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Title: Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake

Abstract

Surface rupturing during the 28 June 1992, Landers, California earthquake, east of Los Angeles, accommodated right-lateral offsets up to about 6 m along segments of distinct, en echelon fault zones with a total length of about 80 km. The offsets were accommodated generally not by faults -- distinct slip surfaces -- but rather by shear zones, tabular bands of localized shearing. In long, straight stretches of fault zones at Landers the rupture is characterized by telescoping of shear zones and intensification of shearing: broad shear zones of mild shearing, containing narrow shear zones of more intense shearing, containing even-narrower shear zones of very intense shearing, which may contain a fault. Thus the ground ruptured across broad belts of shearing with subparallel walls, oriented NW. Each broad belt consists of a broad zone of mild shearing, extending across its entire width (50 to 200 m), and much narrower (a few m wide) shear zones that accommodate most of the offset of the belt and are portrayed by en echelon tension cracks. In response to right-lateral shearing, the slices of ground bounded by the tension cracks rotated in a clockwise sense, producing left lateral shearing, and the slices were forced against themore » walls of the shear zone, producing thrusting. Even narrower shear zones formed within the narrow shear zones, and some of these were faults. Although the narrower shear zones probably are indicators to right-lateral fault segments at depth, the surface rupturing during the earthquake is characterized not by faulting, but by zones of shearing at various scales. Furthermore, understanding of the formation of the shear zones may be critical to understanding of earthquake faulting because, where faulting is associated with the formation of a shear zone, the faulting occurs late in the development of the shear zone. The faulting occurs after a shear zone or a belt of shear zones forms.« less

Authors:
;  [1];  [2]
  1. Geological Survey, Denver, CO (United States)|[Purdue Univ., West Lafayette, IN (United States). Richard H. Jahns Engineering Geology Lab.
  2. Geological Survey, Denver, CO (United States)
Publication Date:
Research Org.:
Geological Survey, Denver, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Research, Washington, DC (United States)
OSTI Identifier:
677052
Report Number(s):
USGS-OFR-93-348
ON: DE99000961; TRN: AHC29821%%185
DOE Contract Number:  
FG02-93ER14365
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1993
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; EARTHQUAKES; ROCK MECHANICS; RUPTURES; GEOLOGIC FAULTS; SHEAR; CRACKS; MAPS

Citation Formats

Johnson, A.M., Cruikshank, K.M., and Fleming, R.W.. Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake. United States: N. p., 1993. Web. doi:10.2172/677052.
Johnson, A.M., Cruikshank, K.M., & Fleming, R.W.. Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake. United States. doi:10.2172/677052.
Johnson, A.M., Cruikshank, K.M., and Fleming, R.W.. Fri . "Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake". United States. doi:10.2172/677052. https://www.osti.gov/servlets/purl/677052.
@article{osti_677052,
title = {Broad belts of shear zones: The common form of surface rupture produced by the 28 June 1992 Landers, California, earthquake},
author = {Johnson, A.M. and Cruikshank, K.M. and Fleming, R.W.},
abstractNote = {Surface rupturing during the 28 June 1992, Landers, California earthquake, east of Los Angeles, accommodated right-lateral offsets up to about 6 m along segments of distinct, en echelon fault zones with a total length of about 80 km. The offsets were accommodated generally not by faults -- distinct slip surfaces -- but rather by shear zones, tabular bands of localized shearing. In long, straight stretches of fault zones at Landers the rupture is characterized by telescoping of shear zones and intensification of shearing: broad shear zones of mild shearing, containing narrow shear zones of more intense shearing, containing even-narrower shear zones of very intense shearing, which may contain a fault. Thus the ground ruptured across broad belts of shearing with subparallel walls, oriented NW. Each broad belt consists of a broad zone of mild shearing, extending across its entire width (50 to 200 m), and much narrower (a few m wide) shear zones that accommodate most of the offset of the belt and are portrayed by en echelon tension cracks. In response to right-lateral shearing, the slices of ground bounded by the tension cracks rotated in a clockwise sense, producing left lateral shearing, and the slices were forced against the walls of the shear zone, producing thrusting. Even narrower shear zones formed within the narrow shear zones, and some of these were faults. Although the narrower shear zones probably are indicators to right-lateral fault segments at depth, the surface rupturing during the earthquake is characterized not by faulting, but by zones of shearing at various scales. Furthermore, understanding of the formation of the shear zones may be critical to understanding of earthquake faulting because, where faulting is associated with the formation of a shear zone, the faulting occurs late in the development of the shear zone. The faulting occurs after a shear zone or a belt of shear zones forms.},
doi = {10.2172/677052},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Dec 31 00:00:00 EST 1993},
month = {Fri Dec 31 00:00:00 EST 1993}
}

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