Faulting parameters of the January 16, 1994 Wyomissing Hills, Pennsylvania earthquakes

C.J. Ammon; Robert B. Herrmann; C.A. Langston; H. Benz

doi:10.1785/gssrl.69.3.261

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Faulting parameters of the January 16, 1994 Wyomissing Hills, Pennsylvania earthquakes

C.J. Ammon·Robert B. Herrmann·C.A. Langston·H. Benz

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Abstract

Two events dominated the January 1994, Wyomissing, PA earthquake sequence, an M w 4.0 foreshock, followed by an M w 4.6 mainshock. We modeled regional waveforms to estimate the event depth and the moment tensors for the two largest events in the sequence, and examine teleseismic waveforms recorded on the ARCESS short-period seismic array to estimate the depth and source time function of the mainshock. Our data constrain the depth of the events to be shallower than 5 km, and prefer a depth of 3–5 km. For an assumed depth of 3 km, the mainshock moment tensor is 75% double couple, with (the major double couple) planes striking at 135°N, 347°N, dips of 49°, 46°, and rakes of 68°, 114°. The estimated moment is 8.9 × 10 22 dyne-cm. The P axis strikes 241°N and plunges 2°, the Tension axis strikes 336°N and plunges 73°. The foreshock inversion results are virtually identical to the mainshock results; for a source depth of three km, we find a major double couple with a strike, dip, and rake of 121°N, 60°, and 66°, respectively. The seismic moment for the foreshock is 1.2 × 10 22 dyne-cm, which is approximately 13% of the mainshock moment release. These events did not excite high-frequency Lg waves as effectively as typical eastern North American events, and the mainshock had a stress drop in the range of 25–50 bars.

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Source-reported bounding extent: 40.153114619966175° to 40.57060094938112° latitude; -76.03346163015975° to -75.25597275862621° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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C.J. Ammon, Robert B. Herrmann, C.A. Langston, H. Benz. 1998. Faulting parameters of the January 16, 1994 Wyomissing Hills, Pennsylvania earthquakes. https://doi.org/10.1785/gssrl.69.3.261

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