Environmental and structural implications of Rhode Island seismic events, 1965–1976

Abstract

Rhode Island, like most of New England, is in a mainly quiet seismic region, and thus, few epicenter locations are available to determine seismically active fault traces. This lack of information has hindered environmental impact siting studies for nuclear power plants because such studies must locate any “capable” (active) faults. Reinvestigation and evaluation of four Rhode Island earthquakes that occurred during the past 12 yr (1965, 1967, 1974, and 1976) indicate that the earthquakes were related to regional lineaments, which are probably caused by faults. In this area of low seismic activity, only isoseismal mapping–rather than simple epicenter locations–can indicate these lineaments. Two of these seismically located lineaments, paralleling each other and trending east, are at the head and mouth of Narragansett Bay, and a third lineament trends northeast through Narragansett Bay itself and along the Taunton River into Massachusetts. Recent re-exploration of coal resources in the Pennsylvanian Narragansett basin in this area has suggested potential new faults. No field relationship between this seismicity and the few known, mapped faults exists, but extensive Pleistocene glacial deposits in the area obscure many geologic structures. In addition, the faults indicated by these regional lineaments may be deeply buried basement features that have been reactivated at various times, at different degrees of activity, up to the present.