HR: 14:10h
AN: T33E-03    [Abstracts]
TI: The Seismogenic Zone in Southern Chile: Insights from high resolution receiver function analysis and seismic Tomography
AU: * Rietbrock, A
EM: A.Rietbrock@liverpool.ac.uk
AF: University of Liverpool, Dept. of Earth and Ocean Sciences 4 Brownlow Street, Liverpool, L693GP, United Kingdom
AU: Haberland, C
EM: haber@geo.uni-potsam.de
AF: University of Potsdam, Institute of Geosciences Karl-Liebknechtstr. 24, Potsdam, 14476, Germany
AU: Lange, D
EM: dlange@geo.uni-potsdam.de
AF: University of Potsdam, Institute of Geosciences Karl-Liebknechtstr. 24, Potsdam, 14476, Germany
AU: Bataille, K
EM: bataille@udec.cl
AF: Universidad de Concepcion, Victor Lamas 1290, Concepcion, XIII, Chile
AB: Subduction zones, the expression of convergent plate boundaries, generate the world's largest and most destructive earthquakes. The Southern Chilean subduction zone is an ideal natural laboratory to study the processes involved in generating these devastat- ing earthquakes and is one of the main aims of the international and interdisciplinary research initiative TIPTEQ (from The Incoming Plate to megaThrust EarthQuake pro- cesses). High resolution images, using different techniques as well as different physi- cal parameters, form the base for identifying the processes involved. Here we present new data from teleseismic receiver function analysis and 3D seismic tomography to study in detail the down-dip end of the seismogenic zone in the nucleation area of the 1960 magnitude Mw=9.5 Valdivia, Chile, earthquake. Within the project TIPTEQ two dense amphibious passive seismic networks have been installed between Nov. 2004 and Oct. 2005, both covering the entire forearc from the trench to the active volcanic front. The Northern array was located between 37° and 39° South including the epicentre of the 1960 Chile earthquake. It consisted out of 120 continuously recording, three component stations on land and 10 continuously recording Ocean Bottom Seismometers/Hydrophones (OBS/H) at sea. The Southern array was located between 41.5° and 43.5° South roughly in the middle of the rupture zone of the Valdivia earthquake. It consisted out of 20 continuously recording three component stations on land and 20 continuously recording Ocean Bottom Seismometers/Hydrophones (OBS/H) at sea. Several hundreds of micro earthquakes could be located using manual picked P- and S-wave arrivals. Joint 2D/3D inversions for earthquake location, P-wave velocity and vp/vs-ratio were carried out and give a detailed image of the structure as well as a snapshot of the seismicity distribution in both study regions. The subducting Nazca plate can be clearly identified in both regions dipping at a similar angle of about 10-15° in the seismogenic zone and increasing to 30° at greater depth suggesting that the age of the subducting plate does not control the subduction angle. For the Northern region 3D migrated receiver function images depict clearly the subducting Nazca plate (oceanic moho) as well as the continental moho intersecting the subducting plate at about 45 km depth. The seismicity is predominantly localized in a sharp band at the seismogenic interface down to a depth of approximately 35-40 km. At greater depth the seismicity pattern is becoming more diffuse and migrating towards the subducting oceanic moho imaged by the receiver function analysis. This transition between inter-plate and intra-plate seismicity also falls into the area determined for the hypocenter of the 1960 Valdivia earthquake suggesting that this transition is one of the crucial controlling parameters for earthquake nucleation and the down-dip limit of the seismogenic zone.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: 2007 Fall Meeting