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USGS maintains a network of active wells to provide basic statistics about groundwater levels.

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Groundwater-Level Response to Virginia Earthquake, August 23, 2011

Overview

A magnitude 5.8 (Mw) earthquake occurred at 1:51 pm EDT (17:51 UTC) on August 23, 2011, at a depth of about 3.7 miles (6 kilometers) beneath the town of Mineral, Virginia, located approximately 27 miles (45 km) east of Charlottesville. The event is among the largest earthquakes recorded in the eastern United States.

How do Earthquakes Affect Groundwater Levels?

Groundwater-level responses to earthquakes have been investigated for decades, and have been documented close to and far from earthquake epicenters. The most common groundwater-level response is a water-level oscillation. This occurs frequently, but often is not recorded because water-level measurements typically are not recorded frequently enough with today’s electronic instrumentation to record the water-level response. An instantaneous water-level offset, or step, is more commonly recorded. These step changes can be large enough to make a well flow at land surface, or to cause a well to go dry near an earthquake. Typically, however, the water-level changes are several feet or less. Recovery to the pre-earthquake water level can be nearly instantaneous, or it may take as long as days or months, or may not recover at all.

Groundwater-level responses most often occur as the earthquake’s seismic wave train arrives (coseismic), though responses have been observed after the wave train passes (postseismic); scientists also are investigating water-level changes observed before an earthquake (preseismic), though research is needed to explain these phenomena.

Step changes in groundwater levels occur 'near field' of an earthquake because the earthquake subjects the earth's crust, including its aquifer systems, to stress and permanent strain (deformation). This deformation process results in altered fluid pressure within the aquifer systems, and consequently, a steplike change in water level would be expected. Changes can be up or down, because the stress and strain effects on the system vary. For upward steps in shallow wells, compaction of overlying sediments may raise the groundwater level. Alternately, in a fractured rock aquifer, the fractures providing water to the well may be widened, unclogged, or sealed by the wave train of an earthquake. New water-bearing fractures may even be created. Water levels in these systems can permanently increase or decrease as a result.

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Example Hydrographs

Sample graphs of groundwater levels (hydrographs) have been selected from USGS wells as examples of the response of measured groundwater levels to the August 2011 earthquake:

The maximum water level change recorded in the USGS real-time groundwater network due to the August 23, 2011, Virginia earthquake was approximately two feet in a well in Pennsylvania. Most water level changes were less than 0.5 feet.

The hydrographs presented here are produced from wells with near real-time instrumentation. Data are provided automatically via satellite in near real time. The USGS monitors other wells in these areas, but measurements from those wells are not available until they are retrieved from the field and loaded into the USGS National Water Information System.



Slide Show of Selected Hydrographs

The six hydrographs below present groundwater levels measured in selected wells monitored by the USGS (all data are from the National Water Information System web site). These graphs were selected as examples of locations where measured groundwater levels responded to the August 23, 2011, Virginia earthquake. The red arrow indicates the approximate time of the mainshock of the earthquake near Mineral, Virginia.

Hydrograph Hydrograph Hydrograph Hydrograph Hydrograph Hydrograph

USGS Site Number

State

Well Depth,
in feet

Aquifer

Hydrograph

372322081241501

West Virginia

152

Pocahontas Formation

hydrograph

394024078273401

Maryland

114.5

Brallier Formation

hydrograph

372150079422301

Virginia

201

Piedmont and Blue Ridge crystalline-rock aquifers

hydrograph

370812080261901

Virginia

450.00

Valley and Ridge aquifers

hydrograph

421157075535401

New York

252

Sonyea Formation

hydrograph

402411077374801

Pennsylvania

110

Brailler and Harrell Formations

hydrograph


Eastern Seaboard Map

The points on the map below indicate approximate locations of selected USGS groundwater monitoring wells where measured groundwater levels responded to the August 23, 2011, Virginia earthquake. Click on a well location to view a graph of the groundwater level measured at that location.


Disclaimer: References to non-U.S. Department of Interior (DOI) products do not constitute an endorsement by the DOI. By viewing the Google Maps API on this web site the user agrees to these Terms of Service set forth by Google.
The USGS information displayed in this map can also be downloaded as a KML file [20KB].

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For More Information

For more information on the effect of earthquakes on wells, streams, and springs, visit the following online resources:

Additional questions can be directed to Rod Sheets (614-430-7710), USGS Water Science Field Team Groundwater Specialist.

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Page Last Modified: Wednesday, 26-Feb-2014 20:13:21 EST