Indonesian Earthquake Response

The national news media recently reported on a USGS groundwater monitoring well in Virginia that responded dramatically to the December 26, 2004 Indonesian earthquake. The earthquake resulted in devastating tsunamis occurring throughout the Indian Ocean. A water level recorder installed in the Virginia well showed a spike in water level of approximately 2 feet. The well did not recover completely from the seismic disturbance for almost 5 hours. Read the Virginia well story by clicking on this link .

Intrigued by the story of the Virginia well reacting to the earthquake, we decided to examine the data from a few local wells to see if the same phenomenon was present. The only criteria used to select a well for examination was depth (greater than 1000 feet) and that the well be in the USGS real-time data network (i.e., the data was readily accessible from the web). The data from eight wells was examined. All wells are located in the west-central Florida area. Every well examined showed some sign of activity on December 26, 2004 (though it was more apparent in some wells than others). The examples below show a sudden rise in water level of about 0.25 to 0.5 feet. The water levels did not completely fall from the seismic activity for more than 24 hours.

Like the well in Virginia, all of the wells examined are installed in a confined limestone aquifer. Presumably, as seismic waves travel through the aquifer, at speeds of about 125 miles per minute, the rock expands and contracts. This elastic motion within the aquifer results in fluctuations in water level. Notice in the examples above that the peak in water level is not smooth. There are dips in the peaks that correspond to aquifer expansion. Limestone is relatively soft and has the capacity to store vast amounts of water, which probably responds to earthquake waves in a more dramatic fashion than hard rock aquifers found in other parts of the United States. This might explain why fluctuations in water level were only seen in certain areas. Click on this link to NASA to see how the planet as a whole was affected by the earthquake.