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Title: Wenchuan earthquake deformation 3D modelling based on ALOS/PALSAR data
Author: Wu, Meng-Che
ISNI:       0000 0004 2735 6023
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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A devastating earthquake of magnitude Mw 7.9 occurred in Wenchuan area of Sichuan Province, China on 12th May 2008 and caused great casualties and economic damage. This study is aiming to investigate the faulting geometry and motion of the major seismic faults in Longmenshan fault thrust belt that caused this earthquake, based on the surface rupture displacement data measured using differential interferometric synthetic aperture radar (DInSAR) and SAR amplitude pixel-offset techniques. The cross-event Japanese ALOS PALSAR data have been used for this study. First, the methodology for recovering the missing data in the decoherence zone of the DInSAR line-of-sight (LOS) surface motion maps was developed. In the area along the seismic fault zone, the coherence between pre- and post-event SAR images is completely lost because of the earthquake induced violent and chaotic destruction on the land surface and as the result, no surface displacement can be measured using the DInSAR technique. An Adaptive Local Kriging (ALK) technique has then been developed to retrieve the interferometric fringe patterns in the decoherence zone. The novel ALK operating in a multi-step approach enables to retrieve and interpolate the values with high fidelity to the original dataset. Thus a map of continuous radar LOS displacement was generated. Then, the horizontal displacement motion maps in ground range and azimuth direction were derived from cross-event SAR amplitude image pairs using advanced sub-pixel offset technique, Phase Correlation based Image Analysis System (PCIAS). Though the ground range pixel-offset is proportional to the LOS displacement, the azimuth pixel-offset data provide extra information of the coseismic motion. Thus the horizontal displacement vector field can be obtained in order to constrain the faulting motions in key areas. Finally, with the constraints of the ALK refined DInSAR data and the horizontal displacement data together with the published seismic focal mechanism solutions, seismic reflection profiles and field observations, forward modelling was proceeded using the Poly3D software to decide the most likely faulting geometry based on the optimal matching between the simulated and the measured surface displacement. In the much disputed Beichuan – Pengguan area, the best fit is achieved only when the Pengguan fault is set as the main fault that intercept the Yingxiu-Beichuan fault at a depth of about 13 kilometres. This geometric relationship between the two faults and the distribution of slip is compatible with them being two adjacent splay faults on a propagating thrust.
Supervisor: Liu, Jianguo Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral