新丰江2012年02月16日M_L5.2级地震前的波速比变化及地震类型探讨

Discussion of Wave Velocity Ratio Variation and Its Type before the M_L5.2 Earthquake on February 16, 2012 in Xingfengjiang

使用和达法计算了新丰江水库库区及周边2007-06～2012-03期间的ML1.5级以上313个地震的平均波速比,以此研究2012-02-16 ML5.2级地震前后平均波速比的变化。结果显示:在观测精度大大提高后,震前波速比变化反而没有早期的明显,但通过T法校验后仍然存在前7个月开始下降的异常现象,此外还发现这一阶段波速比随水库畜水位的变化有反常的表现。将异常阶段发生的地震用固定震中方法交汇得到该地震的异常区空间分布,其异常区的面积约500 km2,最大线度约为26 km,走向大致与此地震破裂方位一致。异常的持续时间和异常区的面积均符合天然地震的经验公式。

This paper calculated Xinfengjiang reservoir area and average wave velocity ratio of 313 earthquakes with ML≥ 1.5 in its neighborhood from June 2007 to March 2012 by using the Wadati method, for researthing the wave velocity ratio variation before and after the ML5.2 earthquake on February 16, 2012. The result shows that when observation accuracy is greatly improved, the change of wave velocity ratio before earthquake is less distinct than early stage, but unusual phenomenon still remains that it began to decline from the first seven months by T method of calibration, in addition, the change of wave velocity ratio with water level of reservoir was abnormal. Fixing epicenters of earthquakes happened during the above-mentioned seven months, we obtained spatial distribution of anomaly area, with an area of about 500 km2, maximum dimension of about 26 km, and its strike is roughly consistent with the direction of MLS.2 earthquake rupture. The anomalous duration and abnormal area are in accordance with the empirical formula of natural earthquake.