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Structure of the subduction transition region from seismic array data in southern Peru

Phillips, Kristin and Clayton, Robert W. (2014) Structure of the subduction transition region from seismic array data in southern Peru. Geophysical Journal International, 196 (3). pp. 1889-1905. ISSN 0956-540X. doi:10.1093/gji/ggt504.

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Data from three seismic arrays installed in southern Peru were analysed using receiver functions from P, PP and PKP wave phases, in order to image the subducted Nazca slab. The arrays cover the transition region from flat slab subduction in central Peru to normal subduction with an angle of about 30° further south. A previous study used data from the first array in the normal subduction region to image the Moho depth and slab, and showed the existence of a mid-crustal structure at 40 km depth that is suggested to be a possible underthrusting of the Brazilian shield. Here, we discuss new observations from the other two arrays that span the transition between the two subduction regimes and the flat subduction region. The results provide an image of the flattened slab from the coast to approximately 300 km inland and also across the transition region from flat to 30° subduction, which appears to be a bend rather than a tear in the slab. In the flat slab region, the slab is well defined near the coast and flattens out at 100 km depth beneath the Altiplano. The slab appears to start flattening some 400 km in advance of the subduction of the Nazca Ridge and the flattening is maintained for 1300 km after its passage. The Moho begins at a depth of around 30 km near the coast and has a maximum depth of 75 km beneath the Altiplano, consistent with the results of the other arrays. Both arrays also show a positive impedance mid-crustal structure at 40 km depth, which if explainable by underthrusting of the Brazilian shield, would add further support to the observations from the normal subduction region and show the northward and westward extent of the signal. The underthrusting hypothesis would explain the missing crust from the shortening budget needed to support the Altiplano. The Vp/Vs ratios for both arrays exhibit average values between 1.73 and 1.75 indicating a lesser likelihood that there is a high degree of partial melting or magma bodies at depth in this region. The receiver function results provide new imaging of the flat slab and transition from normal to flat slab subduction which allows for comparison of different subduction regimes.

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Clayton, Robert W.0000-0003-3323-3508
Additional Information:© 2014 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2013 December 11. Received 2013 December 7. In original form 2013 August 28. First published online: January 10, 2014. We thank the Betty and Gordon Moore Foundation for their support through the Tectonics Observatory at Caltech. This research was partially support by NSF award EAR-1045683. Also thanks to Richard Guy, Paul Davis and Igor Stubailo of the UCLA Center for Embedded Networked Systems, Steven Skinner of the Caltech Seismological Laboratory, Hernando Tavera and Victor Aguilar of the Instituto Geofisico del Peru and Laurence Audin of Institute of Research for Development. We also thank the PULSE and CAUGHT projects for contributing data to this study. Contribution #238 from the Tectonics Observatory.
Group:Caltech Tectonics Observatory, Seismological Laboratory, Division of Geological and Planetary Sciences
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Betty and Gordon Moore FoundationUNSPECIFIED
Caltech Tectonics ObservatoryUNSPECIFIED
Subject Keywords:Seismicity and tectonics; Continental margins: convergent; Crustal structure.
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Caltech Tectonics Observatory238
Issue or Number:3
Record Number:CaltechAUTHORS:20140403-100641102
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Official Citation:Seismology: Kristin Phillips and Robert W. Clayton Structure of the subduction transition region from seismic array data in southern Peru Geophys. J. Int. (March, 2014) 196 (3): 1889-1905 first published online January 10, 2014 doi:10.1093/gji/ggt504
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44630
Deposited By: Ruth Sustaita
Deposited On:03 Apr 2014 17:34
Last Modified:10 Nov 2021 16:54

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