U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3014

February 2012

Probabilistic Seismic Hazard Maps

The probabilistic seismic-hazard maps produced by the 

EAEHMP account for all known earthquakes source regions 

that can affect the Evansville region. They incorporate information about seismic activity and the locations of active faults, 

as well as estimates of the time interval between earthquakes. 

These maps consider a time period of 50 yr, which is the typical 

lifetime of a building. The maps also depict a range of groundvibration frequencies, because structures behave differently in 

Figure 1. Probabilistic seismic-hazard maps. These maps show the ground motions that have a 2-percent probability of being exceeded 

in 50 years. The new maps developed for the Evansville area, which incorporate local geology, are shown on top of the 2008 USGS national 

maps assuming a firm rock site condition. Three different maps are shown for Peak Ground Acceleration (PGA), high frequencies (0.2-second 

(s) period) and low frequencies (1.0-second period). Warmer colors show higher hazard. (Acc, acceleration; g, acceleration of gravity) 

response to different types of earthquake waves (for example, 

long wavelength rumbles or shorter wavelength shaking). For 

each point on the map and for some specific level of probability, 

the maps address the question: “what level of shaking is likely to 

be exceeded?” For example, the maps of the Evansville region 

show the ground motions that have both a 2 percent (fig. 1) and 

a 10 percent chance of being exceeded within the next 50 yr; the 

predicted motions are larger for the 2-percent map because they 

allow for the more infrequent, large earthquakes.

0.1 – 0.2

0.2 – 0.3

0.3 – 0.4

0.4 – 0.5

0.5 – 0.6

0.6 – 0.7

0.7 – 0.8

0.8 – 0.9

0.9 – 1

1 – 1.1

1.1 – 1.2

1.2 – 1.3

1.3 – 1.4

1.4 – 1.5

1.5 – 1.6

1.6 – 1.7

Acc (g)

37 ̊52'30"

87 ̊37'30" 87 ̊22'30" 87 ̊37'30" 87 ̊22'30" 87 ̊37'30" 87 ̊22'30"

38 ̊07'30"

PGA 0.2 -s period 1.0 -s period

EXPLANATION

The region surrounding Evansville, Indiana, has experienced minor damage from earthquakes several times in the past 200 

years (yr). Because of this history and the proximity of Evansville to the Wabash Valley and New Madrid seismic zones, there is 

concern among nearby communities about hazards from earthquakes. Earthquakes currently cannot be predicted, but scientists can 

estimate how strongly the ground is likely to shake as a result of an earthquake and are able to design structures to withstand this 

estimated ground shaking. Earthquake-hazard maps provide one way of conveying such information and can help the region of 

Evansville prepare for future earthquakes and reduce earthquake-caused loss of life and financial and structural loss.

The Evansville Area Earthquake Hazards Mapping Project (EAEHMP) has produced three types of hazard maps for the Evansville area: (1) probabilistic seismic-hazard maps show the ground motion that is expected to be exceeded with a given probability 

within a given period of time; (2) scenario ground-shaking maps show the expected shaking from two specific scenario earthquakes; 

(3) liquefaction-potential maps show how likely the strong ground shaking from the scenario earthquakes is to produce liquefaction. 

These maps complement the U.S. Geological Survey’s National Seismic Hazard Maps (see http://pubs.usgs.gov/fs/2008/3017/) but 

are more detailed regionally and take into account surficial geology, soil thickness, and soil stiffness; these elements greatly affect 

ground shaking. 

Understanding Earthquake Hazards in Urban Areas

Evansville Area Earthquake Hazards Mapping Project

Printed on recycled paper
The probabilistic maps for Evansville show strong local 

variations of ground motions. The ground motions are clearly 

correlated with variations in the thickness of soft soils above 

bedrock. Locations along the Ohio River, where soft soils are 

relatively thick, experience greater ground motions at longer 

wavelengths, which is a problem for larger structures like highrise buildings and bridges. In contrast, regions away from the 

river, where soils are thinner, experience greater ground motions 

at shorter wavelengths, which is a problem for smaller structures like homes.

