温州珊溪水库地震S波分裂研究

A study on S-wave splitting using waveform data from Shanxi reservoir induced earthquakes in Wenzhou of China

通过对温州珊溪水库地震序列开展了近一年的近场源剪切波分裂参数研究,在进行精确定位并确保所用资料满足剪切波窗要求的基础上,采用互相关系数法,借助遗传算法与人工判读相结合,测量了地震序列的快剪切波偏振方向和快慢剪切波的时间延迟.结果表明,地震序列的S波分裂现象明显,台站记录到的地震快剪切波平均偏振方向与区域最大水平主压应力方向基本一致;温州珊溪水库地区快剪切波平均偏振方向在近N-S向;S波分裂快剪切波偏振方向所表现出的离散和空间差异性,认为可能是由于局部构造影响;目前库区应力场稳定,应力调整已经结束,未来发生强余震的可能性较小.

More than 1000 earthquakes induced by the Shanxi reservoir in Wenzhou,Zhejiang province of China,were recorded by both Zhejiang regional digital seismic network and Shanxi reservoir local digital network during the period from Feb.4 to Oct.31,2006.Using wave form data of these earthquakes we studied S-wave splitting characteristics in the reservoir region.The earthquakes were relocated and the S-wave records with travel paths within S-wave window were selected out for analysis.The fast wave polarity azimuth and the slow wave time delay were determined by using the technique of cross-correlation coefficient analysis.The result indicates that S-waves coming from the reservoir earthquakes show notable splitting.The average fast wave polarization azimuth obtained at different stations generally coincides with the orientation of regional maximum principal stress therein.In Shanxi reservoir region the average polarization azimuth of fast S-wave is nearly in N--S direction.The scattering and spatial variation of the deduced fast S-wave polarity may be attributed to the effect of local structure inhomogeneity.Presently the stress field in the reservoir region has recovered to stable state,and there would be little possibility of occurrence of a next strong earthquake.