大同盆地区域应力场变化特征及其与中强地震的关系

Variation Characteristics of Regional Stress Field in Datong Basin and Its Relationship with Medium Strong Earthquakes

通过大量震源机制解结果推断出大同盆地现代地壳应力场的主压应力方向为NEE,仰角变化不定,主张应力方向为NNW-SSE,仰角很小的结论,这与区域构造应力场NE-NEE向挤压作用的结果相符;分析研究认为,1998年1月10日张北6.2级地震、1999年11月1日大同—阳高5.6级地震前于1997年2月出现的P轴趋于一致,同1989年大同—阳高6.1级主震前应力场变化特征很相似;在矛盾符号比低值的过程中,如果应力主轴取向也出现趋于一致的变化,这类异常往往与盆地中等地震有较好的对应关系。山自皂、阳原单台初动向上、向下次数累计百分比在1991年3月26日大同—阳高5.8级地震前具有准同步变化的特点,反映了大震前应力场的一致增强。

Based on many results of focal mechanism solutions, the authors concluded that the principal compressive stress orientation of present crustal stress field in Datong basin is in NEE with indefinite angle of altitude, meanwhile the principal strain stress orientation is in NNW-SSE with small angle of altitude. This conclusion is consistent with the result of the compression structure of regional stress field along NE-NEE direction. According to analysis, the P-axis appeared in Feb. 1997 tended to coincide with that before Jan. 10th, 1998 Zhangbei earthquake of Ms 6.2 on and 1st Nov. , 1999 Datong-Yanggao earthquake of Ms 5.6, similar to the variation characteristics of stress field before the 1989 Datong-Yanggao main earthquake. During the low value of ratio of inconsistent signs, if the variations of orientation of principal stress axis also tend to coincide, this kind of anomaly is usually related with medium earthquakes in basin. Percentage of accumulated times of Up-down of first motions of Shanzizao and Yangyuan stations change synchronously before the Mar. 26th 1991 earthquake of Ms 5.8, indicating the increase in stress field before strong earthquakes.