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Source characteristics of the M (sub w) 6.2 Loreto earthquake of 12 March 2003 that occurred in a transform fault in the middle of the Gulf of California, Mexico

Leobardo Lopez Pineda and Cecilio J. Rebollar
Source characteristics of the M (sub w) 6.2 Loreto earthquake of 12 March 2003 that occurred in a transform fault in the middle of the Gulf of California, Mexico
Bulletin of the Seismological Society of America (April 2005) 95 (2): 419-430

Abstract

We analyzed the Loreto earthquake of 12 March 2003 M (sub w) 6.2, which occurred in the transform fault that joins the Guaymas and Carmen Basins in the middle of the Gulf of California. This event was recorded by a network of autonomous continuously recording broadband seismographs located over the Baja California Peninsula, Sonora, and Sinaloa States of Mexico. The main event was located at 26.615 degrees N and 111.09 degrees W, at a depth of 5.0 + or - 2 km. A foreshock of magnitude 4.2 was recorded and located at 26.580 degrees N and 111.011 degrees W. We located 35 aftershocks, 20% of them were located in the rupture area of the mainshock consistent with a nearly vertical right-lateral strike-slip fault with a northwest-southeast trend. Rupture propagation derived from waveform analysis indicated that the rupture propagated from northwest to southeast. Most of the aftershocks occurred southeaster of the main event. From the statistical analysis of 333 aftershocks we calculated a b-value of 0.68. Focal depth and fault geometry were estimated from body-wave form modeling of P and S waves. Synthetics were calculated using Herrmann's (1987) reflectivity code with a triangular source time function of 6 sec. The best match between synthetics and recorded P and S waves were obtained with a fault geometry given by a strike of 117 degrees + or - 4 degrees , a dip of 79 degrees + or - 2 degrees , and a slip of 168 degrees + or - 2 degrees . We calculated a seismic moment of 2.68 X 10 (super 18) N m (2.68 X 10 (super 25) dyne cm), a source radius of 6.8 + or - 0.7 km, and a static stress drop of 3.8 + or - 1.2 Mp (38 + or - 12 bars). Calculated static stress drops of previous events located in the Gulf of California range from 0.2 to 12.5 Mp (2 to 125 bars).


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 95
Serial Issue: 2
Title: Source characteristics of the M (sub w) 6.2 Loreto earthquake of 12 March 2003 that occurred in a transform fault in the middle of the Gulf of California, Mexico
Affiliation: Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Departamento de Sismologia, Baja California, Mexico
Pages: 419-430
Published: 200504
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 15
Accession Number: 2005-047914
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, sketch maps
N25°00'00" - N28°00'00", W113°00'00" - W109°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200530
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