascadia subduction zone, based on paleoseismic studies of coastal subsidence and tsunami deposits (for example, Atwater and Hemphill-Haley, 1997). We considered two sets of rupture scenarios 

for these events: (1) M9.0±0.2 events that rupture the entire 

Cascadia subduction zone every 500 years on average and 

(2) M8.0–8.7 events with rupture zones that fill the entire zone 

over a period of about 500 years. Each of these large to great 

earthquakes is expected to rupture the entire seismogenic area. 

Ruptures in the latter set of scenarios float along the Cascadia 

subduction zone.

For these maps, we assign a probability of 0.67 to the 

M8.8–9.2 scenario and a probability of 0.33 for the set of 

M8.0–8.7 scenarios with floating ruptures (fig. 20). In the 

2002 maps, M9.0 and M8.3 scenarios were given equal 

probabilities. The higher probability of the M8.8–9.2 rupture 

scenario in this update reflects consensus of scientists and 

others at the March 28–29, 2006, Pacific Northwest NSHMP 

workshop. In that meeting it was concluded that the M9.0± 0.2 

scenario was more likely than more frequent, floating smaller 

earthquakes. Figure 22 shows the magnitude-frequency distribution of the Cascadia subduction zone and a map showing 
30 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Dipuncertainty

models

40 degrees

(0.2)

50 degrees

(0.6)

60 degrees

(0.2)

40 degrees

(0.2)

50 degrees

(0.6)

60 degrees

(0.2)

Fault

models 

Ground-motion

models

Magnitudeuncertainty

models

IMW

faults 

Characteristic

(0.667)

GutenbergRichter

(0.333)

M (SRL)-0.2

(0.2)

M (SRL)

(0.6)

M (SRL)+0.2

(0.2)

M6.5 to M (SRL)-0.2

(0.2)

M6.5 to M (SRL)

(0.6)

M6.5 to M (SRL)+0.2

(0.2)

 ...... as above

 ...... as above

 ...... as below

 ...... as below

 ...... as above

 ...... as above

 Boore and Atkinson (2008)

(0.333)

Chiou and Youngs (2008

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

Figure 17. Logic tree for fault sources in the Intermountain West (IMW). Parameters in this table include some aleatory 

variability as well as depicted epistemic uncertainty. Additional aleatory variability may be associated with all models 

depicted. We treat aleatory variability in ground motion in the hazard code. Most faults in the Intermountain West have 

assigned characteristic magnitudes (see first panel) based on surface-rupture length except where historical earthquakes 

serve as analogs and where the characteristic magnitude is constrained to M7.5 (shown in table G-3 in Appendix G). Short 

faults (less than 17 kilometers) in the region with characteristic magnitude less than 6.5 are treated like the upper branch 

but with full weight. NGA, Next Generation Attenuation; gnd is the logarithm of median spectral acceleration or peak ground 

acceleration; dgnd is uncertainty in median spectral acceleration or peak ground acceleration at a given distance (R) and 

magnitude (M). See table 6.
Western United States 31

Recurrenceuncertainty

models

Dipuncertainty

models

Fault

models 

Wasatch

fault

40 degrees

(0.2)

50 degrees

(0.6)

60 degrees

(0.2)

Characteristic

(0.72)

Floating M7.4*

(0.1)

GutenbergRichter

(0.18)

 ...... as below

 ...... as above

40 degrees ...... as below

(0.2)

50 degrees

(0.6)

60 degrees

(0.2)

 ............... as above ............... 

 ...... as above

Ground-motion

models

Magnitudeuncertainty

models

 Boore and Atkinson (2008)

(0.333)

M (assigned)-0.2

(0.2)

*Paleoevent record 

from Lund (2005)

M7.4 from Lund (2006)

weights for characteristic 

and Gutenberg-Richter 

branches proportional to 

2002 model

M (assigned)

(0.6)

M (assigned)+0.2

(0.2)

Chiou and Youngs (2008)

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

 ...... as below

M6.5 to M (assigned)-0.2

(0.2)

M6.5 to M (assigned)

(0.6)

M6.5 to M (assigned)+0.2

(0.2)

 ...... as above

 ...... as above

 ...... as below

 ...... as above

Paleovent record*

(1.0)

1.2 mm/yr vertical slip rate

(1.0)

1.2 mm/yr vertical slip rate

(1.0)

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

Figure 18. Logic tree for the Wasatch fault in Utah. Parameters in this figure include some aleatory variability as well as depicted 

epistemic uncertainty. Additional aleatory variability may be associated with all models depicted. We treat aleatory variability in 

ground motion in the hazard code. Assigned characteristic magnitudes for segments of the Wasatch fault retained from 2002 model. 

NGA, Next Generation Attenuation; gnd is the logarithm of median spectral acceleration or peak ground acceleration; dgnd is 

uncertainty in median spectral acceleration or peak ground acceleration at a given distance (R) and magnitude (M). See table 6.
32 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Fault

models 

Ground-motion

models

Magnitudeuncertainty

models

PacNW

faults

Characteristic

(0.5)

GutenbergRichter

(0.5)

M (SRL)-0.2

(0.2)

M (SRL)

(0.6)

M (SRL)+0.2

(0.2)

M6.5 to M (SRL)-0.2

(0.2)

M6.5 to M (SRL)

(0.6)

M6.5 to M (SRL)+0.2

(0.2)

 ...... as above

 ...... as above

 ...... as below

 ...... as above

 Boore and Atkinson (2008)

(0.333)

Chiou and Youngs (2008)

(0.333)

Campbell and Bozorgnia (2008)

(0.333)

*

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

Figure 19. Logic tree for fault sources in the compressional region of the Pacific Northwest 

(PacNW). Parameters in this figure include some aleatory variability as well as depicted epistemic 

uncertainty. Additional aleatory variability may be associated with all models depicted. We treat 

aleatory variability in ground motion in the hazard code. Short faults (less than 17 kilometers) in the 

region with characteristic magnitude less than 6.5 are treated like the upper branch but with full 

weight. NGA, Next Generation Attenuation; gnd is the logarithm of median spectral acceleration 

or peak ground acceleration; dgnd is uncertainty in median spectral acceleration or peak ground 

acceleration at a given distance (R) and magnitude (M). See table 6.

Rupture-depth

models

Magnitude

models

Fault

models 

M8.8

(0.2)

M9.2

(0.2)

M8.0–8.7

M9.0

(0.6)

Cascadia

Entire CSZ

(067)

Floating

(0.33)

500-year

return time

 Thermal model

(0.5)

Global analog model (depth ~30 km)

(0.5)

 Elastic layer

(0.2)

Elastic layer + transition

(0.4)

Elastic layer + 1/2 transition

(0.4)

 ...... as above

 ...... as below

Ground-motion

models

Youngs and others (1997)

(0.25) 

Atkinson and Boore (2003; global model)

(0.25) 

Zhao and others (2006)

(0.5) 

Figure 20. Logic tree for Cascadia subduction zone (CSZ). Parameters in this figure include some aleatory variability as well as 

depicted epistemic uncertainty. Additional aleatory variability shown in table K-1 in Appendix K. 
Western United States 33

48°N

46°N

44°N

42°N

126°W 124°W 122°W

top

mid

bottom

base

trench

Washington

Oregon

Figure 21. Location of the eastern edge of earthquakerupture zones on the Cascadia subduction zone for the 

various models used in this study relative to the surficial 

expression of the trench: top, base of the elastic zone; 

mid, midpoint of the transition zone; bottom, base of the 

transition zones; base, base of the model that assumes 

ruptures extend to about 30-kilometers depth. Figure 

provided by Ray Weldon.

the geographic variation of frequency of floating earthquakes. 

The annual rates are calculated using the scenario probabilities 

previously listed. Recurrence rates and weights are shown in 

table K-1.

California Fault Sources

The 1996 and 2002 California seismic hazard models are 

described in Petersen and others (1996), Frankel and others 

(1996, 2002), and Cao and others (2003). For the 2008 seismic 

hazard maps we have updated the fault parameters by adopting 

new information from the Working Group on California Earthquake Probabilities (WGCEP). Changes to the fault source 

models are described in detail in Appendix A of the WGCEP 

report (Wills and others, 2008). The WGCEP modified fault 

locations, fault rupture parameters, and zones of distributed 

shear in California. The major changes to the fault parameters 

described in detail in the WGCEP report and appendixes 

(Field and others, 2008) and outlined below.

We incorporate two types of fault sources (Type A and B) 

into the seismic hazard maps for the WUS. Type-A faults are 

well-known faults that are defined using published information on fault geometry, earthquake sequences, slip rates, and 

dates of previous earthquakes. In California, major strands of 

the San Andreas fault system including the Calaveras, Hayward–Rodgers Creek, San Jacinto, and Elsinore fault zones, 

the Garlock fault zone, and the Cascadia subduction zone 

are modeled as Type-A faults. Detailed, fault-specific models are developed for each Type-A fault. The models include 

characteristic earthquakes on single segments, multisegment 

ruptures, and earthquakes that are shifted uniformly along the 

fault (the “floating earthquake” or “unsegmented” model). 

Type-B faults are characterized by published information on 

slip rates and fault geometry. Coastal California Type-B fault 

sources are modeled assuming 2/3 of the moment is released 

as characteristic earthquakes and 1/3 in earthquakes (fig. 23) 

that follow a truncated Gutenberg-Richter model from 6.5 to 

the maximum magnitude.

Among the most significant changes in the 2008 model 

was the revision of previously described “segments” of the 

southern San Andreas fault into 10 sections: the Parkfield, 

Cholame, Carrizo, Big Bend, Mojave north, Mojave south, 

San Bernardino north, San Bernardino south, San Gorgonio–

Garnet Hill, and Coachella. These sections are defined by 

changes in trend, slip rate, style of faulting, or amount of 

displacement in past earthquakes. Sections were also revised 

on the San Jacinto and Elsinore faults in southern California. 

Slip rates were changed on sections of the San Andreas and 

San Jacinto faults based on recent geologic and geodetic 

studies suggesting that a larger part of the total slip may 

follow the San Jacinto rather than the southern San Andreas 

fault. Because there is significant uncertainty in how much 

of the total slip is on the San Andreas as opposed to the San 

Jacinto, alternative “deformation models” were developed to 

span the range of potential slip rates on the San Andreas and 

San Jacinto faults. The revised slip rates (in particular the 
34 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

7.8 8 8.2 8.4 8.6 8.8 9 9.2 9.4

MOMENT MAGNITUDE

ANNUAL RATE OF EARTHQUAKES

Figure 22. Magnitude-frequency distribution of the Cascadia subduction zone.

decreased slip rate on the section of the San Andreas fault 

through the San Gorgonio Pass) have major effects on the 

potential for large earthquakes to rupture multiple sections of 

the San Andreas fault. In addition to revised slip rates, all of 

the Type-A faults in southern California now have modified 

earthquake recurrence models based on paleoseismic data. 

Two different types of models were developed for California: 

(1) an event-rate model that honors the paleoseismic data 

precisely and (2) a moment-balanced model that is as 

consistent as possible with the event rates, while honoring the 

slip rates precisely. For each of these models, the magnitudes 

were calculated using the Ellsworth type B (Ellsworth, 2003) 

and Hanks and Bakun (2002) magnitude-area equations. The 

four resulting models are weighted equally (25 percent).

The slip rate on the San Andreas fault in San Gorgonio 

Pass is lower than other sections of the fault partly because 

some of the right-lateral shear related to the Pacific-North 

America plate boundary leaves the San Andreas fault near the 

north end of the Coachella Valley and follows right-lateral 

faults in a broad region across the Mojave Desert and along 

the east side of the Sierra Nevada. In the western Basin and 

Range, right-lateral faults including the Death Valley fault 

system accommodate approximately 8 mm/yr of right-lateral 

shear. South of the Garlock fault, slip rates on the faults within 

the eastern California shear zone were revised on the basis of 

recent work of Oskin and others (2007). Revision of fault slip 

rates and the zones of distributed shear, as previously discussed, result in a total right-lateral shear of about 8–10 mm/

yr that continues from the San Andreas fault in the Coachella 

Valley northward across the Mojave Desert and through the 

western Basin and Range, which is consistent with geodetic 

deformation rates in the area.

For many faults in southern California, the fault traces, 

dips, and depth were revised using the new SCEC Community 

Fault Model (CFM) (Plesch and Shaw, 2003, 2007). The 

lower seismogenic depths in CFM are from the maximum 

depth of relocated background seismicity, following Nazareth 

and Hauksson (2004). In addition to providing more detailed 

information on the traces and depths of faults, the CFM 

provided alternative models for several areas where it is not 

clear how faults may interact at depth or which of two possible 

models of faults at depth is correct. The most complex of 

these models covers the Santa Barbara Channel, where one 

of the alternatives includes a low-angle fault that dips toward 

the shoreline. In this case, and possibly others, one of the 

alternatives may result in significantly higher ground motion 

than the other.
Western United States 35

Deformation

models

DM 2.1

(0.5)

DM 2.3

(0.3)

Magnitude-area

relationship

Type A-fault models

Ellsworth-B

(2003)

(0.5)

Hanks and Bakun (2002)

(0.5)

Unsegmented

(0.1)

Segmented

(0.9)

A priori

(0.5)

Mo-rate

balanced

(0.5)

Connect

more Type-Bfaults?

DM 2.2

(0.2)

FM2.1

(0.5)

FM2.4

(0.5)

 ...... as below

Chiou and Youngs (2008)

(0.333)

Boore and Atkinson (2008)

(0.333) 

DM 2.4

(0.5)

DM 2.6

(0.3)

DM 2.5

(0.2)

Yes

(0.5)

No

(0.5)

b-value=0.8

(0.5)

b-value=0

(0.5)

Ground-motion 

models

Earthquake-rate

models

 ...... as below

 ...... as below

 ...... as below

 ...... as below

 ...... as above

 ...... as above

 ...... as above

 ...... as above

 ...... as above

Campbell and Bozorgnia (2008)

(0.333)

Fault 

models

UCERF2 

gnd+dgnd (R,M)

(0.185)

gnd-dgnd (R,M)

(0.185)

NGA team gnd

(0.63)

Figure 23. Logic tree for fault sources in California (UCERF2). Parameters in this table include some aleatory variability as well 

as depicted epistemic uncertainty. Additional aleatory variability may be associated with all models depicted. We treat aleatory 

variability in ground motion in the hazard code. Illustration modified from Working Group on California Earthquake Probabilities 

(Field and others, 2008). NGA, Next Generation Attenuation; gnd is the logarithm of median spectral acceleration or peak ground 

acceleration; dgnd is uncertainty in median spectral acceleration or peak ground acceleration at a given distance (R) and 

magnitude (M). See table 6.
36 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

In northern California, revisions since the 2002 NSHMP 

model are much less extensive. The location, dip, and slip 

rates of several faults along the west side of the southern 

Sacramento Valley have been updated on the basis of the work 

of O’Connell and Unruh (2000), and the West Tahoe fault has 

been added on the basis of the work of Kent and others (2005).

One of the major changes to the source model for 

California is that the moment rate on Type-A and B faults 

have been reduced by 10 percent to account for aseismic slip 

or aftershock slip that does not rupture in independent large 

earthquakes. This change reduces the rate of earthquakes in 

California and, with other modifications in the background 

seismicity and fault models, brings the California model rate 

of earthquakes within the estimated 95-percent confidence 

limits of the historical rate of earthquakes (Petersen and others, 2000; Frankel and others, 2002).

Ground-Motion Relations

We apply published ground-motion prediction equations 

(attenuation relations) to compute the ground motions resulting from each seismic source. The equations relate ground 

shaking to earthquake magnitude, distance from source, style 

of faulting, rupture characteristics (depth to top of rupture, 

hanging-wall and foot-wall shaking differences, and so forth), 

and ground-motion modifications along the path between the 

source and the site. These ground motions are typically quantified in terms of a median value and a probability distribution 

(aleatory variability). The ground motions are calculated for 

each attenuation relation separately then combined using a 

weighted logic tree analysis. We apply different attenuation 

relations for crustal, subduction-zone interface, and deep inslab earthquakes.

Crustal Faults

The 2002 hazard maps applied up to five ground-motion 

prediction equations for crustal faults (Abrahamson and Silva, 

1997; Boore and others, 1997; Campbell and Bozorgnia, 2003; 

Sadigh and others, 1997; and Spudich and others, 1999); 

all of these relations have been replaced by newly updated 

attenuation relations that are the result of Pacific Earthquake 

Engineering Research Center (PEER)—Next Generation 

Attenuation Relation Project (NGA). Results will be published 

in Earthquake Spectra (Power and others, 2008). The project 

developed a global strong-motion database containing 

strong-motion records from 173 earthquakes (fig. 24). Many 

new ground motion records were available for this effort that 

were not used in constructing previous equations, especially 

for large crustal fault ruptures. NGA modelers applied their 

own selection criteria for using earthquake ground motion 

records, but they had to justify why data was discarded and 

document reasons different choices were made in developing the models. Additional 1-d simulations of rock ground 

motions, 1-d simulations of shallow site response, and 3-d 

simulations of basin response were also developed to constrain 

the new models. NGA modelers interacted extensively with 

the each other and with the broader community in developing 

the models.

The new NGA equations differ significantly (especially 

at 1-s period) from previous equations. The USGS convened 

a workshop on NGA equations and a user workshop that gave 

the external community opportunities to comment on the equations and their effects on the maps. In addition to these workshops, we also convened an expert panel on strong ground 

motion to provide advice on implementing the NGA equations 

in the National Seismic Hazard Maps (September 2006). 

This panel felt strongly that the new hazard maps should be 

constructed using the new NGA equations exclusively and that 

additional epistemic uncertainty should be added to account 

for lack of data. The following is a summary of the consensus 

recommendations for the National Seismic Hazard Maps: 

(1) New NGA equations represent significant advances in 

fitting a larger standard dataset of ground motions and source 

and path parameters, and these equations should replace the 

older equations for crustal earthquakes in the WUS. (2) Three 

NGA attenuation models should be used for calculating ground motions from crustal WUS earthquake sources 

weighted equally: Boore and Atkinson (2008), Campbell and 

Bozorgnia (2008), and Chiou and Youngs (2008). (3) Additional epistemic uncertainty should be added to the equations 

to account for sparse data. (4) New hazard maps should not 

consider directivity because it is difficult to separate this effect 

in the current equations.

Figures 25 and 26 show plots comparing the new NGA 

equations and the older equations used in the 2002 maps for 

M6.5 and 7.5 earthquakes at 0.2-s and 1-s spectral acceleration (SA). Ground motions at 0.2-s period are similar for the 

new NGA and older equations for the M6.5 event. However, 

for earthquakes with M7.5, the new equations yield lower 

ground motions for three of the four relations out to distances 

of 100 kilometers. NGA equations for an M6.5 earthquake at 

1-s period are generally lower for three of the four relations 

out to distances of about 20 kilometers and then are similar to 

the older equations at farther distances. NGA ground-shaking 

estimates are generally 50 percent lower for the M7.5 events 

out to distances of 100 kilometers. On the basis of recommendations from the expert panel on ground motions, we assign 

equal weights to each of the three NGA equations.

As in the previous maps, we use a reference site condition that is specified to be the boundary between NEHRP site 

classes B and C, with an average shear-wave velocity in the 

upper 30 meters of the crust of 760 m/s (as recommended by 

participants of the ATC/USGS workshop). The new NGA 

equations allow for direct calculations of ground motions for 

the 760 m/s shear wave velocity. In previous versions of most 

of the attenuation equations, it was impossible to identify 

the underlying shear-wave velocity that corresponded to 

“rock” relations. During the NGA project, the NGA modelers 

determined that the rock Vs30 measurements used in two of 

the attenuation relations averaged about 560 m/s rather than 
Western United States 37

Figure 24. Pacific Earthquake Engineering Research Center (PEER) earthquake database. 

Red diamonds represent the previous data set and the blue diamonds represent the new 

data set. Illustration provided by Yousef Bozorgnia and Ken Campbell.

1.0 10.0 100.0

DISTANCE TO SITE, IN KILOMETERS (Rjb=Rcd)

0.01

0.10

1.00

MEDIAN 0.2-S OR 5-HERTZ SA, IN STANDARD GRAVITY

DISTANCE TO SITE, IN KILOMETERS (Rjb=Rcd)

MEDIAN 0.2-S OR 5-HERTZ SA, IN STANDARD GRAVITY

AS97

BJF97

CB2003

Sadigh97

BA-NGA

CB-NGA

CY-NGA

1.0 10.0 100.0 0.01

0.10

1.00

AS97

BJF97

CB2003

Sadigh97

BA-NGA

CB-NGA

CY-NGA

A B

Figure 25. Western United States ground motion (0.2-s spectral acceleration) for (A) M6.5 earthquakes and (B) M7.5 

earthquakes from strike-slip source at firm-rock site based on AS97 (Abrahamson and Silva, 1997), BJF97 (Boore and others, 

1997), CB2003 (Campbell and Bozorgnia, 2003), Sadigh97 (Sadigh and others, 1997) BA-NGA (Boore and Atkinson, 2008), CB-NGA 

(Campbell and Bozorgnia, 2008), and CY-NGA (Chiou and Youngs, 2008).

0.1 1 10 100 1,000

4

5

8

6

7

DISTANCE, IN KILOMETERS

MAGNITUDE
38 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

1.0 10.0 100.0 0.01

0.10

1.00

1.0 10.0 100.0 0.01

0.10

1.00 A B

AS97

BJF97

CB2002

Sadigh97

BA-NGA

CB-NGA

CY-NGA

AS97

BJF97

CB2002

Sadigh97

BA-NGA

CB-NGA

CY-NGA

DISTANCE TO SITE, IN KILOMETERS (Rjb=Rcd)

MEDIAN 1-S SA, IN STANDARD GRAVITY

DISTANCE TO SITE, IN KILOMETERS (Rjb=Rcd)

MEDIAN 1-S SA, IN STANDARD GRAVITY

Figure 26. Western United States 1-s spectral acceleration (SA) for (A) M6.5 earthquakes and (B) M7.5 earthquakes from strikeslip source at firm-rock site based on AS97 (Abrahamson and Silva, 1997), BJF97 (Boore and others, 1997), CB2003 (Campbell and 

Bozorgnia, 2003), Sadigh97 (Sadigh and others, 1997) BA-NGA (Boore and Atkinson, 2008), CB-NGA (Campbell and Bozorgnia, 

2008), and CY-NGA (Chiou and Youngs, 2008).

760 m/s. Therefore, the 2002 maps incorporated rock attenuation relations that were not 760 m/s, and some of the reduction 

in the new maps for 1-s period is due to this difference.

The NGA review panel also suggested that the national 

maps should incorporate additional epistemic uncertainty in 

the attenuation relations because of data limitations (especially for large earthquakes) and the considerable interaction 

between modelers. This was also discussed at the Applied 

Technology Council user workshop and the California regional 

workshop. We developed ground-motion epistemic uncertainty 

based on number of earthquakes in magnitude-distance bins in 

the NGA database. The ground-motion uncertainty is assumed 

to be 50 percent for M>7 and R<10 kilometers. This is an 

additive factor of 0.4 in log-space (90 percent confidence limits). The factors for other bins are 0.4*√(n/N) where N is the 

number of earthquakes recorded in another bin, and n is the 

number in the M≥7, R<10-kilometer bin. The other bins had 

uncertainties ranging from 10 percent to 50 percent. Following NGA modelers, we partitioned the source space into nine 

bins, three in distance and three in magnitude. Table 6 shows 

the number of earthquakes in each bin that two NGA modeling 

groups used for their ground-prediction estimation effort, and 

the resulting uncertainty using the square-root rule. Boore and 

Atkinson (2008) did not report this information in their paper. 

Finally, we averaged the two estimates (final column of table 

6) and used this average value for the additional epistemic 

ground-motion uncertainty part of the hazard model. This 

uncertainty was applied symmetrically (that is, gnd + dgnd

models were weighed equally with gnd – dgnd models, where 

gnd stands for the logarithm of median spectral acceleration or 

peak ground acceleration for a given ground-motion prediction 

model). The unmodified gnd model is weighted 0.63 and the 

gnd ±dgnd models are weighted 0.185 when the hazard curves 

from these three branches are added. The same dgnd terms are 

applied to all three NGA relations (Boore and Atkinson, 2008; 

Campbell and Bozorgnia, 2008; Chiou and Youngs, 2008) that 

are used with all WUS crustal sources in the hazard model.

Subduction Zone/Plate Interface

Ground motions for great Cascadia earthquakes were 

determined from: Youngs and others (1997), Atkinson and 

Boore (2003; global model), and a new equation published 

by Zhao and others (2006). In the 1996 and 2002 maps, we 

essentially followed the approach of Geomatrix Consultants, 

Inc. (1995) and included the Sadigh and others (1997) relations. The attenuation relations are compared in figure 27. The 

Sadigh and others (1997) relations were included for distances 

less than about 70 kilometers, to address the concern that the 

subduction-zone data may underestimate ground motions at 

close-in distances, since the data from close-in distances used 

in the Youngs and others (1997) relations were dominated by 

records from the Mexican subduction zone. At our workshops, 

concern was expressed about using crustal-attenuation relations for subduction-zone earthquakes (for example, Sadigh 

and others, 1997). In the 2008 update, we use the Zhao and 

others (2006) relation to essentially take the place of Sadigh 

and others (1997; although we apply the Zhao and others, 

2006, relations at all distances). The Zhao and others (2006) 

relations are derived from strong-motion recordings from 

interface earthquakes in Japan. For distances less than about 

100 kilometers, the Zhao and others (2006) relations predict 
Western United States 39

Table 6. Number of earthquakes (N) in each bin for the C&Y (Chiou and Youngs, 

2008) and C&B (Cambell and Bozorgnia, 2008) attenuation relations.

