Shallow swarms of earthquakes comprise one type of seismicity occurring in the northeastern United States. These events occur in basement rocks that lie near the earth’s surface, have focal depths less than 3 km, exhibit maximum magnitudes of about 2 to 4-1/4, and consist of tens to hundreds of events. The swarms also tend to recur in the vicinity of previous swarms. Three recent swarms were recorded by local monitoring networks, supplemented in some cases by portable instrumentation. Detailed analyses of these three swarms, located at Annsville, NY, Tranquility, NJ, and Moodus, CT, show that their source volumes are characterized by a radius less than 1/2 km. The orientation and style of faulting exhibited are consistent with those observed for deeper events nearby. For Annsville and Moodus, where stress was measured in deep boreholes located 20 km and less than 1 km from the swarm epicenters, respectively, the orientation and style of faulting agree with those expected.

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