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ISSN  2096-3955

CN  10-1502/P

Citation: JianHui Tian, Yan Luo, Li Zhao, 2019: Regional stress field in Yunnan revealed by the focal mechanisms of moderate and small earthquakes, Earth and Planetary Physics, 3, 243-252. doi: 10.26464/epp2019024

2019, 3(3): 243-252. doi: 10.26464/epp2019024


Regional stress field in Yunnan revealed by the focal mechanisms of moderate and small earthquakes


Key Laboratory of Earthquake Prediction, Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China


School of Earth and Space Sciences, Peking University, Beijing 100871, China

Corresponding author: Li Zhao,

Received Date: 2019-01-29
Web Publishing Date: 2019-05-01

We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme. Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.

Key words: earthquake focal mechanism, stress field inversion, principle stresses, Yunnan region

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Regional stress field in Yunnan revealed by the focal mechanisms of moderate and small earthquakes

JianHui Tian, Yan Luo, Li Zhao