云南孟连西7.3级、武定6.5级、丽江7.0级三次强震前地震波振幅比的时空演化特征

１９９５年７月１２日至１９９６年２月３日短短７个月，云南地区连续发生了孟连西中缅边境７．３级、武定５．５级、丽江７．０级３次强震，本文研究了近期这几次强震前５个地震台地震图垂直分量Ｓ、Ｐ波最大振幅比的时空演化特征，动态追踪了振幅比明显偏离平稳态的突变过程。发现主震前５—８年，７级大震震中１００ｋｍ范围出现振幅比高（低）值突变，６级强震震中１３０ｋｍ范围出现振幅比高值突变，当振幅比的突变在缓升（降）的背景上骤升（降），或突变异常的地震次数明显增加，则中长期异常进入中短期阶段。在强震震中１３０ｋｍ范围内的地震台（近台）振幅比值高达１５．２以上，而远离强震震中２５０ｋｍ以外的地震台（远台）振幅比最大值仅为９．８，近台的突变幅度至少比远台大３０％。而强震成组发生前一年半时间内，位于强震震中１１０ｋｍ范围内的近台振幅比的突变幅度比远在２５０ｋｍ外远台大５５—７５％。对振幅比的突变和时空演化特征从非线性动力学模型和模拟实验结果进行了初步成因探讨。

THE TIME-SPACE EVOLUTION CHARACTERISTICS OF THE WAVE AMPLITUDE RATIOES BEFORE THE THREE STRONG EARTHQUAKES, THE M 7 3 WEST MENGLIAN EARTHQUAKE, THE M 6 5 WUDING EARTHQUAKE AND THE M 7 0 LIJIANG EARTHQUAKE, IN YUNNAN

The three strong earthquakes, the M 7 3 West Menglian earthquake in the border between China and Myanmar, the M 6 5 Wuding earthquake and the M 7 0 Lijiang earthquake have occurred in Yunnan region in the space of short seven months from July 12, 1995 to Feb. 3, 1996. In this paper, the authors have studied the time-space evolution characteristics of maxium amplitude ratioes on vertical components of S, P waves at the 5 single stations before the three strong earthquakes and traced dynamically abrupt varation process of amplitude ratioes deviated from equilibrium state. It is found that the high (or low) value abrupt variations in amplitude ratioes appeared within 100 km from the epicenters of the M 7 large earthquakes and the high value abrupt variations in amplitude ratioes appeared within 130 km from the epiceters of the M 6 strong earthqukaes 5-8 Years before the main shocks; the medium-long-term anomalies would enter medium-short-term stage when the amplitude ratioes obrubtly rise (drop) on slowly increasing (decreasing) background or the event numbers with abrupt anomalies increase clearly; the amplitude ratio values at the stations (near stations) within 130 km from the epiceters of strong earthquakes came to 15 2, but the maximum value of the amplitude ratioes at the stations (far stations) 250 km far away from the epicenters of strong earthquakes was only 9 8 and the abrupt variation scope at the near stations was at least 30% bigger than at far stations, and the abrupt variation scope of the amplitude ratioes at the near stations within 110 km from the epicenters of strong earthquakes was 55-75% bigger than at the far stations 250 Km far from the epicenter. And also, a preliminary approach to cause of the abrupt variation and time-space evolution of amplitude ratio is made from nonlinear dynamical model and the results of simulation experiment.