M and Rrup 

range

Neq 

(C&Y)

C&Y 

dgnd term

Neq 

(C&B)

C&B 

dgnd term

Average 

dgnd term

5≤M<6,Rrup<10 24 0.22 4 0.53 ±0.375

5≤M<6,10≤Rrup<30 50 0.15 15 0.27 0.21

5≤M<6, Rrup≥30 26 0.21 14 0.28 0.245

6≤M<7,Rrup<10 24 0.22 19 0.24 0.23

6≤M<7,10≤Rrup<30 26 0.21 20 0.25 0.225

6≤M<7, Rrup≥30 23 0.21 18 0.25 0.23

M≥7, Rrup<10 7 0.40 7 0.40 0.40

M≥7,10≤Rrup<30 8 0.37 9 0.35 0.36

M≥7, Rrup≥30 10 0.33 13 0.29 0.31

100 150 200 250 300 350 400 450 500

Rcd (km)

0.01

0.10

1.00

Zhao 8.3

Zhao 9

ABsub 8.3

ABsub 9

Geomatrix 8.3

Geomatrix 9

Sadigh 8.3

Sadigh 9

500 500 100 150 200 250 300 350 400 450 500

Rcd (km)

0.01

0.10

1.00

Zhao 8.3

Zhao 9

ABsub 8.3

ABsub 9

Geomatrix 8.3

Geomatrix 9

Sadigh 8.3

Sadigh 9

A B MEDIAN 0.2-S SA, IN STANDARD GRAVITY MEDIAN 1-S SA, IN STANDARD GRAVITY

Figure 27. Plots comparing the ground-motion attenuation relations for the subduction zone interface at (A) 0.2-s and (B) 

1-s spectral acceleration (SA) at firm-rock site based on Zhao 8.3 and Zhao 9, Zhao and others (2006); ABsub 8.3 and ABsub 9, 

Atkinson and Boore (); Geomatrix 8.3 and Geomatrix 9, Geomatrix Consultants, Inc. (1995); Sadigh 8.3 and Sadigh 9, Sadigh and 

others (1997).

higher ground motions than the Youngs and others (1997) and 

Atkinson and Boore (2003) relations.

Figure 27B shows the attenuation relations for Zhao and 

others (2006) along with recent data from the M8.3 

Tokachi-Oki earthquake in Japan. The Zhao and others 

(2006) relation fits the recent data out to 250 kilometers but 

overpredicts the ground motions at larger distances. The 

overprediction at large distances may be caused by strong 

attenuation along the Japanese Island Arc, which may not 

be applicable to the case of the Cascadia subduction zone. 

We applied new weights to these relations giving the newest 

relation of Zhao and others (2006) half weight and equally 

distributing the remaining half weight to Youngs and others 

(1997) and Atkinson and Boore (2003).

Subduction Zone—In-Slab

To calculate ground motions for intermediate-depth earthquakes (depth greater than 35 kilometers), we incorporated 

two attenuation relations. We used the attenuation relation 
40 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

by Geomatrix Consultants, Inc. (1993) with modification 

for depth dependence that was incorporated in the 1996 and 

2002 maps. In addition, we included the Boore and Atkinson 

(2000) equations for intraslab earthquakes. Deep events were 

assumed to occur at 50-kilometer depth for the ground-motion 

calculations.

Results of the Seismic Hazard 

Calculations

To produce the National Seismic Hazard Maps, we calculated the hazard at several spectral accelerations (SA, periods 

0.2, 0.3, 0.5, 0.75, 1.0, and 2.0 s) and peak horizontal ground 

acceleration (PGA). The hazard curves are then interpolated 

at 0.00211, 0.00103, and 0.00040 annual rate of exceedance 

to obtain the 10-percent, 5-percent, and 2-percent probability 

of exceedance in 50 years, respectively. The hazard model 

assumes Poisson (time-independent) event occurrence. Other 

levels can be interpolated from the hazard curves, but we 

caution use of these curves at low probability levels because 

inclusion of some very low activity faults that are omitted 

from the USGS source model may cause significant differences. These maps are based on uniform firm-rock site conditions defined as a site with average shear wave velocity of 760 

m/s in the upper 30 meters of the crust (Vs30).

Central and Eastern United States Maps

The hazard at 2-percent probability of exceedance in 

50 years in the CEUS is dominated by the New Madrid and 

Charleston seismic zones, but seismicity zones in eastern 

Tennessee and the northeast, as well as the two faults also contribute significantly. The hazard at the 2-percent probability 

of exceedance in a 50-year level is typically a factor of two to 

four higher than the 10 percent in 50-year values in the CEUS. 

Figures 28 to 30 show hazard maps for the CEUS at 2-percent 

probability of exceedance in 50 years for the 0.2- and 1-s SA 

and PGA, hazard values used in building codes. Figures 31 to

33 show hazard maps for the CEUS at 10-percent probability 

of exceedance in 50 years for the 0.2- and 1-s SA and PGA.

We made many comparisons of the 2008 and the 2002 

hazard maps. Ratio maps can be found on the Web site: http://

earthquake.usgs.gov/research/hazmaps/. The PGA and 0.2-s 

SA hazard at 2 percent in 50 years is lower by about 15–

25 percent across much of the Northeastern United States. 

Near New Madrid the high-frequency ground motions are 

significantly lower within several kilometers of the fault 

and are typically lower by 2–15 percent at distances up to 

1,000 kilometers from the fault. For the 1-s SA, the ground 

motions are decreased about 10–15 percent across much of the 

CEUS. Ground-motion hazards near the New Madrid Seismic 

Zone are lower than in 2002. In addition, the motions are also 

lower by 2–10 percent at distances up to 1,000 kilometers 

from sources. The cluster model causes the ground motions 

to be slightly elevated at sites to the northwest and southeast 

of the three modeled sources. Most of the decrease in ground 

motion in the hazard maps is caused by the new attenuation 

relations, changes to the New Madrid fault zone, and addition 

of magnitude uncertainties in the earthquake catalog.

Western United States Maps

The hazard at 2-percent probability of exceedance 

in 50 years in the WUS is controlled by the major faults 

described earlier in the faulting sections. The hazard at the 

2-percent probability of exceedance in 50-year level is typically a factor of 1.5–2 higher than the 10 percent in 50-year 

values in coastal California and from 2–3.5 across the rest of 

the WUS. Figures 34 to 36 show hazard maps for the WUS at 

2-percent probability of exceedance in 50 years for the 0.2- 

and 1-s SA and PGA, hazard values used in building codes. 

Figures 37 to 39 show hazard maps for the WUS at 10-percent 

probability of exceedance in 50 years for the 0.2- and 1-s SA 

and PGA.

Comparisons of the 2008 and the 2002 hazard maps for 

the WUS can also be found at the USGS National Seismic 

Hazard Map Web site. For high-frequency ground motions 

(PGA and 0.2-s SA), the ground motions are mostly within 

about 10 percent of the 2002 maps. The ground motions in 

the Pacific Northwest, coastal California (figs. 40 and 41), 

and the Wasatch fault regions are typically 5–10 percent 

higher whereas the ground motions are about 10 percent lower 

in areas of low seismicity. However, the changes are more 

substantial at longer periods (1-s SA) where ground motions 

have decreased by 5–30 percent in many areas of the Western 

United States (with the exception of rates in an area adjacent 

to the subduction zone, which rose by 10–20 percent). These 

large decreases are due primarily to changes in the attenuation 

relations for crustal and subduction earthquakes (including 

better specification of the Vs30 of 760 m/s in the attenuation equations for crustal faults), reductions in the rate of 

earthquakes due to magnitude-uncertainty introduced in the 

earthquake catalog, and source model changes.

Conclusions and Proposed Future 

Improvements to Maps

The 2008 National Seismic Hazard Maps represent the 

“best available science” based on input from scientists and 

engineers that participated in the update process. This does not 

mean that significant changes will not be made in future maps. 

Future earthquakes and science on earthquake recurrence 

and ground shaking continually improve our understanding 

of the seismic hazard. We plan on holding several workshops 

over the next several years to define uncertainties in the input 

parameters and to refine the methodologies used to produce 
Results of the Seismic Hazard Calculations 41

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0.05

0.05

0.05

0.05

0.1

0.1

0.1

0.1

0.1

0.2

0.2

0.3

0.4

0.5

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0 500

km

0.02

0.03

0.04

0.06

0.07

0.09

0.12

0.15

0.20

0.26

0.33

0.43

0.56

0.72

0.93

1.20

S

A

g

Figure 28. Map of 1-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in the Central 

and Eastern United States in standard gravity (g).
42 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0.1

0.1

0.1

0.2

0.2

0.2

0.2

0.2

0.2

0.4

0.4

0.4

0.4

0.4

0.6

0.6

1.5

1.0

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0 500

km

0.05

0.06

0.08

0.10

0.12

0.16

0.20

0.25

0.31

0.39

0.50

0.61

0.77

0.99

1.21

1.52

1.90

2.39

3.00

S

A

g

Figure 29. Map of 5-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in the 

Central and Eastern United States in standard gravity (g).
Results of the Seismic Hazard Calculations 43

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0.05

0.05

0.05

0.05

0.05

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.2

0.2

0.2

0.2

0.2

0.3

0.3

0.3

0.4

0.4

0.5

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0 500

km

0.02

0.03

0.04

0.06

0.07

0.09

0.12

0.15

0.20

0.26

0.33

0.43

0.56

0.72

0.93

1.20

P

G

A

g

Figure 30. Map of peak ground acceleration (PGA) for 2-percent probability of exceedance in 50 years in the Central 

and Eastern United States in standard gravity (g).
44 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0.05

0.1

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0 500

km

0.01

0.02

0.03

0.04

0.06

0.07

0.10

0.12

0.14

0.16

0.20

0.25

0.30

0.35

S

A

g

Figure 31. Map of 1-hertz spectral acceleration (SA) for 10-percent probability of exceedance in 50 years in the Central 

and Eastern United States in standard gravity (g).
Results of the Seismic Hazard Calculations 45

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0.1

0.1

0.1

0.1

0.

0.2

4

0.6

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

100 ̊W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊ W 70 ̊W

25 ̊ N

30 ̊ N

35 ̊ N

40 ̊ N

45 ̊ N

50 ̊ N

0 500

km

0.02

0.03

0.04

0.06

0.07

0.09

0.12

0.15

0.20

0.26

0.33

0.43

0.56

0.72

0.93

1.20

S

A

g

Figure 32. Map of 5-hertz spectral acceleration (SA) for 10-percent probability of exceedance in 50 years in the Central 

and Eastern United States in standard gravity (g).
46 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

100 ̊ W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊W

25 ̊N

70 ̊ W

30 ̊N

35 ̊N

40 ̊N

45 ̊N

50 ̊N

100 ̊ W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊W

25 ̊N

70 ̊ W

30 ̊N

35 ̊N

40 ̊N

45 ̊N

50 ̊N

0.05

0.05

0.05

0.1

0.1

0.1

0.1

0.2

0.3

100 ̊ W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊W

25 ̊N

70 ̊ W

30 ̊N

35 ̊N

40 ̊N

45 ̊N

50 ̊N

100 ̊ W 95 ̊W 90 ̊W 85 ̊W 80 ̊W 75 ̊W

25 ̊N

70 ̊ W

30 ̊N

35 ̊N

40 ̊N

45 ̊N

50 ̊N

0 500

km

0.01

0.02

0.03

0.04

0.06

0.07

0.10

0.12

0.14

0.16

0.20

0.25

0.30

0.35

P

G

A

g

Figure 33. Map of peak ground acceleration (PGA) for 10 percent probability of exceedance in 50 years in the Central 

and Eastern United States in standard gravity (g).
Results of the Seismic Hazard Calculations 47

Figure 34. Map of 1-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in the Western 

United States in standard gravity (g).

0 200

km

0.01

0.02

0.03

0.04

0.06

0.08

0.10

0.12

0.16

0.21

0.27

0.35

0.46

0.59

0.77

1.00

S

A

g

124 ̊W 122 ̊ 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N

W
48 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Figure 35. Map of 1-hertz spectral acceleration (SA) for 10-percent probability of exceedance in 50 years in the 

Western United States in standard gravity (g).

0 200

km

0.01

0.02

0.03

0.04

0.06

0.08

0.10

0.12

0.16

0.21

0.27

0.35

0.46

0.59

0.77

1.00

S

A

g

124 ̊W 122 ̊W 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N
Results of the Seismic Hazard Calculations 49

Figure 36. Map of 5-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in the 

Western United States in standard gravity (g).

0 200

km

0.03

0.04

0.06

0.08

0.10

0.14

0.19

0.26

0.35

0.48

0.65

0.88

1.19

1.62

2.21

3.00

S

A

g

124 ̊W 122 ̊W 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N
50 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Figure 37. Map of 5-hertz spectral acceleration (SA) for 10-percent probability of exceedance in 50 years in the Western 

United States in standard gravity (g).

0 200

km

0.03

0.04

0.06

0.08

0.10

0.14

0.19

0.26

0.35

0.48

0.65

0.88

1.19

1.62

2.21

3.00

S

A

g

124 ̊W 122 ̊W 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N
Results of the Seismic Hazard Calculations 51

Figure 38. Map of peak ground acceleration (PGA) for 2-percent probability of exceedance in 50 years in the 

Western United States in standard gravity (g). 

0 200

km

0.01

0.02

0.03

0.04

0.06

0.08

0.10

0.12

0.16

0.21

0.27

0.35

0.46

0.59

0.77

1.00

P

G

A

g

124 ̊W 122 ̊W 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N
52 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Figure 39. Map of peak ground acceleration (PGA) for 10-percent probability of exceedance in 50 years in the 

Western United States in standard gravity (g). 

0 200

km

0.01

0.02

0.03

0.04

0.06

0.08

0.10

0.12

0.16

0.21

0.27

0.35

0.46

0.59

0.77

1.00

P

G

A

g

124 ̊W 122 ̊W 120 ̊W 118 ̊W 116 ̊W 114 ̊W 112 ̊W 110 ̊W 108 ̊W 106 ̊W 104 ̊W 102 ̊W 100 ̊W

28 ̊N

30 ̊N

32 ̊N

34 ̊N

36 ̊N

38 ̊N

40 ̊N

42 ̊N

44 ̊N

46 ̊N

48 ̊N

50 ̊N
Results of the Seismic Hazard Calculations 53

Figure 40. Map of 1-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in 

California in standard gravity (g). Red lines are fault sources used in the model.

0 200

km

0.01

0.02

0.03

0.04

0.06

0.08

0.10

0.12

0.16

0.21

0.27

0.35

0.46

0.59

0.77

1.00

S

A

g

125 ̊W 124 ̊W 123 ̊W 122 ̊W 121 ̊W 120 ̊W 119 ̊W 118 ̊W 117 ̊W 116 ̊W 115 ̊W 114 ̊W

31 ̊N

32 ̊N

33 ̊N

34 ̊N

35 ̊N

36 ̊N

37 ̊N

38 ̊N

39 ̊N

40 ̊N

41 ̊N

42 ̊N

43 ̊N
54 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Figure 41. Map of 5-hertz spectral acceleration (SA) for 2-percent probability of exceedance in 50 years in 

California in standard gravity (g). Red lines are fault sources used in the model.

0 100 200

km

0.03

0.04

0.06

0.08

0.10

0.14

0.19

0.26

0.35

0.48

0.65

0.88

1.19

1.62

2.21

3.00

S

A

g

125 ̊W 124 ̊W 123 ̊W 122 ̊W 121 ̊W 120 ̊W 119 ̊W 118 ̊W 117 ̊W 116 ̊W 115 ̊W 114 ̊W

31 ̊N

32 ̊N

33 ̊N

34 ̊N

35 ̊N

36 ̊N

37 ̊N

38 ̊N

39 ̊N

40 ̊N

41 ̊N

42 ̊N

43 ̊N
References 55

and distribute the hazard information. Specific recommendations for future research include: 

CEUS: 

1. Improve source magnitude-frequency distributions at sites 

across the CEUS (including Mmax, b-values, a-values)

2. Estimate magnitude uncertainties and round-off errors, 

and uncertainties in rates implied in the earthquake catalog

3. Study the mechanism for earthquake generation along the 

New Madrid Fault Zone (understand relation of surface 

strain rate and paleoseismic earthquake rate)

4. Constrain the location of the Charleston, South Carolina, 

earthquake sources

5. Assess the range of ground shaking from earthquakes in 

the CEUS (consider regional tectonics and variability in 

stress drops, Kappa, and Q)

6. Convene workshops on CEUS issues: NGA-East ground 

motions, Mmax, Charleston sources, New Madrid sources, 

urban hazard maps

7. Develop attenuation models for the Rocky Mountain and 

other transition regions.

WUS:

1. Reduce discrepancy between model and historical earthquake rates or explain differences

2. Assess fault seismic slip rates, geodetic strain rates, and 

paleoearthquake rates and associated uncertainties and 

resolve discrepancies between datasets

3. Constrain ratio of seismic and aseismic slip on faults and 

develop approach to routinely apply geodetic results to 

seismic hazard analysis

4. Continue to improve estimates of fault geometry, magnitude, and recurrence parameters (especially for urban 

areas)

5. Estimate the various source ruptures along faults including multisegment or multifault ruptures

6. Continue to improve models for depth of rupture 

7. Assess the range of ground shaking from subduction-zone 

earthquakes (interface and in-slab)

8. Continue to improve crustal fault attenuation relations that 

include range of source parameters (for example, directivity) and path parameters (propagation effects and site 

amplification) 

9. Incorporate sedimentary basin models and soil models 

into hazard studies

10. Develop time-dependent models of earthquake ruptures 

and determine how these should be included in future 

maps

11. Convene workshops and perform research on WUS 

issues: NGA-subduction zone, discrepancy between 

model and historical earthquake rates, slip rates and 

uncertainties, urban hazard maps

Acknowledgments

We wish to thank the hundreds of workshop participants 

and reviewers who made valuable suggestions that were incorporated in the maps that significantly improved the quality of 

this product. We give special thanks to the National Seismic 

Hazard Mapping Project Advisory Panel and the NGA expert 

panel (listed in the Introduction). We thank the National Earthquake Hazard Reduction Program (NEHRP) for funding the 

development of these maps. We thank Garry C. Rogers (Geological Survey of Canada) who provided a catalog of deep 

earthquakes beneath the Georgia Strait–Puget Sound region 

and Gail M. Atkinson for providing CEUS attenuation elations 

with different stress drops. The mapping tool GMT (Wessel 

and Smith, 1991) was used to create the maps. 

References

Abrahamson, N.A., and Silva, W.J., 1997, Empirical response 

spectral attenuation relations for shallow crustal earthquakes: Seismological Research Letters, v. 68, p. 94–127.

Algermissen, S.T., and Perkins D.M., 1976, A probabilistic 

estimate of the maximum acceleration in rock in the contiguous United States: U.S. Geological Survey Open-File 

Report 76–416, 45 p., 2 pls., scale 1:7,500,000.

Algermissen, S.T., Perkins, D.M., Thenhaus, P.C., Hanson, 

S.L., and Bender, B.L. 1990, Probabilistic earthquake acceleration and velocity maps for the United States and Puerto 

Rico: U.S. Geological Survey Miscellaneous Field Studies 

Map MF-2120, 2 sheets, scale 1:7,500,000.

Atkinson, G.M., and Boore, D.M., 1995, Ground motion relations for eastern North America: Bulletin of the Seismological Society of America, v. 85, p. 17–30. 

Atkinson, G.M., and Boore, D.M., 2003, Empirical groundmotion relations for subduction-zone earthquakes and their 

application to Cascadia and other regions: Bulletin of the 

Seismological Society of America, v. 93, p. 1703–1729.
56 Documentation for the 2008 Update of the United States National Seismic Hazard Maps

Atkinson, G.M., and Boore, D.M., 2006, Earthquake groundmotion prediction equations for eastern North America: 

Bulletin of the Seismological Society of America, v. 96, 

p. 2181–2205.

Atwater, B.F., and Hemphill-Haley, E., 1997, Recurrence 

intervals for great earthquakes of the past 3,500 years at 

northeastern Willapa Bay, Washington: U.S. Geological 

Survey Professional Paper 1576, 108 p.

Bakun, W.H., and Hopper, M.G., 2004, Magnitudes and locations of the 1811–1812 New Madrid, Missouri, and the 

1886 Charleston, South Carolina, earthquakes: Bulletin of 

the Seismological Society of America, v. 94, p. 64–75.

Behrendt, J.C., Hamilton, R.M., Ackermann, H.D., and 

Henry, V.J., 1981, Cenozoic faulting in the vicinity of the 

Charleston, South Carolina, 1886 earthquake: Geology, v. 9, 

p. 117–122.

Behrendt, J.C., and Yuan, A., 1987, The Helena Banks 

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earthquake area—Results from a marine, high-resolution, 

multichannel, seismic-reflection survey: Geological Society 

of America Bulletin, v. 98, p. 591–601.

Boore, D.M., and Atkinson, G.M., 2008, Ground-motion 

prediction equations for the average horizontal component 

of PGA, PGV, and 5%-damped PSA at spectral periods 

between 0.01 s and 10.0 s: Earthquake Spectra, v. 24, no. 1.

Boore, D.M., Joyner, W.B., and Fumal, T.E., 1997, Equations 

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Campbell, K.W., 2003, Prediction of strong ground motion 

using the hybrid empirical method and its use in the development of ground-motion (attenuation) relations in eastern 

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Campbell, K.W. and Bozorgnia, Y., 2003, Updated near-source 

ground-motion (attenuation) relations for the horizontal 

and vertical components of peak ground acceleration and 

acceleration response spectra: Bulletin of the Seismological 

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PGA, PGV, PGD and 5% damped linear elastic response 

spectra for periods ranging from 0.01 to 10.0 s: Earthquake 

Spectra, v. 24, no. 1.

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Wills, C.J., 2003, The revised 2002 California probabilistic seismic hazard maps June 2003: California Geological 

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Appendixes A-K
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix A. Depth To The Top Of Rupture (Ztor) For Western
 

United States Faults 

By Stephen C. Harmsen and Yuehua Zeng 

Several attenuation relations include terms as a 

function of depth to top of rupture (Ztor) in addition 

to the effect of geometric spreading. We discuss Ztor 

for two source specifications: (1) mapped Quaternary 

faults and (2) background seismicity. 

(1) All Quaternary faults in the hazard model 

have specified depth to top of fault. Most of these 

have tops at the Earth’s surface, and this (large) subset 

is the one we discuss now. In the 1996 and 2002 

probabalistic seismic hazard analysis for the National 

Seismic Hazard Maps, all fault ruptures were modeled 

to fill the rupture width. Now, however, we attempt to 

produce a reasonable distribution of depths to top of 

rupture in our hazard model. The Ztor distribution is 

as follows. All characteristic-source scenarios 

continue to rupture over the entire fault width. 

Gutenberg-Richter scenarios, however, have a downdip distribution of Ztor as shown in table A-1. 

Currently, the Gutenberg-Richter distribution 

has a lower magnitude limit of 6.5. All fault sources 

with M≤6.5, because they are characteristic, rupture 

the entire fault width, as do all sources, characteristic 

or Gutenberg-Richter, with M>7.0. Thus, our 

implementation of down-dip rupture tops on 

Quaternary faults is confined to the GutenbergRichter part of the model, with magnitude range 6.5 to 

7.0. For the special case of the creeping section of San 

Andreas fault, having a Gutenberg-Richter 

distribution of magnitude with magnitude from 6.0 to 

6.7, the model excludes the possibility of non-zero 

Ztor. 

(2) For background (gridded) hazard, that is, for 

sources for which no faults are identified, Ztor is 

currently fixed at 5.0 kilometers for M<6.5 sources, 

and Ztor is 1.0 kilometer for M>6.5 sources. Hazard 

Table A-1. Depth to top of rupture. 

Magnitude Pr Pr Pr
 

range
 [ztor=0] [ztor=2 km] [ztor=4 km] 

6.5≤M≤6.75 0.333 0.333 0.333 

6.75<M≤7.0 0.5 0.5 0 

7.0 < M 1.0 0 0 

from all such sources is, therefore, affected by 

nonsurface-rupture terms in several of the Next 

Generation Attenuation (NGA) ground-motion 

prediction models. For the dip-slip portion of 

background seismicity, an additional hanging-wall 

term (which is a function of Ztor and other 

parameters) is included for two of the Next Generation 

Attenuation (NGA) models. Figure A-1 shows the 

depth to top of rupture for all available earthquakes in 

the NGA database. The average Ztor is 1.0 kilometer 

for M<6.5 and 5.0 for 6.5<M<7.0, respectively. This 

is consistent with our current assumption on Ztor for 

M<6.5 and M>6.5 sources, respectively. The average 

Ztor for earthquakes with M>7.0 is about 0.0 

kilometers in the NGA database. Since the 

background hazard is not related to any surface 

rupture, we decided to fix those M>7.0 events to 

Ztor=1.0. 

Campbell and Bozorgnia (2006) suggested 

using surface rupture relative to magnitude 

probabilities proposed by Wells and Coppersmith 

(1993). Figure A-2 shows this distribution and shows 

an approximate graph of the expected distribution of 

Figure A-1. Plot of probability of surface rupture 

relative to magnitude. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps A-2 

Figure A-2. Plot of depth to top of rupture relative to magnitude for all available earthquakes in the Next Generation 

Attenuation database. 

Ztor for fault sources with Mchar in the 6.5 to 7.0 range 

in our current implementation. This graph is 

approximate because there are complications 

associated with the epistemic and aleatory range of 

magnitudes associated with any given Mchar. 

However, figure A-2 illustrates several features of the 

current model. 

(1) For lower magnitudes, the probability of 

nonsurface rupturing is greater than for higher 

magnitudes. 

(2) The probability of surface rupture increases as the 

weight applied to Gutenberg-Richter distribution 

decreases. 

(3) There are two magnitudes, at M6.75 and M7.0, 

where the probability of surface rupture increases 

substantially. 

The relative positions of the colored curves compared 

to the Wells and Coppersmith (1993) distribution 

will vary depending on the value of Mchar and other 

details. 

The above discussion pertained to faults that 

crop out on the Earth’s surface. The growing 

inventory of blind thrusts (for example, those of the 

Great Valley, San Fernando Valley, and elsewhere in 

California) in the Quaternary fault database may need 

to be included when comparing our model with the 

Wells and Coppersmith (1993) distribution or other 

proposed distributions of depth of surface rupture. 

