STRUCTURE OF THE SOUTHWESTERN FRASER RIVER DELTA AS DETERMINED FROM GEOELECTRIC SOUNDING1

Abstract

AbstractGeoelectrical sounding profiles were collected on the southern part of the Fraser River delta, to provide a geophysical estimate of the subsurface structure and geotechnical properties. The differences between emergent and intertidal areas were assessed, and the geoelectric technique was found to be a viable one in an intermittently exposed tidal‐flat environment. The subsurface geoelectric structure provides a link between reflection seismic data sets for Georgia Strait and the lower mainland. The survey was intentionally designed to complement the conventional exploration information for this basin and the shallow high‐resolution seismic and drilling which focused on the unconsolidated Quaternary section. The electrical models consist of three layers: (I) electrically‐conductive, porous, saturated and under‐saturated marine silts, sands and gravels, overlying (II) less conductive and more consolidated marine clays, and variably reworked glaciomarine deposits together with weathered clastic sedimentary bedrock, which in turn overlies (III) less porous, more resistive, relatively unweathered bedrock. Estimates of thickness and geotechnical properties are obtained for shallow layers which are not available from either the short boreholes or shallow high‐resolution seismic lines. This information is particularly useful in appraising the liquefaction potential of the unconsolidated layers due to earthquake risk.