Earthquake depths and the relation to strain accumulation and stress near strike-slip faults in southern California
- Geological Survey, Menlo Park, CA (United States)
Earthquakes in the major fault zones are predominantly deep. Earthquakes in the crustal blocks bounding the fault zones are predominantly shallow. In the San Jacinto fault zone, maximum earthquake depths correlate with surface heat flow. These relations together with focal mechanisms, geodetic strain measurements, and fault zone models are consistent with the following ideas: (1) Interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes. (2) The aseismic slip in a narrow fault zone in the brittle-plastic transition region concentrates strain at the base of the brittle fault zone. (3) Deep earthquakes occur in thelower part of the brittle fault zone due to stick-slip failure of highly stressed patches. (4) Background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding (deep) and stick-slip (shallow) regions of the fault zone. Furthermore, the difference in seismicity between the San Jacinto and southern San Andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases. (5) Shear stress may be less in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks. (6) In the stress field produced by plate motion and slip in the deep fault zone, the upper brittle fault zone is not oriented favorably for shear failure. Lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation.
- OSTI ID:
- 5073771
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B4; ISSN 0148-0227; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
AFTERSHOCKS
BRITTLENESS
CALIFORNIA
CORRELATIONS
DEPTH
DEVELOPED COUNTRIES
DIMENSIONS
EARTHQUAKES
FEDERAL REGION IX
GEODETIC SURVEYS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
HEAT FLOW
HYPOCENTERS
MECHANICAL PROPERTIES
NORTH AMERICA
ORIENTATION
PLASTICITY
PLATE TECTONICS
SEISMIC EVENTS
SEISMICITY
SLIP
STRAINS
STRESS ANALYSIS
STRESSES
SURVEYS
TECTONICS
USA