One feature of the Wells and Coppersmith 

(1993) distribution that is not in our current Western 

United States fault model is the significant 

probability (greater than 10 percent) of nonsurface 

rupturing M>7 earthquakes on faults that crop out at 

the Earth’s surface. Whether such events should be 

included in the seismic hazard model is a topic of 

current debate. 

References 

Campbell, K.W. and Bozorgnia, Y., 2006, CampbellBozorgnia NGA empirical ground motion model 

for the average horizontal component of PGA, 

PGV, PGD, and SA at selected periods ranging 

from 0.01–10.0 seconds, Pacific Earthquake 

Engineering Research Center report, ver. 1.0, 

October 2006. 

Wells, D.L. and Coppersmith, K.J., 1993, Likelihood 

of surface rupture as a function of magnitude [abs.]: 

Seismological Research Letters, v. 64, p. 54. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix B. Fault Distances to Nonplanar Fault
 

By Yuehua Zeng 

In the 2008 update of the National Seismic 

Hazard Maps, the Joyner-Boore (JB) distance and 

closest fault distance to a nonplanar fault were 

developed. We defined the nonplanar fault based on 

the approach of Zeng and Chen (2001). The fault 

model is constructed by extending the surface traceof 

a multisegment rupture fault down a dipping 

direction based on the average strike for the fault. The 

average strike of the fault is obtained by taking the 

strike of the line connecting the first point with the 

last point of the surface trace. Mathematically, it is 

implemented by assuming x0 and y0 as the location of 

a given point on thefault-surface trace. By defining 

the origin of the coordinateat the first point of the 

fault trace, the direction of the x-axis is given by the 

vectorconnecting the first point with the last point of 

the fault trace. The y-axis is perpendicular to thex-axis 

along the surface projection of the average dip 

direction. For any point on the fault plane, its 

coordinate is given by 

x=x0,
 

y=y0+d*cos(δ), (1B)
 

z=d*sin (δ)
 

where d is the distance along the dip direction, and δ is 

the dip angle. Equation (1B) extends a multisegment 

fault tracealong the free surface to a nonplanar fault 

plane at depth. Although thereal fault structure at 

depth could differ, we assume that thefault model 

given in (1B) is sufficient to represent the earthquake 

rupture plane unless further evidence or data become 

available. 

For a buried fault, we can revise equation (1B) to 

x=x0,
 

y=y0+d*cos(δ), (2B)
 

z=d0+d*sin (δ) 

where d0 is the depth to the top of the fault, and x0 and 

y0 are the location of a given point on thefault top. 

In the previous multisegment fault model used 

in 1996 and 2002 National Seismic Hazard Maps, 

each segment bases the dip direction along the strike 

perpendicular to the segment. Such defined fault 

segments will fan out or pinch inward at the 

connecting point of those segments (fig. B-1). The 

current fault overcomes this problem and provides a 

continuous extending fault plane (fig. B-2). Each fault 

Figure B-1. Schematic plot of multisegment fault defined in previous National Seismic Hazard Maps. Dip direction is 

normal to the strike of each segment. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps B-2 

Figure B-2. Schematic plot of multisegment fault defined in the 2008 update of the National Seismic Hazard Maps. 

The fault plane is constrained to the down-dip direction based on the average strike of the fault. The average strike 

of the fault is the strike of the line connecting the first point with the last point of the surface trace of the fault. 

segment is a parallelogram defined by equation (1B) Reference 

or (2B). We calculate the fault distances to those 

parallelograms analytically. The calculation provides Zeng, Y., and Chen, C.H., 2001, A combined GPS 

tenfold increase in computing time compared to the measurements and strong motion waveform 

numerical solution for the previous fault distance inversion of the source rupture process during the 

calculation for the characteristic-fault hazard example. 1999 Chi Chi, Taiwan earthquake: Bulletin of the 

Seismological Society of America, v. 91, p. 1088– 

1098. 
Appendix C. Distance to a Fault with Random Strike 

By Stephen C. Harmsen 

In the 2008 update of the maps, background 

sources with random strike are assigned a mean 

distance when computing the ground-motion 

integral. The fault is assumed to have vertical dip. 

The Wells and Coppersmith (1994) formula of 

rupture length (L) as a function of moment 

magnitude is used to obtain L whenever M>6. 

Consider a line source with center at P and length L. 

Let L0=L/2. Let the epicentral distance from P to site 

S to be r. There are two cases, L0≥r and L0 <r. 

The first case, L0≥r: 

The distance is found by elementary 

trigonometry to be rsin! . 

The mean distance is 

" 2 2r

<rjb> = !rsin#U(# )d# = . " 0

 Here U(! )is the uniform distribution, 

2 ! U(! ) = for 0 ≤" # . ! 2

We assume that all source strikes are equally likely, 

and by symmetry, the domain of integration may be 

reduced to one mathematical quadrant. 

The second case L0<r: 

In this case, the distance to the fault either 

projects onto the nearest fault endpoint or onto an 

interior point. The angle where the changeover 

occurs is 

L ! 0

0 = arccos( ). r

If ! " ! 0 , the law of cosines is used to obtain the 

distance, 

r

2 = r2 l2

jb + 0 " 2rl0 cos(! ) = a " bcos! with 

a= r

2 + l2

0 and b= 2rl0 or r a bcos jb = " ! and 

if ! > ! 0 , then r r jb = sin! as above. The mean 

distance is 

2 & ) *0 2 #

<rjb>= $

( a ' b cos* d* + r * *

$ ( sin d .!

) * ! % 0 0 "

The first term is found to have an analytic solution 

involving the elliptic integral of the second kind. 

See Gradshteyn and Ryzhik (1980), chapter 2, 

Indefinite integrals of elementary functions, eqn. 2 

at bottom of p. 156, and then p. 905. The second 

term above integrates to r cos(! 0 ). The solution of 

the elliptic integral is available in many Fortran 

libraries, such as “Numerical Recipes in Fortran”, 

by Press and others (1986). Some transformations 

are required to use the Press and others’ el2 

function. While these are of limited interest to the 

general reader, they are included here for 

completeness and will be found in the Fortran code 

hazgridXnga2.f for example. 

(a + b)(1! cos# 0 ) " 0 = , 2(a ! bcos# 0 )

" = asin" 0 ,

x = tan" ,

2b

s

2 = 1! , a + b

s = s

2 ,

e2 = el2(x,s,1.,s

2

),

f = 2 a + b

Here, el2 is the output of the Numerical 

Recipes function call with four arguments. When 

calling el2, we need to ensure that s

2

 is positive, 

which it is mathematically, but may fail to be in 

applications due to numerical precision. Finally, we 

define another term and get the solution, 

2b sin !

t = 0 , a # b cos ! 0

I = e2 f # t,

2

< rjb >= [I + r cos ! 0 ]. "

The grids of stations and sources are used to 

define a matrix of average distances, <rjb>, as a 
Documentation for the 2008 Update of the United States National Seismic Hazard Maps C-2

function of source magnitude from M6 to M7.5. 

These average distances are used, along with the 

companion distance, which we currently write as 

rcd= < r

2 h2

jb > + , 

in the attenuation models, which predict ground otion 

from M and r. In this formula, h is the depth to top of 

fault, which is assumed to have vertical dip. Rjb is the 

Joyner-Boore distance, and rcd is the closest distance 

to any point on the fault or rupture surface. A more 

accurate determination of <rcd>, which also involves 

the elliptic integral of the second kind, is possible. 

Because of limited sensitivity of the ground-motion 

prediction equations to small changes in rcd we believe 

our estimate is adequate. 

References 

Gradshteyn, I.S., and Ryzhik, I.M., 1980, Table of 

integrals, series, and products, corrected and 

enlarged edition, in Jeffrey, A., ed.: New York, 

Academic Press. 

Press, W.H., Flannery, B.P., Teukolsky, S.A., and 

Vettering, W.T., 1986, Numerical recipes—The 

art of scientific computing: New York, 

Cambridge University Press, 818 p.

Wells, D.L. and Coppersmith, K.J., 1994, New 

empirical relationships among magnitude, 

rupture length, rupture width, and surface 

displacements: Bulletin of the Seismological 

Society of America, v. 84, p. 974–1002.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix D. Modeling Dip-Slip Background Sources
 

By Stephen C. Harmsen 

This appendix discusses how we implement a 

hanging-wall effect in the current NSHMP PSHA 

for background sources (that is, faults with no 

specific information except for rate estimates from 

historical seismicity). For many of these gridded 

sources in the WUS, half of them are strike slip and 

half are dip slip. Several of the NGA relations that 

the 2008 PSHA uses to estimate seismic hazard in 

the WUS have a complex response to dip-slip 

sources, much of which is contained in a hangingwall (hw) term. Because this hw term is not 

negligible in many instances, we need to model its 

effect in a fair and reasonable way. 

For the dip-slip part of background seismic 

hazard, the hazard software computes an average 

hanging-wall effect. A set of faults with a random 

but uniformly distributed strike and fixed 50° dip is 

defined. The centers of all dipping faults have depth 

of 7.5 kilometers (not randomized). Furthermore, 

the centers of dipping faults, like the vertical-dip 

counterparts, are co-located with the rate grid at 0.1­

degree increments in latitude and longitude. Our 

implementation of virtual dip-slip faults uses the 

Wells and Coppersmith (1994) all-source A(M) 

formula to estimate fault area A (in square 

kilometers), log(A)=(M–4.07)/0.98. From A, fault 

width is determined assuming an aspect ratio of 1.5; 

a minimum depth of top of fault of 0.5 kilometer 

below Earth’s surface further constrains fault width. 

The hanging-wall term of the relevant Next 

Generation Attenuation (NGA) model is computed 

for each such fault strike for a given distance and 

magnitude, and the samples are averaged. Because 

attenuation model response is defined in “logged” 

ground-motion space, the averages are geometric in 

“unlogged” space. 

Figure D-1 is a schematic diagram of a virtual 

dipping fault with the relevant distances labeled. 

Figure D-1. Schematic diagram of virtual fault with associated distances to site S. Rcd, closest distance to fault; 

Rx, closest distance to top of fault projected indefinitely along strike; Rx<0 on footwall (Rx is used in the Chiou and 

Youngs relation); Repi, picentral distance to center projected to Earth surface; Ztor, depth of top of rupture, and θ

is fault strike, a random variable. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps D-2 

Figure D-2. Effect of including hanging-wall term on median ground motion considering (A) Campbell and 

Bozorgnia (2008), (B) Chiou and Youngs (2008) 1-hertz hanging-wall term, and (C) Chiou and Youngs (2008) 5-hertz 

hanging-wall term (M6.05–7.45 at 1-s period and 50° fault dip). 

Each of the distances Rjb, Rcd, and Rx is computed 

for each virtual fault and is used to determine the 

hw term associated with that sample. 

Figure D-2A shows the resulting average 

effect for the Campbell and Bozorgnia (2008) NGA 

model for M ranging from 6.05 to 7.45 and for 1-s 

SA (corresponding graphs for 0.2-s SA and PGA are 

identical). The x-axis labeled epicentral distance is 

site-to-source-center distance (projected to Earth’s 

surface). The y-axis is the percent increase in the 

median ground motion associated with inclusion of 

this average hw term. For dip-slip background 

sources closest to any given site, this hw effect can 

be 40 percent. 

Figures D-2B and D-2C show the 

corresponding results for the Chiou and Youngs 

(2008) NGA model for 1-s SA and 0.2-s SA, 

respectively. The Chiou and Youngs hanging-wall 

term has a stronger spectral frequency dependence 

than the Campbell and Bozorgnia model, rising with 

frequency in the 0.5-hertz to 5-hertz band. The 

maximum 1-hertz effect is similar to that of the 

Campbell and Bozorgnia model. For the 5-hertz SA, 

however, the median motion is increased by 100 

percent at sites that are close to the dip-slip source. 

The Chiou and Youngs hw-effect on peak ground 

accleration is also relatively large at near-source 

sites. 

When combined with strike-slip sources, this 

illustrated hw-effect is reduced. For the standard 

case in the 2008 update of the maps, 50 percent dip 

slip and 50 percent strike slip, the average hw term 

is multiplied by 0.5. 

When the average hw term is applied to the 

median, it is applied at the average Joyner-Boore 

distance, or Rjb, associated with vertical strike-slip 

faulting, because this version of Rjb is the 

fundamental distance that the USGS gridded-hazard 
pp ng au t.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps D-3 

Figure D-3. Plot showing the increase in Rjb for 

vertical faults compared to 50°-dipping faults as a 

function of average Rjb for the random-strike 

di i f l 

software uses to compute exceedance probability 

from random sourc or distances less than 

60 kilometers. Figure D-3 shows the increase in Rjb 

for vertical faults compared to 50°-dipping faults as 

a function of average Rjb for the random-strike 

dipping fault. From figure D-3, the strike-slip source 

on average can be over 5 kilometers more distant 

than the dip-slip source for earthquakes of random 

orientation having M>7. The software uses an 

approximation to this fairly complicated functional 

relation to associate a given average hanging-wall 

effect with the fundamental distance measure, 

average Rjb for vertical faults. 

References 

Campbell, K.W. and Bozorgnia, Y., 2008, Ground 

motion model for the geometric mean horizontal 

component of PGA, PGV, PGD and 5% damped 

linear elastic response spectra for periods ranging 

from 0.01 to 10.0 s: Earthquake Spectra, v. 24, 

no. 1. 

Chiou, B., and Youngs, R., 2008, A NGA model for 

the average horizontal component of peak ground 

motion and response spectra: Earthquake Spectra, 

v. 24, no. 1. 

Wells, D.L. and Coppersmith, K.J., 1994, New 

empirical relationships among magnitude, rupture 

length, rupture width, and surface displacements: 

Bulletin of the Seismological Society of America, 

v. 84, p. 974–1002. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix E. The Gutenberg-Richter Part of the MagnitudeFrequency Distribution for Western United States Faults 

By Stephen C. Harmsen 

The 2008 model for fault hazard, like earlier 

models, generally distributes hazard into 

characteristic-event and Gutenberg-Richter-event 

components. For events with M≤6.5, all hazard is 

assumed characteristic (noexception: San Andreas 

fault, creeping section). For events with M>6.5, the 

Gutenberg-Richter (GR) part of the hazard is 

developed by redistributing the seismic-moment rate 

that has been determined for that fault onto a set of 

events with M>6.5 and M<Mchar, where Mchar is the 

characteristic-event moment magnitude. The feature 

that is new in the 2008 model compared to earlier 

models is that Mchar is now computed to two 

decimal places rather than one (for example, 6.67 

instead of 6.7) for non-California faults. We continue 

to sample events with a truncated GR-distribution 

with M from 6.5+dM/2 to Mchar–dM/2, and this 

requires us to redefine dM to be an interval-dependent 

quantity, rather than the fixed value of 0.1 that was 

used in earlier maps. The range Mchar–6.5 determines 

the number of samples, with more magnitudes 

sampled as the range increases. Table E-1 shows the 

number of samples, k, as a function of this range, 

which in turn determines dM. This information is 

contained in the Fortran program, fltrate.v2.f. The GR 

distribution is defined by its a- and b-values, where 

10a is the rate of M0 events and b is the slope in the 

equation log(N)=a–bM. In the past, we could say that 

10a is the rate of earthquakes in the interval 

M0±dM/2; now we say that 10a is the rate of events in 

an (unspecified) interval of length dM containing 0 in 

its interior. The moment-rate-conserving calculation 

does not require further knowledge of this interval; it 

concentrates moment at each sampled M (as it always 

did) and does not use information about the 

distribution at nonsampled M values. 

For California faults with a GR component of 

hazard (that is, the so-called Type-B faults) Mchar is 

still defined to one decimal-place accuracy, and dM 

remains 0.1 in the 2008 PSHA. 

The main reason for defining Mchar with twodecimal-place accuracy in the 2008 PSHA was to 

assess the effects of additional epistemic uncertainty 

on approximated features such as fault dip and 

magnitude as a function of fault area. Sensitivity 

studies on k (for example, using k=10 instead of k=8) 

indicate that small changes in k in table E-1 yield a 

negligible effect on the seismic-hazard computation. 

Current upper limits of Mchar on non-California 

faults are 7.5 and 8.0 for dip-slip and strike-slip 

events, respectively. If these bounds were increased, it 

might be necessary to increase k for larger X. 

Table E-1. Sampling interval details for non-California faults, truncated GR distribution. 

X=Mchar – 6.5 K dM 

X≤0.1 1 X 

0.1 <X≤0.3 2 X/2 

0.3 <X≤0.5 4 X/4 

0.5 <X≤0.7 6 X/6 

0.7 < X 8 X/8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix F. New Madrid Temporal Cluster Model
 

By Mark D. Petersen, Stephen C. Harmsen, and Oliver S. Boyd 

In the 2008 hazard model, we have implemented 

a new cluster model that considers ground motions 

from three temporally clustered earthquakes on three 

separate segments of the New Madrid Seismic Zone, 

in contrast to the 2002 model that considers ground 

motions from one earthquake on the three segments 

(Toro and Silva, 2001). In this appendix we describe 

how the temporal cluster model affects the groundmotion hazard by showing two simple example 

calculations for the New Madrid seismic zone. 

To calculate the probability of ground-motion 

exceedance from three temporally clustered 

earthquakes on three segments of the fault we apply 

the equation: 

P= α × {1-[(1-P1) × (1-P2) × (1-P3)]} 

where α is the time-independent cluster rate, P1 is the 

probability of exceeding a certain ground-motion 

level from a rupture of segment 1, P2 is the 

probability of exceeding the same ground-motion 

level from a rupture of segment 2, and P3 is the 

probability of exceeding the same ground-motion 

level from a rupture of segment 3. This formula is 

repeated for each ground-motion level included in the 

hazard curve. The New Madrid cluster model 

considers the ground motions from dependent 

earthquakes on the north, central, and south segments. 

The annual rate of the cluster for these is either 1/500, 

1/750, 1/1,000, or 1/1500, as described in the logic 

tree (see fig. 6). 

For this example, we calculate the 

probability for an M7.5 event with an annual 

occurrence rate of 1/500 on each of the three segments 

using the Toro and others (1997) attenuation relation 

with modifications by Toro (2002). Our example 

shows hazard calculations for two sites to emphasize 

the effect of the cluster model on the hazard. The first 

site is near the northern end of the northern segment in 

Paducah, Ky. (lat 37.072N., long 88.628°W.) and the 

second site is near the intersection of the southern and 

central segments in Tennessee (lat 36.0°N., long 

89.0°W.). To calculate the hazard, we first need to 

calculate the conditional probability of exceeding 

each ground-motion level at a site, for an earthquake 

on each segment. The probabilities are shown in 

Figure F-1. At the Tennessee site, the probability of 

exceeding a ground motion of 0.4 g is 0.0527 for the 

northern rupture and 0.295 for the southern and central 

ruptures. The above formula yields a probability of 

0.529 of exceeding 0.4 g PGA. This probability is 

then multiplied by the cluster rate 1/500 year. The 

Figure F-1. Complementary cumulative plot for P=α×[1-(1-P1)*(1-P2)*(1-P3)] for a site in (A) Paducah, Kentucky, and 

(B) Tennessee. Curve for central and south segments are the same. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps F-2 

Figure F-2. Hazard curves for a site in (A) Paducah, Kentucky, and (B) Tennessee. Curves for central, south, and single 

rupture on three segments are the same. Curves for three independent segment ruptures and the three-segment 

cluster model are similar beyond ground motions of 0.5 g. 

calculation using the above formula yields a 0.00106 

annual rate of exceeding 0.4 g. This calculation is 

repeated for all the points on the hazard curve. 

Figure F-2 shows the hazard curves for the same 

two sites for ruptures on each of the segments 

separately, three independent ruptures, one rupture of 

the three segments, and the temporal cluster of 

ruptures as described previously. For the site in 

Paducah, Ky., located north of the New Madrid 

sources, earthquakes on the northern segment 

contribute most to the hazard while earthquakes on 

the central and southern segments contribute little to 

the total hazard at the selected site. The curves for the 

three independent-rupture models, the single-rupture 

model on each of the three segments, the single 

northern-segment rupture, and the cluster model are 

all similar to each other. For the site in Tennessee, 

earthquakes on the more distant northern segment 

contribute less than earthquakes on the closer central 

and southern segments. The three independent 

ruptures and the cluster models are higher than the 

single rupture of the three segments by about a factor 

of 2. Thus, the result of incorporating this cluster 

model on the hazard maps is that the hazard near the 

central part of the New Madrid Seismic Zone is 

increased compared to the 2002 model, which only 

considered a single rupture of three New Madrid 

segments. 

For the 2008 maps, we included several models 

that are depicted in the logic tree (see fig. 6). Half 

weight is given to the cluster model and half to the 

model with one independent rupture of all three 

segments (the 2002 model). The cluster models 

consider three different weighted scenarios: (1) each of 

the segments rupture on average in 500 years as three 

temporally clustered earthquakes, (2) each of the 

segments rupture on average in 1,000 years as three 

temporally clustered earthquakes, and (3) the northern 

segment ruptures every 750 years and the southern 

and central segments rupture every 500 years as 

temporally clustered earthquakes. To account for the 

latter alternative, we include a cluster every 750 years 

and a second cluster that ruptures only the southern 

two segments every 1,500 years. The sum of these two 

models results in rates of approximately 750 years for 

the north and 500 years (=1/750+1/1500)–1 for the 

southern two segments. 

References 

Toro, G.R. and Silva, W.J., 2001, Scenario 

earthquakes for Saint Louis, MO, and Memphis, 

TN, and seismic hazard maps for the central United 

States region including the effect of site condition: 

Technical report to U.S. Geological Survey, 

Reston, Virginia, under Contract 1434-HQ-97-GR02981, 

http://www.riskeng.com/PDF/Scen_CEUS_Rept.p 

df. 

Toro, G.R., 2002, Modification of the Toro et al. 

(1997) attenuation relations for large magnitudes 

and short distances: Risk Engineering, Inc. report, 

http://www.riskeng.com/PDF/atten_toro_extende 

d.pdf 

Toro, G.R., Abrahamson, N.A., and Schneider, J.F., 

1997, A model of strong ground motions from 

earthquakes in central and eastern North America— 

Best estimates and uncertainties: Seismological 

Research Letters, v. 68, p. 41–57. 
Appendix G. Parameters for Faults in the Intermountain West 

By Kathleen M. Haller and Russell L. Wheeler 

Fault sources in the Intermountain West, as defined in this appendix, are those that are located in the Western 

United States but not in the Pacific Coast States of Washington, Oregon, and California. Faults in those three states are 

discussed elsewhere in the documentation. The Intermountain West faults modeled in the National Seismic Hazard 

Maps include all Quaternary faults that have published geologic or paleoseismic investigations that, at a minimum, 

document slip rate, or sufficient data to calculate slip rate, and (or) rates of large-magnitude earthquakes resulting in 

permanent, geologically recognized surface deformation. In the Intermountain West, all faults with known Holocene 

(younger than 10 ka) surface faulting are included in this model, and many late Quaternary (younger than about 125–

150 ka) faults are represented as well. Thousands of older faults exist in this broad region, which has a long history of 

tectonic deformation. The nearly 250 faults that we modeled as sources in this region are shown in figure G-1.

Figure G-1. Map of fault sources in the Intermountain West showing sense of slip by color. 
Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-2

We updated input parameters for more than 10 percent of the fault sources in the Intermountain West (table G-1) 

based on a literature review that focused on critical data such as slip rate and recurrence intervals. Most of the changes in 

our model resulted from the comprehensive reevaluation of all published paleoseismic studies by the Utah Quaternary 

Fault Working Group (Lund, 2005). Figure G-2 graphically shows changes that improve characterization of mean 

vertical slip rate, which is documented in table G-1. Additional modifications (shown in tables G-1 and G-2) were made 

to maintain internal consistency in the input parameters. 

Figure G-2. Plot of comparison of assigned slip rates for Intermountain West faults grouped by State. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-3 

Table G-1. Updated Intermountain West fault parameters. 

[See http://gldims.cr.usgs.gov/webapps/cfusion/Sites/hazfaults_search/hf_search_main.cfm?hazmap=2008 for further documentation of source material. 

