PRELIMINARY ANALYSIS OF LIDAR DATA ACQUIRED FOR EPICENTRAL AREA OF AUG 23, 2011 M5.8 EARTHQUAKE IN THE CENTRAL VIRGINIA SEISMIC ZONE

LIDAR data acquired for the epicentral area of the M5.8 earthquake near Mineral and Louisa, VA is being used by field geologists to search for fault scarps or other surface features possibly created by recent faulting. From visual inspection of the composite LIDAR bare-earth hillshade image covering 700 sq.km, there are no obvious features that we can identify as surface deformation from the M5.8 event, which agrees with field investigations to date. Three widespread and abundant linear trends which are visible in the LIDAR are identifiable with observed bedrock structure: Paleozoic foliation, trending N30-50E, Mesozoic dike swarms, trending ~N-S to ~N15E, and Cenozoic jointing, trending N45-60W. A widely spaced fabric trending ~E-W does not correlate with any surface feature known to date. The N30E, SE-dipping attitude of the M5.8 earthquake suggests that slippage reactivated a portion of the Paleozoic fabric. Within the zone of where the causative structure projects to the surface, there are only a few N30E-trending linear features identifiable on LIDAR; the longest and most pronounced is a segment of Harris Creek near its confluence with South Anna River. There, recent USGS exploratory trenching has identified deformed Quaternary surficial deposits, so the future utility of LIDAR as a guide to field investigations and for possibly locating Quaternary deformation (paleoseismic features) appears promising. Also, the LIDAR image reveals patterns in regional landscape evolution, which can be used to interpret regional tectonic effects, such as Quaternary flexing of the earth’s surface into domes or areas of subsidence. For example, just west of Mineral, the LIDAR bare-earth model clearly shows an old abandoned channel that would have connected Contrary Creek (presently north flowing) with Northeast Creek (south flowing), indicating stream piracy that is consistent with regional uplift of the epicentral area. Reclassification of raw LIDAR data in existing 1 sq. km areas that are chosen for further seismologic, geologic, or geomorphic study may reveal other features suggestive of Quaternary deformation and lead to further examination by detailed field inspection.