Earthquakes, faulting, and stress in the Los Angeles basin

Journal Article · Mon Sep 10 04:00:00 EDT 1990 · Journal of Geophysical Research; (USA)

DOI:https://doi.org/10.1029/JB095iB10p15365· OSTI ID:6055931

Hauksson, E ^[1]

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1. Univ. of Southern California, Los Angeles (USA)

Since 1920 fourteen moderate-sized (M{sub L} = 4.9-6.4) earthquakes have been reported in the Los Angeles basin. To determine the style of faulting and state of stress in the basin, single-event focal mechanisms for 244 earthquakes of M {ge} 2.5 that have occurred during 1977-1989 have been calculated. Fifty-nine percent of the events are strike-slip and are mostly located near two of the major, northwest striking right-lateral strike-slip faults in the basin, the Newport-Inglewood fault and the Palos Verdes fault. The 1988 Pasadena and the 1988 Upland earthquakes showed left-lateral strike-slip on northeast striking faults. Numerous small earthquakes in the eastern part of the basin show left-lateral strike-slip faulting and form a northeast trend near Yorba Linda. Thirty-two percent of the events have reverse mechanisms and are distributed along two broad zones. The first, the Elysian Park fold and thrust belt, coincides with anticlines along the eastern and northern flank of the Los Angeles basin extending into Santa Monica Bay. The second, the Torrance-Wilmington fold and thrust belt, coincides with anticlines mapped on the southwest flank of the basin and extends from offshore Newport Beach to the northwest into Santa Monica Bay. The trend of the maximum horizontal stress varies from N1{degree}W to N31{degree}E across the basin and consistently forms high angles with the fold axes. The stress field that exists along the flanks of the basin has a vertical minimum stress axis. This stress field and ongoing folding and thrusting suggest that tectonic deformation is concentrated along the flanks of the deep central basin. Today the deformation of the basin consists of uplift and crustal thickening and lateral block movement to accommodate the north-south compression across the basin.

• OSTI ID: 6055931
• Journal Information: Journal of Geophysical Research; (USA), Journal Name: Journal of Geophysical Research; (USA) Vol. 95:B10; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANTICLINES
CALIFORNIA
CONTINENTAL CRUST
DEFORMATION
DIMENSIONS
EARTH CRUST
EARTHQUAKE MAGNITUDE
EARTHQUAKES
FEDERAL REGION IX
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GROUND UPLIFT
HISTORICAL ASPECTS
LOS ANGELES
MECHANICS
NORTH AMERICA
ROCK MECHANICS
SEDIMENTARY BASINS
SEISMIC EVENTS
SLIP
STRESS ANALYSIS
TECTONICS
THICKNESS
USA