Updated 2008 2002 Fault name State References or comment parameter value value 

Hurricane fault zone (southern) Arizona vertical slip rate 0.081 0.1 Fenton and others (2001) 

Sevier/Toroweap fault zone Arizona vertical slip rate 0.11 0.16 Fenton and others (2001) (southern) 

Cuddy Mountain-Lick Creek Idaho length 30 52 Fault location updated based on improved mapping source fault 

Eastern Bear Lake fault Idaho slip rate 0.6 0.8 Lund (2005) based on McCalpin (2003) 

Lost River fault Idaho length (km) 141 159 Fault location updated based on improved mapping source 

Squaw Creek fault Idaho length (km) 48 59 Fault location updated based on improved mapping source 

Rush Peak fault Idaho length (km) 29 26 Fault location updated based on improved mapping source 

Canyon Ferry fault Montana vertical slip rate 0.13 0.1 Anderson and LaForge (2003) 

Hebgen Lake/Red Canyon fault Montana sources combined Lund (2006) 

Monte Cristo Valley fault zone Nevada horizontal slip rate 0.4 0.3 Bell and others (1999) 

vertical slip rate to 8.333E- Peavine Peak fault Nevada 0.1 Ramelli and others (2002) recurrence rate 4 

Warm Springs Valley fault zone Nevada horizontal slip rate 0.5 0.1 dePolo (2006) 

Calabacillas fault New Mexico source added 0.0069 NA1 McCalpin and Harrison (2000) 

East Paradise fault New Mexico source added 0.0096 NA1 Personius and Mahan (2000) 

Embudo fault New Mexico dip 60 90 

Hubbell Springs fault New Mexico vertical slip rate 0.089 0.07 Personius and Mahan (2003) 

La Bajada fault New Mexico vertical slip rate 0.078 0.07 Wong and others (1995) 

La Canada del Amagre fault zone New Mexico vertical slip rate 0.012 0.06 Wong and others (1995) 

Lobato Mesa fault zone New Mexico vertical slip rate 0.0054 0.05 Wong and others (1995) 

vertical slip rate to 5.74E­ Pajarito fault New Mexico 0.068 Gardner and others (2005) recurrence rate 05* 

San Francisco fault New Mexico vertical slip rate 0.063 0.07 Wong and others (1995) 

Socorro Canyon fault New Mexico source added 0.027 NA1 Phillips and others (2003) 

East Cache fault zone Utah vertical slip rate 0.2 0.22 Lund (2005) based on McCalpin (1994) 

Great Salt Lake fault zone Utah vertical slip rate 0.6 0.5 Lund (2005) based on Dinter and Pechmann (2000) (Antelope segment) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-4 

Table G-1. Updated Intermountain West fault parameters.—Continued 

Fault name State Updated 

parameter 

2008 

value 

2002 

value References or comment 

Great Salt Lake fault zone 

(Fremont Island segment) Utah vertical slip rate 0.6 0.5 Lund (2005) based on Dinter and Pechmann (2000) 

Great Salt Lake fault zone 

(Promontory segment) Utah vertical slip rate 0.6 0.5 Updated to be consistent with other two segments of the fault 

Hansel Valley fault Utah vertical slip rate 0.1 0.12 Lund (2005) based on McCalpin (1985) 

Hurricane fault zone (northern) Utah vertical slip rate 0.2 0.1 Lund (2005) based on Stenner and others (1999) 

Joes Valley fault zone Utah vertical slip rate to 

recurrence rate 

1.00 E04 0.2 Lund (2005) based on Foley and others (1986) 

Joes Valley fault zone west fault/ 

Joes Valley fault zone east Utah sources combined Lund (2005) 

fault 

Morgan fault Utah vertical slip rate 0.02 0.09 Lund (2005) based on Sullivan and others (1988) and 

Sullivan and Nelson (1992) 

fault extended to 

Oquirrh-Southern Oquirrh 

Mountain fault Utah included Southern 

Oquirrh Mountain 

63 km 

M7.17 

27 km 

M6.7 Olig and others (2001) 

fault 

North Promontory fault Utah vertical slip rate 0.2 0.53 Lund (2005) based on McCalpin and others (1992) 

Wasatch fault (Brigham City 

segment) Utah recurrence rate 7.69 E04 

8.03 E04 Lund (2005) 

Wasatch fault (Weber segment) Utah recurrence rate 7.14 E04 

5.60 E04 Lund (2005) 

Wasatch fault (Salt Lake City 

segment) Utah recurrence rate 7.69 E04 

7.41 E04 Lund (2005) 

Wasatch fault (Provo segment) Utah recurrence rate 4.17 E04 

4.37 E04 Lund (2005) 

West Cache fault (Clarkston 

segment) Utah source added 0.4 NA1 Lund (2005) based on Black and others (2000) 

West Cache fault (Wellsville 

segment) Utah vertical slip rate 0.1 0.17 Lund (2005) 

West Valley fault zone Utah vertical slip rate 0.4 0.45 Lund (2005) based on Keaton and others (1987) and Keaton 

and Currey (1989) 

Bear River fault zone Wyoming vertical slip rate 1.5 2 Lund (2005) based on West (1994) 

1 Fault source added in 2008 maps, value not applicable. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-5 

Table G-2. Updated fault names for Intermountain West faults. 

2008 Name 2002 Name State 

Peavine Peak fault North Peavine Mountain fault zone Nevada 

East Great Salt Lake fault zone, Antelope segment Great Salt Lake fault zone, Antelope section Utah 

East Great Salt Lake fault zone, Fremont Island segment Great Salt Lake fault zone, Fremont Island section Utah 

East Great Salt Lake fault zone, Promontory segment Great Salt Lake fault zone, Promontory section Utah 

Four new sources were added to the model including the Calabacillas, East Paradise, and Socorro Canyon faults in 

New Mexico and the Clarkston segment of the West Cache fault in Utah. All were the targets of paleoseismologic 

investigations not considered in the 2002 maps. The Calabacillas fault was added based on two trenches that exposed 

evidence of four surface ruptures at approximately 14 ka, 32 ka, 77 ka, and 151 ka resulting in about 1 meter of offset 

(McCalpin and Harrison, 2000). The East Paradise fault was added based on evidence for three surface ruptures resulting 

in a total surface offset of 2.75±1 meters of an eolian sand deposit 286±26 ka (Personius and Mahan, 2000). Similarily, 

trenching and geologic mapping of the Socorro Canyon fault indicates three earthquakes have occurred in the past 

122±18 ka (Phillips and others, 2003). We added the Clarkston segment of the West Cache fault in Utah based on Lund 

(2005). 

Although assigned slip rate is commonly used to characterize fault activity and hence its contribution to seismic 

hazard, the parameter that is actually used is annualized rate of earthquakes of a predefined magnitude. In the 

Intermountain West, few faults have been trenched in more than one location; furthermore, far fewer trenching studies 

constrain the timing of more than a couple of events. Therefore, it is rare that we can use recurrence-interval data based on 

dated events in a trench to improve characterization of faults in our model. However, we were able to update the Peavine 

Peak fault in Nevada, Pajarito fault in New Mexico, and Joes Valley fault in Utah to better reflect their rates of activity. 

Using rate to characterize the Peavine Peak fault is a particularly good choice because the fault, as expressed at the surface, 

is very short. Its short length suggests a magnitude of M6.36. The large amount of reported Holocene displacement 

(Ramelli and others, 2002) results in exceptionally frequent events, a frequency that is not supported by the paleoseismic 

record. Additionally, the Utah Quaternary Fault Working Group (Lund, 2005) also updated mean recurrence intervals for 

the Wasatch fault (fig. G-3) based on consensus reevaluation of the tens of trenching studies that have been conducted 

since the 1980s and recommended that we implement multisegment rupture scenerio for the Wasatch fault (further 

discussed in Appendix J). 

Finally, we have changed the default dip of normal fault in the Intermountain West to 50±10° (F1-3) as 

recommended by the Western States Seismic Policy Council (Lund, 2006). See Appendix J for further discussion of this 

decision. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-6 

Table G-3. Intermountain West fault parameters by State. 

[Refer to http://gldims.cr.usgs.gov/webapps/cfusion/Sites/hazfaults_search/hf_search_main.cfm?hazmap=2008 for further documentation of source material— 

M, characteristic magnitude; mm/yr, millimeters per year; °, degree; km, kilometers] 

Vertical or Gutenberg- Gutenberg­ horizontal Sense Width Length Characteristic Fault name Dip (°) M Richter Richter slip rate of slip (km) (km) rate 

a-value b-value (mm/yr) 

Arizona 

Algodones fault zone 

Aubrey fault zone 

Big Chino fault 

Dutchman Draw fault 

Hurricane fault zone (central) 

Hurricane fault zone (southern) 

Sevier/Toroweap fault zone 

(southern) 

Colorado 

0.15 

0.018 

0.083 

0.075 

0.2 

0.081 

0.11 

50 

50 

50 

50 

50 

50 

50 

NE 

W 

SW 

NW 

NW 

NW 

W 

normal 

normal 

normal 

normal 

normal 

normal 

normal 

20 

20 

20 

20 

20 

20 

20 

19 

65 

49 

16 

108 

100 

171 

6.57 

7.18 

7.04 

6.49 

7.44 

7.4 

7.5* 

2.74E-04 

1.35E-05 

7.59E-05 

1.55E-04 

1.02E-04 

4.39E-05 

1.7188557 

0.31276687 

0.9097004 

NA 

1.3467844 

0.9379256 

1.2597 

0.8 

0.8 

0.8 

NA 

0.8 

0.8 

0.8 

Cheraw fault 

Northern Sangre de Cristo fault 

Southern Sawatch fault 

Idaho 

0.15 

0.18 

0.062 

50 

50 

50 

NW 

W 

E 

normal 

normal 

normal 

17 

20 

20 

45 

185 

45 

7 

7.5* 

6.99 

1.15E-04 

6.19E-05 

2.14217 

1.5098404 

0.94294106 

0.95 

0.8 

0.8 

Beaverhead fault 

Big Flat-Jakes Creek fault 

Cuddy Mountain-Lick Creek 

fault 

Eastern Bear Lake fault 

Lemhi fault 

Lost River fault 

Rush Peak fault 

Squaw Creek fault 

Montana 

0.12 

0.04 

0.05 

0.6 

0.22 

0.15 

0.05 

0.1 

50 

50 

50 

50 

50 

45 

50 

50 

SW 

E 

NW 

W 

SW 

SW 

S 

E 

normal 

normal 

normal 

normal 

normal 

normal 

normal 

normal 

20 

20 

20 

20 

20 

21 

20 

20 

134 

31 

30 

81 

147 

141 

29 

48 

7* 

6.81 

6.79 

7.29 

7* 

7* 

6.78 

7.03 

5.13E-05 

6.67E-05 

3.85E-04 

6.69E-05 

9.43E-05 

1.7037585 

0.66017526 

1.0533264 

1.7621624 

2.0074117 

1.890967 

1.0435416 

0.99330914 

0.8 

0.8 

0.8 

0.8 

0.8 

0.8 

0.8 

0.8 

Blacktail fault 

Canyon Ferry fault 

Centennial fault 

Emigrant fault 

0.03 

0.13 

0.9 

0.25 

50 

50 

50 

50 

NE 

SW 

N 

NW 

normal 

normal 

normal 

normal 

20 

20 

20 

20 

40 

39 

64 

57 

6.94 

6.92 

7.17 

7.12 

3.17E-05 

1.43E-04 

6.90E-04 

2.03E-04 

0.5970158 

1.2292868 

2.0111513 

1.4244301 

0.8 

0.8 

0.8 

0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-7 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Georgia Gulch fault 

Hebgen-Red Canyon fault 

Helena Valley fault 

Jocko fault 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

0.031 

0.5 

0.01 

0.08 

Dip (°) 

50 W 

50 SW 

50 S 

50 NW 

Sense 

of slip 

normal 

normal 

normal 

normal 

Width 

(km) 

20 

20 

20 

20 

Length 

(km) 

14 

25 

20 

16 

M 

6.42 

7.3* 

6.6 

6.47 

Characteristic 

rate 

7.14E-05 

4.99E-05 

1.75E-05 

1.71E-04 

GutenbergRichter 

a-value 

NA 

1.1747674 

0.5579098 

NA 

GutenbergRichter 

b-value 

NA 

0.8 

0.8 

NA 

Madison fault 0.4 50 W normal 20 111 7.45 2.02E-04 1.6542257 0.8 

Mission fault 0.32 50 W normal 20 92 7.36 1.84E-04 1.5176541 0.8 

Red Canyon fault 

Red Rock Hills fault 

0.5 

0.17 

60 SW 

50 W 

normal 

normal 

17 

20 

22 

11 

6.6 

6.27 

7.44E-04 

4.89E-04 

2.18657 

NA 

0.8 

NA 

Red Rock fault 0.5 50 E normal 20 27 6.73 7.29E-04 2.0244016 0.8 

Sweetwater fault 0.04 50 NE normal 20 13 6.38 9.64E-05 NA NA 

Thompson Valley fault 

Nevada 

0.08 50 W normal 20 10 6.22 2.45E-05 NA NA 

Antelope Range-Kingsley 

Mountains fault zone 0.01 50 E normal 20 71 7.23 6.90E-06 -0.04907726 0.8 

Antelope Valley 0.8 50 E normal 20 41 6.95 8.46E-04 0.11249995 0.8 

Bare Mountain fault 0.008 50 E normal 20 19 6.57 1.47E-05 0.44757023 0.8 

Battle Mountain fault 0.1 50 W normal 20 26 6.72 1.47E-04 1.3179169 0.8 

Benton Spring fault, southern 

section 0.26 90 strike slip 15 85 7.32 9.33E-05 1.1789495 0.8 

Beowawe fault 0.1 50 W normal 20 48 7.03 9.37E-05 0.99032956 0.8 

Bettles Well-Petrified Springs 

fault 0.1 90 strike slip 15 71 7.23 4.07E-05 0.72174894 0.8 

Black Hills fault 0.1 50 SE normal 20 9 6.18 3.23E-04 NA1 NA 

Black Rock fault zone 0.19 50 W normal 20 80 7.29 1.20E-04 1.2578105 0.8 

Bloody Run Hills fault 0.01 50 W normal 20 27 6.74 1.44E-05 0.3311862 0.8 

Bonham Ranch fault zone 0.2 50 E normal 20 56 7.11 1.66E-04 1.3262955 0.8 

Buena Vista Valley fault zone 0.1 50 W normal 20 92 7.36 5.71E-05 1.0087095 0.8 

Buffalo Creek fault zone 0.1 50 W normal 20 28 6.77 1.36E-04 1.340194 0.8 

Buffalo Mountain fault 0.1 50 SE normal 20 18 6.54 1.91E-04 1.5277609 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-8 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Buffalo Valley fault zone 0.1 50 E normal 20 41 6.95 1.05E-04 1.1279789 0.8 

Butte Mountains fault zone 0.01 50 W normal 20 61 7.15 7.90E-06 0.04790682 0.8 

California Wash fault 0.28 50 W normal 20 35 6.87 3.32E-04 1.5380037 0.8 

Carico Lake Valley fault zone 0.1 50 E normal 20 42 6.96 1.04E-04 1.1336586 0.8 

Carson City fault 0.1 50 E normal 20 16 6.48 2.11E-04 

Carson Range fault 2 50 E normal 20 53 7.08 1.75E-03 2.3154082 0.8 

Carson Range-Kings Canyon 

faults 2 50 E normal 20 71 7.23 1.38E-03 2.2523534 0.8 

Clan Alpine fault zone 0.15 50 SE normal 20 35 6.87 1.78E-04 1.2685935 0.8 

Coaldale fault 1 0.1 90 strike slip 15 65 7.19 4.30E-05 0.8277135 0.8 

Coaldale fault 2 0.1 90 strike slip 15 17 6.51 1.18E-04 1.2846416 0.8 

Cortez Mountain fault zone 0.1 50 NW normal 20 67 7.2 7.23E-05 1.0636964 0.8 

Coyote Spring fault 0.01 50 W normal 20 15 6.45 2.19E-05 

Crescent Dunes fault 0.01 50 W normal 20 45 7 9.75E-06 0.15092339 0.8 

Desatoya Mountains fault zone 0.1 50 SE normal 20 47 7.02 9.57E-05 0.98844993 0.8 

Diamond Mountains fault 0.1 50 E normal 20 85 7.32 6.11E-05 0.99556833 0.8 

Diamond Valley fault 0.1 50 E normal 20 23 6.67 1.58E-04 1.2925441 0.8 

Dixie Valley fault zone 0.3 50 E normal 20 119 7* 7.73E-04 2.0502302 0.8 

-

Dry Lake fault 0.008 50 W normal 20 49 7.04 7.34E-06 0.104764714 0.8 

Dry Valley-Smoke Creek Ranch 

fault zone 0.1 50 E normal 20 50 7.05 9.12E-05 1.0006925 0.8 

Duck Flat fault 0.1 50 SW normal 20 16 6.49 2.05E-04 NA NA 

Dunn Glenn fault 0.1 50 W normal 20 16 6.48 2.10E-04 NA NA 

East Tahoe fault 0.3 50 W normal 20 26 6.7 3.79E-04 1.70588 0.8 

Eastern Bilk Creek Mountains 

fault zone 0.01 50 E normal 20 30 6.8 1.31E-05 0.055391836 0.8 

Eastern Edwards Creek Valley 

fault zone 0.1 50 NW normal 20 39 6.92 1.10E-04 1.1135823 0.8 

Eastern Granite Range fault 0.1 50 E normal 20 34 6.85 1.22E-04 1.0813034 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-9 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Eastern Independence Valley fault 

zone 0.1 50 W normal 20 46 7.01 9.57E-05 0.97741973 0.8 

Eastern Monitor Range fault zone 0.1 50 E normal 20 105 7.43 5.16E-05 1.039428 0.8 

Eastern Osgood Mountains fault 

zone 0.01 50 SE normal 20 33 6.84 1.24E-05 0.07651044 0.8 

Eastern Osgood Mountains 

piedmont fault 0.01 50 SE normal 20 30 6.79 1.33E-05 0.35366117 0.8 

Eastern Pine Forest Range fault 

zone 0.1 50 E normal 20 10 6.25 2.94E-04 NA NA 

Eastern Pyramid Lake fault 0.1 50 W normal 20 44 6.99 9.85E-05 1.1444507 0.8 

Eastern Tuscarora Mountains 

fault zone 0.01 50 E normal 20 52 7.07 8.81E-06 0.007714621 0.8 

Edna Mountain fault 0.1 50 SE normal 20 35 6.88 1.15E-04 1.0907553 0.8 

Eglington fault 0.1 50 SE normal 20 11 6.5 7.1E-05* NA NA 

Emigrant Peak fault zone 0.76 50 W normal 20 29 6.78 1.03E-03 2.2327015 0.8 

Eugene Mountains fault 0.1 50 W normal 20 10 6.24 3.00E-04 NA NA 

Fairview fault zone 0.1 50 E normal 20 34 7.2 3.70E-05 0.7732189 0.8 

Fox Range fault zone 0.1 50 W normal 20 35 6.86 1.21E-04 1.0893043 0.8 

Freds Mountain fault 0.1 50 E normal 20 29 6.78 1.36E-04 1.351704 0.8 

Frenchman Mountain fault 0.015 50 W normal 20 20 6.59 2.66E-05 0.727833 0.8 

Golden Gate fault 0.01 50 E normal 20 36 6.89 1.14E-05 0.09563966 0.8 

Granite Springs Valley fault zone 0.2 50 E normal 20 49 7.05 1.80E-04 1.2957662 0.8 

Grass Valley fault zone 0.1 50 W normal 20 54 7.09 8.56E-05 1.0170091 0.8 

Hiko fault zone 0.01 50 W normal 20 15 6.46 2.15E-05 NA NA 

Hoppin Peaks fault zone 0.1 50 E normal 20 103 7.41 5.40E-05 1.0377592 0.8 

Hot Springs fault zone 0.1 50 W normal 20 24 6.68 1.58E-04 1.3026237 0.8 

Huntoon Valley fault system 0.1 90 strike slip 15 38 6.92 6.40E-05 0.8796344 0.8 

Independence Valley fault zone 0.1 50 W normal 20 66 7.19 7.40E-05 1.0632656 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-10 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Indian Head fault 0.1 90 strike slip 15 15 6.45 1.29E-04 NA NA 

Indian Hill fault 0.1 50 E normal 20 8 6.13 3.53E-04 NA NA 

Ione Valley fault 0.1 50 W normal 20 79 7.28 6.50E-05 0.97885894 0.8 

Jackson Mountains fault zone 0.1 50 E normal 20 75 7.25 6.80E-05 0.96608203 0.8 

Jakes Valley fault zone 0.01 50 E normal 20 35 6.88 1.16E-05 0.092969574 0.8 

Jersey Valley fault zone 0.1 50 W normal 20 34 6.86 1.20E-04 1.0840122 0.8 

Kane Spring Wash fault 0.01 90 strike slip 15 43 6.97 6.00E-06 -0.09340974 0.8 

Kawich-Hot Creek Ranges fault 

zone 0.2 50 SE normal 20 121 7.49 9.61E-05 1.373548 0.8 

Kings Canyon fault zone 0.2 50 SE strike slip 20 18 6.52 3.97E-04 1.8220319 0.8 

Little Fish Lake Valley fault 0.1 50 W normal 20 43 6.98 1.00E-04 1.1416051 0.8 

Little Valley fault 0.2 50 E normal 20 18 6.54 3.84E-04 1.8298311 0.8 

Lone Mountain fault zone 0.13 50 W normal 20 41 6.95 1.37E-04 1.2428901 0.8 

Marys Mountain fault 0.001 50 E normal 20 20 6.58 1.81E-06 -0.4508271 0.8 

McGee Mountain fault zone 0.01 50 E normal 20 42 6.96 1.03E-05 0.13084666 0.8 

Middlegate fault zone 0.1 50 W normal 20 38 6.92 1.10E-04 1.1128118 0.8 

Montana Mountains/Desert 

Valley fault zone 0.1 50 W normal 20 102 7.41 5.37E-05 1.0355022 0.8 

Monte Cristo Valley fault zone 0.4 90 strike slip 15 29 6.78 3.17E-04 1.7190449 0.8 

Mount Irish Range fault 0.01 50 W normal 20 12 6.32 2.67E-05 NA NA 

Mount Rose fault zone 1.5 50 E normal 20 36 6.89 1.71E-03 2.2719285 0.8 

Nightingale Mountains fault 0.1 50 W normal 20 36 6.88 1.18E-04 1.0987121 0.8 

Northern Butte Valley fault 0.1 50 W normal 20 17 6.49 2.08E-04 NA NA 

Northern Huntington Valley fault 

zone 0.1 50 W normal 20 39 6.93 1.08E-04 1.1160657 0.8 

Northern Roberts Mountains fault 0.1 50 NW normal 20 23 6.65 1.63E-04 1.2830935 0.8 

Northern Simpson Park 

Mountains fault zone 0.1 50 N normal 20 13 6.37 2.46E-04 NA NA 

Paradise Range fault zone 0.1 50 W normal 20 43 6.97 1.02E-04 1.1375 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-11 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Peavine Peak fault zone 0.5 50 NE normal 20 13 6.36 8.33E-04 NA NA 

Penoyer fault 0.016 50 W normal 20 56 7.11 1.34E-05 0.23221329 0.8 

Petersen Mountain fault 0.1 50 E normal 20 26 6.72 1.47E-04 1.3177838 0.8 

Petersen Mountain fault 2 0.05 50 E normal 20 16 6.49 1.03E-05 NA NA 

Pleasant Valley fault zone 0.1 50 W normal 20 68 7.6* 1.85E-05 0.77481645 0.8 

Pyramid Lake fault zone 2 90 strike slip 15 77 7.27 7.71E-04 2.0423502 0.8 

Railroad Valley fault zone 0.07 50 W normal 20 159 7.5* 1.031487 0.8 

Rainbow Mountain fault zone 0.15 90 strike slip 15 72 7.23 6.18E-05 0.9029679 0.8 

Rattlesnake Flat fault 0.1 90 strike slip 15 15 6.46 1.27E-04 NA NA 

Ruby Mountains fault zone 0.28 50 W normal 20 53 7.08 2.45E-04 1.4626777 0.8 

Ruby Mountains fault zone 0.28 50 W normal 20 37 6.9 3.18E-04 1.553986 0.8 

Ruby Valley fault zone 0.1 50 E normal 20 81 7.3 6.23E-05 0.9819613 0.8 

San Emidio fault zone 0.2 50 W normal 20 34 6.86 2.38E-04 1.3822703 0.8 

Sand Springs Range fault 0.1 50 E normal 20 42 6.96 1.03E-04 1.1316223 0.8 

Schell Creek Range fault system 0.01 50 E normal 20 105 7.43 5.14E-06 0.038450907 0.8 

Selenite Range fault zone 0.1 50 W normal 20 18 6.53 1.96E-04 1.5275263 0.8 

Seven Troughs Range fault zone 0.1 50 E normal 20 39 6.93 1.08E-04 1.1189233 0.8 

Sheep Basin fault 0.044 50 W normal 20 22 6.65 7.14E-05 0.92446565 0.8 

Sheep Creek Range southeastern 

fault 0.1 50 SE normal 20 38 6.92 1.10E-04 1.1131995 0.8 

Shoshone Range fault zone 0.1 50 W normal 20 121 7.5* 4.67E-05 1.0706302 0.8 

Simpson Park Mountains fault 

zone 0.22 50 W normal 20 73 7.24 1.51E-04 1.3009341 0.8 

Singatse Range fault zone 0.1 50 E normal 20 34 6.85 1.22E-04 1.0814091 0.8 

Smith Valley fault 0.38 50 E normal 20 94 7.37 2.16E-04 1.5970038 0.8 

Southwest Reese River Valley 

fault 0.1 50 NE normal 20 80 7.29 6.35E-05 0.97973024 0.8 

Spanish Springs Peak fault 0.1 90 strike slip 15 5 6.0 1.97E-04 NA NA 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-12 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Spanish Springs Valley fault 0.1 50 E normal 20 21 6.62 1.72E-04 1.2713587 0.8 

Spruce Mountain Ridge fault 

zone 0.1 50 W normal 20 33 6.83 1.27E-04 1.0750724 0.8 

The Lava Beds fault 0.1 50 E normal 20 26 6.73 1.44E-04 1.3206738 0.8 

Toiyabe Range fault zone 0.22 50 E normal 20 127 7.5* 1.4322273 0.8 

Unnamed faults 0.1 90 strike slip 15 40 6.93 6.38E-05 0.88942795 0.8 

Warm Springs Valley fault zone 0.5 90 strike slip 15 38 6.92 3.20E-04 1.5781618 0.8 

Wassuk Range fault zone 0.55 50 E normal 20 119 7.49 2.61E-04 1.8082168 0.8 

West Gate fault 0.1 50 W normal 20 25 6.69 1.55E-04 1.3073386 0.8 

West Spring Mountains fault 0.045 50 W normal 20 53 7.08 3.90E-05 0.6648692 0.8 

Western Diamond Mountains 

fault zone 0.1 50 W normal 20 65 7.18 7.49E-05 1.0574684 0.8 

Western Granite Range fault 0.2 50 SW normal 20 28 6.76 2.77E-04 1.637748 0.8 

Western Humboldt Range fault 

zone 0.1 50 W normal 20 78 7.28 6.44E-05 0.97469764 0.8 

Western Smoke Creek Desert 

fault 2 0.1 50 E normal 20 19 6.57 1.85E-04 1.548334 0.8 

Western Toiyabe Range fault zone 0.2 50 NW normal 20 139 7.5* 1.4317641 0.8 

White River Valley fault zone 0.045 50 W normal 20 105 7.42 2.39E-05 0.6941244 0.8 

Faults in Excelsior Mountains 0.1 90 strike slip 15 27 6.74 8.33E-05 1.0934577 0.8 

