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Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial Valley, California
Author(s) -
Wei Shengji,
Helmberger Don,
Owen Susan,
Graves Robert W.,
Hudnut Kenneth W.,
Fielding Eric J.
Publication year - 2013
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/grl.50259
Subject(s) - geology , seismology , slip (aerodynamics) , global positioning system , seismogram , geodesy , asperity (geotechnical engineering) , bedrock , inversion (geology) , earthquake swarm , induced seismicity , tectonics , geomorphology , physics , geotechnical engineering , telecommunications , computer science , thermodynamics
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 w 3.9) for path calibration of the velocity structure. Our results indicate that the first ( M w 5.3) event ruptured a strong, concentrated asperity with offsets of ~20 cm centered at a depth of 5 km. The subsequent M w 5.4 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 w 5.3 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.