Liquefaction susceptibility mapping in Boston, Massachusetts

The Boston, Massachusetts, metropolitan area has experienced several historic earthquakes of about magnitude 6.0. A compilation of surficial geologic maps of the Boston, Massachusetts, metropolitan area and geotechnical analyses of Quaternary sedimentary deposits using nearly 3,000 geotechnical borehole logs reveal varying levels of susceptibility of these units to earthquake-induced liquefaction, given the generally accepted design earthquake for the region (M6.0 with 0.12g Peak Ground Acceleration (PGA)). The majority of the boreholes are located within the extensive downtown artificial fill units, but they also allow characterization of the natural deposits outside the downtown area. The geotechnical data were complemented with surficial geologic mapping, combining published and unpublished geologic maps, aerial photographic interpretation, and soil stratigraphy data from an additional 12,000 geotechnical boring logs. Susceptibility maps were developed based on liquefaction-triggering threshold ground motions, which were determined using the borehole data. We rind that much of the non-engineered artificial fill that underlies the downtown Boston area is, when saturated, highly susceptible to liquefaction during seismic loading. Holocene alluvial and marsh deposits in the region are also moderately to highly susceptible to liquefaction. Much of the outlying area is underlain by Pleistocene and Quaternary glacial and glaciofluvial deposits, which have low to moderate susceptibility to liquefaction. This study provides data needed to effectively manage liquefaction hazards in the Boston area, and it will assist in characterizing seismic hazards, mitigating risks, and providing information for urban planning and emergency response.