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Published March 16, 2013 | Supplemental Material + Published
Journal Article Open

Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial Valley, California


We investigate the finite rupture processes of two M > 5 earthquakes in the 2012 Brawley swarm by joint inversion of nearby strong motion and high-rate GPS data. Waveform inversions up to 3 Hz were made possible by using a small event (M_w3.9) for path calibration of the velocity structure. Our results indicate that the first (M_w5.3) event ruptured a strong, concentrated asperity with offsets of ~20 cm centered at a depth of 5 km. The subsequent M_w5.4 event occurred 1.5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event. The second event has a longer rise time and weaker high-frequency energy release compared to the M_w5.3 event. Both events display strong rupture directivity toward the southwest and lack of very shallow (<2 km) coseismic slip. The hypocenters for these events appear to be near or in the bedrock, but most of the slip is distributed at shallower depths (<6 km) and can explain a large part of the GPS offsets for the swarm. The complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets.

Additional Information

© 2013 American Geophysical Union. Received 20 December 2012; revised 12 February 2013; accepted 14 February 2013; published 14 March 2013. The strong motion data were downloaded from the Southern California Seismic Network and USGS. The original TerraSAR-X data is copyright 2012 by the German space agency DLR, provided under the Group on Earth Observation Geohazard Supersite project. Part of this research was supported by the USGS grant G12AP20072, Caltech Tectonics Observatory, NASA Earth Surface and Interior focus area and performed at the JPL, Caltech. The high-rate GPS data were provided by the NSF PBO and archived at UNAVCO. Static offset GPS processing was performed by Jerry Svarc (USGS) and Tom Herring (MIT). The manuscript was improved by the constructive input of Karen Felzer, Gavin Hayes and two anonymous reviewers.

Attached Files

Published - grl50259.pdf

Supplemental Material - 55999Rreadme.txt

Supplemental Material - fig_S1.pdf

Supplemental Material - fig_S2.pdf

Supplemental Material - fig_S3.pdf

Supplemental Material - fig_S4.pdf

Supplemental Material - fig_S5.pdf

Supplemental Material - fig_S6.pdf

Supplemental Material - fig_S7.pdf


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