Source mechanism of strong aftershocks (Ms≥5.6) of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics

Yong Zheng, Hong Sheng Ma*, Jian Lü, Si Dao Ni, Ying Chun Li, Sheng Ji Wei

*Corresponding author for this work

Research output: Contribution to journalArticle

111 Citations (Scopus)

Abstract

Dozens of >M 5, hundreds of >M 4, and much more >M 3 aftershocks occurred after the 2008/05/12 Wenchuan earthquake, which were well recorded by permanent and portable seismic stations. After relocated with P arrival, the >M 3 aftershocks show two trends of distribution, with most of the aftershocks located along the north-east strike consistent with Longmenshan fault system, yet there is a north-west trend around the epicenter. It seems that substantially more aftershocks occur in regions with crystalline bedrocks. Then we collected waveform data from National Digital Seismograph Network and regional seismograph network of China, and employed "Cut and Paste" method to obtain focal mechanisms and depths of the big aftershocks (M ≥ 5.6). While most of those aftershocks show thrust mechanism, there are some strike slip earthquakes in the northern-most end of the rupture. Focal mechanisms show that the events located on the southern part of central Beichuan-Yingxiu Fault (BY) are mainly thrust earthquakes, which is consistent with initial mechanism of the main shock rupture. In the north part the aftershocks along the BY are also dominated by thrust slip, which is quite different from the right slip rupture of the main shock. Around Qingchuan-Pingwu Fault, the focal mechanisms are dominated by right-slip rupture with large depths (∼18 km). So we suspected that in the north part the main shock might rupture on two faults: Beichuan Fault and Qingchuan-Pingwu Fault. The complex pattern of aftershock mechanisms argues for presence of a complicated fault system in the Longmenshan area.

Original languageEnglish
Pages (from-to)739-753
Number of pages15
JournalScience in China, Series D: Earth Sciences
Volume52
Issue number6
DOIs
Publication statusPublished - 2009
Externally publishedYes

Keywords

  • Cutand paste
  • Focal mechanism
  • Seismotectonics
  • Wenchuan earthquake

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