Using aftershock data of the 2008 Wenchuan earthquake, recorded by seismic stations in the seismic source area and around, with the systematic analysis method (SAM) of shear‐waves splitting, this paper analyzes the anisotropic characteristics in the crust along the Longmenshan fault belt where the Wenchuan earthquake occurred and obtains the directions of the principal compressive stress field in the crust and its spatial distributions. The results show spatial differences: plotting a boundary approximately in Anxian area in the middle of Longmenshan fault belt, the polarization directions of fast shear‐waves at stations located at the northeast segment of Longmenshan fault belt are at NE direction, consistent with the strike of the faults. However, the polarization directions of fast shear‐waves at stations located at the southwest segment are at NW direction, perpendicular to the strike of the faults. This pattern also indicates that the southwest segment of the Longmenshan faults are mainly in thrust fault and the northeast segment are of obviously strike‐slip component. In this study, the polarization directions of fast shear‐waves are scattered at stations near the intersection area of the Longmenshan faults, the Xianshuihe faults and the Anninghe–Xiaojiang faults. It is possibly attributed to the local complex geological tectonics around the seismic source area, consistent with the characteristics of the complex direction of the principal compressive stress in this zone.

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shearwave (PFS) is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.

Using the seismic data recorded by 13 seismic stations in north Taiwan from July 1991 to December 2002, this study analyzes the feature of shear‐wave splitting in north Taiwan by SAM method of shear‐wave splitting. The results show that predominant polarization directions of fast shear‐waves at Yilan basin strikes to nearly E‐W, while polarization directions at mountain ranges (Western Foothill, HsüCeshan Range and Central Range) are in NNE or NE direction. Polarizations are scattered if the stations are on seashore or on island, and often have two predominant polarizations, which may be caused by irregular topography or complicated local tectonics. From the spatial distribution of time delays, we also find that taking station TWE as a boundary, time delays at station TWE and north of the station are longer than those at south of the station. It possibly suggests that anisotropy at station TWE and north of the station are stronger than anisotropy at south of the station.

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Using seismic waveform data recorded at station YK (Yingkou) of Liaoning Telemetry Digital Seismic Network, this paper studied the characteristics of shear-wave splitting before and after the Xiuyan M S 5.9 (M L 5.3) earthquake in November 29, 1999 with SAM method. The results show that the predominant polarizations of fast shear-waves at YK is in direction of ENE-WSW, consistent with the direction of regional principal compressive stress and also consistent with the direction of the regional tectonic stress field in North China; time-delays increasing before Xiuyan earthquake may shows accumulation of stress before earthquake. The predominant polarizations of fast shear-waves at YK are also related to the spatial distribution of small earthquakes and correlate with the fault strike. The histogram of monthly average polarizations of fast shear-waves shows that polarizations of fast shear-waves also seems to change from two months before the earthquake, but it still needs more data for verification.