THE SEARCH FOR POTENTIALLY SEISMICALLY ACTIVE FAULTS IN NEW ENGLAND: TARGETS FOR GEOPHYSICAL STUDIES

The identification of seismically active faults is critical for determining the seismic hazard of a region, particularly in an intraplate region like the northeastern U.S. In New England the earthquake activity spreads broadly across the region, but there also are some localized spatial clusters that occur within this region. It has been postulated that these spatial clusters may be the remnant aftershocks of strong earthquakes that took place hundreds of years ago to perhaps a few thousand years ago. If this is true, these localities are places where focused geophysical and geological studies may yield new evidence of active faulting, thus helping to delineate the seismic hazard of this region. There are several places where the local seismic suggests that focused investigations may yield positive results. One is in northeastern Massachusetts where the 1727 Newburyport earthquake took place. Another is in southcentral New Hampshire between Concord and the Lakes Region, where the 1638 earthquake is suspected to have taken place. A tight cluster of seismicity in central Maine near Dover-Foxcroft could be the aftershock activity of a strong earthquake a several hundred years ago. Another target is the Passamaquoddy Bay area where a strong earthquake was centered in 1904 and where persistent minor earthquake activity has taken place in recent decades. An earthquake swarm near Bar Harbor, Maine in 2006 and 2007 illuminated a possible active fault that should outcrop in Frenchman Bay, a locality were ship-based geophysical investigations could be fruitful. Some combination of geophysical surveys, including gravity, magnetics, EM, and GPR, can be used to search for near-surface as well as crustal scale faults that may have been active in the suspected past strong earthquakes.