Hsi-Ping Liu

Effect of cable capacitance on in‐situ borehole geophone calibration

Using 2-Hz electromagnetic moving‐coil geophones as sensing elements, we have constructed and deployed three‐component seismometers in boreholes at various sites for wave‐propagation studies associated with earthquake hazards (Liu et al., 1991). For example, one such seismometer has been deployed in a 88-m deep borehole reaching bedrock in the Marina District of San Francisco since 1990 (Liu et al., 1992) for the purpose of comparing ground motions in the bedrock and those at the surface. Periodic calibrations for such geophones are necessary to check if the geophone parameters have changed because of decreased magnetization of the geophone ferro‐magnet. For example, the coil transductance of the vertical‐component geophone of the borehole seismometer mentioned above was calibrated to be 121 V-s/m using phase‐ellipse test and step test before deployment. Sixty six months after the deployment, the coil transductance, when calibrated in situ and with a 100-m intervening cable between the geophone and the ca...

Integrated Surface and Borehole Strong-Motion, Soil-Response Arrays in San Francisco, California

An integrated set of four borehole arrays and ten surface installations is installed in the city of San Francisco, California to measure the response of soft-soil deposits to strong earthquake ground motions. The borehole arrays extend through thick layers of soft water-saturated soils of Holocene age and older more consolidated soils of Pleistocene age into bedrock at depths up to 90 m. The surface installations are configured in pairs to provide simultaneous comparative surface measurements of soft soils and nearby rock. The rock locations also permit comparative measurements of rock as observed at the surface and in nearby boreholes. The arrays are designed to address a wide variety of scientific and engineering issues, and especially the issue of anelastic and nonlinear soil response at high strain levels as might be recorded during a large regional earthquake. Recordings of ground motions from the largest regional earthquakes which have occurred since the installation of the arrays show marked evidence of amplification as measured on the borehole and surface arrays. Implications of the results for low-strain site coefficients in present U.S. building codes are discussed.