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Source characteristics of the 17 January 1994 Northridge, California, earthquake from regional broadband modeling

Song, Xi J. and Jones, Laura E. and Helmberger, Donald V. (1995) Source characteristics of the 17 January 1994 Northridge, California, earthquake from regional broadband modeling. Bulletin of the Seismological Society of America, 85 (6). pp. 1591-1603. ISSN 0037-1106.

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Broadband regional records are modeled to determine source mechanism, seismic moment, fault dimension, and rupture directivity for the 17 January 1994 Northridge earthquake. Modeling is done using both theoretical Green's functions (tGf) and empirical Green's functions (eGf). From the theoretical modeling, we obtain a source mechanism with strike 128°, dip 33°, and rake 106° for the mainshock, using a source estimation algorithm by Zhao and Helmberger (1994). While the fault orientation seems resolvable from regional data, the moment estimation is less reliable due to inadequate synthetic waveform fits to the observed surface waves. This appears to be caused by the combination of propagational effects and fault complexities. Further investigation of the source characteristics is carried out with a new method of using eGf's. As an eGf, we select the 17 January 1994 17:56 GMT aftershock, which occurred near the onset of the mainshock and had a similar source mechanism. The source duration of the mainshock, as seen from the regional surface waves observed at various stations, is obtained by searching for the trapezodial far-field source-time function for each station that, when convolved with the aftershock data, best simulates the mainshock data. Stations to the north record shorter source durations than stations to the south. Modeling these with theoretical predictions of rupture on a square fault, we constrain the effective fault dimension to be 14 km with rupture along the direction of the average rake vector. A moment of (1.4 ± 0.9) × 10^(26) dyne-cm with a stress drop of ∼120 bars is obtained for the mainshock from our eGf study.

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Additional Information:© 1995 by the Seismological Society of America. Manuscript received 10 May 1994. We thank Craig Scrivner, Hiroo Kanamori, Chandan Saikia, and one anonymous reviewer for their reviews of the manuscript. This research was supported by SCEC, Contract No. 569933 NSF EAR89-20136. Contribution No. 5545, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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Southern California Earthquake Center (SCEC)569933
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Caltech Division of Geological and Planetary Sciences5545
Issue or Number:6
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35806
Deposited By: Tony Diaz
Deposited On:05 Dec 2012 19:26
Last Modified:03 Oct 2019 04:31

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