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Bulletin of the Seismological Society of America; February 2009; v. 99; no. 1; p. 87-94; DOI: 10.1785/0120080192
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The Mw 7.7 Tocopilla Earthquake of 14 November 2007 at the Southern Edge of the Northern Chile Seismic Gap: Rupture in the Deep Part of the Coupled Plate Interface

Bertrand Delouis

Géosciences Azur, University of Nice, Sophia Antipolis, CNRS, IRD, 250 rue A. Einstein, Valbonne, 06560, France delouis{at}geoazur.unice.fr

Mario Pardo and Denis Legrand*

Departamento de Geofisica, Universidad de Chile, Blanco Encalada 2002, Santiago, Chile mpardo{at}dgf.uchile.cl denis{at}dgf.uchile.cl

Tony Monfret

Géosciences Azur, University of Nice, Sophia Antipolis, CNRS, IRD, 250 rue A. Einstein, 06560 France monfret{at}geoazur.unice.fr

* Present address: Universidad Nacional Autónoma de México (UNAM), Instituto de Geofisica, Departamento de Vulcanologia, Ciudad Universitaria, Del. Coyoacan México D.F., C.P. 04510, denis@geofisica.unam.mx.

The slip distribution of the Mw 7.7 Tocopilla earthquake was obtained from the joint inversion of teleseismic and strong-motion data. Rupture occurred as underthrusting at the base of the seismically coupled plate interface, mainly between 35 and 50 km depth. From the hypocenter, located below the coast 25 km south of the town of Tocopilla, the rupture propagated 50 km northward and 100 km southward. Overall, the slip distribution was dominated by two slip patches, one near the hypocenter and the other 70 km to the south where slip reached its maximum value (3 m). An additional branch of moderate slip propagated at shallower depth toward the west near the northern tip of the Mejillones peninsula. Rupture velocity remained close to 2.8 km/sec, with a total rupture duration of 45 sec. The first 2 weeks of aftershocks located with a local seismic network display a strong correlation with the slip distribution. The 2007 rupture ended below the Mejillones peninsula, where the 1995 Antofagasta rupture also ended (Ruegg et al., 1996; Delouis et al., 1997; Pritchard et al., 2006). This corroborates the role of barrier played by this structure. The downdip end of the seismically coupled zone at 50 km depth, evidenced by previous studies for the 1995 event, is also confirmed. The 2007 Tocopilla earthquake contributed only moderately to the rupturing of the great northern Chile seismic gap, which still has the capacity for generating a much larger underthrusting event.




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B. Delouis, J. Charlety, and M. Vallee
A Method for Rapid Determination of Moment Magnitude Mw for Moderate to Large Earthquakes from the Near-Field Spectra of Strong-Motion Records (MWSYNTH)
Bulletin of the Seismological Society of America, June 1, 2009; 99(3): 1827 - 1840.
[Abstract] [Full Text] [PDF]


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