Lateral variations of the subsurface velocity, East Mesa Geothermal Field, Imperial Valley, California
Using an array of nine short periods, high-gain, three-component seismographs with a combination of active and passive seismic techniques, we have investigated the subsurface characteristics of the East Mesa Geothermal Field. Microearthquakes with ray paths external to the geothermal field have sharp arrivals and short periods. Microearthquakes with hypocenters located within the 150 sq km areal extent of the geothermal field have longer periods and more emergent first arrivals. High frequency seismic waves from local microearthquakes in the region are attenuated as they cross the geothermal field. In addition, shear waves are absent on some records and difficult to distinguish on others. To map the fine structures of the subsurface and to measure the anisotropy and lateral variations of the compressional wave velocity in the immediate area of the East Mesa Geothermal Field, we exploded six calibration blasts of strengths ranging from 9 to 90 kg. The shotholes, ranging in depth from 15 to 60 m, were arranged to give a reasonable distribution of directions and areal coverage. Detailed analysis of the refraction records indicates anomalous delays in the travel times along certain ray paths. We propose that a low velocity region, with horizontal dimensions of a few kilometers, is present beneath the East Mesa Geothermal Field and can be used to delineate the anomalous thermal region.
- Research Organization:
- Univ. of Texas, Dallas
- OSTI ID:
- 7284685
- Journal Information:
- EOS, Trans., Am. Geophys. Union; (United States), Journal Name: EOS, Trans., Am. Geophys. Union; (United States) Vol. 57:3; ISSN EOSTA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys
CALIFORNIA
EARTHQUAKES
GEOPHYSICAL SURVEYS
GEOTHERMAL FIELDS
IMPERIAL VALLEY
MICROEARTHQUAKES
NORTH AMERICA
REFRACTION
SEISMIC EVENTS
SEISMIC SURVEYS
USA
VARIATIONS
WESTERN REGION