Structure of the seismogenic zone of the southcentral Chilean margin revealed by local earthquake traveltime tomography

Haberland, C. and Rietbrock, A. and Lange, D. and Bataille, Kl. and Dahm, T. (2009) Structure of the seismogenic zone of the southcentral Chilean margin revealed by local earthquake traveltime tomography. Journal of Geophysical Research - Solid Earth, 114. B01317. DOI 10.1029/2008JB005802

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Abstract

We use traveltime data of local earthquakes and controlled sources observed by a large, temporary, amphibious seismic network to reveal the anatomy of the southcentral Chilean subduction zone (37–39°S) between the trench and the magmatic arc. At this location the giant 1960 earthquake (M = 9.5) nucleated and ruptured almost 1000 km of the subduction megathrust. For the three-dimensional tomographic inversion we used 17,148 P wave and 10,049 S wave arrival time readings from 439 local earthquakes and 94 shots. The resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests. The downgoing lithosphere is delineated by high seismic P wave velocities. High v p/v s ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle. The subducting oceanic crust can be traced down to a depth of 80 km, as indicated by a low velocity channel. The continental crust extends to approximately a 50-km depth near the intersection with the subducting plate. This suggests a wide contact zone between continental and oceanic crust of about 150 km, potentially supporting the development of large asperities. Eastward the crustal thickness decreases again to a minimum of about a 30-km depth. Relatively low v p/v s at the base of the forearc does not support a large-scale serpentinization of the mantle wedge. Offshore, low v p and high v p/v s reflect young, fluid-saturated sediments of forearc basins and the accretionary prism.

Item Type: Article
Uncontrolled Keywords: 08AREP; IA58;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Journal of Geophysical Research - Solid Earth
Volume: 114
Page Range: B01317
Identification Number: 10.1029/2008JB005802
Depositing User: Sarah Humbert
Date Deposited: 11 Jul 2009 13:02
Last Modified: 23 Jul 2013 09:55
URI: http://eprints.esc.cam.ac.uk/id/eprint/1096

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