These probabilistic seismic-hazard maps can be useful to 

zoning and planning officials in deciding about new development and can be useful to the financial and insurance industries 

in their assessment of seismic risk to a portfolio of structures.

Scenario-Based Ground Motion Maps

The second product produced by the EAEHMP is a set 

of scenario ground-motion maps. Figure 2 shows these maps 

for a period of vibration of 0.2 seconds. These maps differ 

from probabilistic seismic-hazard maps in that they consider 

a single earthquake source. As a result, the maps show the 

expected ground motions from a particular earthquake. The 

scenario maps may be particularly useful to emergency responders in anticipating and preparing for the potential effects of 

earthquakes.

The two greatest concerns for the Evansville region are 

earthquakes from New Madrid and the Wabash Valley. The 

New Madrid earthquakes of 1811–1812, although over 100 

miles (mi) away, produced the strongest ground shaking (Mercalli intensity VII) historically recorded near Evansville, and 

earthquakes from the New Madrid seismic zone are considered 

a viable threat to the region. The Wabash Valley, although less 

active in historic times, also poses a significant earthquake 

threat, particularly given its proximity to the region. Scenarios 

were thus developed for each of these seismic zones, using 

maximum credible (that is, worst case) earthquake magnitudes. 

For the New Madrid, a magnitude 7.7 earthquake was modeled from the northern section of the seismic zone, and for the 

Wabash Valley, a magnitude 6.8 was modeled approximately 

25 mi from the Evansville region.

The resulting scenario ground-motion models predict 

strong local variations across the Evansville area, with similar 

patterns for both the New Madrid and the Wabash valley scenarios. Ground motions along the Ohio River tend to be high at 

long periods (a problem for large structures), whereas ground 

motions away from the river tend to be high at short periods 

(a problem for small structures). In general, ground motions 

tend to increase towards the earthquake source, which is to the 

northwest for the earthquake in the Wabash Valley seismic zone 

and to the southwest for the earthquake in the New Madrid 

seismic zone.

If either of these scenario earthquakes were to occur 

today, significant damage would be expected. The Wabash 

Valley earthquake scenario is expected to produce a modified 

Mercalli intensity between VIII and IX along the Ohio River. 

This intensity would result in considerable damage to masonry 

structures. Wood-frame structures could be thrown off of their 

foundations. Intensities closer to VII would be experienced in 

much of the remaining area. At this level of ground shaking, 

chimneys would be damaged and masonry walls cracked. For 

the New Madrid scenario, intensities along the Ohio River are 

expected to be between VII and VIII and near VI elsewhere in 

the Evansville area.

37 ̊52'30"

87 ̊37'30" 87 ̊30' 87 ̊37'30" 87 ̊30'

38 ̊00'

SA (g)

0 – 0.07 5

0.07 5 –0 .1 5

0.15 –0 .22 5

0.22 5 – 0 .3

0.3 – 0.3 75

0.37 5– 0 .4 5

0.45 – 0 .52 5

0.52 5 – 0 .6

0.6 – 0.6 75

0.67 5 –0 .7 5

0 –0 .15

0.15 –0.3

0.3 –0.45

0.45 –0.6

0.6 –0.75

0.75 –0.9

0.9 –1.05

1.05 –1.2

1.2 –1.35

1.35 –1.5

New Madrid M 7.7 Wabash Valley M 6.8

EXPLANATION EXPLANATION

SA (g)

