Seismicity near the slip maximum of the 1960 Mw 9.5 Valdivia earthquake (Chile): Plate interface lock and reactivation of the subducted Valdivia Fracture Zone.

Dzierma, Yvonne, Thorwart, Martin, Rabbel, Wolfgang, Siegmund, Claudia, Comte, Diana, Bataille, Klaus, Iglesia, Paula and Prezzi, Claudia (2012) Seismicity near the slip maximum of the 1960 Mw 9.5 Valdivia earthquake (Chile): Plate interface lock and reactivation of the subducted Valdivia Fracture Zone. Journal of Geophysical Research - Solid Earth, 117 (B06312). DOI 10.1029/2011JB008914.

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Abstract

Understanding the processes behind subduction-related hazards is an important
responsibility and major challenge for the Earth sciences. Few areas demonstrate this as
clearly as south-central Chile, where some of the largest earthquakes in human history
have occurred. We present the first observation of local seismicity in the Villarrica region
(39°–40°S), based on a temporary local network of 55 stations installed from the Chilean
coast into the Argentinian back-arc for one year. While consistent with the Chilean national
catalog (SSN), our results allow us to observe smaller magnitudes with a completeness
of about 2.0 and image the geometry of the Wadati-Benioff Zone from the Chile Trench
down to 200 km. Offshore, a gap in interplate seismicity is observed in the region of the
1960 Valdivia earthquake slip. Above the interface, two offshore seismicity clusters
possibly indicate ongoing stress relaxation. In the subducting Nazca Plate, we find a
prominent seismicity cluster along the extrapolated trace of the oceanic Valdivia Fracture
Zone (VFZ). The seismicity cluster is observed between 70 and 130 km depth and
comprises mainly strike-slip events. It indicates weakening and reactivation of the major
VFZ by dehydration of oceanic crust and mantle. Interpreting the subducted VFZ section
as a localized reservoir of potential fluid release offers an explanation for the Villarrica
volcanic complex that is located above the reactivated VFZ and shows the highest volcanic
activity in South America. Crustal seismicity is observed near Puyehue volcano, which
recently started to erupt (June 2011).

Document Type: Article
Keywords: Valdivia earthquake, Chile, seismicity
Research affiliation: OceanRep > SFB 574
OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2011JB008914
ISSN: 0148-0227
Projects: Future Ocean
Date Deposited: 14 May 2014 10:16
Last Modified: 31 Jul 2019 06:50
URI: http://oceanrep.geomar.de/id/eprint/23901

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