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Structure of the subduction system in southern Peru from seismic array data

Citation

Phillips-Alonge, Kristin Eileen (2013) Structure of the subduction system in southern Peru from seismic array data. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:11302012-163616170

Abstract

Southern Peru represents a subduction transition region from normal subduction in the southernmost part of Peru to flat slab subduction in central Peru. In order to learn more about the structure of southern Peru, causes of flat slab subduction, and the nature of the transition from normal to flat slab subduction, we installed three seismic arrays utilizing a total of about 100 broadband stations. The first installed array samples the normal subduction region, while the second samples the transition from normal to flat subduction, and the third samples the flat slab region near where the Nazca Ridge is presently subducting. Data from teleseismic events greater than 30 degrees distance from Peru was analyzed using the receiver function method that makes use of P to S converted phases at interfaces such as the Moho to provide information about the structure directly beneath each station. A strong signal from the Moho was observed for each array and was found to have a maximum depth of around 75 km beneath the Altiplano. The average crustal Vp/Vs ratio was also estimated and was found to have an average value of around 1.75 beneath the Altiplano. The shape of the slab was also clarified for the three arrays. The transition from normal to flat slab subduction appears to be a contortion rather than a break in the slab. In addition to those signals, a positive impedance midcrustal signal at about 40 km depth was widely observed for stations on the eastern side of the arrays. The midcrustal signal is indicative of a velocity increase in the lower crust and is suggested to be an observation of the underthrusting Brazilian shield which would have implications for the timing of uplift in the Andes. Finite difference modeling with velocity models that include a midcrustal structure produces synthetics which are consistent with receiver function observations. Receiver function results and other related methods provide a simple way of making direct observations of key structural interfaces and the current state of the subduction system which has relevance in studies of the tectonic evolution of the region and estimations of causes of flat slab subduction.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Southern Peru, subduction, receiver functions
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Clayton, Robert W.
Thesis Committee:
  • Stock, Joann M. (chair)
  • Helmberger, Donald V.
  • Avouac, Jean-Philippe
  • Ampuero Saenz, Jean-Paul
  • Clayton, Robert W.
Defense Date:21 November 2012
Author Email:k.phillips.alonge (AT) gmail.com
Record Number:CaltechTHESIS:11302012-163616170
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:11302012-163616170
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7300
Collection:CaltechTHESIS
Deposited By: Kristin Phillips-Alonge
Deposited On:10 Dec 2012 21:45
Last Modified:29 May 2014 22:33

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