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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。
This paper analyzes the data of 147 earthquakes before and after Haicheng MS 7.3 on February 4, 1975. The results show that the seismic velocity ratio before the main shock has obvious abnormal changes. The V / P ratio of V_p / V_s behaves as an “ascending-descending” anomaly. The negative anomaly has occurred at least four years before the main shock. The maximum anomalous amplitude is about 10%. The main shock occurs 10 months after the negative anomaly. Before the main shock wave velocity anomaly larger than the area; and near the source of the small area, only in the region before the wave velocity ratio picked up after the onset of a sharp negative anomaly. Before the main shock, the change of the S-wave velocity was not large, and the P-wave velocity and the anomalous wave velocity showed anomalous changes. In the first two months of a 4.8 magnitude aftershock, the wave velocity ratio also showed a negative anomaly. This article also analyzed eight artificial explosions, but did not find the abnormal changes in wave velocity ratio before the main shock. About the reason of the abnormal wave velocity ratio, it is preliminarily thought to be caused by the concentrated action of tectonic stress and the change of elastic properties and the large number of micro-cracks in the interior.