【摘要】 本文分析了1975年2月4日海城7.3级地震前后147次地震的资料。结果表明,主震前地震波速比有明显的异常变化。纵横波速比V_p/V_s表现为“下降—回升”的异常形态,负异常至少在主震前四年已出现,最大异常幅度为10％左右,负异常结束后十个月发生主震。主震前波速比异常区较大;而震源附近的小区域,仅在全区波速比回升后的临震前才出现了急剧的负异常。主震前横波速度变化不大,纵波和虚波速度出现异常变化。在一次4.8级强余震前两个月,波速比也出现了负异常。 本文还分析了8次人工爆破,但未发现主震前波速比的异常变化。 关于波速比异常的原因,初步认为是岩石在构造应力的集中作用下,弹性性质发生变化、内部出现大量微裂隙而造成的。更多还原

【Abstract】 In this paper, the data of 147 earthquakes occurred before and after the Haicheng Earthquake of February 4, 1975, M = 7.3 have been analysed. The results obtained, indicate that before the main shock, anomalous variations of the velocity ratio Vp/Vs was quite obvious. Its values began to fall at first and then recovered. This negative anomaly of Vp/Vs seems to have been started at least 4 years ago. Maximum negative value of Vp/Vs can reach about 10% of its normal. Nearly 10 months after the conclusion of the anomaly, the main shock took place. Before the main event, the area occupied by the anomaly was quite large, while only in a small region around the earthquake source area, negative anomaly of the velocity ratio suddenly appeared immediately before the main shock, at a time when the value of Vp/Vs increased to the normal. Before the main event, the variation in the S-wave velo-city was not appreciable. However, P-wave velocity and its virtual velocity showed anomalous changes. About two months before an aftershock of magnitude 4.8, the value of Vp/Vs also appeared to be anomalous.Eight explosion records were also analysed, but no apparent velocity ratio anomaly was observed.As regards to the cause of the velocity ratio anomaly, we merely suppose that under the action of concentrated tectonic stress, rocks change in their elastic property and numerous microfractures are formed.更多还原