Improved Understanding of Intraplate Earthquakes in the Southeastern USA with Matched Filter Detection

Most earthquakes occur along plate boundaries and are caused by the repeated accumulation and release of strain in the rocks of tectonic plates moving past one another. However, the same forces driving these interplate earthquakes does not account for intraplate earthquakes, which are located within the interiors of a tectonic plate. The relatively long recurrence intervals between large earthquakes, causal fault locations, and driving mechanisms of intraplate earthquakes present a challenge to understanding their physical mechanisms and the seismic hazard in intraplate regions.

To better understand earthquake and fault properties in intraplate settings, a more complete detection of earthquakes, precise locations, and magnitude estimations are critical. Traditional earthquake catalogs tend to miss smaller earthquakes due to high background noise or during
intensive sequences, which results in an incomplete catalog. To overcome this, we use a matched filter method to detect microseismicity and build a more complete catalog. This technique applies cross correlation to detect previously uncatalogued events in continuous data by using the
waveforms of known earthquakes as templates.

This thesis focuses on earthquake detection in the Southeastern United States, an intraplate region on the North American Plate, which hosts several seismic zones not well understood yet. In particular, I focus on the Piedmont Province in Georgia and South Carolina, Eastern Tennessee
Seismic Zone (ETSZ), and Middleton Place Summerville Seismic Zone (MPSSZ) near Charleston, South Carolina.

In the Piedmont Province, I found that the 2014 Mw 4.1 Edgefield, South Carolina in the Piedmont Province had a deficient aftershock sequence, suggesting that most of the strain was released during the mainshock. The mainshock and its largest M3.0 aftershock also had relative shallow
hypocentral depth of 3 4 km, which may account for their low stress drops and the low number of aftershocks. I also examined the recent 2018 Mw 4.4 earthquake in the ETSZ, and detected very few aftershocks. In addition, the mainshock had a depth range of 5 6 km, shallower than the
typical background seismicity in the ETSZ. By performing rupture directivity analysis, I found that the mainshock appears to rupture bi laterally along an E/NE trending strike slip fault, which is consistent with the relocated aftershock locations and one of the nodal planes of the mainshock.
The occurrence of the 2018 Mw 4.4 mainshock at a relatively shallow depth and its close proximity to the nearby Watts Bar Nuclear Power Plant, highlight the need to reevaluate seismic hazard associated those moderate size earthquakes along the ETSZ.