APPLICATION OF GROUND-PENETRATING RADAR TO INVESTIGATION OF NEAR-SURFACE FAULT PROPERTIES IN THE SAN-FRANCISCO BAY-REGION

In many geologic environments, ground-penetrating radar (GPR) provides high-resolution images of near-surface Earth structure. GPR data coll ection is nondestructive and very economical. The scale of features de tected by GPR lies between those imaged by high-resolution seismic ref lection surveys and those exposed in trenches and is therefore potenti ally complementary to traditional techniques for fault location and ma pping. Sixty-two GPR profiles were collected at 12 sites in the San Fr ancisco Bay region. Results show that GPR data correlate with large-sc ale features in existing trench observations, can be used to locate fa ults where they are buried or where their positions are not well known , and can identify previously unknown fault segments. The best data ac quired were on a profile across the San Andreas fault, traversing Plei stocene terrace deposits south of Olema in Marin County; this profile shows a complicated multi-branched fault system from the ground surfac e down to about 40 m, the maximum depth for which data were recorded.