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Fine structure of the rupture zone of the April 26 and 27, 1997, Northridge aftershocks

Venkataraman, Anupama and Mori, Jim and Kanamori, Hiroo and Zhu, Lupei (2000) Fine structure of the rupture zone of the April 26 and 27, 1997, Northridge aftershocks. Journal of Geophysical Research B, 105 (B8). pp. 19085-19093. ISSN 0148-0227. doi:10.1029/2000JB900067.

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We investigated the rupture geometry of two M_w ∼4.5 earthquakes (April 26, 1997, and April 27, 1997) that occurred on the western edge of the aftershock zone of the 1994, M_w 6.7, Northridge earthquake. Both events have thrust mechanisms with a steep plane dipping ∼75°SE and a shallow plane dipping ∼45°NE. An empirical Green's function deconvolution followed by a waveform inversion was used to determine the slip distribution of the two events. The inversion results show that the steep plane fits the data slightly better than the shallow plane. The background seismicity (aftershocks of the 1994 Northridge event) in the epicentral region shows the existence of a north dipping fault plane, similar to that of the 1971 San Fernando earthquake. However, the spatial trend of the two April 1997 events and their aftershocks reveals tightly clustered seismicity on a steep plane dipping south. Relative relocation of the April 26 and 27 events shows that the April 27 event ruptured ∼1.4 km N70°E of the April 26 event and at a slightly shallower depth, i.e., almost along strike and on a steep plane dipping south. These observations suggest that the steep plane is the fault plane of both events. The two events ruptured on a plane which is almost perpendicular to the trend of the regional background seismicity. Thus the seismogenic structure beneath the Transverse Ranges exhibits complexity on scales of a few kilometers. The rupture area for both the April 26 and 27 events is ~1 km^2 with a stress drop of at least 20 to 30 bars.

Item Type:Article
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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 2000 American Geophysical Union. Received February 22, 1999; revised February 11, 2000; accepted February 23, 2000. Paper number 2000JB900067. This research was supported by the USGS grant USGS.HQGR0035 and the Southern California Earthquake Center (SCEC). SCEC is funded by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. This is SCEC contribution 460. Contribution 8619 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Southern California Earthquake Center (SCEC)UNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences 8619
Southern California Earthquake Center (SCEC)460
Issue or Number:B8
Record Number:CaltechAUTHORS:20141112-102714681
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Official Citation:Venkataraman, A., J. Mori, H. Kanamori, and L. Zhu (2000), Fine structure of the rupture zone of the April 26 and 27, 1997, Northridge aftershocks, J. Geophys. Res., 105(B8), 19085–19093, doi:10.1029/2000JB900067
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51643
Deposited By: Ruth Sustaita
Deposited On:12 Nov 2014 21:44
Last Modified:10 Nov 2021 19:13

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