THE 2006 EARTHQUAKE SEQUENCE NEAR BAR HARBOR, MAINE

From September to November 2006 Acadia National Park in Maine was shaken by a number of earthquakes ranging in magnitude up to M 4.2. The sequence started on September 22 with an M 3.4 earthquake that was preceded by several foreshocks and was followed by a burst of aftershock activity that lasted several days. The strongest earthquake in the sequence took place on the evening of October 2 (EDT). The M 4.2 event, which was felt throughout most of Maine, caused a number of rockfalls in Acadia Park. Immediately following this earthquake, the water level in a well located near Bar Harbor and monitored by the USGS began dropping; the water level measured a few days later was approximately 2 m lower than the level measured before the earthquake. The M 4.2 earthquake was followed by a rather weak aftershock sequence during the next month. Earthquake locations determined from regional seismic network data suggest a NNW trend along Frenchman's Bay, while first-motion focal mechanisms for the two largest events show that these were thrust earthquakes on a NW trending fault. Strong Rg waves recorded by the regional seismic network stations indicate that the focal depths were less than about 2 km. In the epicentral area, no earthquakes had been detected prior to 2006 and no faults are mapped. Accurate relative locations of the events are being computed to refine the image of the structure upon which these earthquakes occurred.