Temporal changes in shear wave splitting after the M =5.2 shimian earthquake of June 9, 1989 |
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Authors: | Tian-Chang Chen Zhi-Jun Li Run-Sheng Zhang Guo-Guang Du and Wan-Xing Peng |
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Institution: | (1) Seismological Bureau of Sichuan Province, 610041 Chengdu, China;(2) Seismological Office of Ya’an District, 625000 Ya’an, China;(3) Seismological Office of Shimian County, 625400 Shimian, China |
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Abstract: | Just after the occurrence of anM=5.2 earthquake in Shimian, Sichuan, two three-component seismometers were set up near the epicenter of the earthquake. Field
observations were made for the four-year period from 1989 to 1992. Analysis of the data recorded from either aftershocks following
theM=5.2 earthquake or from small earthquakes scattered in this region indicates the presence of shear wave splitting. And shear
wave splitting varies with time. The mean direction of polarization of the faster shear waves is N18°W during the period of
aftershock activity, which is consistent with the strike of the faulting plane of the mainshock; but has turned to N46°W from
1990 to 1992, which is consistent with the regional maximum compressive stress. The time delays between split shear waves
measured on records from 1990 to 1992 are about half of that in 1989. The results obtained from observations at two temporary
stations are similar. This indicates that the temporal changes may be related to the occurrence of theM=5.2 mainshock.
This study was supported by the Chinese Joint Seismological Science Foundation.
The English version is improved by Prof. Xin-Ling QIN, Institute of Geophysics, SSB, China. |
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Keywords: | Sichuan seismic wave transverse wave arrival time |
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