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Title: Changes in shear wave splitting at Anza near the time of the North Palm Springs earthquake

Abstract

Changes in shear wave splitting are observed at KNW before and after the M = 6 North Palm Springs earthquake of July 8, 1986. KNW is a station of the Anza seismic network monitoring the Anza seismic gap on the San Jacinto fault, southern California. The gradual increase in the delays between the split shear waves over 3 years at KNW, reported by Peacock et al. (1988), ended in June 1986. The further 2 years of observations analyzed here show that the behavior of the delays changed abruptly near the time of the North Palm Springs earthquake, 33 km north of KNW. Peacock et al. demonstrated that the increase in delays could be simulated by increasing the aspect ratio of stress-aligned fluid-filled inclusions, and speculated that this increase might be the result of a buildup of stress before an impending earthquake. The new data appear to confirm this speculation, but the temporal variations require a more complex interpretation, although they still suggest that the changes in shear wave splitting are caused by earthquake-induced stress changes to the fluid-filled inclusions throughout the rockmass. Central to interpretation of temporal changes in shear wave splitting is the well established existence, throughout at leastmore » the uppermost 10 to 20 km of the crust, of small fluid-filled cracks, microcracks, and pores. The existence of such inclusions introduces a compliant quality to otherwise stiff crustal rock. The authors term these distributions of inclusions extensive dilatancy anisotropy or EDA, and the individual inclusions EDA cracks because, although they may include a wide range of shapes, many of the seismic properties can be simulated by distributions of thin parallel cracks.« less

Authors:
; ;  [1];  [2];  [3]
  1. British Geological Survey, Edinburgh (Scotland)
  2. Univ. of Reading (England)
  3. Geological Survey, Menlo Park, CA (USA)
Publication Date:
OSTI Identifier:
5446695
Report Number(s):
CONF-880531-
Journal ID: ISSN 0148-0227; CODEN: JGREA
Resource Type:
Conference
Journal Name:
Journal of Geophysical Research; (United States)
Additional Journal Information:
Journal Volume: 95:B7; Conference: 3. international workshop on seismic anisotropy, Berkeley, CA (United States), 31 May - 4 Jun 1988; Journal ID: ISSN 0148-0227
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; GEOLOGIC FAULTS; EARTHQUAKES; SEISMIC S WAVES; BIREFRINGENCE; AFTERSHOCKS; ANISOTROPY; CONTINENTAL CRUST; DATA ANALYSIS; FORESHOCKS; GEOLOGIC FISSURES; GEOLOGIC FRACTURES; INCLUSIONS; POROSITY; RESERVOIR FLUIDS; STRESS ANALYSIS; TIME DELAY; VARIATIONS; WAVE PROPAGATION; DEVELOPED COUNTRIES; EARTH CRUST; FEDERAL REGION IX; FLUIDS; GEOLOGIC STRUCTURES; NORTH AMERICA; REFRACTION; SEISMIC EVENTS; SEISMIC WAVES; USA; 580000* - Geosciences

Citation Formats

Crampin, S, Booth, D C, Evans, R, Peacock, S, and Fletcher, J B. Changes in shear wave splitting at Anza near the time of the North Palm Springs earthquake. United States: N. p., 1990. Web.
Crampin, S, Booth, D C, Evans, R, Peacock, S, & Fletcher, J B. Changes in shear wave splitting at Anza near the time of the North Palm Springs earthquake. United States.
Crampin, S, Booth, D C, Evans, R, Peacock, S, and Fletcher, J B. Tue . "Changes in shear wave splitting at Anza near the time of the North Palm Springs earthquake". United States.
@article{osti_5446695,
title = {Changes in shear wave splitting at Anza near the time of the North Palm Springs earthquake},
author = {Crampin, S and Booth, D C and Evans, R and Peacock, S and Fletcher, J B},
abstractNote = {Changes in shear wave splitting are observed at KNW before and after the M = 6 North Palm Springs earthquake of July 8, 1986. KNW is a station of the Anza seismic network monitoring the Anza seismic gap on the San Jacinto fault, southern California. The gradual increase in the delays between the split shear waves over 3 years at KNW, reported by Peacock et al. (1988), ended in June 1986. The further 2 years of observations analyzed here show that the behavior of the delays changed abruptly near the time of the North Palm Springs earthquake, 33 km north of KNW. Peacock et al. demonstrated that the increase in delays could be simulated by increasing the aspect ratio of stress-aligned fluid-filled inclusions, and speculated that this increase might be the result of a buildup of stress before an impending earthquake. The new data appear to confirm this speculation, but the temporal variations require a more complex interpretation, although they still suggest that the changes in shear wave splitting are caused by earthquake-induced stress changes to the fluid-filled inclusions throughout the rockmass. Central to interpretation of temporal changes in shear wave splitting is the well established existence, throughout at least the uppermost 10 to 20 km of the crust, of small fluid-filled cracks, microcracks, and pores. The existence of such inclusions introduces a compliant quality to otherwise stiff crustal rock. The authors term these distributions of inclusions extensive dilatancy anisotropy or EDA, and the individual inclusions EDA cracks because, although they may include a wide range of shapes, many of the seismic properties can be simulated by distributions of thin parallel cracks.},
doi = {},
journal = {Journal of Geophysical Research; (United States)},
issn = {0148-0227},
number = ,
volume = 95:B7,
place = {United States},
year = {1990},
month = {7}
}

Conference:
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