新疆伽师强震群区的横波分裂与应力场特征

利用在新疆伽师地区布设的流动台阵记录到的地方震波形数据,研究了伽师强震群附近各台站横波分裂现象,给出了相应的快波偏振方向的平面场分布. 发现在台阵的塔里木盆地一侧,波偏振方向为近SN向,与塔里木盆地的区域主压应力方向一致,但在塔里木盆地北部边缘的褶皱变形带内,快波偏振方向变为近EW向,特别是在柯坪断裂附近,快波偏振方向与阿图什地震的震源断层方向基本一致. 由于快波偏振方向平行于主压应力方向,给出的快波偏振方向反映了相应的主压应力场特征. 结果表明,伽师强震群的成因很可能是塔里木盆地北缘横向非均匀变形造成的局部张性剪切应变能的释放.

FEATURES OF THE S-WAVE SPLITTING AND STRESS FIELD IN THE XINJIANG JIASHI STRONG EARTHQUAKE REGION

Recent years, many attentions have been paid to the shear wave splitting in the crack medium. In this paper we investigated the S-wave splitting at each stations nearby the Jiashi strong earthquake sequence from the local event data recorded by our portable seismic array. The polarization directions of fast wave at each station have been obtained. A planar field of the maximal compressive stress direction nearby the Jiashi earthquake sequence is also inferred from the polarization direction of the S-waves. From our observations it has been found that in the side of the Tarim basin the fast polarization direction is toward the NS direction, which is consistent with the previous results. In the fold deformation belt to the north of the Tarim basin, the direction of the maximal compressive stress gradually becomes to the EW direction. Especially, nearby the Kalpin faults the fast polarization direction becomes consistent with that of the fault plane of the Atux earthquake. From our results we propose that the Jiashi earthquake sequence is caused probably due to the release of the localized tensile strain-energy by lateral inhomogeneous deformation at the north edge of the Tarim basin.