New Mexico 

Alamogordo fault 0.11 50 W normal 20 121 7.5 5.11E-05 1.1098998 0.8 

Black Mesa fault zone 0.02 50 NW normal 20 18 6.54 3.81E-05 0.82740765 0.8 

Caballo fault 0.025 50 W normal 20 22 6.64 4.17E-05 0.67914515 0.8 

-

Calabacillas fault 0.0069 50 E normal 20 33 6.83 8.73E-06 0.086238175 0.8 

Cañones fault 0.02 50 W normal 20 31 6.81 2.56E-05 0.3580615 0.8 

County Dump fault 0.038 50 E normal 20 37 6.89 4.40E-05 0.68327254 0.8 

East Paradise fault zone 0.0096 50 W normal 20 13 6.38 2.33E-05 NA NA 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-13 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Embudo fault 0.09 90 strike slip 15 66 7.19 3.90E-05 0.7851453 0.8 

Gallina fault 0.02 50 E normal 20 39 6.93 2.17E-05 0.41997 0.8 

Hubbell Springs fault 0.089 50 W normal 20 45 7 8.72E-05 1.1024992 0.8 

Jemez-San Ysidro fault 0.02 50 E normal 20 54 7.09 1.70E-05 0.31491816 0.8 

La Bajada fault 0.078 50 W normal 20 42 6.96 8.10E-05 1.0260626 0.8 

La Canada del Amagre fault zone 0.012 50 E normal 20 17 6.5 2.44E-05 NA NA 

La Jencia fault 0.021 50 E normal 20 33 6.84 2.57E-05 0.3945969 0.8 

Lobato Mesa fault zone 0.0054 50 W normal 20 19 6.56 1.00E-05 0.27112764 0.8 

Nacimiento fault 0.02 50 E normal 20 83 7.3 1.27E-05 0.2915034 0.8 

Nambe fault 0.02 50 W normal 20 50 7.05 1.81E-05 0.29710352 0.8 

Organ Mountains fault 0.15 50 E normal 20 30 6.79 1.98E-04 1.5264946 0.8 

Pajarito fault NA 50 E normal 20 50 7.05 9.90E-05 1.0362936 0.8 

Picuris-Pecos fault 0.05 50 W normal 20 99 7.39 2.78E-05 0.7286884 0.8 

Pojoaque fault 0.02 50 W normal 20 48 7.03 1.87E-05 0.29133075 0.8 

Puye fault 0.03 50 E normal 20 20 6.59 5.31E-05 1.028595 0.8 

San Andres Mountains fault 0.1 50 E normal 20 130 7.5* 1.100531 0.8 

San Felipe fault zone 0.043 50 E normal 20 43 6.97 4.42E-05 0.7741354 0.8 

San Francisco fault 0.063 50 W normal 20 28 6.76 8.77E-05 1.1385194 0.8 

Sawyer Canyon fault 0.024 50 E normal 20 8 6.15 8.24E-05 NA NA 

Socorro Canyon fault zone 0.027 50 E normal 20 49 7.04 2.50E-05 0.42780202 0.8 

Southern Sangre de Cristo fault 0.13 50 W normal 20 104 7.42 6.83E-05 1.1506004 0.8 

Tijeras-Canoncito fault 0.09 90 strike slip 15 81 7.29 3.40E-05 0.708118 0.8 

Zia fault 0.038 50 E normal 20 33 6.84 4.68E-05 0.65372443 0.8 

Texas 

Acala fault 

Amargosa fault 

Arroyo Diablo fault 

0.088 

0.11 

0.013 

50 SW 

50 NE 

50 SW 

normal 

normal 

normal 

20 

20 

20 

7 

70 

14 

6.09 

7.22 

6.41 

3.27E-04 

7.77E-05 

3.03E-05 

NA 

0.9918686 

NA 

NA 

0.8 

NA 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-14 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Caballo fault 0.11 50 SW normal 20 42 6.97 1.12E-04 1.1767493 0.8 

Campo Grande fault 0.048 50 SW normal 20 45 7 4.67E-05 0.8312168 0.8 

East Baylor Mountain - Carizzo 

Mountain fault 0.008 50 SE normal 20 41 6.96 8.22E-06 0.03237028 0.8 

East Franklin Mountains fault 0.1 50 E normal 20 48 7.03 9.40E-05 0.99157643 0.8 

East Sierra Diablo fault 0.02 50 E normal 20 35 6.86 2.42E-05 0.3905596 0.8 

West Delaware Mountains fault 

zone 0.024 50 SW normal 20 25 6.7 3.65E-05 0.6902017 0.8 

West Eagle Mountains-Red Hills 

fault 0.013 50 SW normal 20 24 6.69 2.00E-05 0.4178935 0.8 

West Indio Mountains fault 0.044 50 SW normal 20 23 6.66 7.13E-05 0.9353471 0.8 

West Lobo Valley fault zone 0.034 50 E normal 20 61 7.15 2.69E-05 0.5796732 0.8 

Utah 

East Cache fault zone 0.2 50 W normal 20 83 7.31 1.23E-04 1.2883028 0.8 

Great Salt Lake fault zone, 

Antelope Island segment 0.6 50 W normal 20 39 6.93 6.52E-04 1.8982953 0.8 

Great Salt Lake fault zone, 

Fremont Island segment 0.6 50 W normal 20 32 6.83 7.46E-04 1.8456042 0.8 

Great Salt Lake fault zone, 

Promontory segment 0.6 50 W normal 20 54 7.09 5.11E-04 1.793224 0.8 

Hansel Valley fault 0.1 50 E normal 20 13 6.6 1.13E-04 1.3680598 0.8 

Hurricane fault zone (northern) 0.2 50 NW normal 20 47 7.02 1.89E-04 1.2834035 0.8 

Joes Valley fault zone NA 50 W normal 20 47 7 1.02E-04 1.4678782 0.8 

Morgan fault 0.02 50 W normal 20 17 6.52 3.93E-05 0.81770503 0.8 

North Promontory fault 0.2 50 W normal 20 27 6.73 2.92E-04 1.6267301 0.8 

Oquirrh fault zone 0.2 50 W normal 20 27 6.7 2.59E-04 1.54073 0.8 

Oquirrh-Southern Oquirrh 

Mountains fault zone 0.2 50 W normal 20 63 7.17 1.53E-04 1.3553717 0.8 

Paragonah fault 0.46 50 NW normal 20 27 6.75 6.47E-04 1.995324 0.8 

Sevier/Toroweap fault zone 

(northern) 0.36 50 W normal 20 87 7.33 2.18E-04 1.5575325 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-15 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Stansbury fault zone 0.4 50 W normal 20 54 7.09 3.43E-04 1.6193315 0.8 

Strawberry fault 0.1 50 W normal 20 39 6.92 1.11E-04 1.1174334 0.8 

Utah Lake faults 0.4 50 W normal 20 31 6.81 5.17E-04 1.6635933 0.8 

Wasatch fault (floating M7.4) 1.2 50 W normal 20 327 7.4 3.21964 0.8 

Wasatch fault, Brigham City 

segment 50 W normal 20 41 6.9 7.7E-4 0.6 2.29257 0.8 

6.7 7.7E-4 0.2 

7.1 7.7E-4 0.2 

Wasatch fault, Levan segment 50 W normal 20 32 6.8 2.37E-4 0.6 1.56260 0.8 

6.6 2.37E-4 0.2 

7.0. 2.37E-4 0.2 

Wasatch fault, Nephi segment 50 W normal 20 44 7.0 4E-4 0.6 2.20522 0.8 

6.8 4E-4 0.2 

7.2. 4E-4 0.2 

Wasatch fault, Provo segment 50 W normal 20 77 7.4 4.2E-4 0.6 2.03881 0.8 

7.2 4.2E-4 0.2 

7.6 4.2E-4 0.2 

Wasatch fault, Salt Lake City 50 W normal 20 48 7.0 7.7E-4 0.6 2.26023 0.8 

segment 7.2 7.7E-4 0.2 

6.8 7.7E-4 0.2 

Wasatch fault, Weber segment 50 W normal 20 63 7.2 7.1E-4 0.6 2.11524 0.8 

7.0 7.1E-4 0.2 

7.4. 7.1E-4 0.2 

West Cache fault, Clarkston 0.4 50 E normal 20 23 6.66 6.48E-04 1.8939321 0.8 

segment 

West Cache fault, Wellsville 0.1 50 NE normal 20 20 6.6 1.76E-04 1.559867 0.8 

segment 

West Valley fault zone 0.4 50 E normal 20 16 6.48 8.45E-04 
 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-16 

Table G-3. Intermountain West fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) M Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Wyoming 

Bear River fault zone 1.5 50 W normal 20 37 6.9 4.35E-04 1.6894047 0.8 

Eagle Bay fault 0.48 50 E normal 20 32 6.82 6.13E-04 1.748995 0.8 

East Mount Sheridan faults 1.4 50 E normal 20 22 6.64 2.32E-03 2.4247884 0.8 

Grand Valley fault 1.1 50 W normal 20 55 7.1 9.31E-04 2.0645933 0.8 

Greys River fault 0.62 50 W normal 20 50 7.05 5.64E-04 1.7916788 0.8 

Hoback fault 0.071 50 SW normal 20 19 6.56 1.33E-04 1.39176 0.8 

Rock Creek fault 1.7 50 W normal 20 41 6.95 1.79E-03 2.3599827 0.8 

Teton fault 1.3 50 E normal 20 62 7.16 9.96E-04 2.1593647 0.8 

Upper Yellowstone Valley faults 0.37 50 E normal 20 18 6.54 7.06E-04 2.0950741 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-17 

References 

Anderson, L.W., and LaForge, R., 2003, Seismotectonic study for Canyon Ferry Dam, Missouri River Basin 

Project, Montana: Bureau of Reclamation Seismotectonic Report 2003-1, 70 p. 

Bell, J.W., dePolo, C.M., Ramelli, A.R., Sarna-Wojcicki, A.M., Meyer, C.E., 1999, Surface faulting and 

paleoseismic history of the 1932 Cedar Mountain earthquake area, west-central Nevada, and implications for 

modern tectonics of the Walker Lane: Geological Society of America Bulletin, v.111, p. 791–807. 

Black, B.D., Giraud, R.E., and Mayes, B.H. , 2000, Paleoseismic investigation of the Clarkston, Junction Hills, 

and Wellsville faults, West Cache fault zone, Cache County, Utah: Utah Geological Survey Special Study 

98, 23 p. 

dePolo, C.M., 2006, Determination of fault slip rates, paleoearthquake history, and segmentation of the Warm 

Springs Valley fault system: Technical report to U.S. Geological Survey, Reston, Virginia, under Contract 

04HQGR0082, 35 p. 

Dinter, D.A., and Pechmann, J.C., 2000, Paleoseismology of the East Great Salt Lake fault: U.S. Geological 

Survey National Earthquake Hazards Reduction Program, Annual Summary, v. 42, USGS External Grant 

award no. 98HQGR1013, 6 p. Available at http://erp-web.er.usgs.gov/reports/annsum/vol42/ni/ 

ni_vol42.htm. 

Fenton, C.R., Webb, R.H., Pearthree, P.A., Cerling, T.E., and Poreda, R.J., 2001, Displacement rates on the 

Toroweap and Hurricane faults—Implications for Quaternary downcutting in the Grand Canyon, Arizona: 

Geology, v. 29, p. 1035–1038. 

Foley, L.L., Martin, R.A., Jr., and Sullivan, J.T., 1986, Seismotectonic study for Joes Valley, Scofield and 

Huntington North Dams, Emery County and Scofield Projects, Utah: Bureau of Reclamation 

Seismotectonic Report 86-7, 132 p., 3 pls. 

Gardner, J.N., Lewis, C.J., Lavine, A., Reneau, S.L., and Schultz, E., 2005, Evaluating seismic hazards at Los 

Alamos National Laboratory—Geology and paleoseismology of the Pajarito fault system, Rio Grande Rift, 

New Mexico: Los Alamos National Laboratory Report LA-UR-05-4662, 42 p. (36 MB Microsoft 

Powerpoint file). 

Keaton, J.R., and Currey, D.R., 1989, Earthquake hazard evaluation of the West Valley fault zone in the Salt 

Lake City urban area, Utah: Technical report to U.S. Geological Survey, Salt Lake City, under Contract 14­

08-001-G1397, 69 p. 

Keaton, J.R., Currey, D.R., and Olig, S.J., 1987, Paleoseismicity and earthquake hazards evaluation of the West 

Valley fault zone, Salt Lake urban area: Technical report to U.S. Geological Survey, under Contract 14-08­

0001-22048, April 1986 (Draft), 18 p. 

Lund, W.R., 2005, Consensus preferred recurrence-intervals and vertical slip-rate estimates—Review of Utah 

paleoseismic-trenching data by the Utah Quaternary Fault Parameters Working Group: Utah Geological 

Survey Bulletin 134, 114 p., http://ugspub.nr.utah.gov/publications/bulletins/B-134.pdf. 

Lund, W.R., ed., 2006, Basin and Range Province Earthquake Working Group seismic-hazard 

recommendations to the U.S. Geological Survey National Seismic Hazard Mapping Program: Utah 

Geological Survey Open-File Report 477, 23 p. 

McCalpin, J.P., 1985, Quaternary fault history and earthquake potential of the Hansel Valley area, north-central 

Utah: U.S. Geological Survey Final Technical Report, 37 p. 

McCalpin, J.P., 1994, Neotectonic deformation along the East Cache fault zone, Cache County, Utah: Utah 

Geological Survey Special Study 83, 37 p. 

McCalpin, J.P., 2003, Neotectonics of the Bear Lake Valley, Utah and Idaho; A preliminary assessment: Utah 

Geological Survey Miscellaneous Publication 03-4, 43 p. 

McCalpin, J.P., and Harrison, J.B.J., 2000, Paleoseismicity of Quaternary faults near Albuquerque, New 

Mexico: Final Technical Report to U.S. Geological Survey for contract 99HQGR0056, 46 p. 

McCalpin, J., Robison, R.M., and Garr, J.D., 1992, Neotectonics of the Hansel Valley-Pocatello Valley corridor, 

northern Utah and southern Idaho, in Gori, P.L., and Hays, W.W., eds., Assessment of regional earthquake 

hazards and risk along the Wasatch front, Utah: U.S. Geological Survey Professional Paper 1500, p. G1– 

G18. 

Olig, S.S., Gorton, A.E., Black, B.D., and Forman, S.L., 2001, Paleoseismology of the Mercur fault and 

segmentation of the Oquirrh-East Great Salt Lake fault zone, Utah: Technical report to U.S. Geological 

Survey, Reston, Virginia, under Contract 98HQGR1036, January 25, 2001, variously paginated. 

Personius, S.F., and Mahan, S.A., 2003, Paleoearthquakes and eolian-dominated fault sedimentation along the 

Hubbell Spring fault zone near Albuquerque, New Mexico: Bulletin of the Seismological Society of 

America, v. 93, no. 3, p. 1355–1369. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps G-18 

Personius, S.F., and Mahan, S.A., 2000, Paleoearthquake recurrence on the East Paradise fault zone, 

metropolitan Albuquerque, New Mexico: Bulletin of the Seismological Society of America, v. 90, no. 2, 

p. 357–369. 

Phillips, F.M., Ayarbe, J.P., Harrison, J.B.J., and Elmore, D., 2003, Dating rupture events on alluvial fault scarps 

using cosmogenic nuclides and scarp morphology: Earth and Planetary Science Letters, v. 215, p. 203–218. 

Ramelli, A.R., Bell, J.W., dePolo, C.M., and Yount, J.C., 1999, Large-magnitude, late Holocene earthquakes on 

the Genoa fault, west-central Nevada and eastern California: Bulletin of the Seismological Society of 

America, v. 89, p. 1458–1472. 

Ramelli, A.R., dePolo, C.M., and Bell, J.W., 2002, Paleoseismic studies of the Peavine Peak fault: Technical 

report to U.S. Geological Survey, Reston, Virginia, under Contract 01HQGR0167, 14 p. 

Stenner, H.D., Lund, W.R., Pearthree, P.A., and Everitt, B.L., 1999, Paleoseismic investigation of the Hurricane 

fault in northwestern Arizona and southwestern Utah: Arizona Geological Survey Open-File Report 99-8, 

137 p. 

Sullivan, J.T., and Nelson, A.R., 1992, Late Quaternary displacement on the Morgan fault, a back valley fault in 

the Wasatch Range of northeastern Utah, in Gori, P.L., and Hays, W.W., eds., Assessment of regional 

earthquake hazards and risk along the Wasatch front, Utah: U.S. Geological Survey Professional Paper 1500, 

p. I1–I19. 

Sullivan, J.T., Nelson, A.R., LaForge, R.C., Wood, C.K., and Hansen, R.A., 1988, Central Utah regional 

seismotectonic study for USBR dams in the Wasatch Mountains: Bureau of Reclamation Seismotectonic 

Report 88-5, 269 p. 

West, M.W., 1994, Paleoseismology of Utah, Volume 4—Seismotectonics of north-central Utah and 

southwestern Wyoming: Utah Geological Survey Special Study 82, 93 p., 5 pls. 

Wong, I., Kelson, K., Olig, S., Kolbe, T., Hemphill-Haley, M., Bott, J., Green, R., Kanakari, H., Sawyer, J., Silva, 

W., Stark, C., Haraden, C., Fenton, C., Unruh, J., Gardner, J., Reneau, S., and House, L., 1995, Seismic hazards 

evaluation of the Los Alamos National Laboratory: Technical report to Los Alamos National Laboratory, 

Las Alamos, New Mexico, February 24, 1995, 3 volumes, 12 pls., 16 appendixes 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix H. Parameters for Faults in the Pacific 

Northwest 

By Kathleen M. Haller and Russell L. Wheeler 

In the 2008 model, we made several subtle changes in the treatment of crustal faults in the Pacific Coast 

States of Oregon and Washington to integrate feedback from the Working Group on Pacific Northwest faults, 

Western Seismic Safety Policy Council (WSSPC), and the regional Pacific Northwest workshop. First, we 

included region of predominately normal faults in southeastern Oregon into a set of files, orwa_n.* to reduce 

the default dip to 50° (fig. H-1) as applied in adjacent regions to the east and southeast. We also allow for 

variable dip as discussed in Appendix J. These faults are modeled following the logic tree in figure 17. The 

other crustal faults in Oregon and Washington are modeled following the logic tree in figure 19, which does not 

carry dip uncertainty, and truncated Gutenberg-Richter and characteristic magnitude distributions are given 

equal weight, as in the 2002 model. This compressional-zone weight scheme has roughly the same effect on 

probabilistic ground motion as including dip uncertainty and a 2/3 char, 1/3 GR weight scheme that is used for 

the faults in the extensional region. 

Three new sources were added to the model including the Lake Creek–Boundary Creek and Boulder 

Creek faults and the Stonewall anticline feature. The Lake Creek–Boundary Creek fault is located near Port 

Angeles, Wash. Recent paleoseismic investigations of this fault suggest that two closely spaced late Holocene 

events were preceded by a period of quiescence up to 10 k.y. (Nelson and others, 2007), which complicates 

assigning mean slip rate. However, we assigned a mean slip rate of 0.43 mm/yr to this fault. The Boulder Creek 

fault is near the Canadian border near Bellingham, Wash. 

Figure H-1. Map of fault sources in the Pacific Northwest showing sense of slip by color. 
 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps H-2 

Paleoseismic investigations (Haugerud and others, 2005; Barnett and others, 2006, 2007; Siedlecki and 

Schermer, 2007) indicate 2.5 meters of slip has occurred over 7,600 years, which suggests slip rate of 

0.33 mm/yr. The fault is expressed as two short scarps. We assigned a fixed characteristic magnitude of M6.8 

based on reported average slip per event of 70 cm. Because of the short length of the fault and the initial work 

on this fault is ongoing, we do not currently carry the truncated Gutenburg-Richter branch for this source. The 

Stonewall anticline had not been considered in previous versions of the maps; we add it to this version based 

on Yeats and others (1998). 

Based on input from the Pacific Northwest workshop, we changed the single fault location for the South 

Whidbey Island fault to three subparallel faults that share the total 0.6 mm/yr slip rate used in prior models. The 

faults in the new fault representation are longer; thus, the characteristic magnitudes have increased 

approximately 0.2 magnitude units. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps H-3 

Table H-1. Pacific Northwest fault parameters by State. 

[Refer to http://gldims.cr.usgs.gov/webapps/cfusion/Sites/hazfaults_search/hf_search_main.cfm?hazmap=2008 for further documentation of source material— 

mm/yr, millimeters per year; °, degree; km, kilometers] 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) Magnitude Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Oregon 

Abert Rim fault 0.5 50 W normal 20 45 7 4.92E-04 1.8536639 0.8 

Alvin Canyon fault 6.4 90 strike slip 15 71 7.23 2.61E-03 2.529093 0.8 

Battle Rock fault zone 0.1 50 NE normal 20 45 7 9.73E-05 1.1503175 0.8 

Beaver Creek fault zone 0.2 50 SE normal 20 17 6.52 3.96E-04 1.8206571 0.8 

Bolton fault 0.013 60 SW reverse 17 9 6.19 3.28E-05 NA NA 

Cape Blanco anticline 1.4 45 S thrust 21 47 7.02 1.56E-03 2.20199 0.8 

Chemult graben fault system normal 

(east) 0.052 50 W 20 62 7.16 3.98E-05 0.76154273 0.8 

Chemult graben fault system normal 

(west) 0.44 50 E 20 68 7.21 3.13E-04 1.5856717 0.8 

Coquille anticline 0.24 60 SW reverse 17 29 6.78 2.54E-04 1.6225786 0.8 

Cottonwood Mountain fault 0.09 50 NE normal 20 42 6.97 9.16E-05 1.09056 0.8 

Daisy Bank fault 5.7 90 strike slip 15 81 7.3 2.08E-03 2.5063807 0.8 

Gales Creek fault zone 0.016 90 strike slip 15 27 6.75 1.31E-05 0.3024114 0.8 

Goose Lake 0.1 50 W normal 20 60 7.14 7.99E-05 1.0417969 0.8 

Grant Butte fault 0.11 50 NW normal 20 9 6.21 3.41E-04 NA NA 

Happy Camp fault 0.025 60 N reverse 17 20 6.58 3.55E-05 0.8424882 0.8 

Helvetia fault 0.014 60 NE reverse 17 14 6.4 2.56E-05 NA NA 

Juniper Mountain fault 0.01 50 N normal 20 18 6.53 1.94E-05 0.52264785 0.8 

Klamath graben fault system normal 

(east) 0.2 50 W 20 92 7.36 1.15E-04 1.3133024 0.8 

Klamath graben fault system normal 

(west) 0.16 50 E 20 51 7.06 1.42E-04 1.2051246 0.8 

Lacamas Lake fault 0.026 90 strike slip 15 24 6.67 2.44E-05 0.48052972 0.8 

Metolius fault zone 0.038 50 SW normal 20 92 7.36 2.18E-05 0.5904285 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps H-4 

Table H-1. Pacific Northwest fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) Magnitude Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Mount Angel fault 0.067 60 NE reverse 17 30 6.8 6.85E-05 0.77476245 0.8 

Mount Hood fault 0.16 50 NE normal 20 11 6.29 4.45E-04 NA NA 

Newberg fault 0.016 90 strike slip 15 34 6.85 1.14E-05 0.053293127 0.8 

Paulina Marsh fault 0.29 50 SW normal 20 10 6.26 8.41E-04 NA NA 

Pine Valley graben fault normal 

system, Brownlee section 0.008 50 SW 20 19 6.56 1.50E-05 0.445314 0.8 

Pine Valley graben fault normal 

system, Halfway-Posey 

Valley section 0.008 50 NE 20 38 6.91 8.96E-06 0.014196634 0.8 

Portland Hills fault 0.1 60 SW reverse 17 50 7.05 7.07E-05 0.8903394 0.8 

Sandy River fault zone 0.016 90 strike slip 15 17 6.5 1.89E-05 NA NA 

Santa Rosa fault system 0.13 50 W normal 20 171 7.5* 5.39E-05 1.3327227 0.8 

Sky Lakes fault zone 0.28 50 E normal 20 53 7.08 2.45E-04 1.4632595 0.8 

South Slough thrust and reverse 

faults 0.62 60 W reverse 17 11 6.29 1.33E-03 NA NA 

Southeast Newberry fault zone 0.51 50 SW normal 20 68 7.2 3.74E-04 1.7777597 0.8 

Steens fault zone 0.3 50 E normal 20 214 7.5* 1.24E-04 1.7935853 0.8 

Tule Springs Rim fault 0.1 50 W normal 20 37 6.9 1.12E-04 1.1019461 0.8 

Turner and Mill Creek faults 0.007 60 SE reverse 17 20 6.59 9.79E-06 0.29409804 0.8 

Waldport fault 0.14 60 E reverse 17 15 6.43 2.47E-04 NA NA 

Wallowa fault 0.14 50 NE normal 20 53 7.08 1.21E-04 1.1553462 0.8 

Warner Valley faults (east) 0.11 50 W normal 20 147 7.5 1.1963375 0.8 

Warner Valley faults (west) 0.11 50 E normal 20 44 6.99 1.08E-04 1.1843001 0.8 

Wecoma fault 8.5 90 strike slip 15 88 7.34 2.95E-03 2.7000494 0.8 

Whaleshead fault zone 2.55 90 strike slip 15 46 7.01 1.45E-03 2.1573264 0.8 

Winter Rim fault system 0.43 50 E normal 20 66 7.19 3.18E-04 1.6960521 0.8 

Yaquina faults 0.6 60 N reverse 17 8 6.14 1.62E-03 NA NA 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps H-5 

Table H-1. Pacific Northwest fault parameters by State.—Continued 

Fault name 

Vertical or 

horizontal 

slip rate 

(mm/yr) 

Dip (°) Sense 

of slip 

Width 

(km) 

Length 

(km) Magnitude Characteristic rate 

GutenbergRichter 

a-value 

GutenbergRichter 

b-value 

Washington 

Boulder Creek fault 0.33 60 reverse 17 11 6.8* 3.24E-04* 

Devils Mountain fault 0.15 60 N reverse 17 125 1.1531128 0.8 

Hite fault system 0.02 90 strike slip 15 88 7.34 6.92E-06 0.0706793 0.8 

Horse Haven Hills structure reverse 

(NW trend) 0.031 60 W 17 59 7.14 1.92E-05 0.4226207 0.8 

Lake Creek-Boundary Creek reverse 

fault 0.43 60 N 17 30 6.79 6.64E-04 1.8786485 0.8 

Mill Creek Thrust fault 0.038 60 S reverse 17 56 7.11 2.48E-05 0.5012743 0.8 

Rattlesnake-Wallula fault reverse 

system 0.043 60 SW 17 109 7.44 1.73E-05 0.5754388 0.8 

Saddle Mountain fault 0.052 60 S reverse 17 91 7.35 2.39E-05 0.6193971 0.8 

Seattle fault zone-middle 45 S thrust 21 64 7.2 1.11 0.8 

Seattle fault zone-northern 45 S thrust 21 71 7.2 2.00E-04 1.15 0.8 

Seattle fault zone-southern 45 S thrust 21 56 7.1 1.16 0.8 

Southern Whidbey Island fault- oblique 

middle 0.2 60 N 17 109 7.44 1.34E-04 1.24270 0.8 

Southern Whidbey Island fault oblique 

northern 0.2 60 N 17 105 7.42 1.40E-04 1.23295 0.8 

Southern Whidbey Island fault- oblique 

southern 0.2 60 N 17 105 7.42 1.40E-04 1.23519 0.8 

Strawberry Point fault 0.25 90 oblique 15 26 6.73 2.11E-04 1.4862921 0.8 

Stonewall anticline 60 reverse 17 30 6.8 1.6484004 0.8 

Utsalady Point fault 0.15 90 oblique 15 25 6.69 1.36E-04 1.2508161 0.8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps H-6 

References 

Barnett, E.A., Kelsey, H.M., Sherrod, B.L., Blakely, R.J., Hughes, J.F., Schermer, E.R., Haugerud, R.A., Weaver, 

C.S., and Siedlecki, E., 2006, Active faulting at the northeast margin of the greater Puget Lowland—A 

paleoseismic and magnetic-anomaly study of the Kendall Scarp, Whatcom County, northwest Washington: 

Eos, Transactions, American Geophysical Union, v. 87, Abstract S31A-0183. 

