The Preliminary Application Of S-Wave Splitting In Xinjiang

Based on reading enough literatures about shear-wave splitting, we research of shear-wave splitting in Xinjiang using SAM (Systematic Analysis Method of shear-wave splitting), mainly discuss shear-wave splitting parameters'spatial characteristics in Kashi and temporal characteristics in Wushi, and get four following conclusions:1.In Kashi, we analyze the spatial distribution characteristics of average time delays of 8 stations, in which the number of seismic records within shear-wave window is more than 5. It is found that time delays decrease from south to north. According to EDA theory, we think this spatial characteristic reflects a decreasing trend of local stress level in Kashi from south to north. Seismic activities are relatively strong around some stations, which time delays are bigger than background value. Whereas seismic activities are relatively weaker around some stations, which time delays are smaller than background value. This characteristic reflects that seismic activity can affect time delay.2.The spatial distribution of polarization directions in Kashi present that among 8 stations, the polarization directions of two stations are parallel with directions of maximum principal compressive stress, and those of the other stations are parallel with strikes of faults nearby stations. Those reflect that both stress-induced crack anisotropy and fault anisotropy can decide the direction of fast shear-wave, and reflect that the effect of the latter on fast shear-wave direction is more than the former in this given period.3.In Wushi, the values of time delays are scattering and randomicity before August of 2003. But after that date, an temporal increase, lasting about 14 months, of time delays is observed. Some of related researches show that increasing of time delays reflects the stress accumulation, and show that longer of duration, more of accumulated stress, and greater the magnitude of being occurred earthquakes. The duration-magnitude relationship, concluded by Crampin and Gao Yuan, shows that duration of stress accumulation of a MS 6.0 earthquake is about 1 year, which is better coherence with our result. An abrupt decrease of time delays of two small earthquakes show a process of stress relaxation within one month before Wushi Earthquake in a certain extent. The average of time delays after the earthquake is smaller than before. This change shows that the earthquake has resulted in decreasing of stress level around the hypocenter.4. From the temporal variation of polarization directions in Wushi, we find that the...