Spatial variability of modern tectonic stress fields in the north‐eastern margin of Tibetan Plateau

Abstract

A modern tectonic stress field for the north‐eastern margin of Tibetan Plateau was determined using linear inversion. Focal mechanism solutions and the depths of 54 earthquakes from 2009 to 2017 were obtained from broadband seismic waveforms. We derived the tectonic stress field using the SATSI (Spatial and Temporal Stress Inversion) software based on the damped linear inversion method. The stress tensor structures are primarily indicative of strike‐slip and thrust faulting; their distributions are controlled by the West Qinling and Haiyuan faults. The Longxi Block is surrounded by two faults dominated by thrust faulting; the regions in the periphery of the faults, (e.g., West Qingling Fault Zone and Liupanshan Basin) are primarily characterized by strike‐slip faulting. However, normal faulting has developed in the Haiyuan–Zhongwei Belt of Liupanshan Basin, indicating that the latest tectonic regime is an NNW–SSE extension instead of a strike‐slip fault with a thrust component, as has been previously suggested. This anomalous stress mechanism reflects the combined effects of block rotation and local extension resulting from movement along strike‐slip faults. The West Qinling Fault is dominated by thrust faulting instead of strike‐slip faulting. The Haiyuan–Liupanshan and Niushoushan–Luoshan faults are predominantly strike‐slip faulting. The directions of the maximum stress axes (σ1) in both Liupanshan Basin and the Longxi Block are ENE–WSW down to Liupanshan in the south and West Qinling Fault Zone, where the stress axes gradually rotate clockwise to E–W. The modern tectonic stress field implies that regional stress originates from far‐field effects of Indian and Eurasian plate collision.