丽江大震前长-中-短-临地震学异常的演化过程

THE EVOLUTION PROCESS OF LONG-MEDIUM-SHORT- IMPENDING SEISMOLOGICAL ANOMALIES BEFORE THE LIJIANG EARTHQUAKE

本文通过丽江大震前地震学各项异常的动态追踪，研究了长－中－短－临异常伴随大震孕育、发生的演化过程，结果表明：在强震的缺震、强震的重复、中强震密集、诱发地震、相关地震等多项长期异常的背景上，出现了中小地震活跃、调制小震频繁、复发周期降低、震源深度加深和震级差增大、地震序列ｈ值下降等同步的中期异常，而１９９５年中小地震活跃后的平静、低复发周期的回升、震源深度为２５公里和震级差在１０—１１级的地震次数增加则预示了大震的逼近，尤其异常平静为该震前的显著短临标志。作者认为，远场强震对处于不稳定状态的孕震系统，产生的扰动主要表现为发生震级较大中小地震，一旦中小地震的频度和能量同步突变。

Through dynamically tracing various seismological anomalies before the great Lijiang earthquake, the evolution process of long-medium-short-impending anomalies accompanying the preparation and occurrence of the great earthquake is studied in this paper. The results show that the synchronous medium term anomalies, including brisk medium and small earthquakes, frequent modulation small earthquakes, reduction in reoccurrence period, increase in focal depths and differences between magnitudes and decline in h value of seismic sequence appeared on the background of many long term anomalies, such as, absence and recurrence of strong shocks, moderate-strong shock concentration, induced and relative earthquakes, whereas seismic quiet after the brisk medium and small events of 1995, rising again in low recurrence period and increase in frequency of events with focal depths of 25 Km and the differences between magnitudes of 1 0—1 1 meant the approach to the large earthquake; especially anomalous quiet was a striking short-impending sign prior to the earthquake. The author thinks that the disturbance of farfield strong earthquake to the seismogenic system in unstable state is mainly to generate medium and small earthquakes with relatively high magnitudes, and once synchronous mutation of frequency and energy of the medium and small earthquakes appears, the large earthquake will occur in this area.