THE EASTFORD LINEAMENT - EVIDENCE FOR A LATE-STAGE REGIONAL FRACTURE ZONE IN EASTERN CONNECTICUT AND SOUTH-CENTRAL MASSACHUSETTS: IMPLICATIONS FOR THE ORIGIN OF MOODUS AREA SEISMICITY

Using an integration of Light Detection And Ranging (LiDAR) imagery, topographic maps, geological field mapping, and geophysical data, we have identified a 120-km long regional lineament in eastern Connecticut and south-central Massachusetts that we have named the Eastford lineament based on its coincidence with the 50-km-long Eastford fault. Close examination of LiDAR imagery and topographic maps suggests that the Eastford fault and its lineament extensions continue southwestward through the Willimantic dome, the Moodus seismic area, and then beyond to the village of Ponset where it coincides with a 7-km long fault that offsets the Jurassic Higganum diabase dike. To the northeast we trace the Eastford lineament into south-central Massachusetts where it coincides with mapped faults that cut the Oxford antilcine.

Comparison of borehole geophysical data from the 1987 ~1.5-km-deep Moodus research drill hole (fortuitously located 150 m northwest of the lineament) with seismic data from the nearby 1987 earthquake swarm and preferred nodal planes of fault-plane solutions for the 1987 swarm suggest that the Moodus segment of the Eastford lineament is the surface expression of a steep, NW-dipping fault that intersects the bore hole at ~400 m depth at a unique dense zone of fractures. Seismic profile data that we acquired across the lineament during 2010 near the 1987 earthquake cluster revealed steep, NW-dipping faults along the lineaments trace, confirming our hypothesis that the Moodus segment of the Eastford lineament is the surface expression of a fault and that it is a likely source of the 1987 Moodus earthquakes (See Alexander et al. elsewhere in this volume). We consider that the alignment of individual collinear faults (e.g., the Eastford fault and the new Moodus fault) and LiDAR-linears comprising the Eastford lineament may not be coincidental and may represent a composite late-stage structure that transgresses the eastern highlands of southern New England.