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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６．５级和丽江７．０级３次强震．本文研究了近期强震前５个地震台单台波速比和多台波速比的时空演化特征．发现：在７级大震前５～８年，大震震中１２０ｋｍ范围内出现了波速比高（低）值突变的中长期源兆，当波速比的突变幅度骤升（降）或突变地震次数骤增时，中长期源兆进入中短期阶段；６级强震在震前３～６年，４０和１５０ｋｍ范围内出现了波速比高值突变的中长期源兆和中长期近场场兆，但向中短期阶段过渡的识别指标不明显．强震震中１５０ｋｍ范围出现的波速比突变异常高达３．０左右，而远在强震震中２５０ｋｍ以外的地区最大值为２．３６，显示出离强震震中近的地区突变幅度比离强震震中远的地区大的特征，即源兆和近场场兆异常幅度比远场场兆大２０％～６０％．并对波速比突变数据的可靠性和物理机制进行了探讨．
From July 12, 1995 to February 3, 1996, in the short span of seven months, there were consecutive occurrences of the Menglian West-Myanmar border 7.3, the Wuding 6.5, and the Lijiang 7.0 7.0 shock. In this paper, the temporal and spatial evolution characteristics of single wave velocity ratio and multiple wave velocity ratios of the five seismographic stations before strong earthquakes are studied. It is found that in the period of 5 ~ 8 years before the MS7 earthquake, medium- and long-term sources of sudden change in wave velocity ratio occur within 120 km of the epicenter, and when the sudden change in the wave velocity ratio suddenly decreases or the number of sudden earthquakes In the period of 3 to 6 years before the earthquake, mid- and long-term source trunks and mid-long term near-field trillion trunks appeared in the range of 40 and 150 km, However, the indicators for the transition to the medium and short term are not obvious. The abrupt change in wave velocity ratio appeared in the range of 150km after strong earthquakes was as high as 3.0, while the maximum value was 2.36 in the area 250km far from the epicenter of strong earthquakes, indicating that the abrupt change of amplitude from strong earthquakes Far large features of the region, that is, the magnitude of the source trillion and the near-field trillion anomaly is 20% ~ 60% larger than that of the far field. The reliability and physical mechanism of the abrupt change of wave velocity ratio are also discussed.