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Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate

Dougherty, Sara L. and Clayton, Robert W. (2015) Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate. Geophysical Journal International, 200 (1). pp. 534-555. ISSN 0956-540X. doi:10.1093/gji/ggu415.

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Rapid changes in slab geometry are typically associated with fragmentation of the subducted plate; however, continuous curvature of the slab is also possible. The transition from flat to normal subduction in southern Peru is one such geometrical change. The morphology of the subducted Nazca Plate along this transition is explored using intraslab earthquakes recorded by temporary regional seismic arrays. Observations of a gradual increase in slab dip coupled with a lack of any gaps or vertical offsets in the intraslab seismicity suggest warping of the slab. Concentrations of focal mechanisms at orientations which are indicative of slab bending are also observed along the change in slab geometry. The presence of a thin ultra-slow velocity layer (USL) atop the horizontal Nazca slab is identified and located. The lateral extent of this USL is coincident with the margin of the projected linear continuation of the subducting Nazca Ridge, implying a causal relationship wherein increased hydration of the ridge results in the formation of the USL downdip. Waveform modelling of the 2-D structure in southern Peru using a finite-difference algorithm provides constraints on the velocity and geometry of the slab's seismic structure and confirms the absence of any tears in the slab. The seismicity and structural evidence suggests smooth contortion of the Nazca Plate along the transition from flat to normal subduction. The slab is estimated to have experienced 10 per cent strain in the along-strike direction across this transition.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle Information
Dougherty, Sara L.0000-0002-5327-3286
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 2014 October 21. Received 2014 October 17; in original form 2014 June 17. This study was supported by the Gordon and Betty Moore Foundation through the Tectonics Observatory at California Institute of Technology and NSF award EAR-1045683. We are grateful to the CAUGHT project team for providing waveform data. We thank Joann Stock for enlightening discussions. We also thank Editor Saskia Goes, Megan Anderson and an anonymous reviewer for helpful comments which improved the manuscript.
Group:Caltech Tectonics Observatory, Seismological Laboratory
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:Seismicity and tectonics; Body waves; Computational seismology; Subduction zone processes
Issue or Number:1
Record Number:CaltechAUTHORS:20150402-103259901
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Official Citation:Sara L. Dougherty and Robert W. Clayton Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate Geophys. J. Int. (January, 2015) 200 (1): 534-555 doi:10.1093/gji/ggu415
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56306
Deposited By: Tony Diaz
Deposited On:02 Apr 2015 18:37
Last Modified:10 Nov 2021 20:57

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