Abstract

A series of small, felt earthquakes occurred in Richmond, Virginia, during December 1986 and January 1987. Historie records show that such a sequence is unique for Richmond. There were at least 11 felt events, of which six were instrumentally recorded and four were located. Duration magnitudes of these four ranged from 1.5 to 2.2. A focal mechanism solution was calculated and indicates reverse faulting on a plane striking north-northwest and dipping either 45° northeast or 44° southwest. Epicentral intensity reports, up to MMI V, and felt areas do not conform to usual intensity - magnitude relationships. Independent estimates of depth suggest that extremely shallow foei (<2.5 km) may be the cause for this anomaly. The shallow focal depths have important implications concerning the stability of the crust around any shallow underground facilities sited in the area, especially with respect to protection of the groundwater environment.

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