Barnett, E.A., Kelsey, H.M., Sherrod, B., Blakely, R.J., Hughes, J., Schermer, E.R., Haugerud, R.A., Weaver, C., 

Siedlecki, E.M., and Blakely, R.J., 2007, Active faulting at the northeast margin of the greater Puget 

Lowland; a trenching and wetland coring study of the Kendall Fault scarp, Whatcom County, northwest 

Washington: Geological Society of America Abstracts with Programs, v. 39, p. 61. 

Haugerud, R.A., Sherrod, B.L., Wells, R.E., Hyatt, T., 2005, Holocene displacement on the Boulder Creek Fault 

near Bellingham, WA and implications for kinematics of deformation of the Cascadia Forearc: Geological 

Society of America Abstracts with Programs, v. 37, p. 476. 

Nelson, A.R., Personius, S.F., Buck, J., Bradley, L-A., Wells, R.E., and Schermer, E.R., 2007, Field and 

laboratory data from an earthquake history study of scarps of the Lake Creek-Boundary Creek fault between 

the Elwha River and Siebert Creek, Clallam County, Washington: U.S. Geological Survey Scientific 

Investigations Map SIM-2961, 2 sheets. 

Siedlecki, E.M., and Schermer, E.R., 2007, Paleoseismology of the Boulder Creek fault, Kendall, WA: 

Geological Society of America Abstracts with Programs, v. 39, p. 26. 

Yeats, R.S., Kulm, L.D., Goldfinger, C., and McNeill, L.C., 1998, Stonewall anticline—an active fold on the 

Oregon continental shelf: Geological Society of America Bulletin, v. 110, p. 527–587. 
 

 

 

 

 

 

 

 

Appendix I. Parameters for Faults in California 

From Working Group on California Earthquake Probabilities report (Field and others, 2008; Wills 

and others, 2008) 

Table I-1. Rupture-model data for Type-A faults. Rupture names include the segments involved; see table 2 of Field and 

others (2008) for segment name definitions. “Ellsworth” and “Hanks and Bakun” represent Ellsworth (2003) B magnitudearea relationship and Hanks and Bakun (2002) magnitude-area relationships, respectively. The values under “Ellsworth-B 

Rate” and “Hanks and Bakun Rate” are for the moment-balanced models (using Deformation Model D2.1). 

Rupture name 

(segments involved) 

Elsinore fault 

Area 

(km2) 

Ellsworth 

mag 

Hanks and 

Bakun 

mag 

A-priori 

rate 

Ellsworth-B 

rate 

Hanks and 

Bakun 

rate 

W 674.8 7.03 6.84 7.14E–04 9.27E–04 1.37E–03 

GI 488.6 6.89 6.67 2.55E–03 1.19E–03 2.19E–03 

T 734.9 7.07 6.89 6.10E–04 1.24E–04 3.46E–04 

J 

CM 

1426.1 

517.3 

7.35 

6.91 

7.28 

6.69 

Unlikely 

5.71E–04 

3.85E–05 

1.04E–03 

2.48E–05 

2.11E–03 

W+GI 

GI+T 

1163.4 

1223.5 

7.27 

7.29 

7.16 

7.19 

Unlikely 

8.90E–04 

2.48E–05 

1.25E–04 

1.42E–04 

1.25E–04 

T+J 2161 7.53 7.52 Unknown 1.27E–04 1.26E–04 

J+CM 1943.3 7.49 7.45 Unknown 1.74E–04 2.92E–04 

W+GI+T 

GI+T+J 

1898.3 

2649.6 

7.48 

7.62 

7.44 

7.63 

Unlikely 

Unknown 

2.48E–05 

1.26E–04 

9.07E–05 

1.27E–04 

T+J+CM 2678.2 7.63 7.64 2.50E–04 2.83E–04 2.54E–04 

W+GI+T+J 

GI+T+J+CM 

3324.4 

3166.9 

7.72 

7.7 

7.77 

7.74 

Unlikely 

2.50E–04 

2.52E–05 

1.83E–04 

2.48E–05 

1.27E–04 

W+GI+T+J+CM 

Total 

3841.7 7.78 7.85 Unlikely 

5.84E–03 

2.49E–05 

4.43E–03 

2.52E–05 

7.37E–03 

Garlock fault 

GE 519.3 6.92 6.7 6.80E–04 3.61E–04 6.21E–04 

GC 1276.1 7.31 7.21 7.84E–05 9.26E–05 8.32E–05 

GW 1290.9 7.31 7.22 2.36E–04 2.19E–04 2.61E–04 

GE+GC 1795.4 7.45 7.41 7.84E–05 9.05E–05 8.32E–05 

GC+GW 2567.1 7.61 7.62 3.13E–04 5.99E–04 5.50E–04 

GE+GC+GW 3086.3 7.69 7.72 3.13E–04 5.83E–04 5.78E–04 

Total 1.70E–03 1.95E–03 2.18E–03 

San Jacinto fault 

SBV 725.7 7.06 6.88 2.31E–03 4.39E–04 4.42E–04 

SJV 686.7 7.04 6.85 2.43E–03 4.50E–04 4.49E–04 

A 

C 

CC 

1193.9 

786.1 

681.5 

7.28 

7.1 

7.03 

7.17 

6.93 

6.85 

Unlikely 

Unlikely 

8.89E–04 

8.83E–05 

8.87E–05 

4.50E–04 

8.82E–05 

8.98E–05 

4.48E–04 

B 403.6 6.81 6.59 4.82E–03 4.45E–04 4.43E–04 

SM 325.8 6.71 6.49 1.09E–03 1.50E–03 4.01E–03 
 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-2 

Table I-1. Rupture-model data for Type-A faults.—Continued 

Rupture name Area Ellsworth Hanks and A-priori Ellsworth-B Hanks and 

(segments involved) (km2) mag Bakun rate rate Bakun 

mag rate 

SBV+SJV 1412.4 7.35 7.27 1.32E–03 4.49E–04 4.41E–04 

SJV+A 1880.6 7.47 7.44 Unknown 4.41E–04 4.50E–04 

A+C 1980.1 7.5 7.47 3.15E–03 1.21E–03 1.16E–03 

A+CC 1875.4 7.47 7.43 Unlikely 8.82E–05 9.00E–05 

CC+B 1085.1 7.24 7.12 8.89E–04 4.50E–04 4.47E–04 

B+SM 729.4 7.06 6.89 1.09E–03 4.40E–04 4.43E–04 

SBV+SJV+A 2606.4 7.62 7.62 Unknown 4.47E–04 4.48E–04 

SJV+A+C 2666.8 7.63 7.64 Unknown 4.48E–04 4.51E–04 

SJV+A+CC 2562.2 7.61 7.61 Unlikely 8.91E–05 8.93E–05 

A+CC+B 2279.1 7.56 7.55 Unlikely 9.02E–05 8.95E–05 

CC+B+SM 1411 7.35 7.27 8.89E–04 4.48E–04 4.40E–04 

SBV+SJV+A+C 3392.5 7.73 7.78 1.05E–03 4.49E–04 4.41E–04 

SBV+SJV+A+CC 3287.9 7.72 7.76 Unlikely 8.94E–05 9.03E–05 

SJV+A+CC+B 2965.8 7.67 7.7 Unlikely 8.82E–05 8.89E–05 

A+CC+B+SM 2604.9 7.62 7.62 Unlikely 8.93E–05 8.96E–05 

SBV+SJV+A+CC+B 3691.5 7.77 7.83 Unlikely 8.80E–05 8.97E–05 

SJV+A+CC+B+SM 3291.6 7.72 7.76 Unlikely 8.94E–05 9.03E–05 

SBV+SJV+A+CC+B+SM 4017.3 7.8 7.88 Unlikely 8.90E–05 8.82E–05 

Total 1.99E–02 9.05E–03 1.15E–02 

Northern San Andreas fault 

SAO 1469.9 7.37 7.29 4.93E–04 1.16E–03 1.01E–03 

SAN 2044.4 7.51 7.48 2.09E–05 2.00E–05 1.99E–05 

SAP 1078.4 7.23 7.11 5.31E–04 1.22E–04 1.05E–05 

SAS 838.5 7.12 6.97 7.64E–04 2.09E–03 2.40E–03 

SAO+SAN 3514.3 7.75 7.8 1.07E–03 2.77E–03 2.99E–03 

SAN+SAP 3122.8 7.69 7.73 Unlikely 2.08E–06 2.11E–06 

SAP+SAS 1916.9 7.48 7.45 1.03E–03 2.19E–03 3.63E–03 

SAO+SAN+SAP 4592.7 7.86 7.95 8.21E–05 7.10E–05 4.91E–05 

SAN+SAP+SAS 3961.3 7.8 7.87 2.52E–05 2.32E–05 2.27E–05 

SAO+SAN+SAP+SAS 5431.1 7.93 8.05 2.84E–03 9.97E–04 3.09E–04 

Total 6.85E–03 9.45E–03 1.05E–02 

Southern San Andreas fault 

PK 78 6.09 5.87 3.46E–02 2.49E–02 5.26E–02 

CH 750.2 7.08 6.9 5.00E–05 5.21E–05 5.46E–05 

CC 891.2 7.15 7 3.00E–04 1.60E–04 5.74E–05 

BB 751 7.08 6.9 3.00E–04 5.68E–04 5.26E–04 

NM 556.5 6.95 6.73 2.00E–04 1.05E–04 1.44E–04 

SM 1279 7.31 7.21 5.00E–04 6.45E–04 6.78E–04 

NSB 451.9 6.86 6.64 7.00E–04 7.12E–04 6.64E–04 

SSB 555.5 6.94 6.73 5.00E–05 5.10E–05 5.17E–05 

BG 843 7.13 6.97 5.00E–04 1.88E–04 1.35E–05 

CO 693.4 7.04 6.86 2.50E–03 6.70E–03 1.21E–02 
 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-3 

Table I-1. Rupture-model data for Type-A faults.—Continued 

Rupture name Area Ellsworth Hanks and A-priori Ellsworth-B Hanks and 

(segments involved) (km2) mag Bakun rate rate Bakun 

mag rate 

PK+CH 828.2 7.12 6.96 1.60E–03 4.36E–03 7.01E–03 

CH+CC 1641.4 7.42 7.36 3.00E–04 2.39E–04 2.15E–04 

CC+BB 1642.2 7.42 7.36 Unknown 5.02E–06 5.07E–06 

BB+NM 1307.5 7.32 7.23 Unlikely 1.01E–06 1.01E–06 

NM+SM 1835.4 7.46 7.42 7.00E–04 4.95E–06 5.04E–06 

SM+NSB 1730.9 7.44 7.39 6.00E–04 8.79E–04 8.90E–04 

NSB+SSB 1007.4 7.2 7.07 8.00E–04 1.05E–03 1.22E–03 

SSB+BG 1398.5 7.35 7.26 9.00E–04 5.03E–06 4.95E–06 

BG+CO 1536.4 7.39 7.32 7.00E–04 2.83E–04 4.10E–04 

PK+CH+CC 1719.4 7.44 7.38 7.00E–04 4.26E–04 4.19E–04 

CH+CC+BB 2392.4 7.58 7.58 Unlikely 9.94E–07 9.93E–07 

CC+BB+NM 2198.7 7.54 7.53 Unlikely 1.00E–06 1.01E–06 

BB+NM+SM 2586.4 7.61 7.62 2.50E–04 1.88E–04 2.67E–04 

NM+SM+NSB 2287.4 7.56 7.55 1.00E–04 7.24E–05 6.69E–05 

SM+NSB+SSB 2286.4 7.56 7.55 4.00E–04 6.05E–04 7.55E–04 

NSB+SSB+BG 1850.4 7.47 7.43 4.00E–04 2.22E–04 3.05E–05 

SSB+BG+CO 2091.9 7.52 7.5 4.00E–04 2.23E–04 2.48E–04 

PK+CH+CC+BB 2470.4 7.59 7.59 4.00E–04 8.20E–04 8.34E–04 

CH+CC+BB+NM 2948.8 7.67 7.7 Unlikely 9.91E–07 9.99E–07 

CC+BB+NM+SM 3477.7 7.74 7.79 4.00E–04 1.95E–04 4.99E–06 

BB+NM+SM+NSB 3038.4 7.68 7.71 Unlikely 9.95E–07 1.00E–06 

NM+SM+NSB+SSB 2842.9 7.65 7.68 2.00E–04 1.04E–04 1.02E–04 

SM+NSB+SSB+BG 3129.4 7.7 7.73 3.00E–04 2.92E–04 1.97E–04 

NSB+SSB+BG+CO 2543.8 7.61 7.61 4.00E–04 2.23E–04 2.17E–04 

PK+CH+CC+BB+NM 3026.9 7.68 7.71 7.00E–04 1.54E–03 1.66E–03 

CH+CC+BB+NM+SM 4227.8 7.83 7.9 5.00E–04 4.16E–04 2.67E–04 

CC+BB+NM+SM+NSB 3929.6 7.79 7.86 1.00E–04 8.64E–05 5.55E–05 

BB+NM+SM+NSB+SSB 3593.9 7.76 7.81 5.00E–05 4.92E–05 5.42E–05 

NM+SM+NSB+SSB+BG 3685.9 7.77 7.83 1.00E–04 6.19E–05 3.29E–05 

SM+NSB+SSB+BG+CO 3822.8 7.78 7.85 4.00E–04 3.58E–04 4.16E–04 

PK+CH+CC+BB+NM+SM 4305.9 7.83 7.92 2.00E–03 1.04E–03 6.43E–04 

CH+CC+BB+NM+SM+NSB 4679.8 7.87 7.96 Unlikely 9.91E–07 9.89E–07 

CC+BB+NM+SM+NSB+SSB 4485.1 7.85 7.94 1.00E–04 9.04E–05 6.76E–05 

BB+NM+SM+NSB+SSB+BG 4436.9 7.85 7.93 Unlikely 1.01E–06 1.01E–06 

NM+SM+NSB+SSB+BG+CO 4379.2 7.84 7.93 1.00E–04 6.01E–05 3.90E–05 

PK+CH+CC+BB+NM+SM+NSB 4757.8 7.88 7.97 5.00E–04 4.21E–04 3.49E–04 

CH+CC+BB+NM+SM+NSB+SSB 5235.3 7.92 8.03 5.00E–05 5.00E–05 5.09E–05 

CC+BB+NM+SM+NSB+SSB+BG 5328.1 7.93 8.04 5.00E–05 4.44E–05 3.00E–05 

BB+NM+SM+NSB+SSB+BG+CO 5130.2 7.91 8.02 5.00E–05 4.50E–05 4.70E–05 

PK+CH+CC+BB+NM+SM+NSB+SS 5313.3 7.93 8.04 1.00E–04 1.00E–04 1.09E–04 

B 

CH+CC+BB+NM+SM+NSB+SSB+B 6078.2 7.98 8.12 Unlikely 9.95E–07 1.01E–06 

G 
 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-4 

Table I-1. Rupture-model data for Type-A faults.—Continued 

Rupture name Area Ellsworth Hanks and A-priori Ellsworth-B Hanks and 

(segments involved) (km2) mag Bakun rate rate Bakun 

mag rate 

CC+BB+NM+SM+NSB+SSB+BG+C 

O 

PK+CH+CC+BB+NM+SM+NSB+SS 

B+BG 

CH+CC+BB+NM+SM+NSB+SSB+B 

G+CO 

PK+CH+CC+BB+NM+SM+NSB+SS 

B+BG+CO 

Total 

Hayward–Rogers Creek fault 

RC 734.5 7.07 6.89 4.36E–03 2.69E–03 5.21E–03 

HN 250.7 6.6 6.38 3.48E–03 2.73E–03 4.27E–03 

HS 377.7 6.78 6.56 3.72E–03 2.86E–03 4.59E–03 

RC+HN 985.2 7.19 7.06 5.22E–04 4.67E–04 5.68E–04 

HN+HS 628.3 7 6.8 2.64E–03 1.43E–03 3.97E–03 

RC+HN+HS 1362.8 7.33 7.25 3.09E–04 2.75E–04 3.62E–04 

Total 1.50E–02 1.05E–02 1.90E–02 

Calaveras fault 

CN 470.2 6.87 6.65 1.03E–03 1.29E–03 2.31E–03 

CC 155.5 6.39 6.17 7.66E–03 6.82E–03 1.45E–02 

CS 42.5 5.83 5.61 1.05E–02 1.98E–02 4.25E–02 

CN+CC 625.7 7 6.8 1.29E–04 1.34E–04 1.58E–04 

CC+CS 198 6.5 6.28 2.60E–03 3.28E–03 6.32E–03 

CN+CC+CS 668.2 7.02 6.84 9.07E–04 1.25E–03 2.85E–03 

Total 2.28E–02 3.26E–02 6.86E–02 

6021.5 7.98 8.11 1.00E–05 9.66E–06 9.24E–06 

6156.3 7.99 8.12 5.00E–05 4.65E–05 4.09E–05 

6771.6 8.03 8.18 Unlikely 1.01E–06 9.93E–07 

6849.7 8.04 8.18 1.00E–04 8.29E–05 6.59E–05 

5.42E–02 4.88E–02 8.37E–02 

Table I-2. Significant changes to California Type-B fault models. Following changes represent all updated slip rates and 

changes in length, width, and dip of the fault of more than 10 percent. 

[mm/yr, millimeters per year; km2, square kilometers] 

Fault name Updated parameter 2008 

value 

2002 

value 

Anacapa-Dume length 51 75 

width 21.9 28 

Blackwater slip rate 0.5 0.6 

Burnt Mtn dip -67 90 

width 17.3 13 

Calico-Hidalgo length 117 95 

slip rate 1.8 0.6 

Casmalia (Orcutt Frontal fault) slip rate 0.2 0.25 

Channel Island Thrust dip 20 17 

width 21.3 34 

Chino-Central Ave length 24 28 

width 14.8 17 
 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-5 

Table I-2. Significant changes to California Type-B fault models.—Continued 

2008 2002 Fault name	 Updated parameter value value 

Clamshell-Sawpit dip 50 45 

Cleghorn width 15.5 13 

Coronado Bank width 8.6 13 

Cucamonga dip -45 45 

width 11 18 

Death Valley-graben dip -60 60 

length 76 54 

Death Valley-south length 42 62 

Deep Springs dip -60 60 

Earthquake Valley width 18.8 15 

Eureka Peak width 15 13 

Fish Slough dip -60 60 

Gravel Hills-Harper Lake width 11.4 13 

Great Valley 13 dip -15 15 

top of rupture 9.1 7 

width 23.6 10 

Great Valley 14	 dip -22 15 

top of rupture 8.1 7 

width 38.4 10 

Great Valley 3	 dip 20 15 

slip rate 1.2 1.5 

top of rupture 9 7 

width 14.6 10 

Great Valley 5	 dip 90 15 

Length 32 28 

slip rate 1 1.5 

top of rupture 10 7 

Hat Creek-McArthur-Mayfield dip -60 60 

Helendale-S. Lockhart length 114 97 

Hollywood width 18.4 14 

Holser dip 58 65 

width 21.9 14 

Hosgri dip -80 90 

width 6.9 12 

Independence dip 64 60 

length 54 49 

Johnson Valley N width 15.9 13 

Landers length 95 83 

width 15.1 13 

Lenwood-Lockhart-Old Woman Springs slip rate 0.9 0.6 

Malibu Coast dip 74 75 

width 17.3 13 

Mission Ridge-Arroyo Parida-Santa Ana dip 70 60 

width 8.1 15 

Newport-Inglewood width 15.1 13 

Newport-Inglewood offshore width 10.2 13 
 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-6 

Table I-2. Significant changes to California Type-B fault models.—Continued 

2008 2002 Fault name	 Updated parameter value value 

North Channel Slope dip -26 26 

length 51 68 

slip rate 1 2 

top of rupture 1.1 10 

width 7.8 23 

North Frontal fault zone-eastern dip 41 45 

width 25.3 18 

North Frontal fault zone-western dip 49 45 

width 20.8 18 

Northridge dip 35 42 

top of rupture 7.4 5 

width 16.4 22 

Oakridge Mid Channel Montalvo-Oak	 dip 16 28 

length 30.2551 36.5286 

slip rate 3 1 

top of rupture 0.4 5 

width 44.6 11 

Owens Valley length 86 121 

Pinto Mtn width 15.5 13 

Pisgah-Bullion Mtn-Mesqite Lk slip rate 0.8 0.6 

Pleito Thrust dip -46 45 

width 18.9 16 

Raymond dip -79 75 

width 15.9 13 

Red Mountain dip 56 60 

length 101 39 

width 17 15 

Rose Canyon width 7.7 13 

S. Sierra Nevada length 113 76 

San Cayetano dip -42 60 

width 23.9 15 

San Gabriel dip -61 90 

width 16.8 13 

San Joaquin Hills Thrust dip -23 23 

width 26.6 15 

San Jose dip 74 75 

width 16.4 13 

Santa Cruz Island length 69 50 

Santa Monica dip -50 75 

width 15.1 13 

Santa Rosa Island width 8.7 13 

Santa Susana dip -53 55 

length 43 27 

width 13.3 16 

Santa Ynez-east segment dip -70 80 

Santa Ynez-west segment dip -70 80 

width 9.8 13 

Sierra Madre dip 53 45 
 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-7 

Table I-2. Significant changes to California Type-B fault models.—Continued 

Fault name Updated parameter 2008 

value 

2002 

value 

Simi-Santa Rosa dip -60 60 

width 12.8 15 

Tank Canyon dip -53 60 

width 10.4 15 

Upper Elysian Park width 15.7 13 

Ventura-Pitas Point dip 64 75 

width 15.6 13 

Verdugo dip 55 45 

White Wolf dip 75 60 

width 15.1 21 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-8 

Table I-3. Type-B Faults and Connected-B Faults. “Ellsworth-B” and “Hanks and Bakun” represent Ellsworth (2003) B magnitude-area relationship and Hanks and 

Bakun (2002) magnitude-area relationships, respectively. 

