Active and Passive Seismic Surveys Along the Eastern Shoreline of San Francisco Bay for Earthquake Hazard Assessment

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Active and passive seismic surveys were conducted along the eastern shoreline of San Francisco Bay for earthquake hazard assessment. The surveys were motivated by the need for better site characterizaton of the rapidly developing East Bay. Shallow surveys were conducted at several locations along the Hayward and San Leandro shorelines. Sites include undisturbed marsh, former oxidation ponds, and areas filled with dredge spoils. Shear wave velocity was estimated using surface wave methods. The spatial autocorrelation (SPAC) method was used to obtain a dispersion curve that was inverted to obtain a shear-wave velocity model. Passive data were acquired using both cabled and nodal systems. The cabled system used a 48-channel spread with maximum sensor separation of 96 m at most sites, which typically provided depth penetration of at least 40 m. Shear-wave velocity in the upper 5 m was commonly 70-100 m/s, while velocity at 30-40 m depth was usually 200-300 m/s.

Passive nodal surveys were conducted using about 20 sensors with a maximum offset ranging from about 800 m to 2000 m, depending on the survey. Shear wave velocities were obtained to depths of 800 m at two sites and 1500 m at a third site. At a depth of 500 m, velocities at all three sites were similar, at 900 to 1000 m/s. At one of the sites, velocity at a depth of 1500 m was estimated to be 1750 m/s.

Presenting Author: Mitchell Craig

Authors