Retrieving three-dimensional coseismic displacements of the 2008 Gaize, Tibet earthquake from multi-path interferometric phase analysis

In this paper, synthetic aperture radar (SAR) data from ENVISAT ASAR ascending, descending and ALOS PALSAR ascending orbits are collected to investigate the coseismic displacements of the Mw 6.4 earthquake occurred in Gaize, Tibet on January 9, 2008 and the Mw 5.9 aftershock on January 16, 2008. Two interferometric phase analysis techniques, i.e., D-InSAR and multi-aperture InSAR, are employed to process the SAR data, with which the displacement measurements along three different line-of-sight (LOS) and three different azimuth directions are retrieved, respectively. Complete three-dimensional (3-D) coseismic displacement fields caused by the earthquake are then resolved by integrating the obtained LOS and azimuth displacement measurements with a weighted least squares adjustment, whose distributions are conformed to the two north-northeast trending northwest-dipping normal faults detected in previous studies. Ground subsidence and uplift are observed in the hanging wall and footwall of the main fault, respectively, and the subsidence reaches its maximum in the hanging wall of the second fault as a superimposed result of the Gaize earthquake and its aftershock. Anti-symmetric horizontal movements are also detected during the seismic events, which move inward in the focal region, but outward at the marginal. The left-lateral motions near the main fault indicate a small striking slip component caused by the Gaize earthquake. Finally, we discuss the potential of applying the derived spatially continuous 3-D displacement fields to determine the high-resolution 3-D strain fields of the Gaize earthquake, which provide important knowledge for assessing the source mechanism.