Abstract

On 7 October 1983 a magnitude 5.1 (mb) earthquake occurred in the central Adirondack Mountains, near the town of Goodnow, New York. The earthquake was well recorded both by regional stations and by a large number of digital and analog seismographs in North and South America and Europe. These regional and teleseismic data are complemented by accurate locations of aftershocks recorded by a portable network from 17 hours after the main shock, providing an unusually complete dataset to study the source process of an intraplate earthquake. The results of an analysis involving the formal inversion of the vertical component Rayleigh waves and of short-period P waves show that the earthquake was due to reverse faulting with a centroidal depth of 7.5 km, striking north-south and dipping at 60° to the west. The scalar seismic moment is 1.9 × 1023 dyn cm. For P waves, for paths from northeastern United States, plausible values of t* (attenuation) range from 0.4 to 0.7 sec, and for these values the estimates of source duration range from 0.60 to 0.35 sec. Assuming a circular crack model with a rupture velocity of 3.0 km/sec, the bounds on source duration give upper and lower limits for the fault radius of 0.9 and 0.5 km, and for the stress drop of 670 and 115 bars. The preferred value of t* = 0.6 sec yields a source duration of 0.45 sec, a radius of 0.7 km, and a stress drop of 265 bars. This fault radius agrees with that inferred from the spatial distribution of aftershocks. The inferred stress drop of the Goodnow earthquake is higher than generally observed for interplate events. If the Goodnow earthquake is representative of events in eastern North America, the high stress drop may partially explain the large felt areas produced by these relatively small intracontinental earthquakes.

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