Groundwater-Level Response to Earthquakes

Science Center Objects

Did you know that earthquakes can cause changes in groundwater levels? Very large earthquakes can even cause water-level fluctuations in some wells thousands of miles away, depending on the local geological conditions around the well.

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.

USGS Groundwater Well

USGS groundwater site 414831072173002 in Tolland County, Connecticut, near the Hydrogeophysics Branch office.

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 step-like 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.


Changes in groundwater hydrographs after an earthquake

Over time, USGS has observed a network of groundwater wells monitored by USGS and cooperating agencies where water-level changes have been observed after large earthquakes around the world. Not all wells show water-level changes after every quake, and the response can vary from well to well. A graph of groundwater levels over time is called a hydrograph. In the event of a large earthquake, users can view the real-time hydrographs for some of these wells through the USGS National Water Information System (NWIS).

Comparison of water-level responses in two wells

A USGS groundwater monitoring site in Christiansburg, Montgomery County, Virginia, is well known to display water-level fluctuations as a result of large earthquakes worldwide. Observation well 27F2 SOW 019 is sensitive to teleseismic waves generated by large earthquakes (usually greater than magnitude 6.0) that occur around the world. This well is 450 feet deep, finished in carbonate rocks of the Elbrook Formation, and water enters the well via fractures or cracks in the rock. Compression and expansion of these fractures by seismic waves cause the water to be drawn in and out of the well, similar to the way bellows work.  As groundwater moves in and out of the well, the water level in the well rapidly rises and falls. This water-level oscillation is recorded at 5-minute intervals by a pressure transducer and data logger maintained by the Virginia Department of Environmental Quality.  Every hour, these data are transmitted via satellite to a computer located at the U.S. Geological Survey Virginia Water Science Center in Richmond, Va. 

The USGS groundwater monitoring site 414831072173002 (observation well CT-MS 80 Mansfield, CT) in Tolland County, Connecticut also collects water-level measurements every five minutes.

By comparing the water-level response at these two sites to a large earthquake in Alaska on January 23, 2018, we can observe and study the relationship between groundwater levels and earthquakes.


Two Wells showing depth change

The graph above shows measured depth to water level in feet below land surface for these two wells for January 21 to 25, 2018, which includes the period for a large earthquake in Alaska on January 23, 2018. The top line (blue) is the water level recorded in the Connecticut well (USGS 414831072173002) with depth below land surface shown on the left axis, and the bottom line (red) is the recorded water level in the Virginia well (USGS 370812080261901) with depth below land surface shown on the right axis. The data indicate a possible groundwater-level change in the Virginia well due to the earthquake, but no change was measured in the Connecticut well. (At the time this figure was created, these data were preliminary or provisional and were subject to revision. Water levels had not been corrected for barometric pressure and Earth tide affects. Approved data are now available.)

Example Hydrographs from M7.9 Gulf of Alaska Earthquake

magnitude 7.9 earthquake occurred at 12:32 am Alaska time (09:32 UTC) on January 23, 2018, at a depth of about 8.76 miles (14.1 kilometers) beneath the Gulf of Alaska. Hydrographs indicating possible groundwater-level changes due to this earthquake are shown below. These provisional data are presented in a combined, simplified figure to highlight the observed change in water levels associated with the earthquake. Note that water levels have not been corrected for barometric pressure and Earth tide affects.

graphs showing groundwater level change

Hydrographs indicating possible groundwater level changes due to January 23, 2018, Gulf of Alaska M7.9 earthquake. Learn how to use the R dataRetrieval to create a figure like this. (These data are preliminary or provisional and are subject to revision.)


Example Hydrographs from 2011 Mineral, Virginia, Earthquake

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. Sample 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 2011 Virginia earthquake was approximately two feet at the NP 820 Northampton County Observation Well in Pennsylvania. Most observed water-level changes were less than 0.5 feet.

The six hydrographs below present groundwater levels measured in selected wells monitored by the USGS. The hydrographs presented here are produced from wells with near real-time instrumentation. 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.