Shallow shear wave seismic reflection profiling in the Fraser River delta, British Columbia

Abstract

Shallow shear wave seismic reflection methods were used to identify the top of’ Pleistocene sediments beneath the Fraser River delta in southwestern British Columbia. Three profiles were recorded using a hammer and mass energy source in the southern part of the delta were previous compressional wave surveys had encountered some difficulties due to near-surface gas accumulations. Based on correlations with nearby borehole logs, the Holocene/Pleistocene surface was interpreted to range in depth from approximately 35 m to 80 m and exhibit significant local variations (e.g., dip). The survey was also successful in imaging the top of Pleistocene even when it was composed of different materials (i.e., stiff glacial till or sand/silt deposits). A structure map of the top of Pleistocene sediments beneath the Fraser River delta would provide valuable input for accurate earthquake hazard modeling in the area. This study suggests that shear wave reflection techniques, combined with borehole and existing compressional wave reflection data, might effectively be used to produce such a map.