Coseismic deformation and ionospheric variation associated with Wenchuan earthquake estimated from InSAR

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Coseismic deformation and ionospheric variation associated with Wenchuan earthquake estimated from InSAR


Author: Feng, Guangcai
Title: Coseismic deformation and ionospheric variation associated with Wenchuan earthquake estimated from InSAR
Degree: Ph.D.
Year: 2011
Subject: Ionosphere.
Atmospheric electricity.
Remote sensing.
Wenchuan Earthquake, China, 2008.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Land Surveying and Geo-Informatics
Pages: x, 145 leaves : ill. (some col.) ; 30 cm.
InnoPac Record:
Abstract: On 12 May 2008, Mw 7.9 Wenchuan earthquake struck the eastern edge of the Tibetan plateau and devastated cities along the northwest margin of the Sichuan basin, causing more than 80000 dead and 380,000 injured. The location and amplitude of this event shocked many geophysicists and geologists even though some prior observations suggested that the faults in this area were active. The distribution of the coseismic slip is needed in order to understand this event, and therefore to evaluate regional seismic hazard. Although InSAR technique with ALOS/PALSAR data has been used to study the Wenchuan earthquake, the ionospheric effect on coseismic SAR interferograms has previously not been considered. Most of coseismic fault slip models were estimated by ionospheric contaminated interferograms. This thesis presents first study of ionospheric variation associated with Wenchuan earthquake using ALOS/PALSAR data. We find that the ionospheric total electron content (TEC) in the area affected by the earthquake varied significantly both in space and in time over a period of about two months starting tens of days before the earthquake. The anomalous TEC variations can be generally correlated in time to the main shock and the aftershocks. We also find that the ionospheric variations can significantly distort the coseismic SAR interferograms, hence resulting in erroneous, often misleading, coseismic deformation measurements. Accurate "ionosphere free" coseismic deformation interferograms are generated by using SAR images that were not affected by the anomalous variations of the ionosphere. We infer coseismic fault slip of the 2008 Mw 7.9 Wenchuan earthquake jointly using "ionosphere free" InSAR and GPS observations of ground deformation. We propose a new algorithm to downsampled the unwrapped interferogram based on the fringe rate and the spatial coherence of the interferogram. We find that the amount of thrust-slip decreases to the NE along the Beichuan fault, and that the strike-slip increases to the NE. Hence, thrust-slip dominates the southernmost region of the Beichuan fault near the hypocenter, with right-lateral slip dominating to the NE. We also find that there is a small amount of thrust-slip on the parallel and shallower dipping Pengguan fault to the SE of the Beichuan. Thrust-slip is concentrated in several regions of the fault, with maximum slip of almost 7 m at shallow depths near the Yingxiu and Beichuan counties, while the largest strike-slip offsets (over 4 m) are located near the Pingtong and Nanba counties.

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