Temporal changes in shear wave splitting after the M=5. 2 Shimian Earthquake of June 9,1989
Tian-Chang CHEN; Zhi-Jun LI; Run-Sheng ZHANG; Guo Guang DU and Wan-Xing PENG(Seismological Bureau of Sichuan Province, Chengdu 610041, China)(Seismological Office of Ya'an District, Ya'an 625000, China)(Seismological Office of Shimian County, Shimaian 625
Just after the occurrence of an M=5. 2 earthquake in Shimian, Sichuan, two three-component seismometerswere set up near the epicenter of, the earthquake. Field observations were made for the four-year period from1989 to 1992. Analysis of the data recorded from either aftershocks following the M=5. 2 earthquake or fromsmall earthquakes scattered in this region indicates the presence of shear wave splitting. And shear wave splittingvaries with ti-cue. The mean direction of polarization of the faster shear waves is N18°W during the pened of aftershock activity, which is consistent with the strike of the faulting plane of the mainshock; but has turned toN46"W from 1990 to 1992, which is consistent with the regional maximum compressive stress. The time delaysbetween split shear waves measured on records from 1990 to 1992 are about half of that in 1989. The results ohtamed from observations at two temporary stations are similar. This indicates that the temporal changes may berelated to the occurrence of the M= 5.2 mainshock.
【CateGory Index】： P315