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The 1992 Landers Earthquake Sequence: Seismological Observations

Hauksson, Egill and Jones, Lucile M. and Hutton, Kate and Eberhard-Phillips, Donna (1993) The 1992 Landers Earthquake Sequence: Seismological Observations. Journal of Geophysical Research B, 98 (B11). pp. 19835-19858. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20131127-090400676

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Abstract

The (M_W 6.1, 7.3, 6.2) 1992 Landers earthquakes began on April 23 with the M_W6.1 1992 Joshua Tree preshock and form the most substantial earthquake sequence to occur in California in the last 40 years. This sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long. The faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the San Andreas fault. The M_W6.1 Joshua Tree preshock at 33°N58′ and 116°W19′ on 0451 UT April 23 was preceded by a tightly clustered foreshock sequence (M≤4.6) beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks. The aftershocks extended along a northerly trend from about 10 km north of the San Andreas fault, northwest of Indio, to the east-striking Pinto Mountain fault. The M_w7.3 Landers mainshock occurred at 34°N13′ and 116°W26′ at 1158 UT, June 28, 1992, and was preceded for 12 hours by 25 small M≤3 earthquakes at the mainshock epicenter. The distribution of more than 20,000 aftershocks, analyzed in this study, and short-period focal mechanisms illuminate a complex sequence of faulting. The aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults, and 40 km to the south, crossing the Pinto Mountain fault through the Joshua Tree aftershock zone towards the San Andreas fault near Indio. The rupture initiated in the depth range of 3–6 km, similar to previous M∼5 earthquakes in the region, although the maximum depth of aftershocks is about 15 km. The mainshock focal mechanism showed right-lateral strike-slip faulting with a strike of N10°W on an almost vertical fault. The rupture formed an arclike zone well defined by both surficial faulting and aftershocks, with more westerly faulting to the north. This change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west. A 20-km-long linear cluster of aftershocks occurred 10–20 km north of Barstow, or 30–40 km north of the end of the mainshock rupture. The most prominent off-fault aftershock cluster occurred 30 km to the west of the Landers mainshock. The largest aftershock was within this cluster, the M_w6.2 Big Bear aftershock occurring at 34°N10′ and 116°W49′ at 1505 UT June 28. It exhibited left-lateral strike-slip faulting on a northeast striking and steeply dipping plane. The Big Bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north. The Landers mainshock occurred near the southernmost extent of the Eastern California Shear Zone, an 80-km-wide, more than 400-km-long zone of deformation. This zone extends into the Death Valley region and accommodates about 10 to 20% of the plate motion between the Pacific and North American plates. The Joshua Tree preshock, its aftershocks, and Landers aftershocks form a previously missing link that connects the Eastern California Shear Zone to the southern San Andreas fault.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/93JB02384DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/93JB02384/abstractPublisherArticle
ORCID:
AuthorORCID
Hauksson, Egill0000-0002-6834-5051
Jones, Lucile M.0000-0002-2690-3051
Additional Information:© 1993 American Geophysical Union. Received April 12, 1993; revised August 10, 1993; accepted August 19, 1993. D. Oppenheimer, M. Rymer, J. Dolan, and two Journal of Geophysical Research reviewers, C. Thurber and S. Jaume, provided helpful critical reviews. We thank K. Sieh for stimulating discussions about the tectonics of the Landers earthquake and for providing a map of the surface rupture. We are grateful to the seismic analysts of Caltech and the USGS for quick and competent processing of the earthquake data. This research was partially supported by USGS grant 14-08-0001-G1761 and USGS cooperative agreement 1434-92-A-0960 to Caltech and the Southern California Earthquake Center (SCEC) under NSF cooperative agreement EAR-8920136 and USGS cooperative agreement 14-08-0001-0899. SCEC publication 54. Contribution 5268, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
USGS14-08-0001-G1761
USGS1434-92-A-0960
Southern California Earthquake Center (SCEC)UNSPECIFIED
NSFEAR-8920136
USGS14-08-0001-0899
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5268
Southern California Earthquake Center (SCEC)54
Issue or Number:B11
Record Number:CaltechAUTHORS:20131127-090400676
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20131127-090400676
Official Citation:Hauksson, E., L. M. Jones, K. Hutton, and D. Eberhart-Phillips (1993), The 1992 Landers Earthquake Sequence: Seismological observations, J. Geophys. Res., 98(B11), 19835–19858, doi:10.1029/93JB02384.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42750
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:02 Dec 2013 16:19
Last Modified:24 Feb 2020 10:30

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