Structure of the Coalinga area and thrust origin of the earthquake

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

OSTI ID:5542486

Zoback, M D ^[1]; Wentworth, C M

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1. Stanford Univ., CA (USA)

The 1983 Coalinga main shock occurred at the eastern margin of the Coast Ranges beneath Coalinga anticline, which forms the northwest segment in a 100-km-long zone of young anticlines about 35 km northeast of the San Andreas fault. Northeast-directed thrusts (here named the Coalinga thrust zone) terminated beneath the anticline at a depth of about 10 km in a series of upward-splaying reverse faults, above which the anticline has grown in the past 2 Ma. A distinct flattening near the center of the northeastern limb of the fold separates it into upper and lower tiers, which are related to separate reverse-fault splays below. The main shock appears to have occurred at the base of a reverse-fault splay beneath the upper tier of the fold and produced a focal mechanism with a gently southwest-dipping focal plane that strikes parallel to the fold axis. Rupture propagated bilaterally back down the thrust and up the reverse fault. Thrusting of the type responsible for the growth of Coalinga anticline probably extends the length of the Coalinga-Kettleman Hills-Lost Hills anticlinal trend, with tear faults at the echelon steps in the trend. The earthquake occurred east of the north-trending Pleasant Valley cross-structure. The structural setting for this recent thrusting east of the San Andreas fault was established in the Mesozoic under a different tectonic regime. The basement shallows northeastward from its 15-km depth beneath the Diablo Range, first at 15{degree}-20{degree} beneath the west side of the San Joaquin Valley and then more gently. This shallowing of basement probably limited northeastward penetration of the Franciscan wedge and seems to be limiting the more recent thrusting as well.

• OSTI ID: 5542486
• Journal Information: United States Geological Survey, Professional Paper; (USA), Vol. 1487
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
EARTHQUAKES
SEDIMENTARY BASINS
ROCK MECHANICS
GEOLOGIC STRUCTURES
AFTERSHOCKS
ANTICLINES
BASEMENT ROCK
BOUNDARY CONDITIONS
DEFORMATION
DEPTH
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGY
GROUND UPLIFT
MESOZOIC ERA
ORIGIN
QUATERNARY PERIOD
REFLECTIVITY
REGIONAL ANALYSIS
RUPTURES
SEISMIC SURVEYS
SEISMIC WAVES
STRATIGRAPHY
TECTONICS
WAVE PROPAGATION
CENOZOIC ERA
DEVELOPED COUNTRIES
DIMENSIONS
FAILURES
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOPHYSICAL SURVEYS
MECHANICS
NORTH AMERICA
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SEISMIC EVENTS
SURFACE PROPERTIES
SURVEYS
USA
580000* - Geosciences