Geophysical Imaging of Subsurface Structures in the Charleston-Summerville, South Carolina Intraplate Seismic Zone

Session: Seismicity and Tectonics of Stable Continental Interiors
Type: Oral
Date: 4/30/2020
Time: 11:30 AM
Room: 240
Description: 

The Charleston-Summerville area in South Carolina is a well-known intraplate seismic zone but there is limited information regarding faults that have ruptured in the past or may pose significant seismic risk in the future. The region was the site of an M~7.0 earthquake in 1886 which heavily damaged urban areas, but the causative fault remains unknown. Modern seismicity (mostly <M3.0) occurs in a (~23 x 15 km) tabular zone. As seismogenic structures are likely to be buried beneath Mesozoic and Cenozoic sedimentary strata, geophysical imaging of the subsurface is required. In the summer of 2019, the USGS contracted airborne geophysical surveys to better image both basement structures (via magnetic data) and variations in shallow sediments (via radiometric data). Derivative and filtered magnetic anomaly maps of the reduced-to-pole data highlight numerous lineaments. These include narrow (<2 km wide) N- to NNW-trending lineaments likely representing Mesozoic dikes, wider (2-5 km wide) ESE- to ENE-trending lineaments subparallel to structures of the Mesozoic South Georgia rift basin and longer NE-trending lineaments or terminations of magnetic anomalies that likely represent Paleozoic structures. Some modern earthquakes coincide with E- and ESE-trending anomalies that are at most 20 km long. If these magnetic anomalies represent the full length of the associated fault or faults, then it is unlikely that they represent the fault that ruptured in 1886. In contrast, the NE-trending lineaments are up to 60 km long, with some crossing estimated epicenters for the 1886 event and thus present more favorable candidates for faults capable of Mw7.0 or greater rupture. Ongoing work includes analyses of seismic reflection and ground-penetrating radar data to determine whether and where recent slip has disturbed the shallow sedimentary cover near these anomalies.

Presenting Author: Anjana K. Shah

Authors