UNDERSTANDING EARTHQUAKE HAZARDS IN URBAN AREAS 

St. Louis Area Earthquake Hazards Mapping Project 

St. Louis has experienced minor earthquake damage at least 12 times in 

the past 200 years. Because of this history and its proximity to known 

active earthquake zones, the St. Louis Area Earthquake Hazards Mapping 

Project will produce digital maps that show variability of earthquake 

hazards in the St. Louis area. The maps will be available free via the internet. They 

can be customized by the user to show specific areas of interest, such as neighborhoods or transportation routes. 

Earthquakes currently cannot be partners to develop detailed maps for urban 

predicted, but scientists can estimate how areas vulnerable to strong ground shaking. 

strongly the ground is likely to shake as the These partners include the University of 

result of an earthquake. Earthquake hazard Missouri-Rolla, Missouri Department of 

maps provide one way of conveying such Natural Resources, Illinois State Geological 

estimates. The U.S. Geological Survey Survey, Saint Louis University, Missouri 

(USGS), which produces earthquake hazard State Emergency Management Agency, and 

maps for the Nation, is working with local URS Corporation. 

92° 86° 90° 88° 

Champaign

40° Decatur Indianapolis Springfield 

1909

ILLINOIS Terre Haute 

MISSOURI 

Columbia Wabash Valley 1987 seismic zone St. Louis 1838

1891 INDIANA 

2002

38° 1917 Evansville 1968

1965 KENTUCKY 

1895

Paducah 

1812 Clarksville 

1812 New Madrid Nashville seismic zone 36° 1865

ARKANSAS Jonesboro 1811 Jackson 

TENNESSEE 

Memphis 

Florence Huntsville 

Little Rock 

MISSISSIPPI Decatur 

Pine Bluff ALABAMA 34° 

Earthquakes (circles) of the New Madrid and Wabash Valley seismic zones (orange patches). 

Red circles are earthquakes that occurred from 1974 to 2002. Green circles are earthquakes that 

occurred prior to 1974. Larger earthquakes are represented by larger circles. Yellow patches 

show larger urban areas. 

Looking west from a geophysical measurement site in east St. Louis, Mo. (Photograph by 

Dave Hoffman.) 

What is Earthquake 

Hazard? 

Earthquake hazard refers to a measure 

of the shaking, or ground motion, during earthquakes that can damage our built environment. 

The hazard depends on the magnitudes and 

locations of likely earthquakes, how often they 

occur, and the properties of the rocks and sediments that earthquake waves travel through. In 

the central U.S., earthquakes occur along the 

New Madrid and Wabash seismic zones and in 

a zone of earthquakes that are scattered across 

southern Illinois and eastern Missouri. 

Who Uses Earthquake 

Hazard Maps? 

Public and private groups can use hazard 

maps for planning, mitigation, and response 

efforts in order to minimize losses resulting 

from earthquake shaking. Portfolio managers in 

the lending, insurance, and wealth management 

industries can use the maps to better manage 

risk exposure. Planning and zoning professionals can use the maps for hazard considerations 

in locating new development, critical facilities, 

and transportation corridors. Business continuity managers can use the maps to minimize 

earthquake-related losses to their facilities, 

supply networks, and market share. The scale 

of the maps will not allow them to be used in a 

site-specific manner, but rather as a guide as to 

where more detailed studies are needed. 

Fact Sheet 2007–3073 U.S. Department of the Interior Printed on recycled paper September 2007 U.S. Geological Survey 
sediment properties determined in this project 

Alluvium 

(soft) 

Floodplain 

Loess 

As much as 

50 m thick 

Soil 

Soil 

Bedrock 

(hard) 

Earthquake waves 

can amplify in soft 

soil such as alluvium 

Upland 

Upland 

Making Earthquake 

Hazard Maps 

Geologists map earth materials at the 

ground surface. Properties of these surficial materials, how deeply they extend, and 

properties of the bedrock below them are 

determined from measurements made in 

boreholes and cores drilled for construction 

projects and from oil, gas, mining, and waterwell data. Information about the subsurface is 

obtained from imaging techniques, much like The diagram above is a block model showing simplified geology typical of the St. Louis area. 

The national seismic hazard map (above) shows the level of shaking in percent “g” (100 percent 

g is equivalent to the acceleration of a falling object caused by gravity). 

The highlighted box within the inset shows the location of the recently completed seismic 

hazard map for Memphis, Tenn., where sediment is taken into account. The differences in 

seismic hazard between the national-scale and Memphis area maps result directly from 

including the effects of the sediments in the urban-scale map. 

Earthquake hazard maps such as these, and those planned for St. Louis, will help the region 

prepare for future earthquakes and reduce losses. 

X-ray or ultrasound imaging is used to view 

the interior of the human body. These data are 

then combined to construct a three-dimensional (3-D) model of the layering of rock, 

soil, and alluvium. 

Soil (weathered bedrock), loess, and 

alluvium layers change the way earthquake 

waves travel through them from an earthquake below. The 3-D model describes the 

layering beneath any location, and is used to 

calculate how the shaking from the waves will 

vary from place to place. For example, the 

sediments in the river floodplain may amplify 

some types of shaking more than at sites 

located on the upland areas. 

The investigations done to produce the 

St. Louis area hazards maps will result in a 

variety of other products. Among these are 

maps of the surficial geologic materials as well 

as maps showing the likelihood of liquefaction. 

Liquefaction occurs when water-saturated 

sediments lose their cohesive strength during 

violent ground shaking. An online database of 

is also planned. 

EXPLANATION

Highest hazard 

320+
 

240
 

160
 %g 80 

40 

20 

0 

Lowest hazard 

Loess is a soft sediment carried and deposited by wind during the last glacial episode about 

15,000 years ago; soils are soft materials often developed by weathering of bedrock; alluvium 

is soft river-deposited sediment that comprises most of the Missouri and Mississippi River 

floodplains. Structures located in the floodplains will likely experience stronger ground 

shaking and a greater likelihood of liquefaction. Bedrock is most commonly a hard 350 millionyear-old limestone in the St. Louis area. Structures built on or near bedrock, such as in the 

upland areas out of the floodplains, will tend to have lower levels of earthquake ground 

shaking. Earthquake hazard maps, like the ones in development for St. Louis, provide needed 

information for the design of new structures and retrofitting of existing ones. 

Memphis 

area 

ARKANSAS

TENNESSEE

MISSISSIPPI

MISSISSIP P I RIVER 

For more information contact: 

Eugene Schweig 

Earthquake Hazards Program 

U.S. Geological Survey 

3876 Central Avenue, Suite 2 

Memphis, TN 38152 

901-678-4974 

schweig@usgs.gov 

Phyllis Steckel 

Consulting Geologist 

psteckel@charter.net 

St. Louis Hazard Mapping website: 

http://earthquake.usgs.gov/ 

regional/ceus/urban_map/st_louis/ 

index.php 

Earthquake Hazards Program: 

http://earthquake.usgs.gov/ 

Partners: 

Missouri Department of 

Natural Resources, Illinois State 

Geological Survey, University 

of Missouri-Rolla, Missouri 

State Emergency Management 

Agency, Saint Louis University, 

URS Corporation.