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Shaking in the southeastern United States; examining earthquakes and blasts in the central Georgia-South Carolina seismic region

Rachel E. Marzen, James B. Gaherty, Donna J. Shillington and Won-Young Kim
Shaking in the southeastern United States; examining earthquakes and blasts in the central Georgia-South Carolina seismic region
Seismological Research Letters (July 2021) 92 (5): 3145-3164

Abstract

Seismicity in the southeastern United States is relatively poorly characterized and thus not well understood. Structures and heterogeneities from multiple stages of Appalachian orogenesis, continental rifting, and magmatism as well as rivers and reservoirs may be influencing seismic activity in the region, but previous constraints are limited. The addition of seismic stations from the U.S. Transportable Array and the Southeastern Suture of the Appalachian Margin Experiment Array in 2012-2014 provide an opportunity to characterize seismicity in the central Georgia-South Carolina region. We develop a seismic catalog of >1000 events from March 2012 to May 2014 within or near the instrument array boundaries 30.1 degrees -35.2 degrees N, 80.9 degrees - 85.7 degrees W. Many of the events detected were industrial blasts, so multiple strategies were tested to discriminate between earthquakes and blasts based on event locations, timing, and spectral amplitude of the P and S arrivals. Based on this analysis, approximately 10% of the events in the catalog were classified as earthquakes. Most earthquakes southeast of the eastern Tennessee seismic zone are located in the Carolina terrane, particularly where the Carolina terrane intersects major rivers or reservoirs. One prominent region of seismicity along the Savannah River near Thurmond Lake corresponds with an approximately 4.5 m rise in water levels in 2013. A temporal cluster of earthquakes in April 2013 was followed by increased levels of ambient seismicity preceding the nearby Mw 4.1 earthquake in 2014. Focal mechanisms based on first-motion polarities indicate strike-slip to oblique-thrust motion on structures trending approximately north-south or east-west, and a maximum horizontal stress orientation consistent with the regional trend of approximately N60 degrees E, implying that seismicity may reactivate more optimally oriented structures in the Carolina terrane that are oblique to the trend of the Appalachians. Seismicity in central Georgia appears to be controlled by a complex interaction between preexisting crustal structure and hydrologic variability.


ISSN: 0895-0695
EISSN: 1938-2057
Serial Title: Seismological Research Letters
Serial Volume: 92
Serial Issue: 5
Title: Shaking in the southeastern United States; examining earthquakes and blasts in the central Georgia-South Carolina seismic region
Affiliation: Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, United States
Pages: 3145-3164
Published: 20210707
Text Language: English
Publisher: Seismological Society of America, El Cerrito, CA, United States
References: 106
Accession Number: 2021-049242
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch maps
N31°00'00" - N35°00'00", W85°00'00" - W81°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202134
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