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Compression directions in southern California (from Santa Barbara to Los Angeles Basin) obtained from borehole breakouts

Wilde, Melita and Stock, Joann (1997) Compression directions in southern California (from Santa Barbara to Los Angeles Basin) obtained from borehole breakouts. Journal of Geophysical Research B, 102 (B3). pp. 4969-4983. ISSN 0148-0227. doi:10.1029/96JB03734.

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Borehole elongation in 71 drill holes was used to infer breakout orientation and directions of maximum horizontal principal stress S_H for six areas west of the San Andreas fault in southern California: Santa Barbara, Ojai, Central Ventura Basin, East Ventura Basin, West Los Angeles Basin, and East Los Angeles Basin. Breakouts were determined from analysis of oriented four-arm caliper data. The breakouts form at the position of the maximum compressive stress on the borehole wall; if the borehole is vertical and parallel to one of the principal stress directions, the breakouts will form parallel to the minimum horizontal principal stress S_h orthogonal to the maximum horizontal principal stress S_H. Observations from deviated boreholes permit some constraints on the relative magnitudes of the principal stresses. In most cases the data permit either a thrust faulting (S_v<S_h<S_H) or strike-slip faulting (S_h<S_v<S_H) stress regime with NE to NW directions of S_H. These results are broadly consistent with results from focal mechanism studies [Hauksson, 1990; Li, 1996] and with breakout and focal mechanism data present in the world stress map database [Zoback, 1992]. However, we find systematic variations in S_H directions suggestive of strong heterogeneity in the stress field at shallow depths, similar to that present in the Cajon Pass borehole [Shamir and Zoback, 1992]. Anomalous NW directions of S_H in the San Fernando Valley region and near the Whittier fault may be related to structural complexities and/or lateral ramps in nearby fault systems.

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Stock, Joann0000-0003-4816-7865
Additional Information:© 1997 American Geophysical Union. A Paper number 96JB03734. Received March 15, 1996; revised October 1, 1996; accepted November 27, 1996. Some data were graciously provided by J. Scott Hornafius and Laird Thompson of Mobil Exploration & Producing U.S. This work was supported by the Southern California Earthquake Center via NSF grant EAR 89-20136. Contribution 5656 of the Caltech Seismological Laboratory. SCEC publication 320. The early phases of this research were supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award 1434-93-G-2297. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. We thank Colleen Barton and an anonymous reviewer for very helpful reviews. Further details of the observations presented in this paper can be accessed on the internet at
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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Southern California Earthquake Center (SCEC)UNSPECIFIED
NSFEAR 89-20136
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5656
Southern California Earthquake Center320
Issue or Number:B3
Record Number:CaltechAUTHORS:20140415-093934915
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Official Citation:Wilde, M., and J. Stock (1997), Compression directions in southern California (from Santa Barbara to Los Angeles Basin) obtained from borehole breakouts, J. Geophys. Res., 102(B3), 4969–4983, doi:10.1029/96JB03734.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44951
Deposited By: Ruth Sustaita
Deposited On:15 Apr 2014 17:27
Last Modified:10 Nov 2021 16:58

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