A sizeable body (150 records) of three-component, wideband (0.2 to 50 Hz) digital seismic data has allowed a direct comparison between earthquakes at The Geysers geothermal area, California and along nearby active faults of the San Andreas system. An attempt has been made to find analog or spectral parameters which would permit discrimination between 12 events within the steam production field and 30 outside it. Results of the study for both classes of events are: (1) seismic moments vary with local magnitude ML as log M0 = (1.06 ± 0.11) ML + 16.9 ± 0.1; (2) the ratio of vertical P-wave to horizontal S-wave spectral corner frequencies is near unity; (3) seismic stress drops are low (1.0 to 10 bars); and (4) focal mechanisms are quite comparable during the time period of this study.

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