茅山断裂带及邻区地震震源机制解计算及应力场反演
摘要
利用2001年1月~2014年4月江苏及邻区数字地震波形资料,采用P波、S波初动和振幅比联合求解方法计算了茅山断裂带及邻区149次中小地震震源机制解。震源机制解特征分析表明,研究区中小地震震源类型以走滑型为主,兼有一定比例的正断层类型,而逆冲型相对较少,P、T轴优势方向分别为NEE-SWW、NNW-SSE向。利用149次地震的震源机制解,采用自助线性应力反演(LSIB)方法反演了研究区应力张量。结果显示,最大主应力S_1方位角为254.2°,俯角为2.6°,最小主应力S_3方位角为163.9°,俯角为9.5°。为了进一步印证所得应力张量的可靠性,又利用1970年以来M_L≥3.5地震震源机制解再次反演,所得结果中最大主应力S_1方位角为252.4°,俯角为8.4°,最小主应力S3方位角为160.4°,俯角为12°。2份不同的震源机制解资料反演所得应力张量十分接近。应力张量结果表明,茅山断裂带及邻区处于以NEE-SWW向水平压应力和NNW-SSE向水平张应力为主的现代构造应力场中。
Using the digital earthquake data in Jiangsu Province and its adjacent area from January 2001 to April 2014,the paper studies the focal mechanism of 149 small and moderate earthquake cases in the Maoshan fault zone and its adjacent area with the combination of motion with amplitude ratio of P-wave and S-wave. The analysis of the characteristics of the focal mechanism solution shows that the type of the small and moderate earthquake in the study area is dominated by the strike- slip type with some normal fault type. The thrust earthquake is comparatively rare. The predominant orientation of P and T axes is NEE- SWW and NNW-SSE direction respectively. With the LSIB method,the stress tensor in the study area is inverted with the focal mechanism of 149 earthquake cases. The results indicate that the maximum principal compressive stress orientation angle S1 is 254.2°,the angle of depression is 2.6°. The minimum principal compressive stress orientation angle S3 is 163.9°,the angle of depression is 9.5°. In order to prove the reliability of the stress tensor,we use the focal mechanism solution of ML≥3.5 since1970 to invert. The maximum principal compressive stress orientation angle S1 is 252.4°,the angle of depression is 8.4°. The minimum principal compressive stress orientation angle S3 is 160.4°,the angle of depression is 12°. The stress tensor inverted by the data of the two focal mechanism solution is very close. The solution of stress tensor indicates the Maoshan fault zone and its adjacent area is mainly under a modern tectonic stress field of NEE- SWW direction horizontal compressive stress and NNW-SSE direction horizontal tensile stress.
引文
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