南北地震带震源机制解与构造应力场特征

Translated title of the contribution: Focal mechanisms and tectonic stress field in the North-South Seismic Belt of China

Xiao Shan Wang, Jian Lü*, Zu Jun Xie, Feng Long, Xiao Yan Zhao, Yong Zheng

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)

Abstract

The North-South Seismic Belt is the boundary between the first-order blocks of the tectonic stress field in China. The focal mechanisms of 819 events that occurred in this belt from 1970 to 2014 are used to study its tectonic stress field, which is important for understanding the mechanism of continental earthquakes, tectonic deformation and seismic stress interaction. According to the classification criteria of World Stress Map (WSM), focal mechanism solutions are divided into six types, in which the horizontal projections of P axes mark the movement direction of the block. The stress tensors and the orientations of the maximum horizontal stress of the North-South Seismic Belt were determined by the MATLAB Package for Spatial And Temporal Stress Inversion (MSATSI) using 2°×2° grids with the damping parameter 1.6 at the 95% confidence level. The spatial distribution of different types of focal mechanisms is consistent with the nature of tectonic activity in the North-South Seismic Belt. It demonstrates that the regional tectonic stress field is controlled by tectonic movement. The horizontal projections of P axes show the segmentation patterns from north to south: NNE-NE-nearly EW-NW-nearly NS-NNE direction, the horizontal projections of T axes exhibit the most prominent characteristic of spatial differences in the Sichuan-Yunnan block and neighboring regions, a clockwise rotational pattern. The spatial distribution of stress regime and the orientation of the maximum horizontal stress has obvious regional characteristics, i.e. NE direction strike-slip type stress state in the northern section, NEE-EW-NWW direction thrusting type in the middle section, SE-SSE-NS-NNE direction strike-slip and normal faulting type in the southern section, and the stress regime in the northern part and west boundary of the Sichuan-Yunnan block is EW-SE-SSE direction normal faulting. The normal fault stress regime in the western boundary of the Sichuan-Yunnan block is consistent with the scope of the low velocity zone in mid-lower crust observed by the high resolution seismic array, the ductile flow of eastern expansion of the Tibetan Plateau and the weakness of lateral boundaries (Lijiang-Xiaojinhe fault) facilitate energy release, limiting earthquake magnitude. It also localizes the transition from normal fault earthquakes with N-S extension to normal faulting with E-W extension. The results suggest that the lithospheric stress field of the North-South Seismic Belt is controlled jointly by the NE or NNE directed horizontal compressive stress from the Indian plate and eastward motion of the material of the Tibetan Plateau that slip towards SE along large strike-slip faults. Stress regime is almost consistent with the rupture mechanism of all types of earthquakes, verifying the reliability of the inversion. It can offer a reference for simulation of geodynamic processes and determination of the nature of fault slip.

Translated title of the contributionFocal mechanisms and tectonic stress field in the North-South Seismic Belt of China
Original languageChinese
Pages (from-to)4149-4162
Number of pages14
JournalChinese Journal of Geophysics
Volume58
Issue number11
DOIs
Publication statusPublished - 1 Nov 2015
Externally publishedYes

Keywords

  • Focal mechanism
  • North-South Seismic Belt
  • Orientation of the maximum horizontal stress
  • Tectonic stress field

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