Focal mechanism analyses for Virginia and eastern Tennessee earthquakes (1978-1984)
Technical Report
·
OSTI ID:5516486
Focal mechanisms are presented for 11 earthquakes from the Giles County, Virginia, seismic zone and its vicinity and for 12 earthquakes from the Central Virginia seismic zone. These earthquakes (0 less than or equal to M less than or equal to 4) were monitored by local networks between January 1978 and October 1984. In Giles County, the data base consists of 43 P-wave polarities and 50 SB to P amplitude ratios (SV/P) that yielded six single event focal mechanisms (SEFM's) and five composite event focal mechanisms (CFM's). In Central Virginia, 79 P-wave polarities and 51 SV/P ratios are used to determine 11 SEFM's and four CFM's. A computer program FOCMEC was used to determine the focal mechanism solutions. The results for the Giles County seismic zone show mainly strike-slip mechanisms on steeply dipping (73/sup 0/ +- 16/sup 0/) NNE (right lateral motion) and ESE (left lateral motion) trending nodal planes. However, some (4/11) of the solutions show similar movement on nodal planes rotated 45/sup 0/ counterclockwise. The P axes in Central Virginia are generally northeast trending for shallow earthquakes (>8 km) and northwest trending for deeper ones (<8 km). In Giles County, where the seismic activity is occurring beneath the Appalachian decollement, faulting and inferred stress orientations are more uniform than in Central Virginia, some 200 km away, where the seismicity is occurring near and above the decollement. 38 refs., 32 figs., 11 tabs.
- Research Organization:
- Virginia Polytechnic Inst. and State Univ., Blacksburg (USA). Seismological Observatory; Memphis State Univ., TN (USA). Tennessee Earthquake Information Center
- OSTI ID:
- 5516486
- Report Number(s):
- NUREG/CR-4288; ON: TI85901862
- Country of Publication:
- United States
- Language:
- English
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