DISCOVERY OF SUBMERGED RING STRUCTURES AND BATHYMETRIC LINEAMENTS IN THE WESTERN GULF OF MAINE: FURTHER EVIDENCE FOR THE GREAT METEOR HOTSPOT TRACK AND A POSSIBLE ASSOCIATION WITH THE 1755 CAPE ANN, MA, EARTHQUAKE

Enhancements of recently available digital sonar data from the western Gulf of Maine have revealed a northwest-trending belt of ring-shaped structures between southeastern New Hampshire and the New England seamounts that appears to support the existence of the Great Meteor hotspot track. The rings are best developed east-southeast of Cape Ann, MA, and are mostly arc-shaped depressions, although a few rings are elevated above the seafloor. South of Cape Cod, the rings are more subtle, perhaps because of greater sedimentation in this area. The largest ring east of Cape Ann is ~30 km in diameter while an even larger, ~50-km-size ring occurs just west of the Bear seamount. The belt trends northwest-southeast between Great Bay, NH, and the Gulf of Maine east of Cape Ann. It then trends south-southeast to Nantucket Island, beyond which it changes direction again to a northwest-southeast trend toward the New England seamounts. The southeast convex geometry of Nantucket Shoals is similar in appearance to the series of curved, ring-shaped canyons northeast of Cape Cod, suggesting that they too may reflect partial ring structures beneath the seafloor sediments. Two partial ring structures near the east side of the shoals appears to cause the Great South Channel to curve eastward in a couple of places.

Several northwest-trending bathymetric lineaments and linear positive gravity anomalies were also identified from the sonar data and a gravity image illuminated from the northeast. These lineaments crosscut the rings offshore from northeastern Massachusetts, some of which lie near a cluster of small earthquakes located ~40 km east-northeast of Cape Ann, MA, suggesting that these lineaments are fault related and that small displacements have recently occurred on some of them. These lineaments are also located in the area that is most likely the epicentral area of the 1755 Cape Ann earthquake, suggesting that one of these lineaments may have been the source of this event. The presence of several small submarine landslides in many areas east and southeast of Cape Ann also supports the occurrence of past earthquakes in the Gulf of Maine east of the Boston area. If these conclusions are true, then the proposed hotspot track may have provided a zone of weakness along which the proposed active faults in the western Gulf of Maine have formed.