Map prepared by U.S. Geological Survey

National Earthquake Information Center

23 August 2011

Map not approved for release by Director USGS

EARTHQUAKE SUMMARY MAP U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

DISCLAIMER

Base map data, such as place names and political

boundaries, are the best available but may not be

current or may contain inaccuracies and therefore

should not be regarded as having official significance.

Wilmington

Bowie

Columbia

Dundalk

Ellicott

City

Frederick

Gaithersburg

Germantown

Silver

Spring

Towson

Wheaton-Glenmont

Camden

Toms

River

Trenton

Vineland

Lancaster

Levittown

Reading

Annandale

Arlington

Burke

Dale

City

Hampton

Lynchburg

Newport

News

Portsmouth

Reston

Richmond

Roanoke

Suffolk

Washington

Baltimore

Philadelphia

Pittsburgh

Norfolk

Virginia

Beach

Dover

Dover

Harrisburg

Harrisonburg

Staunton

Morgantown

76°

76°

78°

78°

80°

80°

40° 40°

38° 38°

D STATES

CO

TH

ICA

TE

Gulf

of

Mexico

Rio Grande R iver

Manitoba

Ontario

North Minnesota

Dakota

Michigan Wisconsin

Nova

Scotia

South

Dakota

New

Hampshire

Vermont

Iowa

Nebraska

Pennsylvania

Illinois

Ohio

Connecticut

Indiana

West

Missouri Virginia

Kansas Delaware

Maryland

Oklahoma

Tennessee

Kentucky Virginia

North

Arkansas Carolina

South

Carolina

Alabama

Mississippi

Georgia

Tamaulipas

Florida

Texas

Quebec

Newfoundland

Prince

Edward

Island

New

Brunswick

Maine

Massachusetts

New York

Louisiana

Bahamas

Winnipeg

Montreal

Minneapolis

Toronto

M Rochester ilwaukee Buffalo

Detroit Boston

Cleveland

Pittsburgh

Columbus Indianapolis

Cincinnati Baltimore

Kansas

City

Washington

D.C.

St.

Louis

Memphis

Dallas

Jacksonville

New

Orleans

Houston

Miami

Chicago

New York

Philadelphia

60°

60°

70°

70°

80°

80°

90°

90°

50° 50°

40° 40°

30° 30°

M5.8 Virginia Region Earthquake of 23 August 2011

0 125 250

Kilometers

Canada

United States

Montreal

Minneapolis

Toronto

M Rochester ilwaukee Buffalo

Detroit Boston

Cleveland

Pittsburgh

Columbus Indianapolis

Baltimore Cincinnati

Kansas

City Washington

D.C.

St.

Louis

Memphis

Dallas

Jacksonville

New

H Orleans ouston

Miami

Chicago

New York

Philadelphia

60°

60°

70°

70°

80°

80°

90°

90°

50° 50°

40° 40°

30° 30°

DATA SOURCES

EARTHQUAKES AND SEISMIC HAZARD

USGS, National Earthquake Information Center

NOAA, National Geophysical Data Center

HDF (unpublished earthquake catalog) (Engdahl, 2003)

Global Seismic Hazard Assessment Program

BASE MAP

NIMA and ESRI, Digital Chart of the World

USGS, EROS Data Center

NOAA GEBCO and GLOBE Elevation Models

ESRI Online

0 250 500 1,000 1,500

Kilometers

Scale

Prepared in

cooperation

with the Global

Seismographic

Network

Tectonic Setting

Seismic Hazard

Epicentral Region

The Virginia earthquake of 2011 August 23 occurred as reverse faulting on a north or northeast-striking plane

within a previously recognized seismic zone, the “Central Virginia Seismic Zone.” The Central Virginia Seismic

Zone has produced small and moderate earthquakes since at least the 18th century. The previous largest historical

shock from the Central Virginia Seismic Zone occurred in 1875. The 1875 shock occurred before the invention of

effective seismographs, but the felt area of the shock suggests that it had a magnitude of about 4.8. The 1875

earthquake shook bricks from chimneys, broke plaster and windows, and overturned furniture at several locations.

A magnitude 4.5 earthquake on 2003, December 9, also produced minor damage.

Previous seismicity in the Central Virginia Seismic Zone has not been causally associated with mapped geologic

faults. Previous, smaller, instrumentally recorded earthquakes from the Central Virginia Seismic Zone have had

shallow focal depths (average depth about 8 km). They have had diverse focal mechanisms and have occurred over

an area with length and width of about 120 km, rather than being aligned in a pattern that might suggest that they

occurred on a single causative fault. Individual earthquakes within the Central Virginia Seismic Zone occur as the

result of slip on faults that are much smaller than the overall dimensions of the zone. The dimensions of the

individual fault that produced the 2011 August 23 earthquake will not be known until longer-term studies are done,

but other earthquakes of similar magnitude typically involve slippage along fault segments that are 5 – 15 km long.

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a

much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a

similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at

many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A

magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and

sometimes causes damage as far away as 40 km (25 mi).

Seismic hazard is expressed as peak

ground acceleration (PGA) on firm

rock, in meters/sec2, expected to be

exceeded in a 50-yr period with a

probability of 10 percent.

0 250 500 1,000 1,500

Kilometers

Scale

Scale 1:2,000,000

Peak Ground Acceleration in m/sec**2

.2 .4 .8 1.6 2.4 3.2 4.0 4.8

EPICENTRAL REGION

1:20,000,000

1:20,000,000

EPICENTRAL REGION

Note on earthquakes: Through 1989, earthquakes shown are from the US

Catalog, magnitudes greater than 0. From 1990-present, earthquakes are

from NEIC, magnitudes greater than 0.

A'

EXPLANATION

Main Shock

Earthquake Locations

Magnitude

<3.0

3.0 - 3.9

4.0 - 4.9

5.0 - 5.9

Aftershocks

US Metropolitan Areas

TECTONIC SUMMARY

EXPLANATION

Main Shock

Main Shock

Earthquake Locations

Magnitude

< 4.0

4.0 - 5.0

5.0 - 5.9

PAGER

Did You Feel It?

ShakeMap

Significant Earthquakes Mag >= 4.0 Since 1973

Year Mon Day Time Lat Long Dep Mag

1984 04 23 0136 39.921 -76.355 5 4.4

1984 08 17 1805 37.868 -78.324 8 4.2

1994 01 16 0042 40.327 -76.007 5 4.0

1994 01 16 0149 40.33 -76.037 5 4.6

2003 12 09 1854 37.587 -77.903 5 4.5

2011 08 23 1751 37.936 -77.933 6 5.8

M 5.8 Virginia Region Earthquake of 23 August 2011

23 August 2011 17:51:03 UTC

37.975° N., 77.968° W.

Depth 6 km

Mw = 5.8 (USGS)