Three-dimensional fault geometry and kinematics of the 2008 M-W 7.1 Yutian earthquake revealed by very-high resolution satellite stereo imagery

摘要

Three-dimensional (3-D) fault geometry and surface slip are key factors for understanding fault behaviour and earthquake mechanics. Previous studies of the 2008 Yutian earthquake occurred on the northwestern Tibetan Plateau, and are limited by a lack of detailed measurements of fault structures and near-fault motion due to the inaccessibility and extreme weather of the area and severe decorrelation of InSAR. In this paper, we use a very high resolution (VHR) DEM of the 2008 rupture zone extracted from the Pleiades satellite stereo imagery to measure the 3-D fault geometry and on-fault slip. The maximum vertical and horizontal coseismic displacement is 3.6 m and 2.8 m respectively. Despite the overall normal faulting, near-fault reverse vertical motion was observed, ranging from 0.5 m to 1.9 m, caused by the transformation of strike-slip motion into localised shortening due to local fault geometric variations. Measurements of the near-surface dip for the three fault segments (55 degrees, 62 degrees, and 58 degrees) show good consistency, different from previous studies (43 degrees, 60 degrees, and 52 degrees). Joint inversion of InSAR and the near-fault measurements of surface slip also show that the fault geometry does not change much along strike. The local ratio of the cumulative to the coseismic vertical offset recorded on an old alluvial fan and an ice tongue ranges from 1.86 to 2.79, suggesting at least 1-2 historical events occurred here before the 2008 earthquake.