从高波速比试论云南丽江7级地震的孕震模式

利用震中周围多台地震波资料计算平均波速比， 并对计算误差作了统计和分析， 提出了在介质存在横向不均匀的情况下数据处理方法。在资料有相当可信度的基础上， 动态追踪了１９９６ 年２ 月３ 日云南丽江７ 级地震前滇西北地区波速比的十余年时空演化图象。显示出： 丽江地震孕震区的高波速比异常图象经历了由小到大、由大到小并再次扩大的过程；而低波速比的异常图象则由大到小、由小到大并再次缩小的过程； 地震发生在低波速比异常区包围的高波速比异常区的交汇部位。其时间进程的演化显示丽江地震的孕震区在１９８８年耿马—澜沧７６ 、７２ 级地震后进入非线性阶段， １９９５ 年孟连西中缅边境７３ 级地震前进入失稳阶段。结合滇西北地区地震垂直分布图象和对照含硬包体试样在破裂孕育过程中波速场的演化图象， 表明丽江地震的孕震区具备了坚固体孕震模式的高波速特征

A DISCUSSION OF SEISMOGENIC MODE OF YUNNAN LIJIANG EARTHQUAKE OF M 7 0 FROM HIGH WAVE VELOCITY RATIO

The averaging wave velocity ratios are calculated by data obtained at multi stations around the peicenter.The calculating errors are statistically calculated and analyzed.A data processing method has been put forward in transveres inhomogeneous medium.On the basis of data reliability,the spatialtemporary evolution patterns of wave velocity ratio for more than 10 years were traced dynamically before Lijiang earthquake of M 7 0 on February 3,1996.It shows that the anomalous patterns of high wave velocity ratios in the Lijiang seismogenic area had experienced a small big,big small and big again process.However,the anomalous patterns of low velocity ratios had experienced a big small,small big and small again process.The earthquake happened in the place of anomalous area of high wave velocity ratio surrounded by low wave velocity ratio.The time processing evolution shows that the Lijiang seismogenic area had entered a non linear step after the 1988 Lancang Gengma earthquakes of 7 6 and 7 2,and entered a unstable step before the 1995 west Menglian earthquake of M 7 3 Combining the seismic vertical distribution pattern in west Yunnan with the evolution pattern of wave velocity field in the process of breaking of hard inclusion.It shows that the Lijiang seismogenic area has the features of high wave velocity of seismogenic mode of hard body.