南北地震带中南段典型强震震前跨断层形变特征分析

基于南北地震带中南段18个不同震级的典型震例震前跨断层形变观测异常特征, 结合《中国震例》已有研究结果, 定性分析了各地震震前跨断层形变观测异常的类型和时、 空变化特征。 结果表明, 对于8.0级以下地震, 震前2~3年异常数量明显增多、 震前1~1年半左右异常达到峰值、 震前部分场地异常恢复的特征对区域强震预测在时间上具有一定的中期或短期前兆意义; 震前跨断层场地异常震中距和异常类型对强震震级具有一定的预测意义; 无论是跨断层异常类型、 空间分布, 还是异常的时间进程特征均与区域强震发生地点没有显著的统计关系。 汶川M_S8.0地震前出现趋势异常多、 中短期异常较少、 外围异常多和中心异常少的特征; 异常最早出现在7~8年前, 震前3年左右明显增加, 震前部分异常恢复; 异常以趋势异常和速度变化为主, 没有破年变异常。

Abnormal Characteristics of Cross-fault Observation in the Southern Segment of the North-South Seismic Belt

Based on abnormal characteristics of cross-fault observation in and around the mid-southern segment of the North-South Seismic Belts, and combined with the results from Earthquake cases in China, this paper qualitatively analyse temporal and spatial variation characteristics of cross-fault anormalies before typical earthquakes happened in the research zone. The results show that, for earthquakes less than M_S8.0, time variation characteristics that cross-fault anomaly increased obviously two to three years before earthquake happened, reached top value one year to a year and a half before earthquake occurred, and some anomalies disappeared before earthquake happened, may have relations to the prediction of the occurrence time of the large earthquakes which maybe happened in 1~2 years, or in several months; the epicentral distance and abnormal types of abnormal cross-fault observations are related to the prediction of the magnitude of the earthquake in the future; and all of the abnormal types, the spatial distribution characteristics and the time variations characteristics have no relationship with the place which the earthquake will happened in the future. For Wenchuan earthquake, it shows that there were more trend anomalies, little short term anomalies, more peripheral anomalies, and little in the center near the epicenter. The anomaly of Wenchuan earthquake first occurred about seven or eight years ago, and increased obviously about three years and some anomaly disappeared before the earthquake. The main types of these anomalies were trend and velocity variations, and there were no breaking yearly changes.