Comparison of phase velocities from array measurements of Rayleigh waves associated with microtremor and results calculated from borehole shear-wave velocity profiles
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Open-File Report↗
Geology topics
R.E. Warrick
Publications and source records attributed to R.E. Warrick.
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 calibration instrument, was found to be 114 V-s/m.
Geophysics↗
A general earthquake-observation system (GEOS)
Microprocessor technology has permitted the development of a General Earthquake-Observation System (GEOS) useful for most seismic applications. Central-processing-unit control via robust software of system functions that are isolated on hardware modules permits field adaptability of the system to a wide variety of active and passive seismic experiments and straightforward modification for incorporation of improvements in technology. Various laboratory tests and numerous deployments of a set of the systems in the field have confirmed design goals, including: wide linear dynamic range (16 bit/96 dB); broad bandwidth (36 hr to 600 Hz; greater than 36 hr available); selectable sensor-type (accelerometer, seismometer, dilatometer); selectable channels (1 to 6); selectable record mode (continuous, preset, trigger); large data capacity (1. 4 to 60 Mbytes); selectable time standard (WWVB, master, manual); automatic self-calibration; simple field operation; full capability to adapt system in the field to a wide variety of experiments; low power; portability; and modest costs. System design goals for a microcomputer-controlled system with modular software and hardware components as implemented on the GEOS are presented. The systems have been deployed for 15 experiments, including: studies of near-source strong motion; high-frequency microearthquakes; crustal structure; down-hole wave propagation; teleseismicity; and earth-tidal strains.
Bulletin of the Seismological Society of America↗