Structure of the Coalinga area and thrust origin of the earthquake

Journal Article · Mon Jan 01 04:00:00 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), Journal Name: United States Geological Survey, Professional Paper; (USA) Vol. 1487; ISSN XGPPA
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
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ANTICLINES
BASEMENT ROCK
BOUNDARY CONDITIONS
CALIFORNIA
CENOZOIC ERA
DEFORMATION
DEPTH
DEVELOPED COUNTRIES
DIMENSIONS
EARTHQUAKES
FAILURES
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC FAULTS
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GEOLOGIC STRUCTURES
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GEOPHYSICAL SURVEYS
GROUND UPLIFT
MECHANICS
MESOZOIC ERA
NORTH AMERICA
OPTICAL PROPERTIES
ORIGIN
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QUATERNARY PERIOD
REFLECTIVITY
REGIONAL ANALYSIS
ROCK MECHANICS
RUPTURES
SEDIMENTARY BASINS
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