From August through October, 1981 an intense microearthquake swarm of over 500 events was detected near Moodus, Connecticut, the site of persistent small earthquake activity throughout the historical record. The swarm consisted of 39 foreshocks which preceded the magnitude 2.1 mainshock, a normal pattern of aftershocks which immediately followed the main shock, and later smaller bursts of microearthquakes associated with migrations of the event epicenters. The shocks were all within 1 km of the earth's surface and located along a 5 km long segment of the Salmon River. Earthquakes of magnitude less than 1 were felt and events as small as magnitude 0 were heart by people living near the epicenters.