LIDAR LINEAMENT ANALYSIS OF THE CENTRAL VIRGINIA SEISMIC ZONE – METHODOLOGY AND PRELIMINARY RESULTS

Following the 2011 M5.8 Mineral, Virginia earthquake, high-resolution, QL1 (post-spacing 0.33 m) airborne LiDAR data was collected over a 1300 km² area in the epicentral region. The VA Department of Mines, Minerals and Energy and U.S. Geological Survey are currently analyzing these data to identify linear features potentially associated with neotectonic faulting in the Central Virginia Seismic Zone (CVSZ).

Hillshade (shaded relief), slope, and aspect raster datasets have been generated from the LiDAR-derived bare-earth digital elevation data. Methodology for lineament analysis follows Mabee et al. (1994) published in Ground Water, v. 32, n.6. First, linear features are identified independently by two different geologists via visual inspection of each of the raster datasets in ArcGIS at a map scale between 1:10,000 and 1:15,000. The inspection is repeated twice for each dataset by both geologists as a “double blind” test. Next, lineaments visually identified twice by a single geologist are compared to those twice identified by the other for each dataset – those that were recognized by both workers are raised to a higher level of significance. This subset of lineaments is then compared to those identified for each of the other datasets. Lineaments identified by both geologists on multiple datasets are graded by level of significance: Grade A – identified by both authors on all three datasets; Grade B - identified by both authors on two of three datasets; Grade C - identified by both authors on a single dataset; Grade D – identified by a single author on one or more dataset.

Preliminary analysis suggests that lineaments in the epicentral area are strongly controlled by lithologic contacts and regional joint sets. Surface weathering, stream incision and neotectonic uplift in the seismic zone have all contributed to the topographic expression of these lineaments. Apparent changes in joint set density and spacing occur within major rock units. Although no linear features have yet been conclusively associated with recent faulting in the CVSZ, there is a potential that these lithologic bedding, joint, or foliation planes could have acted as planes of movement in the geologic past, or could be a focus for future rupture.