Name Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Anacapa-Dume, alt 1 7.2 7.1 3 1115.8 50.9 9.038E+16 F2.1 

Anacapa-Dume, alt 2 7.2 7.1 3 1006.2 64.7 8.15E+16 F2.2 

Bartlett Springs 7.3 7.2 6 1305.2 174 2.114E+17 F2.1, F2.2 

Battle Creek 6.7 6.5 0.5 330.6 29 4.463E+15 F2.1, F2.2 

Big Lagoon-Bald Mtn 7.5 7.5 0.5 2041.9 90.1 2.757E+16 F2.1, F2.2 

Birch Creek 6.6 6.4 0.7 262.8 15.5 4.967E+15 F2.1, F2.2 

Blackwater 7.1 6.9 0.5 720 59.5 9.72E+15 F2.1, F2.2 

Burnt Mtn 6.8 6.5 0.6 364.7 21.1 5.908E+15 F2.1, F2.2 

Calico-Hidalgo 7.4 7.4 1.8 1624.3 116.9 7.894E+16 F2.1, F2.2 

Casmalia (Orcutt Frontal) 6.7 6.5 0.25 300.7 29 2.03E+15 F2.1, F2.2 

Cedar Mtn-Mahogany Mtn 7.1 7 1 852.9 77.8 2.303E+16 F2.1, F2.2 

Channel Islands Thrust 7.3 7.2 1.5 1263 59.2 5.115E+16 F2.1, F2.2 

Chino, alt 1 6.7 6.4 1 285.9 24.3 7.719E+15 F2.1 

Chino, alt 2 6.8 6.6 1 424 28.7 1.145E+16 F2.2 

Clamshell-Sawpit 6.7 6.4 0.5 293.3 16 3.959E+15 F2.1, F2.2 

Cleghorn 6.8 6.6 3 391.9 25.3 3.174E+16 F2.1, F2.2 

Collayomi 6.7 6.4 0.6 284.9 28.5 4.615E+15 F2.1, F2.2 

Coronado Bank 7.4 7.3 3 1602.2 186.3 1.298E+17 F2.1, F2.2 

Cucamonga 6.7 6.5 5 308.8 28 4.169E+16 F2.1, F2.2 

Death Valley (Black Mtns Frontal) 7.3 7.1 4 1141.5 76 1.233E+17 F2.1, F2.2 

Death Valley (No of Cucamongo) 7.2 7.1 5 998.3 76.8 1.348E+17 F2.1, F2.2 

Death Valley (No) 7.3 7.3 5 1385 106.5 1.87E+17 F2.1, F2.2 

Death Valley (So) 6.9 6.7 4 544.6 41.9 5.881E+16 F2.1, F2.2 

Deep Springs 6.8 6.6 0.8 429.9 25.3 9.285E+15 F2.1, F2.2 

Earthquake Valley 6.8 6.6 2 382.8 20.4 2.067E+16 F2.1, F2.2 

Elmore Ranch 6.7 6.5 1 330.5 29 8.924E+15 F2.1, F2.2 

Elysian Park (Upper) 6.7 6.5 1.3 315.7 20.2 1.108E+16 F2.1, F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-9 

Table I-3. Type-B Faults and Connected-B Faults.—Continued 

Name Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Eureka Peak 6.7 6.4 0.6 282.7 18.8 4.58E+15 F2.1, F2.2 

Fickle Hill 7.1 6.9 0.6 728 32.1 1.179E+16 F2.1, F2.2 

Fish Slough 6.8 6.6 0.2 440.7 26 2.38E+15 F2.1, F2.2 

Gillem-Big Crack 6.8 6.6 1 412.8 32.5 1.115E+16 F2.1, F2.2 

Gravel Hills-Harper Lk 7.1 6.9 0.7 742 65.1 1.402E+16 F2.1, F2.2 

Great Valley 1 6.8 6.6 0.1 438.8 43.7 1.185E+15 F2.1, F2.2 

Great Valley 10 6.5 6.3 1.5 216.6 21.6 8.773E+15 F2.1, F2.2 

Great Valley 11 6.6 6.4 1.5 245.8 24.5 9.954E+15 F2.1, F2.2 

Great Valley 12 6.4 6.2 1.5 175.2 17.4 7.096E+15 F2.1, F2.2 

Great Valley 13 (Coalinga) 7.1 6.9 1.5 743.7 31.6 3.012E+16 F2.1, F2.2 

Great Valley 14 (Kettleman Hills) 7.2 7 1.5 922.3 24 3.735E+16 F2.1, F2.2 

Great Valley 2 6.5 6.3 0.1 219.8 21.9 5.935E+14 F2.1, F2.2 

Great Valley 3, Mysterious Ridge 7.1 6.9 1.25 751.5 51.4 2.536E+16 F2.1, F2.2 

Great Valley 4a, Trout Creek 6.6 6.4 1.25 280.3 19.2 9.459E+15 F2.1, F2.2 

Great Valley 4b, Gordon Valley 6.8 6.6 1.25 416.1 28.5 1.404E+16 F2.1, F2.2 

Great Valley 5, Pittsburg Kirby Hills 6.7 6.5 1 319 31.9 8.613E+15 F2.1, F2.2 

Great Valley 7 6.9 6.6 1.5 447.8 44.6 1.814E+16 F2.1, F2.2 

Great Valley 8 6.8 6.6 1.5 409.7 40.8 1.659E+16 F2.1, F2.2 

Great Valley 9 6.8 6.6 1.5 391.5 39 1.586E+16 F2.1, F2.2 

Hartley Springs 6.8 6.6 0.5 418.6 24.7 5.65E+15 F2.1, F2.2 

Hat Creek-McArthur-Mayfield 7.2 7.1 1.5 1071.5 96.7 4.34E+16 F2.1, F2.2 

Helendale-So Lockhart 7.4 7.3 0.6 1459.2 114 2.364E+16 F2.1, F2.2 

Hilton Creek 6.9 6.7 2.5 497.4 29.3 3.357E+16 F2.1, F2.2 

Hollywood 6.7 6.5 1 309.9 16.8 8.366E+15 F2.1, F2.2 

Holser, alt 1 6.8 6.6 0.4 430.1 19.6 4.645E+15 F2.1 

Honey Lake 7 6.8 2.5 631.8 57.4 4.264E+16 F2.1, F2.2 

Hosgri 7.3 7.2 2.5 1182.2 171.2 7.98E+16 F2.1, F2.2 
 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-10 

Table I-3. Type-B Faults and Connected-B Faults.—Continued 

Name 

Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Hunter Mountain-Saline Valley 7.2 7 2.5 897.2 72.4 6.056E+16 F2.1, F2.2 

Hunting Creek-Berryessa 7.1 6.9 6 715.8 59.6 1.16E+17 F2.1, F2.2 

Imperial 7 6.8 20 607.2 45.8 3.279E+17 F2.1, F2.2 

Independence 7.2 7.1 0.2 1028.8 54 5.556E+15 F2.1, F2.2 

Johnson Valley (No) 6.9 6.7 0.6 559.8 35.2 9.068E+15 F2.1, F2.2 

Laguna Salada 7.3 7.2 3.5 1322.9 99.5 1.25E+17 F2.1, F2.2 

Landers 7.4 7.3 0.6 1427.2 94.5 2.312E+16 F2.1, F2.2 

Lenwood-Lockhart-Old Woman 

Springs 7.5 7.4 0.9 1915.8 145.1 4.655E+16 F2.1, F2.2 

Likely 7 6.9 0.3 703.7 64 5.7E+15 F2.1, F2.2 

Lions Head 6.8 6.6 0.02 428.2 41.4 2.312E+14 F2.1, F2.2 

Little Lake 6.9 6.7 0.7 516.1 39.7 9.755E+15 F2.1, F2.2 

Little Salmon (Offshore) 7.3 7.2 1 1183.3 45.5 3.195E+16 F2.1, F2.2 

Little Salmon (Onshore) 7.1 7 5 890.7 34.3 1.202E+17 F2.1, F2.2 

Los Alamos-West Baseline 6.9 6.7 0.7 555.4 27.8 1.05E+16 F2.1, F2.2 

Los Osos 7 6.8 0.5 627.9 44.4 8.477E+15 F2.1, F2.2 

Maacama-Garberville 7.4 7.3 9 1590.6 220.9 3.865E+17 F2.1, F2.2 

Mad River 7.2 7 0.7 943.2 41.6 1.783E+16 F2.1, F2.2 

Malibu Coast, alt 1 6.7 6.5 0.3 305.1 37.8 2.471E+15 F2.1 

Malibu Coast, alt 2 7 6.8 0.3 652.4 37.8 5.285E+15 F2.2 

McKinleyville 7.2 7.1 0.6 1073 47.3 1.738E+16 F2.1, F2.2 

Mission Ridge-Arroyo Parida-Santa 

Ana 6.9 6.7 0.4 556.7 68.8 6.013E+15 F2.1, F2.2 

Mono Lake 6.8 6.6 2.5 436.1 25.7 2.944E+16 F2.1, F2.2 

Monte Vista-Shannon 6.5 6.3 0.4 223.2 45.1 2.411E+15 F2.1, F2.2 

Monterey Bay-Tularcitos 7.3 7.2 0.5 1168.2 83.4 1.577E+16 F2.1, F2.2 

Mount Diablo Thrust 6.7 6.5 2 325.1 25 1.756E+16 F2.1, F2.2 

Newport-Inglewood (Offshore) 7 6.8 1.5 677.5 66.4 2.744E+16 F2.1, F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-11 

Table I-3. Type-B Faults and Connected-B Faults.—Continued 

Name Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Newport-Inglewood, alt 1 7.2 7.1 1 980.5 65.3 2.647E+16 F2.1 

Newport-Inglewood, alt 2 7.2 7.1 1 991.9 65.7 2.678E+16 F2.2 

North Channel 6.8 6.6 1 392.8 50.6 1.061E+16 F2.2 

North Frontal (East) 7 6.8 0.5 678 26.8 9.153E+15 F2.1, F2.2 

North Frontal (West) 7.2 7.1 1 1043 50.1 2.816E+16 F2.1, F2.2 

North Tahoe 6.7 6.5 0.43 332.1 19.6 3.856E+15 F2.1, F2.2 

Northridge 6.9 6.7 1.5 546.4 33.3 2.213E+16 F2.1, F2.2 

Oak Ridge (Offshore) 7 6.7 3 565.4 37.9 4.58E+16 F2.2 

Oak Ridge (Onshore) 7.2 7.1 4 1001.4 49.3 1.082E+17 F2.1, F2.2 

Ortigalita 7.1 6.9 1 771.5 70.1 2.083E+16 F2.1, F2.2 

Owens Valley 7.3 7.2 1.5 1156.9 85.7 4.686E+16 F2.1, F2.2 

Owl Lake 6.7 6.5 2 302.4 25.2 1.633E+16 F2.1, F2.2 

Palos Verdes 7.3 7.2 3 1347.9 99.1 1.092E+17 F2.1, F2.2 

Panamint Valley 7.4 7.3 2.5 1424.5 109.6 9.615E+16 F2.1, F2.2 

Pinto Mtn 7.3 7.1 2.5 1147.8 74.1 7.748E+16 F2.1, F2.2 

Pisgah-Bullion Mtn-Mesquite Lk 7.3 7.2 0.8 1158.8 88.5 2.503E+16 F2.1, F2.2 

Pitas Point (Lower)-Montalvo 7.3 7.2 2.5 1349.1 30.2 9.107E+16 F2.1 

Pitas Point (Lower, West) 7.3 7.1 2.5 1127.2 34.7 7.608E+16 F2.1 

Pitas Point (Upper) 6.9 6.6 1 449 34.9 1.212E+16 F2.2 

Pleito 7.1 7 2 823.8 43.6 4.449E+16 F2.1, F2.2 

Point Reyes 6.9 6.7 0.3 557.2 47.4 4.513E+15 F2.1, F2.2 

Puente Hills 7.1 7 0.7 835.7 44.1 1.579E+16 F2.1 

Puente Hills (Coyote Hills) 6.9 6.6 0.7 467.4 17.4 8.834E+15 F2.2 

Puente Hills (LA) 7 6.8 0.7 622 21.9 1.176E+16 F2.2 

Puente Hills (Santa Fe Springs) 6.7 6.4 0.7 288 11.4 5.443E+15 F2.2 

Quien Sabe 6.6 6.3 1 228.5 22.8 6.168E+15 F2.1, F2.2 

Raymond 6.8 6.5 1.5 357.2 22.5 1.447E+16 F2.1, F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-12 

Table I-3. Type-B Faults and Connected-B Faults.—Continued 

Name Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Red Mountain 7.4 7.4 2 1709.6 100.5 9.232E+16 F2.1, F2.2 

Rinconada 7.5 7.4 1 1907.7 190.8 5.151E+16 F2.1, F2.2 

Robinson Creek 6.7 6.4 0.5 283 16.7 3.821E+15 F2.1, F2.2 

Rose Canyon 6.9 6.7 1.5 538.1 69.9 2.179E+16 F2.1, F2.2 

Round Valley 7.1 6.9 1 734.7 43.3 1.984E+16 F2.1, F2.2 

San Andreas (Creeping Segment) 6.7 6.7 34 131.6 121.8 3.859E+16 F2.1, F2.2 

San Cayetano 7.2 7.1 6 1005 42 1.628E+17 F2.1, F2.2 

San Gabriel 7.3 7.2 1 1198.7 71.3 3.236E+16 F2.1, F2.2 

San Joaquin Hills 7.1 6.9 0.5 730.1 27.4 9.856E+15 F2.1, F2.2 

San Jose 6.7 6.5 0.5 322.8 19.6 4.357E+15 F2.1, F2.2 

San Juan 7.1 7 1 880.3 67.7 2.377E+16 F2.1, F2.2 

San Luis Range (So Margin) 7.2 7 0.2 901.6 63.8 4.869E+15 F2.1, F2.2 

Santa Cruz Island 7.2 7 1 919 69.1 2.481E+16 F2.1, F2.2 

Santa Monica, alt 1 6.6 6.4 1 267.4 14.4 7.22E+15 F2.1 

Santa Monica, alt 2 6.8 6.6 1 423.6 28 1.144E+16 F2.2 

Santa Rosa Island 6.9 6.7 1 500.5 57.5 1.351E+16 F2.1, F2.2 

Santa Susana, alt 1 6.9 6.7 5 540.7 27.2 7.299E+16 F2.1 

Santa Ynez (East) 7.2 7.1 2 967.5 68.4 5.224E+16 F2.1, F2.2 

Santa Ynez (West) 7 6.8 2 660.5 67.5 3.567E+16 F2.1, F2.2 

Sierra Madre 7.2 7.1 2 1012 56.9 5.465E+16 F2.1, F2.2 

Sierra Madre (San Fernando) 6.7 6.5 2 332.6 18.1 1.796E+16 F2.1, F2.2 

Simi-Santa Rosa 6.9 6.7 1 501.8 39.1 1.355E+16 F2.1, F2.2 

So Emerson-Copper Mtn 7.1 6.9 0.6 761.8 54 1.234E+16 F2.1, F2.2 

So Sierra Nevada 7.5 7.5 0.1 1996.2 112.4 5.39E+15 F2.1, F2.2 

Superstition Hills 6.8 6.6 4 410.3 36.2 4.431E+16 F2.1, F2.2 

Surprise Valley 7.2 7.1 1.3 1094 87.3 3.84E+16 F2.1, F2.2 

Bluff 7.2 7 0.6 897.9 48.8 1.455E+16 F2.1, F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-13 

Table I-3. Type-B Faults and Connected-B Faults.—Continued 

Name Ellsworth-B 

mag 

Hanks and 

Bakun 

mag 

Slip rate 

(mm/yr) 

Area 

(km2) 

Length 

(km) 

Moment rate 

(Newton-meters/yr) Fault model 

Tank Canyon 6.4 6.2 1 173 16 4.672E+15 F2.1, F2.2 

Trinidad 7.5 7.5 0.7 2003.3 88.4 3.786E+16 F2.1, F2.2 

Ventura-Pitas Point 7 6.8 1 681.8 43.8 1.841E+16 F2.1, F2.2 

Verdugo 6.9 6.7 0.5 513.5 29 6.932E+15 F2.1, F2.2 

West Napa 6.7 6.5 1 295.7 29.6 7.983E+15 F2.1, F2.2 

West Tahoe 7.1 7 0.6 870.3 51.3 1.41E+16 F2.1, F2.2 

San Cayetano 7.2 7.1 6 1005 42 1.628E+17 F2.1, F2.2 

White Mountains 7.4 7.3 1 1438.3 110.6 3.883E+16 F2.1, F2.2 

White Wolf 7.2 7 2 957.6 63.4 5.171E+16 F2.1, F2.2 

Zayante-Vergeles 7 6.9 0.1 694.4 57.9 1.875E+15 F2.1, F2.2 

Table I-4. Connected-B Faults. Ellsworth (2003) and Hanks and Bakun (2002). “Ellsworth-B” and “Hanks and Bakun” represent Ellsworth (2003) B magnitude-area 

relationship and Hanks and Bakun (2002) magnitude-area relationships, respectively. 

[mm/yr, millimeters per year; km2, square kilometers] 

Name Ellsworth 

-B mag 

Hanks 

and 

Slip 

rate 

Area 

(km2) 

Length 

(km) 

Moment rate 

(NewtonFault model 

Connected B-Fault Names 

Bakun (mm/yr) meters/yr) 

mag 

Death Valley 7.8 7.9 4.58568 4069.4 301.3 5.038E+17 F2.1, Death Valley (No of Cucamongo); Death Valley (No); 

Connected F2.2 Death Valley (Black Mtns Frontal); Death Valley (So) 

Green Valley 6.8 6.6 4.66633 412 56.4 5.19E+16 F2.1, Concord; Green Valley (So); Green Valley (No) 

Connected F2.2 

Greenville 7 6.8 2 676.4 50.1 3.652E+16 F2.1, Greenville (So); Greenville (No) 

Connected F2.2 

Hunter Mountain 7.6 7.6 2.5 2321.6 181.9 1.567E+17 F2.1, Hunter Mountain-Saline Valley; Panamint Valley 

Connected F2.2 

Little Salmon 7.5 7.5 2.71787 2074 79.8 1.522E+17 F2.1, Little Salmon (Onshore); Little Salmon (Offshore) 

Connected F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-14 

Table I-4. Connected-B Faults.—Continued 

Name Ellsworth 

-B mag 

Hanks 

and 

Slip 

rate 

Area 

(km2) 

Length 

(km) 

Moment rate 

(NewtonFault model 

Connected B-Fault Names 

Bakun (mm/yr) meters/yr) 

mag 

Newport 7.5 7.5 1.27675 2196.1 201.6 7.571E+16 F2.1 Rose Canyon; Newport-Inglewood (Offshore); NewportInglewood Inglewood, alt 1 

Connected alt 1 

Newport 7.5 7.5 1.27533 2207.5 202 7.601E+16 F2.2 Rose Canyon; Newport-Inglewood (Offshore); NewportInglewood Inglewood, alt 2 

Connected alt 2 

Oak Ridge 7.4 7.3 3.63915 1566.8 87.3 1.539E+17 F2.2 Oak Ridge (Offshore), west extension; Oak Ridge 

Connected (Offshore); Oak Ridge (Onshore) 

Palos Verdes 7.7 7.7 3 2950.2 285.4 2.39E+17 F2.1, Palos Verdes; Coronado Bank 

Connected F2.2 

Pitas Point 7.3 7.1 1 1130.8 78.7 3.053E+16 F2.2 Pitas Point (Upper); Ventura-Pitas Point 

Connected 

San Gregorio 7.5 7.4 5.49298 1899.5 175.9 2.817E+17 F2.1, San Gregorio (South); San Gregorio (North) 

Connected F2.2 

Santa Monica 7.3 7.3 2.61336 1383.2 65.3 9.76E+16 F2.1 Anacapa-Dume, alt 1; Santa Monica, alt 1 

Connected alt 1 

Santa Monica 7.4 7.3 2.40751 1429.8 92.7 9.294E+16 F2.2 Anacapa-Dume, alt 2; Santa Monica, alt 2 

Connected alt 2 

Santa Ynez 7.4 7.4 2 1628 135.8 8.791E+16 F2.1, Santa Ynez (West); Santa Ynez (East) 

Connected F2.2 

Sierra Madre 7.3 7.2 2 1344.5 75 7.26E+16 F2.1, Sierra Madre (San Fernando); Sierra Madre 

Connected F2.2 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps I-15 

References 

Ellsworth, W., 2003, Appendix D—Magnitude and area data for strike slip earthquakes, in Working Group on 

California Earthquake Probabilities, Earthquake probabilities in the San Francisco Bay region—2002– 

2031: U.S. Geological Survey Open-File Report 03-214, 6 p. 

Field, E., T. Dawson, W. Ellsworth, K. Felzer, A. Frankel, V. Gupta, T. Jordan, T. Parsons, M. Petersen, R. 

Stein, R. Weldon, C. Wills, 2008, The Uniform California Earthquake Rupture Forecast, Version 2 

(UCERF 2): U.S. Geological Survey Open File Report and California Geological Survey Special Report 

203, 97 p. 

Hanks, T.C., and Bakun, W.H., 2002, A bilinear source-scaling model for M–log A observations of continental 

earthquakes: Bulletin of the Seismological Society of America, v. 92, pp. 1841–1846. 

Kent, G.M., Babcock, J.M., Driscoll, N.W., Harding, A.J., Dingler, J.A., Seitz , G.G., Gardner, J.V., Mayer, L.A., 

Goldman, C.R., Heyvaert, A.C., Richards, R.C., Karlin, R., Morgan, C.W., Gayes, P.T., and Owen, L.A., 2005, 

60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip 

rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe: Geology, v. 33, no. 5, p. 365­

368. 

O’Connell, D.R.H., and Unruh, J.R., 2000, Updated Seismiotectonic Evaluation of faults within 10 km of 

Monitcello Dam, Solano Projedt, California: Bureau of Reclamation, Geophysics, Paleohydrology and 

Seismotectonics Group, Geotechnical Services, Denver Co. 101 p. 

Oskin, M., Perg, L., Blumentritt, D., Mukhopadhyay, S., and Iriondo, A., 2007: Slip rate of the Calico fault: 

Implications for geologic versus geodetic rate discrepancy in the Eastern California shear zone, Journal of 

Geophysical Research - Solid Earth, v. 112, doi:10.1029/2006JB004451 

Wills, C.J., Weldon, R.J., II, and Bryant, W.A., 2008, California Fault Parameters for the National Seismic 

Hazard Maps and Working Group on California Earthquake Probabilities, Appendix A, in Field, E., 

Dawson, T., Ellsworth, W., Felzer, K., Frankel, A., Gupta, V., Jordan, T., Parsons, T., Petersen, M., Stein, R., 

Weldon, R., and Wills, C., The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2): 

U.S. Geological Survey Open File Report and California Geological Survey Special Report 203, 51 p. 

15 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix J. Fault-Model Changes in the Western United
 

States 

By Kathleen M. Haller and Stephen C. Harmsen 

We changed the 2002 fault source model for this 

update based on recommendations submitted by a 

number of different sources; these changes impact the 

maps in a variety of ways. We will address the most 

significant changes first followed by the less 

significant changes in this appendix. 

Rounding M 

In these maps, characteristic magnitude for faults 

outside of California, which is assigned based on fault 

length-magnitude relation of Wells and Coppersmith 

(1994), was rounded to two decimal places instead of 

one decimal place as in prior versions of the maps. 

Although originally considered to better capture 

epistemic uncertainty in the magnitude-area relations 

implemented in the California part of the maps 

(discussed elsewhere in the documentation), we 

retained rounding magnitude to nearest hundredth 

outside of California. This change in methodology 

affects earthquake recurrence-rate estimates and 

probabilistic ground motions through either 

increasing or decreasing the assigned characteristic 

magnitude for the source by up to 0.05-magnitude 

units. An overestimate by 0.05 magnitude units can 

mean a lowering of event rate by 16 percent. 

Similarly, an underestimate by 0.05-magnitude units 

can increase event rates by 20 percent as depicted by 

the blue diamonds in figure J-1. For sites near these 

faults, this has considerable impact. 

Dip of Normal Faults 

The Western States Seismic Policy Council 

(WSSPC) held a workshop to address issues of 

importance in the Intermountain West region. One of 

their recommendations was to reduce the average dip 

of normal faults from 60° to 50±10° (Lund, 2006). 

Although we cannot resolve the question of how steep 

Intermountain West normal faults dip or even if they 

are planar in nature; multiple lines of evidence exist 

that support implementing their recommendation. 

The basis for 60° dip is grounded in fault mechanics 

(Anderson, 1951), which later was supported by 

studies by Doser and Smith (1989) who determined 

that the dip of normal faults in the Western United 

States range from 40° to 90°, with an average dip of 

60°. Seismic reflection studies and other subsurface 

information support this average dip (Walsh and 

Watterson, 2002; Smith and Bruhn, 1984; Zoback, 

1983). Jackson (2002) compiled a worldwide data set 

of normal surface faulting earthquakes that shows that 

at the depth of the historical normal earthquakes fault 

planes dip between 30° and 70°. The mode of this 

dataset is 40–50°, and the mean somewhere between 

40° and 60°. Although this particular data set is small, 

no nodal-plane solution suggests very gently dipping 

or very steeply dipping seismically active normal 

faults. Jackson (2002) does not include a list of 

earthquakes considered in his analysis, but historical 

earthquakes in the Intermountain West also were on 

planes dipping around 40°–60°. Therefore, we have 

changed the preferred dip of most normal faults to 

50°. In addition, we give modest weight (20 percent 

each) to alternative models that characterize fault dip 

as 40° and 60° (see fig. 17). An exception is the Lost 

River fault, which is assigned 45±10° dip. As in past 

versions of the maps, all of our assigned slip rates are 

expressed as either vertical or horizontal rates; 

therefore, any change in dip will subsequently 

increase or decrease the fault parallel slip rate used in 

Figure J-1. Plot of the ratio (2008/2002 hazard maps) of 

rate of characteristic earthquakes resulting from 

rounding characteristic magnitude (M) to two 

decimal places and alternative fault-dip models. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps J-2 

our calculations. When one changes the dip of faults 

in the model from 60° to 50°, the rate of earthquakes 

increases by more than 20 percent in addition to the 

change in earthquake rate due to magnitude rounding. 

When the dip of the fault is changed from 60° to 40° 

the rate of earthquakes increases nearly 55 percent. 

Figure J-1 demonstrates the combined result when 

changes in default dip are combined with rounding 

the characteristic magnitude to two decimal places. 

For some faults that dip 50°, the rate of earthquakes is 

increased up to 66 percent. Similarly for some of our 

fault sources that dip 40°, the rate of earthquakes 

increases nearly 45 percent. Faults modeled with a dip 

of 60° show the same plus or minus 20 percent 

variation as other faults in the model that did not have 

a change in dip (fig. J-1). Therefore, assuming that the 

normal faults dip at a lower angle than our previous 

preferred dip of 60° can significantly affect 

probabilistic ground motions due to increases the rate 

of events. 

Ratio of Magnitude-Frequency 

Distributions in the Intermountain 

West 

Contribution by Robert L. Wesson 

Another WSSPC recommendation was to 

change the ratio of characteristic and GutenbergRichter magnitude-frequency distributions in the 

Intermountain West region to reflect similar event 

weighting used in coastal California: 67 percent 

characteristic and 33 percent Gutenberg-Richter. This 

has generally lowered the hazard, but the specific 

amount depends on the assigned characteristic 

magnitude; the longer the fault, the larger the impact. 

Many faults in the Intermountain West, as they are 

depicted in these maps, are actually long fault zones 

that contain considerable complexity, and until this 

version of the map, the competing models were 

weighted the same, or equal likelihood of being the 

failure mode. 

The problem of estimating the magnitudefrequency distribution of future earthquakes along a 

fault zone is not resolved but is hotly contested in the 

scientific community. In some instances, 

paleoseismic data may be available to provide some 

constraints on the interpretation of the behavior of the 

fault in the past. The estimation of the future 

magnitude-frequency behavior of the fault, even in the 

presence of these kinds of data, remains controversial. 

