Complex faulting structure inferred from local seismic observations of M ge 1. 0 aftershocks, May 2-June 30, 1983

Journal Article · Mon Jan 01 04:00:00 EST 1990 · United States Geological Survey, Professional Paper; (USA)

OSTI ID:5599826

Eberhart-Phillips, D; Reasenberg, P A

The geometric structure of aftershocks of the May 2 earthquake supports a complex model of faulting for the Coalinga earthquake sequence. Local seismic observations after the M{sub L} = 6.5 main shock were used to determine 4,412 hypocenters and 3,108 fault-plane solutions for aftershocks during the first 2 months of the sequence. The resulting distribution and orientation of a subset of 2,618 well-determined hypocenters and 677 well-determined fault-plane solutions were analyzed for evidence of faulting structure. The model consists of two principal planes between 5- and 12.5-km depth. The planes join at the depth of the main-shock hypocenter (10 km), defining a wedge-shaped horst beneath the Coalinga anticline and the east side of Pleasant Valley. This horst may have been uplifted during the earthquake sequence by displacement on one or both planes. The distribution of aftershocks during the first 3 to 6 hours after the main shock suggests that the first and largest displacement was probably on the southwest-dipping plane. Analysis of the aftershock distribution allows the introduction of further complexity into this model. The southwest-dipping surface appears to dip less steeply below 10-km depth and may represent a listric main-shock fault. Extension of the aftershock distribution to shallow depths on the northeast-dipping plane defines the Nunez fault rupture on a plane consistent with surface observations of the Nunez fault scarp. Shallow to moderately deep aftershocks beneath the northeast flank of the Coalinga anticline suggest secondary fault slip parallel to bedding.

• OSTI ID: 5599826
• Journal Information: United States Geological Survey, Professional Paper; (USA), Journal Name: United States Geological Survey, Professional Paper; (USA) Vol. 1487; ISSN XGPPA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AFTERSHOCKS
ANTICLINES
CALIFORNIA
DATA ANALYSIS
DEFORMATION
DEPTH
DEVELOPED COUNTRIES
DIMENSIONS
DISTRIBUTION
EARTHQUAKE MAGNITUDE
EARTHQUAKES
FAILURES
FEDERAL REGION IX
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
GROUND UPLIFT
HYPOCENTERS
MECHANICS
MORPHOLOGY
NORTH AMERICA
ORIENTATION
ROCK MECHANICS
RUPTURES
SEDIMENTARY BASINS
SEISMIC EVENTS
SEISMIC SURVEYS
SURVEYS
USA