Microearthquake distribution and mechanisms of faulting in the Fontana-San Bernardino area of Southern California
- Creators
- Hadley, David
- Combs, Jim
Abstract
The major, historically active San Jacinto and San Andreas fault systems pass through the San Bernardino Valley area of southern California. An array of six portable, high-gain seismographs was operated for five 2-week recording sessions during the summer of 1972 and winter and spring of 1973 in order to detail the microseismicity of the region. A crustal model for the Valley, modified after Gutenberg, was established using a 6-km reversed seismic refraction profile and a series of monitored quarry blasts. Fifty-five microearthquakes were used to establish a magnitude scale (1.5 to 3.3) based on coda lengths recorded by instruments peaked at 20 Hz. Forty-five hypocenters from the analysis of over 6,000 hr of low-noise records define two northeast trending lineations within the western portion of the Valley. A composite first-motion plot of 22 microearthquakes from these lineations indicates left-lateral strike-slip faulting. Fluctuations in microseismicity appear to reflect rapid changes in the stress patterns of southern California. Minor activity along the strike of the San Jacinto fault zone suggests a purely right-lateral strike-slip motion. Only minimal strain release was observed along the San Andreas fault zone.
Additional Information
© 1974 Seismological Society of America. Manuscript received January 18, 1974. We express our thanks to Drs. Shawn Biehler and Lewis Cohen for reviewing the manuscript, to Steve Smith who was equally responsible for the data collected during the summer of 1972, to the National Science Foundation for supporting the work accomplished in the summer of 1972, to the California Institute of Technology for providing information on seismic activity within the San Bernardino Valley, to the California-Portland Cement Company for information on quarry blasts, to Karoly Fogassy for the illustrations, and to Dr. W. H. K. Lee of the U.S. Geological Survey for the computer program used to locate events. Financial support was provided by a University of California-Riverside Intramural Research Grant.Attached Files
Published - 1477.full.pdf
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Additional details
- Eprint ID
- 49651
- Resolver ID
- CaltechAUTHORS:20140912-093840519
- University of California, Riverside
- Created
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2014-09-12Created from EPrint's datestamp field
- Updated
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2019-10-03Created from EPrint's last_modified field