HYDROLOGIC RESPONSE TO THE MW5.8 MINERAL, VIRGINIA, EARTHQUAKE —LESSONS LEARNED

The M_w5.8 Mineral, Virginia, earthquake on August 23, 2011, affected groundwater levels in 34 bedrock water-level monitoring wells as far away as 553 km. These water-level offsets correlated with intensities of 2.2 or greater, which led to our conclusion that ground motion from seismic waves caused these offsets. The existing groundwater-level monitoring network for the fractured-rock and karst aquifers of the eastern United States was not designed for monitoring earthquake response, but proved very useful in assessing the hydrologic response to the Mineral earthquake. The lack of water-level offsets south of Virginia combined with the directional nature of the offsets observed was correlated with the distribution of peak ground acceleration on the National Seismic Hazards Map. Our experience with the analysis of these data also provides some insight into the existing water-level network. The time-consuming process of identifying water levels potentially affected by the Mineral earthquake illustrates the need for a real-time network of observation wells known to be affected by seismic events. In order to better assess the initiation, magnitude of offset, slope, and duration of the hydroseismic response , an increased frequency of data collection (ideally 5-minute intervals) is needed, along with a precision and dynamic range capable of discerning small (<0.01 m) short-term and large (several meters) long-term changes. Topographic position of observation wells also is an important factor in how the offsets are interpreted. Finally, evaluation of hydrologic responses to teleseismic events may provide insight to seismic hazard mapping in areas of limited earthquake activity and supplement the lack of high resolution seismometers.