RELATIONSHIP BETWEEN THE 1727 NEWBURY, MASSACHUSETTS, EARTHQUAKE AND A RESTRAINING BEND ALONG THE POSTULATED SOUTHWEST CONTINUATION OF THE NORUMBEGA FAULT SYSTEM

The recent availability of high-resolution LiDAR data in central New England, combined with topographic, geologic, aeromagnetic and seismicity data, suggest the presence of a northwest-trending fault near Newbury, MA, displacements along which may have produced the 1727 MM VII Newbury, MA, earthquake and the 1999 microearthquakes near Amesbury, MA. The features which support the presence of this fault include the northwest-trending nodal planes generated from the 1999 Amesbury earthquake, the abrupt southeast bend in the Merrimack River northwest of Newburyport, the proximity of the 1727 liquefaction sites to this northwest trend, the northwest trend formed by this reach of the Merrimack River with its tributary to the northwest, the Powwow River, and the presence of higher terrain and a Pleistocene shoreline along the southwest side of this reach of the Merrimack River. Its proximity to a 12° restraining bend along the southwest continuation of the Norumbega fault system to the northwest near Kingston, NH, suggests that compression along this fault bend may be causing displacements along this northwest fault. Just west of the Newbury area are several short, linear, mostly negative, northwest-trending aeromagnetic anomalies, the longest of which is at least 25 km long and extends from just west of Byfield, MA, to Bakers Island in Massachusetts Bay. We have named this feature the Georgetown anomaly. Although there is no linear magnetic anomaly along the postulated fault near Newbury, its parallelism with the northwest-trending aeromagnetic anomalies to the west suggests that all these features may be related. The crosscutting relationship of these northwest-trending features with the mapped northeast-trending terranes and faults suggest that the northwest-trending anomalies may be basement faults beneath the overthrust terranes. Because these features are located just north of Boston, further studies are needed to determine if they are capable of producing large damaging earthquakes.