LIQUEFACTION HAZARD MAPS FOR BOSTON, MASSACHUSETTS

BAISE, L.G., Department of Civil and Environmental Engineering, Tufts University, Medford, MA 02155, and BRANKMAN, C.M., Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, laurie.baise@tufts.edu, brankman@fas.harvard.edu.

We have completed a study to characterize the surface and subsurface distribution of potentially liquefiable sediments and artificial fill in the City of Boston, Massachusetts. The greater Boston area is a highly populated urban and industrial center and has experienced several large historic earthquakes of M>6.0 (e.g. 1727 and 1755). Much of the study area, especially in the downtown Boston area, is underlain by extensive regions of non-engineered artificial fill that, when saturated, are susceptible to liquefaction during seismic loading. In addition, 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 a low susceptibility to liquefaction. We used a combination of Quaternary geologic mapping, geotechnical analyses, and statistical analysis to determine liquefaction susceptibility. The geotechnical and statistical analyses were based on a digital database of 2963 geotechnical boreholes. We characterized the liquefaction susceptibility using sample based liquefaction probability values. The characterization included, probabilistically characterizing the sample population, evaluating the spatial correlation of the population, and finally providing a local and/or global estimate of the distribution of high liquefaction probability values for the deposit. When spatial correlation was present, ordinary kriging was used to evaluate spatial clustering of high liquefaction probability values within a geologic unit which in turn was used in the regional liquefaction susceptibility characterization. When spatial correlation was not present in the data, then a global estimate was used to estimate the percentage of samples within the deposit which have a high liquefaction probability.