TOWARDS A LONG-TERM EARTHQUAKE RECORD FOR EASTERN MASSACHUSETTS: A MULTIPROXY ANALYSIS OF DEFORMATION FEATURES IN LAKE SEDIMENTS

In the historic past, New England and adjacent areas have experienced damaging earthquakes, yet the recurrence intervals of these events remain largely unknown. Here, we present two ~1000-year long well-dated sedimentary records from Sluice Pond and Walden Pond in eastern Massachusetts that show event horizons that correlate with historic as well as prehistoric earthquakes. Both lakes were chosen because of favorable lake basin geometry and their vicinity to historic epicenters. Robust age models based on pollen stratigraphy, radioisotopes, and onset of industrial contaminants have been developed and allow accurate dating of deformed sediment horizons as well as correlation between the two records. In both lakes rather homogeneous organic-rich sediments accumulate at slow rates requiring a multiproxy approach to isolate abrupt sedimentation events from background deposition. Using a combination of sedimentological, geophysical, geochemical and palynological proxies, we were previously able to trace the 1755 Cape Ann earthquake, the largest historic earthquake in New England, in Sluice Pond sediments. The earthquake is recorded as a turbidite generated by subaqueous mass movements that transported characteristic nearshore and slope material to the center of the lake. Using a similar multiproxy approach, we scanned older sediments in both lakes for other distinct event layers. In Walden Pond, two sedimentary horizons can be associated with a historic fire in the early 1900s and a possible large fire event around 1200-1300 CE. The 1755 Cape Ann earthquake, that occurred at a greater distance to Walden Pond, might have mobilized nearshore sediment; however, this event is masked by the effects of land clearing in the region around the time of the earthquake. Another historically reported earthquake in 1638 might have caused some disturbance in Walden Pond, but the evidence is not consistent throughout all records. A sudden influx of coarse terrigenous sediment dated to the 1400s can be seen in multiple sediment cores of Walden Pond, pointing towards a basin-wide mass wasting event possibly triggered by a prehistoric seismic event. In Sluice Pond, besides the 1755 turbidite, a similar normally graded unit occurs at a depth corresponding to ca. 1450 CE, potentially correlating to the event horizon in Walden Pond.