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Probing Crustal Rheology using Postseismic Motion associated with Major Earthquakes in Tibet

Isabelle Ryder(1), Roland Burgmann(1), Eric Fielding(2) and Zhenhong Li(3)

(1) UC Berkeley, McCone Hall, Berkeley 94704 CA, United States
(2) California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA, United States
(3) University of Glasgow, Department of Geographical and Earth Sciences, G12 8QQ, Glasgow, United Kingdom

Abstract

In just over a decade there have been four major earthquakes on the Tibetan Plateau: the 1997 M 7.5 Manyi earthquake, the 2001 M 7.9 Kokoxili earthquake on the Kunlun fault, the March 2008 M 7.2 Yutian earthquake, and the May 2008 M 7.9 Wenchuan-Beichuan earthquake. The first two of these were left-lateral strike-slip events, the Yutian earthquake occurred on a normal fault, and the most recent event in China occurred on a thrust fault. Together these large earthquakes offer an opportunity to study crustal rheology beneath the Tibetan Plateau, through observation of their postseismic transients. Specifically, we wish to determine whether postseismic stress relaxation is distributed, implying viscous flow, or localized, implying elastic behaviour of the crust. The postseismic transient following the Manyi event was well-documented in the ERS InSAR study of Ryder et al. (2007), and Envisat data are showing promising results for the Kokoxili postseismic phase. We plan to augment the postseismic dataset for the Kunlun earthquake by acquiring and processing ALOS data from mid-1996 onwards. Our initial tests with postseismic PALSAR data show that the coherence at L-band in this area is very good, so a long enough temporal baseline should allow us to see any continuing postseismic deformation. We have also started to obtain ALOS data for the Yutian earthquake in northwestern Tibet. The extensional nature of this event offers the potential to determine crustal rheology less ambiguously than for the earlier strike-slip events. Coseismic Envisat interferograms demonstrate that it is possible to use InSAR in this area, despite permanent ice cover in the vicinity of the rupture. We aim to use PALSAR data alongside Envisat SAR data to help constrain the coseismic model and, subsequently, to measure the postseismic transient. Finally, PALSAR data promises to be useful for investigating deformation following the Wenchuan-Beichuan earthquake, particularly if C-band data in this area suffers from poor coherence.

 

 

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