Virginia Regional Seismic Network. Final report, 1977-1985
Eight years of monitoring with a 20-station regional network has produced epicenters (M less than or equal to 4), focal depths and mechanisms of adequate number and quality to reveal considerable differences between the two seismically active portions of Virginia. Those two areas (southwestern (Giles County) and central parts of the state) are separated by only some 200 km. Despite their proximity, the two zones exhibit remarkable differences in geometrical/mechanical characteristics. In Giles County, seismic energy is released by predominately strike-slip faulting in a near vertical, tabular zone (approx.40 km long) that is below the Appalachian decollement. In central Virginia, the seismicity is derived from mixed dip-slip and strike-slip faulting in a large, coin shaped volume (approx.100 km diameter; approx.10 km vertical thickness), above the major detachment faulting. Stress estimates, as derived from single- and composite-focal mechanism solutions P-axes, are NE to ENE in Giles County and NW to NE in central Virginia. The causes for the observed variability are unknown. The two zones are in different tectonostratigraphic (suspect) terranes and that difference could be relevant. The recently proposed Hydroseismicity model (Costain and Bollinger, 1985) ascribes the observed seismicity variations in Virginia and throughout the Southeast to different drainage basin hydrologic characteristics plus differences in upper crustal fracturing. 15 figs.
- Research Organization:
- Virginia Polytechnic Inst. and State Univ., Blacksburg (USA). Seismological Observatory
- OSTI ID:
- 6184516
- Report Number(s):
- NUREG/CR-4502; ON: TI86900809
- Country of Publication:
- United States
- Language:
- English
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