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We investigate the slip distribution of the 2008 May 12 Wenchuan M 7.9 earthquake using GPS data and InSAR measurements under a linear inversion scheme, with emphasis on the effect of three factors, including constraint on rake, different discretizations, and layered elastic model. Within our inversion parameterization context, we find the most influential factor would be constraint on rake. Without constraint on rake, the slip model seems physically wrong under the depth of 15 km, due to the limited depth resolution of the geodetic data used, especially the one orbit of InSAR measurements. Thus it is necessary to add a priori to the slip rake to obtain a reasonable fault source model. Different discretizations of the subfault patches have a notable impact on the slip distribution. Also, the layered elastic model predicts more slip at depth than does the half-space model, by about 15-20 per cent. The characteristics of slip distribution established through our inversions include some points as follows: (1) the most reliable results would be expected at depth range of 0-15 km; (2) three peak-slip asperities are inverted, at Yingxiu county (near epicentre), Yuejiashan county, and Beichuan county, respectively; (3) the inverted rake along the Yingxiu-Beichuan fault changes from dominantly thrusting motion at the southwest segments to dominant right-lateral or even pure right-lateral strike slip at the northeast segments, and (4) only thrust slip is occurred on the Guanxian-Jiangyou fault. [ABSTRACT FROM AUTHOR]

Abstract: GPS displacement vectors show that the crust in east Tibet is being squeezed in an easterly direction by the northward motion of the Indian plate, and the Sichuan Basin is resisting this stream and redirecting it mainly towards Indochina. The Longmen Shan, containing the steepest rise to the high plateau anywhere in Tibet, results from the strong interaction between the east Tibetan escape flow and the rigid Yangtze block (Sichuan Basin), but the kinematics and dynamics of this interaction are still the subject of some debates. We herein present results from a dense passive-source seismic profile from the Sichuan Basin into eastern Tibet in order to study the deep structure of this collision zone. Using P and S receiver function images we observe a sudden rise of the Lithosphere–Asthenosphere Boundary (LAB) from 120 to 150km beneath the Sichuan Basin and from 70 to 80km beneath eastern Tibet. In contrast, the depth of the crust–mantle boundary (Moho) increases from 36 to 40km beneath the Sichuan Basin and from 55 to 60km beneath eastern Tibet. The 410km discontinuity is depressed below eastern Tibet by about 30km, although the 660 remains at nearly the same depth throughout the LMS. From these observations, we conclude that the mode of collision that occurs between Tibet and the Sichuan Basin is very different to that found between India and Tibet. In southern Tibet, we observe in essence the subduction of the Indian plate, which penetrates northwards for several hundred kilometers under central Tibet. The very thin mantle part of the lithosphere beneath eastern Tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow. This process leads to the exceptionally steep topography at the eastern Tibetan margin as a result of gravitational buoyancy. This view is supported by the very unusual depression of the 410km discontinuity beneath eastern Tibet, which could be caused by the dynamics of the sub-vertical downward asthenospheric flow. [Copyright &y& Elsevier]