【摘要】 以活动地块为单元,研究了青藏高原北部地区1970年以来的30次MS≥5 0级地震前ML≥2 0级小震的频度、b值、缺震、调制比4项活动性参数的短临异常特征,结果发现,这30次中强地震前,4项指标异常持续时间和异常结束至发震的时间,大部分都在1～6个月之内,尤其是异常结束到发震的时间,在1～6个月内的占异常总数的77%以上。而且30次地震前,4项指标均出现异常的有15次,占地震总数的50%;震前3项指标出现异常的5次,占地震总数的17%;2项指标出现异常的有6次,占地震总数的20%;1项指标出现异常的有3次,占总数的10%。特别是祁连山地块,异常比较丰富,以4项和3项指标异常为主,同时又以5项次以上异常的数量特征表现。更多还原

【Abstract】 Setting active block as a cell, short-impending anomalous characters of the four seismicity parameters, witch are earthquake frequency N value, b value, lack of earthquake and ratio of modulating earthquakes Rm value of M_L≥2.0 small earthquakes before 30 M_S≥5.0 earthquakes in the north of Qinghai-Tibet plateau since 1970, have been studied. The results show that the anomalous lasting time and time from anomalies ending to earthquake generating of the four parameters before the 30 moderate earthquakes are main within 1 to 6 months. Especially the time from anomalies ending to earthquake generating within 1 to 6 months is over 77 percent of all anomalies. Before fifteen of the 30 moderate earthquakes, the four parameters were all anomalous, occupying 50 percent of all earthquakes. Before five earthquakes, three of the four parameters were all anomalous, occupying 17 percent of all earthquakes. Before six earthquakes, two of the four parameters were all anomalous, occupying 20 percent of all earthquakes. Before five earthquakes, one of the four parameters was all anomalous, occupying 10 percent of all earthquakes. In Qilian block there are more anomalies that characterized mainly four or three parameters presented over five anomalies once a time.更多还原