Near-surface shear wave reflection surveys in the Fraser River delta, B.C., Canada

Shallow shear wave reflection surveys using high frequency vibroseis techniques provides information about the Tertiary bedrock surface and Pleistocene sediments on the Fraser River delta, in B.C., Canada. Besides the clear advantage of shear wave profiling in this shallow gas environment, the added resolution potential and ability to measure the shear wave velocity field enhances the fusion of this surface seismic data into earthquake site response estimations. Surface materials ranging from undisturbed, native delta sediments to clay/ rubble fill used in dike construction seemed amenable to the generation and recording of shear waves when using a small (6,000 kg) vibrator and engineering recording systems. The thickness of Pleistocene sediments and depth to Tertiary bedrock were mapped at three locations within the delta where gaps existed in the geologic record. These three sites provided cultural and near-surface settings that uniquely tested this shallow imaging technique.