Owing to the relative youth of earthquake science, we 

have yet to have complete observations of repeated 

ruptures on the same fault. Thus the models used in 

hazard estimation are simplistic and uncertain. 

In the preparation of the National Seismic 

Hazard Maps, two kinds of magnitude-frequency 

relationships are considered. These are termed the 

“characteristic” and the “truncated Gutenberg-Richter” 

models. Both of these terms may have different 

meanings in different contexts; the ways they are used 

in these maps are described here. The “characteristic” 

model means that all future ruptures along the fault 

will occur only as ruptures of individual, predefined 

segments; the magnitude for each segment is 

estimated from the length of the segment. The 

“characteristic” model enjoyed considerable 

popularity in the 1980s and 1990s, but historical 

earthquake ruptures show complex rupture patterns 

that include such phenomena as significant stopovers 

(for example, Landers) and branching on to other 

faults (for example, Denali). Therefore, the concept of 

segmentation (at least based on current knowledge) is 

increasingly questioned. In the application of this 

model, the magnitude (or moment) of the earthquakes 

is determined from the length of a segment, and the 

frequency of the characteristic earthquakes is 

determined by dividing the moment of an individual 

event by the long-term moment rate of the fault (that 

is, the slip rate multiplied by the area of the 

characteristic event). 

The alternative model considered in the National 

Seismic Hazard Maps is the “truncated GutenbergRichter” model. The word “truncated” is used because 

in all cases a lower magnitude of 6.5 is considered. 

The general Gutenberg-Richter frequency-magnitude 

relation, found to be typical of any significant-sized 

region over a long period of time, says that the 

logarithm number of earthquakes in a specified 

magnitude interval is a linear function of the 

magnitude, that is 

log( n) = a bM 

(It can be shown that a similar relation with the same 

value of b, but a different value of a, holds for the 

logarithm of the number of earthquakes above a 

particular value of magnitude. Knowing the value of b

and the magnitude interval, one type of a-value can be 

calculated from the other.) So the “truncated 

Gutenberg-Richter” magnitude-frequency 

distribution describes a model with a b-value 

typically determined from regional seismicity, a 

maximum magnitude determined from the length of 

the fault segment, and the a-value calculated such that 

the sum of the moments of all the earthquakes with 

this magnitude-frequency relationship between 6.5 

and the maximum magnitude equals the moment rate 

determined for the fault from the slip rate. In essence, 

the “truncated Gutenberg-Richter” provides for the 

possibility that earthquakes less than the maximum 

will occur. In the calculations, all possible positions 

of the smaller earthquakes along the fault are 

considered. This is referred to as letting the 

earthquakes “float.” The difficulty with the “truncated 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps J-3 

Gutenberg-Richter” relation is that it suggests more 

earthquakes smaller than the maximum magnitude 

than are actually observed. 

The fact that neither of these relations appears to 

be satisfactory led to the use of using a weighted sum 

from these two models. Originally, the two models 

were each weighted 50 percent, but subsequently in 

some regions (California in particular), where 

arguments were made that the earthquakes favored the 

characteristic model, the weights were two-thirds 

characteristic and one-third truncated GutenbergRichter. 

As mentioned previously, the weight of opinion 

has been moving against a pure application of the 

“characteristic” model for the reasons described. For 

example, the Working Group for the San Francisco 

Bay Region (2003) considered such a wide variety of 

multisegment ruptures, uncertainties in magnitudearea relations, floating earthquakes and other issues, in 

a region where one would think that we know a good 

deal about the faults, as to represent a very significant 

backing away from the “characteristic” model. A 

similar approach was adopted in the current statewide 

review in California (Field and others, 2008). 

In the Intermountain West we have only a few 

historical ruptures; furthermore, few faults have been 

the target of more than one or two paleoseismic 

investigations. Thus we have a rather limited basis of 

experience on which to define fault segments, 

notwithstanding the arguments above. Over 

10 percent of the faults are more than 100 kilometers 

long and assigned characteristic M7.4 or greater; 

another 10 percent are between 66 and 100 kilometers 

long and are assigned characteristic M7.2 or M7.3. To 

overemphasize the likelihood that most of the seismic 

moment is released in only the largest earthquakes 

risks very significantly underestimating the frequency 

of small but still potentially damaging earthquakes. 

Probabilities and Magnitudes of 

Multisegment Rupture 

Issue 4 of the Western States Seismic Policy 

Council recommendations (Lund, 2006) addresses 

how fault segmentation is characterized in the 

National Seismic Hazard maps. We recognize that 

faults in the region are capable of producing M7.3 

earthquakes (for example, Pleasant Valley, Nev., and 

Hebgen Lake, Mont., earthquakes) in which surface 

rupture jumped across gaps that some investigators 

assume to be the location of a fundamental boundary. 

Even though many faults in the Intermountain West 

have tentative segmentation models, most segments 

are short less than 20–25 kilometers) and, thus, would 

be modeled with frequent low-magnitude 

earthquakes. Therefore, most faults in the 

Intermountain West in our model are considered in 

the model to rupture from end to end in the 

“characteristic” part of the model. This practice 

permits many “multisegment” ruptures by 

constraining “characteristic” magnitude large enough 

to sustain rupture of the entire fault and floating 

earthquakes of magnitudes from M6.5 to the 

characteristic magnitude without explicitly defining 

segments boundaries. Explicit segmentation results 

in artificially high hazard at segment boundaries due 

to the influence of earthquakes on adjoining 

segments. If we consider the Lost River fault in Idaho 

as an example, using the existing segmentation model 

would overestimate the frequency of known Holocene 

surface-rupturing earthquakes by nearly a factor of 

five. 

The longest faults in the region are divided into 

smaller parts of the fault, which are defined in the 

literature as multiple segments. The Hurricane fault 

that crosses the border between Utah and Arizona is 

divided into three parts, and the nearby SevierToroweap fault is divided into two parts. Explicit 

segmentation models for the Wasatch fault in Utah 

and the Carson Range system in Nevada were 

modified in these maps to, in a sense, permit 

“multisegment” rupture that was not part of the 2002 

maps. 

Wasatch Fault 

The Wasatch fault, bounding the eastern side of 

the Utah urban corridor, is one of the few faults in the 

model with explicit segmentation defined. Twenty 

years of trenching studies conducted on every 

segment but the northernmost makes this the second 

best studied fault in the Western United States. Over 

the years, studies have reviewed and analyzed the 

reasonably well dated event chronology to determine 

if individual surface ruptures crossed segment 

boundaries forming “multisegment” ruptures. In these 

maps, we have included a “floating” M7.4 (10 percent 

probability) to include that possibility (see fig. 18), 

with recurrence interval of 500 years somewhere along 

strike. Assigned maximum magnitude for each 

segment is retained from the 2002 models and 

therefore does not carry two-decimal-place rounding 

as other faults in the Intermountain West. However, 

we added aleatory uncertainty on the characteristic 

magnitudes. This was done using a similar a priori 

model as we now use in California for Type-A faults 

(that is, the recurrence model does not change, but 

some variation in the characteristic magnitude is 

permitted). The aleatory uncertainty is distributed 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps J-4 

Figure J-2. Plot of results of Utah Quaternary Fault Parameter Working Group showing the preferred slip rate for 16 

faults in Utah with associated uncertainties. 

with dM of 0.2 on either side of the preferred M. 

Carson Range System 

We have included a new model for the Carson Range 

(Genoa) fault system near Carson City, Nev., based on 

recommendations from the Nevada Bureau of Mines 

and Geology and Ramelli and others (1999). The 

Carson Range fault (as named in our model) extends 

along the precipitous east front of the Sierra Nevada 

from south of Markleeville, Calif., northward to south 

of U.S. Highway 50, northwest of Carson City, Nev. 

Near the north end of the Carson Range fault, the 

Indian Hill, Carson City, and Kings Canyon faults 

splay off of the Carson Range fault and trend 

northeast, away from the range front. All three of these 

faults are short, less than 17 kilometers long, and are 

characterized in the 2002 model as having 

characteristic earthquakes of magnitudes 6.5 or less. 

Although historical surface faulting has occurred as 

the result of earthquakes of M6.5 and less, the size of 

the fault scarps near Carson City and their lateral 

continuity suggest they were formed in larger events 

that also ruptured the Carson Range fault (Ramelli 

and others, 1999). We assign 75-percent probability of 

synchronous rupture along these faults based on 

evidence that likely characterizes the fault behavior in 

the past two events; however, we cannot rule out the 

possibility that rupture occurred so closely spaced in 

time that they are geologically indistinguishable. In 

addition, the four faults may rupture independently; 

therefore, each are assigned a 25-percent probability 

that they are independent sources. 

Similar treatment was given to the Mount Rose 

and Little Valley faults to the north, between Carson 

City and Reno. The Little Valley fault is parallel to 

and sympathetic to the Mount Rose fault; their 

proximity suggests that they probably merge at depth. 

Therefore, in this model the Little Valley fault is 

assigned a 25-percent probability that it ruptures 

independently from the nearby Mount Rose fault. 

Western States Seismic Policy 

Council Recommendations 

One of the short-term recommendations of 

WSSPC was to incorporate uncertainties in slip rates 

and recurrence intervals for the more significant faults 

in the Basin and Range Province. Specifically, they 

recommended incorporating the uncertainties 

determined by the Utah Quaternary Fault Parameters 

Working Group (Lund, 2005) The working group’s 

effort is the first in the region to assemble uncertainty 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps J-5 

in fault slip rate and recurrence intervals to augment 

preferred values; their results show the range in 

uncertainty generally is between one-half the preferred 

value and 2 times the preferred value (fig. J-2). Before 

we incorporate these types of uncertainties, we would 

like to expand the dataset to include faults in adjacent 

States. 

Another recommendation focused on improving, 

or at least including, alternative models for determining 

characteristic magnitude. As has been stated many times 

in this documentation, we assign characteristic 

magnitude in the Intermountain West based on the 

regression relations of Wells and Coppersmith (1996). 

However, there is considerable uncertainty in surfacerupture length due to incomplete knowledge of the 

extent of individual ruptures on long faults and variable 

preservation of deformation features in the landscape. 

To compensate for possible longer or shorter ruptures, 

we use magnitude uncertainty (see fig. 17). For instance, 

for a fault having an assigned characteristic magnitude 

of M7.0 based on a surface-rupture length of 45 

kilometers, we also allow epistemic uncertainty in the 

characteristic magnitude of 0.2 magnitude units larger 

or smaller than the characteristic event. Thus, the 

modeled surface-rupture length approximates 30– 

60 kilometers. Probably a more vexing problem is 

faults in our model that are so short they are assigned 

characteristic magnitudes less than M6.5. 

There are nearly 30 faults in the Intermountain 

West that fall into this category (about 13 percent, fig. J3). Fault scarps that are large enough to be preserved on 

the landscape for thousands of years identify the 

location and extent of these faults. Therefore, it is 

unlikely that they are the result of earthquakes that 

generally do not rupture the surface and when they do, 

have very small surface offsets. Wells and Coppersmith 

(1993) showed that only one-fourth of the historical 

M5±0.1 to 6±0.1 earthquakes rupture the surface, and 

fewer than one in three M6.0±0.1 to 6.4±0.1 earthquakes 

rupture the surface. In their data set all the earthquakes 

above M7.4±0.1 ruptured the surface. Youngs and 

others (2003) show, however, that the probability of 

surface rupture is higher in the Great Basin and northern 

Basin and Range above M5.6 and 6.25, respectively. 

Arbitrarily promoting the short faults in our model to 

M6.5 only exacerbates the excess of earthquakes at that 

magnitude. This step also requires creating hypothetical 

faults of the proper length or large stress-drop 

earthquakes. We did not implement this 

recommendation at this time. 

References 

Anderson, E.M., 1951, The dynamics of faulting: 

Edinburgh, Oliver & Boyd, 2d edition, 206 p. 

Doser, D.I., and Smith, R.B., 1989, An assessment of 

source parameters of earthquakes in the cordillera of 

the western United States: Bulletin of the 

Seismological Society of America, v. 79, p. 1383– 

1409. 

Field, E., T. Dawson, W. Ellsworth, K. Felzer, A. 

Frankel, V. Gupta, T. Jordan, T. Parsons, M. Petersen, 

R. Stein, R. Weldon, C. Wills, 2008, The Uniform 

California Earthquake Rupture Forecast, Version 2 

(UCERF 2): U.S. Geological Survey Open File 

Report and California Geological Survey Special 

Report 203, 97 p. 

Jackson, J.A., 2002, Active normal faulting and crustal 

extension, in Holdsworth, R.E., and Turner, J,P., 

compilers, Extensional tectonics—Faulting and 

related processes: The Geological Society, Key 

Issues in Earth Sciences, part 2, p. 135–149. 

Lund, W.R., ed., 2006, Basin and Range Province 

Earthquake Working Group seismic-hazard 

recommendations to the U.S. Geological Survey 

National Seismic Hazard Mapping Program: Utah 

Geological Survey Open-File Report 477, 23 p. 

Smith, R.B., and Bruhn, R.L., 1984, Intraplate 

extensional tectonics of the eastern Basin-Range; 

inferences on structural style from seismic reflection 

data, regional tectonics, and thermal-mechanical 

models of brittle-ductile deformation: Journal of 

Geophysical Research, v. 89, p. 5733–5762. 

Walsh, J.J., and Watterson, J., 2002, Dips of normal 

faults in British Coal Measures and other 

sedimentary sequences, in Holdsworth, R.E., and 

Turner, J,P., compilers, Extensional tectonics— 

Faulting and related processes: The Geological 

Society, Key Issues in Earth Sciences, part 2, p. 25– 

39. 

Wells, D.L. and Coppersmith, K.J., 1994, New empirical 

relationships among magnitude, rupture length, 

rupture width, and surface displacements: Bulletin of 

the Seismological Society of America, v. 84, p. 974– 

1002. 

Working Group on California Earthquake Probabilities, 

2003, Earthquake probabilities in the San Francisco 

Bay region—2002–2031: U.S. Geological Survey 

Open-File Report 03-214. 

Youngs, R.R., Arabaz, W.J., Anderson, R.E., Ramelli, 

A.R., Ake, J.P., Slemmons, D.B., McCalpin, J.P., 

Doser, D.I., Fridrich, C.J., Swan, F.H., III, Rogers, 

A.M., Yount, J.C., Anderson, L.W., Smith, K.D., 

Bruhn, R.L., Knuepfer, P.L.K., Smith, R.B., dePolo, 

C.M., O’Leary, D.W., Coppersmith, K.J., Pezzopane, 

S.K., Schwartz, D.P., Whitney, J.W., Olig, S.S., Toro, 

G.R., 2003, A methodology for probabilistic fault 

displacement hazard analysis: Earthquake Spectra, 

v. 19, p. 191–217. 

Zoback, M.L., 1983, Structure and Cenozoic tectonism 

along the Wasatch fault zone, Utah, in Miller, D.M., 

Todd, V.R., and Howard, K.A., eds., Tectonic and 

stratigraphic studies in the eastern Great Basin: 

Geological Society of America Memoir 157, p. 3–27. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix K. Cascadia Subduction Zone
 

By Arthur D. Frankel and Mark D. Petersen 

The geometry and recurrence times of large 

earthquakes associated with the Cascadia Subduction 

Zone (CSZ) were discussed and debated at a March 

28–29, 2006, Pacific Northwest workshop for the 

USGS National Seismic Hazard Maps. 

The CSZ is modeled from Cape Mendocino in 

California to Vancouver Island in British Columbia. 

We include the same geometry and weighting scheme 

as was used in the 2002 model (Frankel and others, 

2002) based on thermal constraints (fig. 21) (Flück 

and others, 1997, and a reexamination by Wang and 

others, 2003, fig. 11, eastern edge of intermediate 

shading). This scheme includes four possibilities for 

the lower (eastern) limit of seismic rupture: the base 

of elastic zone (weight 0.1), the base of transition zone 

(weight 0.2), the midpoint of the transition zone 

(weight 0.2), and a model with a long north-south 

segment at long 123.8°W. in the southern and central 

portions of the CSZ, with a dogleg to the northwest in 

the northern portion of the zone (weight 0.5). The 

latter model was derived from the approximate 

average longitude of the contour of the 30-kilometer 

depth of the CSZ as modeled by Flück and others. 

(1997). A global study of the maximum depth of 

thrust earthquakes on subduction zones by Tichelaar 

and Ruff (1993) indicated maximum depths of about 

40 kilometers for most of the subduction zones 

studied, although the Mexican subduction zone had a 

maximum depth of about 25 kilometers (Roland 

LaForge, oral commun., 2006). The recent inversion 

of GPS data by McCaffrey and others (2007) shows a 

significant amount of coupling (a coupling factor of 

0.20.3) as far east as long 123.8°W. in some portions 

of the CSZ. Both of these lines of evidence lend 

support to the model with a north-south segment at 

long 123.8°W. 

The primary constraint on our Cascadia 

earthquake model is that great earthquakes occur on 

average once every 500 years beneath sites on the 

coast over the CSZ, based on paleoseismic studies of 

coastal subsidence and tsunami deposits (for example, 

Atwater and Hemphill-Haley, 1997). We considered 

two sets of rupture scenarios for these events: (1) 

M9.0±0.2 events that rupture the entire CSZ every 

500 years on average and (2) M8.0–8.7 events whose 

rupture zones fill up the entire zone over a period of 

about 500 years. The rupture zones in the latter set of 

scenarios are moved systematically or floated along 

the strike of the CSZ. 

Various lines of evidence are used to assess the 

relative likelihood of these two sets of rupture 

scenarios. The A.D. 1700 earthquake that caused a 

tsunami in Japan is thought to have ruptured the 

entire zone in an earthquake about M9.0 (Satake and 

others 1996, 2003). Furthermore, recent 

sedimentation studies along the continental shelf also 

provide evidence that great earthquakes usually 

rupture most of the Cascadia subduction interface 

(Goldfinger and others, 2003). In contrast, Nelson and 

others (2006) and Kelsey and others (2002, 2005) 

reported tsunami deposits along northern California 

and southern Oregon that give evidence for additional 

M8.0–8.6 earthquakes that are not apparent in studies 

along the Washington coast. We have applied the 

M8.0–8.7 model for the entire CSZ lacking any 

evidence for different rupture behavior between the 

north and southern portions of the fault. 

For the WGCEP and the NSHMP model we 

assign a probability of 0.67 to the M8.8–9.2 scenario 

and a probability of 0.33 for the set of M8.0–8.7 

scenarios with floating rupture zones. In the 2002 

maps, we used M9.0 and M8.3 scenarios with equal 

probabilities. To be clear, when we say “probability of 

a scenario” this indicates that the effective rate of the 

scenario in the hazard calculation is the probability of 

that scenario multiplied by the recurrence rate 

calculated for that scenario as if it were the only 

scenario. The higher probability of the M8.8–9.2 

complete CSZ rupture scenario in the 2008 update 

compared to that in the 2002 maps reflects the 

consensus of attendees at the Pacific Northwest 

workshop that the former represents a more likely 

scenario for the great earthquakes than the set of 

floating M8 scenarios. 

Here we describe the scenarios in more detail. In 

the first model, we consider rupture of the entire 

length of the CSZ with great earthquakes having a 

magnitude of M8.8 (weight 0.2), M9.0 (0.6), and M9.2 

(0.2). The average recurrence time for such an event 

was taken to be 500 years based on the palesoeismic 

evidence. In the second model we consider a set of 

floating ruptures between M8.0 and M8.7. The key 

constraint of the second model is that the annual rate 

of having a rupture zone beneath any given site along 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps K-2 

the coast is 1/500, to be consistent with the 

paleoseismic observations. This procedure is similar 

to the model applied in Geomatrix Consultants, Inc. 

(1995), where rupture zones for each magnitude were 

assumed to fill the CSZ every 500 years. We calculate 

the overall rate of earthquakes for the CSZ for a given 

magnitude so that the rate of having a rupture zone 

occurring beneath any given site is 1/500, on average. 

When rupture zones are floated along the CSZ using 

equal distance increments, sites near the middle of the 

CSZ will have a higher rate of ruptures beneath them 

compared to sites near the northern and southern ends 

of the CSZ. We used the magnitude-length relation 

for subduction-zone earthquakes determined by 

Geomatrix Consultants, Inc. (1995). The rupture 

zones were floated using 5-kilometer increments. The 

average rate of rupture zones under a site was 

calculated for a set of sites along the coast separated 

by 0.1 degree in latitude and extending the entire 

length of the CSZ. Probabilities were assigned to 

scenarios with magnitudes at one-tenth magnitude 

unit intervals from M8.0 to M8.7. The recurrence 

parameters for each magnitude interval are shown in 

table K-1; probabilities in the last column of table KTable K-1. Recurrence parameters for M8.0–8.7 events. 

[yr, years] 

1 sum to 0.33, which is the weight of this model. The 

magnitude-frequency distribution of earthquakes 

along the Cascadia subduction zone can be observed 

in figure 22 of the main text. The implied recurrence 

intervals for M8.0 to M8.2 earthquakes are between 78 

and 107 years, shorter than the observed seismic 

history that does not contain any of these events. To 

account for this lack of historical earthquakes between 

M8 and M8.2, we have weighted the probability of 

these rupture scenarios by one-half, compared to the 

intervals between M8.3 and M8.7, to make the rates 

more compatible with the earthquake record. 

The effective recurrence rate of each scenario in 

the hazard calculation is the recurrence rate multiplied 

by the probability of that scenario. In the final model, 

considering all of the M9 and floating M8 rupture 

scenarios and their probabilities, the effective 

recurrence time (reciprocal of the mean rate) for 

earthquakes with M≥8.0 is 270 years. The reason for 

this relatively short recurrence time is that we are 

treating the M8 earthquakes as independent events, 

whereas they were likely clustered in time in order to 

explain the similar timing of coastal subsidence 

events found along the CSZ. 

Magnitude a-value b-value Recurrence (yr) under 

any site, on average 

Recurrence (yr) 

along entire CSZ 

Number of 

ruptures in 

500 years 

Probability 

of scenario 

8.0 4.51 0.8 500 78 6 0.026 

8.1 4.52 0.8 500 91 5 0.026 

8.2 4.53 0.8 500 107 5 0.026 

8.3 4.53 0.8 500 129 4 0.051 

8.4 4.54 0.8 500 151 3 0.051 

8.5 4.55 0.8 500 178 3 0.051 

8.6 4.56 0.8 500 209 2 0.051 

8.7 4.57 0.8 500 245 2 0.051 

References 

Atwater, B.F., and Hemphill-Haley, E., 1997, 

Recurrence intervals for great earthquakes of the past 

3,500 years at northeastern Willapa Bay, 

Washington: U.S. Geological Survey Professional 

Paper 1576, 108 p. 

Flück, P., Hyndman, R.D., and Wang, K., 1997, Threedimensional dislocation model for great earthquakes 

of the Cascadia subduction zone: Journal of 

Geophysical Research, v. 102, p. 20539–20550. 

Frankel, A.D., Petersen, M.D., Mueller, C.S., Haller, 

K.M., Wheeler, R.L., Leyendecker, E.V., Wesson, 

R.L., Harmsen, S.C., Cramer, C.H., Perkins, D.M., 

Rukstales, K.S., 2002, Documentation for the 2002 

update of the National Seismic Hazard Maps: 

U.S. Geological Survey Open-File Report 02-420, 

39 p. 

Goldfinger, C., Nelson, C.H., Johnson, J.E., and the 

Shipboard Scientific Party, 2003, Deep-water 

turbidites as Holocene earthquake proxies—The 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation for the 2008 Update of the United States National Seismic Hazard Maps K-3 

Cascadia subduction zone and northern San 

Andreas fault systems: Annuals of Geophysics, 

v. 46, p. 1169–1194. 

Geomatrix Consultants, Inc., 1995, Seismic design 

mapping state of Oregon: Final report prepared 

for the Oregon Department of Transportation, 

Salem, Oregon. 

Kelsey, H.M., Nelson, A.R., Hemphill-Haley, E., 

and Witter, R.C., 2005, Tsunami history of an 

Oregon coastal lake reveals a 4600 yr record of 

great earthquakes on the Cascadia subduction 

zone: Geological Society of America Bulletin, 

v. 117, p. 1009–1032. 

Kelsey, H.M., Witter, R.C., and Hemphill-Haley, E., 

2002, Plate-boundary earthquakes and tsunamis 

of the past 5500 yr, Sixes River estuary, 

southern Oregon: Geological Society of 

America Bulletin, v. 114, p. 298–314. 

McCaffrey, R., Qamar, A.I., King, R.W., Wells, R., 

Khazaradze, G. , Williams, C.A., Stevens, C.W., 

Vollick, J.J., and Zwick, P.C., 2007, Fault 

locking, block rotation and crustal deformation 

in the Pacific Northwest: Geophysical Journal 

International, v. 169, p. 1315–1340. 

Nelson, A.R., Kelsey, H.M., and Witter, R.C., 2006, 

Great earthquakes of variable magnitude at the 

Cascadia subduction zone: Quaternary Research, 

v. 65, p. 354–365. 

Satake, K., Shimazaki, K., Tsuji, Y., and Ueda, K., 1996, 

Time and size of a giant earthquake in the Cascadia 

inferred from Japanese tsunami records of January 

1700: Nature, v. 379, p. 246–249. 

Satake, K., Wang, K., and Atwater, B., 2003, Fault slip 

and seismic moment of the 1700 Cascadia 

earthquake inferred from Japanese tsunami 

descriptions: Journal of Geophysical Research, 

v. 108, 2535, doi:10.1029/2003JB002521. 

Tichelaar, B.W., and Ruff, L.J., 1993, Depth of seismic 

coupling along subduction zones: Journal of 

Geophysical Research, v. 98, 2017–2037. 

Wang, K., Wells, R., Mazzotti, S., Hyndman, R.D., and 

Sagiya, T., 2003, A revised dislocation model of 

interseismic deformation of the Cascadia subduction 

zone: Journal of Geophysical Research, v. 108, 

no. B1, 2026, doi:10.1029/2001JB001227.