RECENT EARTHQUAKE ACTIVITY IN NEW ENGLAND: IMPLICATIONS FOR REGIONAL SEISMIC HAZARD

Recent earthquake activity in New England has provided some new clues concerning the seismic hazard in the region. During 2006-2007, there was an uptick in the rate of earthquake activity in New England, and the MLg 4.2 event at Bar Harbor, ME in October 2006 was the largest earthquake in New England since 1988. An analysis of the sequence of at least 38 earthquakes at Bar Harbor, ME in the fall of 2006 has revealed the location and orientation of the fault upon which these earthquakes took place. Also, many small earthquakes were detected in the accreted terranes of Maine, New Hampshire and Massachusetts in the fall of 2007, adding support to earlier studies that have suggested that there may be some short-term causal connections between earthquakes throughout this region. Small earthquakes occurred in October 2007 at Littleton, MA and Amesbury, MA. At both of these localities, small earthquakes are detected on a rather regular basis every few years. This steady rate of small earthquake activity at these localities is interpreted to support the hypothesis that these small earthquakes are late aftershocks of larger earthquakes that took place several hundred years ago. An analysis of the M≥2.7 earthquakes since 1979 shows that there is a 10-20% increase in the earthquake activity rate in fall compared to the rate in spring in New England. This suggests that there is a somewhat greater likelihood of strong earthquakes in the autumn than in the spring, consistent with the past earthquake history in the region. Taken together, the recent earthquakes help to better define the spatial and temporal variations in the earthquake hazard of New England.