High-frequency observations and source parameters of microearthquakes recorded at hard-rock sites

We have estimated the source parameters of 53 microearthquakes recorded in July 1983 which were aftershocks of the Miramichi, New Brunswick, earthquake that occurred on 9 January 1982. These events were recorded by local three-component digital seismographs at 400 sps/component from 2-Hz velocity transducers sited directly on glacially scoured crystalline basement outcrop. Hypocentral distances are typically less than 5 km, and the hypocenters and the seven digital seismograph stations established all lie essentially within the boundaries of a granitic pluton that encompasses the faults that ruptured during the main shock and major aftershocks. The P-wave velocity is typically 5 km/sec at the surface and at least 6 km/sec at depths greater than about 1 km.