Looking for the Possible Epicenters and Magnitudes of Strong Prehistoric Earthquakes Near Boston, Massachusetts

Abstract This study examines evidence of widespread mass wasting that was found in the sediments of Walden Pond (WP), Concord, Massachusetts, and Sluice Pond (SP), Lynn, Massachusetts, deposited between 1380 and 1520 C.E. and shortly after 1386–1509 C.E., respectively, along with 15 landslides in the sensitive glaciomarine deposits of the Presumpscot Formation in southern Maine, all of which took place between 1221 and 1454 C.E. In addition, the sediments in WP show evidence of mass wasting between 1050 and 1320 C.E., which is not seen in SP or in Maine. Whereas the younger event horizons in WP and SP and possibly the landslides in southern Maine are attributed to an earthquake in ~1400 C.E., the older anomalous layer in WP is attributed to an event in ~1200 C.E. We carried out a modeling analysis to find the range of possible locations and magnitudes of earthquakes that could have disturbed the sediments in the ponds and caused the landslides in Maine. For an earthquake in ~1400 C.E., the area of possible epicenters is in eastern Massachusetts or southeastern New Hampshire, with a possible magnitude range of 5.6≤Mw≤6.7 (±0.3 uncertainty). If the earthquake also caused the landslides in Maine and with a magnitude as small as Mw 4.7 ± 0.3 with an epicenter in eastern Massachusetts if the earthquake did not cause the landslides in Maine. An earthquake in ~1200 C.E. with Mw 4.7 ± 0.3 or a little larger near or west of WP is most likely, although an earthquake as large as Mw 6.2 ± 0.3 and an epicenter as far west of WP as Worcester, Massachusetts, is possible. The results of this study suggest that the seismic hazard in eastern Massachusetts and southeastern New Hampshire might need re-evaluation.