A Fine Velocity and Strain Rate Field of Present-Day Crustal Motion of the Northeastern Tibetan Plateau Inverted Jointly by InSAR and GPS

Interferometric synthetic aperture radar (InSAR) data from 6 Envisat ASAR descending tracks; spanning the 2003⁻2010 period; was used to measure interseismic strain accumulation across the Northeastern Tibetan Plateau. Mean line-of-sight (LOS) ratemaps are computed by stacking atmospheric-corrected and orbital-corrected interferograms. The ratemaps from one track with different atmospheric-corrected results or two parallel; partially overlapping tracks; show a consistent pattern of left-lateral motion across the fault; which demonstrates the MERIS and ECMWF atmospheric correction works satisfactorily for small stain measurement of this region; even with a limited number of interferograms. By combining the measurements of InSAR and GPS; a fine crustal deformation velocity and strain rate field was estimated on discrete points with irregular density depending on the fault location; which revealed that the present-day slip rate on the Haiyuan fault system varies little from west to east. A change (2⁻3 mm/year) in line-of-sight (LOS) deformation rate across the fault is observed from the Jinqianghe segment to its eastern end. Inversion from the cross-fault InSAR profiles gave a shallow locking depth of 3⁻6 km on the main rupture of the 1920 earthquake. We therefore infer that the middle-lower part of the seismogenic layer on the 1920 rupture is not yet fully locked since the 1920 large earthquake. Benefit from high spatial resolution InSAR data; a low strain accumulation zone with high strain rates on its two ends was detected; which corresponds to the creeping segment; i.e., the Laohushan fault segment. Contrary to the previous knowledge of squeezing structure; an abnormal tension zone is disclosed from the direction map of principal stress; which is consistent with the recent geological study. The distribution of principal stress also showed that the expanding frontier of the northeastern plateau has crossed the Liupan Shan fault zone; even arrived at the northeast area of the Xiaoguan Shan. This result agrees with the deep seismic reflection profile.