COMPILATION OF BRITTLE FAULT DATA FOR CONNECTICUT: RELATIONSHIPS TO EARTHQUAKE DISTRIBUTION

Fault location information was compiled from all published geologic maps of Connecticut at the 1:24,000 scale and incorporated into an ArcMap layer. Where possible, faults were differentiated as to whether they were brittle or ductile in order to evaluate the potential for seismic reactivation.

Five major brittle fault zones were identified. The westernmost fault zone extends from Bridgeport northward though Nortfolk, CT, and forms the eastern boundary of the Pomperaug basin. It consists of a series of subparallel north-south striking normal faults. The central three fault zones are associated with the Hartford basin half-graben. The lower displacement western border faultextends northward from the Mixville fault near New Haven to Southwick, MA, whilethe larger displacement eastern border fault zoneextends northeastward from Branford to Hampden, MA, and consists of a series of linked fault segments. Within the basin, numerous north-south and northeast-striking normal faults cut the Triassic-Jurassic sequence. The easternmost fault zone is associated with the 12-14 km wide Lake Char fault zone and consists of north-south striking thrust faults and northwest striking high-angle tear faults. Subsidiary brittle fault zones include those faults near Moodus and the local parts of Honey Hill fault zone.

Historical seismicity data (1976-2012) was compared with the mapped brittle faultsto determine any association with fault distribution. No seismic events appear to be related to the westernmost fault, the western border fault, or the intra-basin faults. However, a plot of hypocenter depths between 2 to 13.5km and their distance from the eastern border fault suggest a down-to-the-west listric geometry. Only one epicenter is located on the lake Char fault zone whereas the Moodus area has the most epicenter located 3 to 12 km east of the nearest mapped brittle structures.