The 15 February 2014 M-w 4.1 South Carolina Earthquake Sequence: Aftershock Productivity, Hypocentral Depths, and Stress Drops

The border between Georgia and South Carolina has a moderate amount of seismicity typical of the Piedmont Province of the eastern United States and greater than most other intraplate regions. Historical records suggest on average a M-w 4.5 earthquake every 50 yr in the region of the J. Strom Thurmond Reservoir, which is located on the border between Georgia and South Carolina. The M-w 4.1 earthquake on 15 February 2014 near Edgefield, South Carolina, was one of the largest events in this region recorded by nearby modern seismometers, providing an opportunity to study its source properties and aftershock productivity. Using the waveforms of the M-w 4.1 mainshock and the only cataloged M w 3.0 aftershock as templates, we apply a matched-filter technique to search for additional events between 8 and 22 February 2014. The resulting six new detections are further employed as new templates to scan for more events. Repeating the waveform-matching method with new templates yields 13 additional events, for a total of 19 previously unidentified events with magnitude 0.06 and larger. The low number of events suggests that this sequence is deficient in aftershock production, as compared with expected aftershock productivities for other mainshocks of similar magnitudes. Hypocentral depths of the M-w 4.1 mainshock and M-w 3.0 aftershock are estimated by examining the differential time between a depth phase called sPL and P-wave arrivals, as well as by modeling the depth phase of body waves at shorter periods. The best-fitting depths for both events are around 3-4 km. The obtained stress drops for the M-w 4.1 mainshock and M-w 3.0 aftershock are 3.75 and 4.44 MPa, respectively. The corresponding updated moment magnitude for the aftershock is 2.91.