The largest onshore early Mesozoic fault zone in New England, the Watch Hill fault, has been gradually revealed by a long series of varied and detailed geophysical studies in combination with local geologic, geomorphic and remote sensing data. This normal fault, which dips moderately northwestward and has an en echelon pattern showing a slight left-lateral component of movement, extends over 230 km northeastward from offshore of south-central Long Island to Massachusetts Bay. The complex zone separates Late Proterozoic and Permian granites in the southwest and follows the southeastern border of the Pennsylvanian Narragansett Basin in the northeast. The fault breaks are generally well expressed as valleys, lakes, swamps and bays as well as locally controlling glacial moraines and the shape of the Narragansett Bay. The general position of the fault is expressed on regional aeromagnetic and gravity data, but proved difficult to follow due to its en echelon nature, many fault offsets, and fracture zones along which magnetite has been altered and the density lowered. The latter produce both magnetic and gravity lows as well as low velocities. Detailed surface and shipboard surveys were then used to resolve the problems. The fault lies along the southwestern projection of the Mesozoic faults in the Bay of Fundy and the Gulf of Maine and provides a key to the understanding of the offshore Mesozoic structure of both the Long Island Platform and the basins offshore of Massachusetts in addition to providing control for locating late Mesozoic cross-cutting seismically active faults.
AEG New England has now moved to an every-other-month meeting schedule. The next speaker and topic will be posted the end of October. Please check back at that time for meeting details