Publication Date:
2016-04-07
Description:
An eight-station seismic network was installed in August 2011 in the epicentral area of the 1886 Charleston, South Carolina, earthquake, within and near the town of Summerville. The network operated for one year and located 134 earthquakes with duration magnitudes ranging from –1.8 to 2.6. The earthquakes occurred in a tabular zone striking ~N186°E, with dip of about 43° to the west. The focal depths range from 13 km to the top of the early Mesozoic section at a depth ~1 km. The dimensions of the seismic zone are ~23 km along strike and 15 km down-dip. Many of the earthquakes are concentrated in the 2–6.5 km depth range, near shallow faults imaged on seismic-reflection profiles adjacent to the Ashley River. Our hypocenter relocations of 228 earthquakes occurring in the period 1977–2005 are consistent with the results obtained from the recent one-year station deployment. The 48 well-constrained focal mechanisms derived from the one-year deployment are predominantly reverse motion, and ~30% exhibit north–south-trending nodal planes consistent with the orientation of the seismic zone. The seismicity near Summerville has characteristics in common with the aftershock sequence of the 23 August 2011 Mineral, Virginia, earthquake. We interpret these results to indicate that the modern seismicity is the lingering aftershock sequence of the 1886 shock and that the mainshock occurred on a south-striking, west-dipping fault plane with predominantly reverse motion, possibly with a component of right-lateral strike-slip. Most moment release probably occurred at depths greater than 6 km. Online Material: Tables listing hypocenters and focal mechanisms, and an animation showing hypocenter profiles oriented along different azimuths.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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