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本文讨论了视波速比与介质真实波速比的关系。假设地壳为水平双层结构,上层地壳内包含一个水平延伸的波速异常区.计算了γ的理论值。结果表明,对于以往用水平传播的直达波测不出异常的某些情况(例如直达波没有穿过异常区;异常区的水平尺度很小等),只要反射波穿过异常区,根据γ值的变化,仍有可能把异常较为有效地检测出来。 应用这一方法研究了溧阳地震台记录的马鞍山人工爆破资料,发现1979年7月9日溧阳6.0级地震前γ值呈现负异常,平均幅度约为5％,异常时间为15—17个月。为了解释这一异常,直达波在异常区内的路程应当很短,或者根本不穿过异常区。 本文结果表明,主要使用反射波,可能会改善用人工波源方法观测震前波速变化的前景。
This paper discusses the relationship between the apparent velocity ratio and the true velocity ratio of the medium. Assuming that the crust is a horizontal double-layered structure, the upper crust contains a horizontal anomalous velocity anomalies, and the theoretical value of γ is calculated. The results show that some cases (for example, the direct wave does not pass through the anomaly region; the horizontal scale of the anomalous region is small, etc.) can not be detected for the horizontal waves propagating horizontally in the past; as long as the reflected waves pass through the anomaly region, It is still possible to detect anomalies more effectively. Using this method, the data of Ma’anshan artificial blasting recorded by Liyang Seismic Station were studied. It is found that the γ value before the Ms 6.0 Liyang earthquake on July 9, 1979 shows a negative anomaly with an average amplitude of about 5% and an anomaly of 15-17 months. To account for this anomaly, the direct wave should travel short within the anomalous zone or not at all through the anomalous zone. The results of this paper show that the main use of reflected waves may improve the prospect of using artificial wave sources to observe changes in velocity before earthquakes.