InSAR-derived present-day crustal movement of Daliangshan on the southeastern margin of the Qinghai–Tibetan Plateau

Abstract

SUMMARY The Daliangshan area of Sichuan, China, is located on the southeastern margin of the Qinghai–Tibetan Plateau. It marks the central section of the left-lateral Xianshuihe–Xiaojiang Fault System (XXFS), which plays a crucial role in accommodating clockwise vertical-axis rotation of the expanding Qinghai–Tibetan Plateau relative to the South China Block. The area is seismically and tectonically active, and three major active faults—the Anninghe fault (ANHF), Zemuhe fault (ZMHF) and Daliangshan fault (DLSF)—together accommodate a significant amount of left-lateral strike-slip motion. Here, we present a geodetic study of the Daliangshan area mainly based on satellite interferometric synthetic aperture radar (InSAR). We processed Advanced Land Observing Satellite-2 (ALOS2) Phased-Array L-band Synthetic Aperture Radar-2 (PALSAR2) imagery to reconstruct the present-day interseismic deformation field. We developed an optimal atmospherics phase correction strategy to overcome the significant artefacts caused by ionospheric and tropospheric. By applying a multitemporal analysis on corrected interferograms, for the first time we generated a spatially continuous deformation rate field for the Daliangshan area. The satellite line-of-sight (LOS) rate field agrees with Global Positioning System (GPS) and levelling data to ∼2 mm yr–1, confirming that our processing approach is suitable for use in heavily vegetated areas. The InSAR rate map reveals displacements along the central and southern segments of the DLSF and ZMHF. By applying an inversion based on the Okada model, we quantitatively estimated the kinematic parameters of fault segments. Assuming a simple rectangular fault plane for each fault segment and constrained with the prior knowledge of the left-lateral slip, we determined that the ZMHF has a slip rate of 5.06$\pm 0.99{\rm{\ mm}}\,{\rm{yr}}^{-1}$ with a rake angle of ∼$38^\circ $ gently dipping to the SW. The southern section of the DLSF has a rake of $- 48^\circ \,\,{\rm to}\,\, - 41^\circ $ with the total slip rate of $4.93 \pm 0.4{\rm{\ mm}}\,{\rm{yr}}^{-1}$, dipping towards to the NE at $63.50^\circ \pm 2.31^\circ $. The modelled 3-D rate field has been validated with GPS and levelling measurements. Additionally, the inversion model and strain field suggest that the middle section of the DLSF undergoes strong deformation. We considered the implications of three factors—oblique convergence, gravity-driven movement, and the ELIP beneath the Sichuan–Yunnan area—for complex 3-D velocities in the transitional Daliangshan area.