Figure 2. Scenario-based ground motion maps. These maps show the expected ground motions at a period of 0.2 seconds for two 

scenario earthquakes: a M 7.7 New Madrid earthquake and a M 6.8 Wabash Valley earthquake. (M, magnitude; SA, spectral acceleration; 

g, acceleration of gravity) 
Liquefaction-Potential Maps

The third product produced by the EAEHMP is a set of 

liquefaction-potential maps (fig. 3). These maps were generated for the two scenario earthquakes described above. Results 

indicate the degree to which liquefaction is likely at sampled 

sites across the region; results also indicate the severity of 

the potential ground deformation. For example, sites with a 

liquefaction potential of 5 or greater are likely to experience 

liquefaction, while sites with liquefaction potential greater 

than 12 are likely to see lateral spreading (substantial lateral 

movement of the land). Values for the liquefaction-potential 

index are high along the Ohio River, where the soil profiles are 

predominantly sand. Values away from the river in the uplands 

are lower, owing to the predominance of clay. For the Wabash 

Valley scenario, major liquefaction would be expected in the 

downtown Evansville area.

Like the scenario-based ground-motion maps, liquefactionpotential maps can be useful to emergency management in 

preparing for earthquakes. But, like the probabilistic maps, they 

can also help public officials make decisions about new development and locating critical infrastructure. 

0 – 0.1

0.1 – 0.2

0.2 – 0.3

0.3 – 0.4

0.4 – 0.5

0.5 – 0.6

0.6 – 0.7

0.7 – 0.8

New Madrid M 7.7 Wabash Valley M 6.8

Average LPI PGA (g)

0.0 0 –2 .0 0

2.0 1 –5 .0 0

5.0 1 –1 2 .00

12 .0 1– 1 5.0 0

15 .0 1– 2 0.0 0

20 .0 1– 3 0.0 0

37 ̊52'30"

87 ̊37'30" 87 ̊30' 87 ̊37'30" 87 ̊30'

38 ̊00'

EXPLANATION

Figure 3. Liquefaction potential index (LPI) maps. These maps show the mean liquefaction potential index from two scenario 

earthquakes: a M 7.7 New Madrid earthquake and a M 6.8 Wabash Valley earthquake. A LPI value of 5 means that there is a surface 

expression of liquefaction. A value of 12 indicates lateral spreading. (PGA, peak ground acceleration; g, acceleration of gravity) 
Acknowledgments

The Evansville seismic-hazard maps are a collaborative 

effort among the USGS and several regional partners including: Purdue University; the Center for Earthquake Research and 

Information at the University of Memphis (CERI); the State 

Geologic Surveys of Kentucky, Illinois, and Indiana; the Southwest Indiana Disaster Resistant Community Corporation; and 

the Central U.S. Earthquake Consortium State Geologists.

For more information, contact: 

Oliver Boyd 

Earthquake Hazards Program 

U.S. Geological Survey 

3876 Central Avenue, Suite 2 

Memphis, TN 38152 

901-678-3463

olboyd@usgs.gov

Evansville Hazard Mapping Reports:

Probabilistic Maps: http://pubs.usgs.gov/of/2011/1231/

Scenario Maps: http://pubs.usgs.gov/of/2011/1260/

Liquefaction Maps: http://pubs.usgs.gov/of/2011/1203/

Evansville Hazard Mapping website:

http://earthquake.usgs.gov/regional/ceus/urban_map/evansville/

Earthquake Hazards Program:

http://earthquake.usgs.gov/

For more information on seismic hazard assessments, see: 

United States National Seismic Hazard Maps, 

http://pubs.usgs.gov/fs/2008/3017/

Urban Seismic Hazard Mapping for Memphis, Shelby County, 

Tennessee, http://pubs.usgs.gov/fs/2005/3142/

St. Louis Area Earthquake Hazards Mapping Project, 

http://pubs.usgs.gov/fs/2007/3073/

isasteresistant ommunity

Institute of Natural Resource Sustainability

ILLINOIS STATE GEOLOGICAL SURVEY

Partners:

Purdue University

Center for Earthquake Research and Information at the 

 University of Memphis

Kentucky Geological Survey

Illinois State Geological Survey

Indiana Geological Survey

Southwest Indiana Disaster Resistant Community Corporation

Central U.S. Earthquake Consortium State Geologists