The earthquake and its aftershocks from May 2 through September 30, 1983
Analysis of the Coalinga earthquake sequence, based on the Allen/Ellis real-time-processor (RTP) automatic P-phase-onset times and duration measurements, provides hypocentral and magnitude determinations for more than 6,000 events from May 2 through September 30, 1983. Focal mechanisms and local magnitudes of more than 140 of the larger aftershocks were calculated from more detailed observations obtained from magnetic-tape playbacks from both the temporary Coalinga seismic network and the permanent telemetered central California seismic network (Calnet). The combined catalog appears to be substantially complete for events of M {ge} 3 within about 3 hours, and for events of M {ge} 1.7 within about 1 day, after the main shock. The first-motion plot of the main shock offers two choices for the main-shock fault; a thrust fault striking N. 53{degree}W. and dipping 23{degree}SW. (the preferred fault plane), or a high-angle reverse fault striking N. 53{degree}W. and dipping 67{degree}NE. Focal mechanisms of the larger aftershocks also indicate predominantly thrust or reverse faulting. The long axis of the aftershock zone, which is 35 km long and 15 to 20 km wide, coincides with the axis of the Anticline Ridge-Guijarral Hills structure at the Coast Ranges-Great Valley boundary northeast of Coalinga. A transverse (southwest to northeast) quiet band with very few events crosses the aftershock zone where northwest-trending Anticline Ridge joins broader, east-west-trending Joaquin Ridge just northwest of the main shock. The smaller aftershocks occur mostly in the hanging-wall blocks above the faults outlined by the larger aftershocks.
- OSTI ID:
- 5471383
- Journal Information:
- United States Geological Survey, Professional Paper; (USA), Vol. 1487
- Country of Publication:
- United States
- Language:
- English
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Complex faulting structure inferred from local seismic observations of M ge 1. 0 aftershocks, May 2-June 30, 1983
Tectonic setting
Related Subjects
CALIFORNIA
EARTHQUAKES
DATA ANALYSIS
AFTERSHOCKS
ANTICLINES
DIMENSIONS
EARTHQUAKE MAGNITUDE
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
HYPOCENTERS
ROCK MECHANICS
SEISMIC ARRAYS
SEISMIC EVENTS
TIME DEPENDENCE
DEVELOPED COUNTRIES
FEDERAL REGION IX
GEOLOGIC FRACTURES
MEASURING INSTRUMENTS
MECHANICS
NORTH AMERICA
USA
580000* - Geosciences