USGS RESPONSE TO THE MINERAL, VIRGINIA MW5.8 EARTHQUAKE OF 23 AUGUST 2011

The Mw5.8 earthquake that struck Louisa County, VA on 23 August 2011 was among the largest to occur along the eastern seaboard in historic time. The earthquake caused damage as far as Washington D.C. and Baltimore, MD and was felt by more people than any other in US history. The earthquake occurred on a northeast-striking plane within a region of diffuse seismicity known as the central Virginia seismic zone. USGS web and internet broadcast of earthquake data (location, magnitude, depth expected shaking, and felt area) happened within minutes of the event.

The USGS mobilized within hours, sending seismic deployment crews and equipment from Golden, CO, Menlo Park and Pasadena, CA to coordinate with crews and staff from other earthquake research institutions. Five portable seismographs were operational by 24 August, and captured data from the largest aftershock (Mw3.9, 25 August). By 1 September, more than 40 3-component seismographs, and 200 single-component recorders had been located throughout the region, making this the best-recorded aftershock sequence in the eastern U.S.

USGS staff from Reston, VA and Golden, CO arrived in the area soon after the earthquake to begin damage assessment and search for seismically-induced ground deformation. Systematic damage assessment began on 24 August; USGS personnel worked closely with the VA Dept of Mines, Minerals and Energy. Damage assessment was conducted primarily to assist Louisa County with relief efforts. The second task, documenting ground deformation, was time-critical, as a major storm was projected to affect the region by Saturday, 27 August; rainfall from this event would significantly modify or destroy these features. Several sand boils, river-bank slumps and rock falls were located over a wide area in the region.

Since the earthquake, USGS has implemented cross-program science and management coordination teams, with five goals: 1) understand the regional geological and geophysical setting; 2) characterize the source of the earthquake; 3) characterize the severity and distribution of seismic shaking; 4) document the distribution and characteristics of ground deformation; and 5) update eastern US seismic hazard assessments and preparedness. The work conducted in the days immediately after the main shock set a solid foundation for implementation of these goals.