青藏亚板块强震时空演化特征研究

Spatio-temporal Evolution Characteristics of Strong Earthquakes in Qinghai-Tibet Subplate

以中国大陆及邻区的亚板块分区为基础，研究了1900～2005年间青藏亚板块区内7级强震活动的时空演化特征。结果表明：在时间序列上，7级强震活动可划分为5个活跃期和4个平静期。活跃期持续时间平均为（12±3）年，7级强震的平均频度为8．5次，80％的活跃期最大地震震级达8级以上；平静期持续时间平均为7年，前3个平静期较短，仅4～7年。在空间演化特征上，活跃期内存在A、B两类平静区。此外，在35°N纬线附近存在东西响应迁移区，26°N纬线以南的云南地区有7级强震由南向北迁移轮回的现象。沿东西和南北方向，将研究区分为东、中、西三部分和北、中、南三段进行研究，发现主体活动区的地震活动存在由东部→西部→中部→东部，以及由北段→中段→南段→北段的迁移轮回现象。根据上述特征，对青藏亚板块下一活跃期可能的开始时间、丰体活动区及强震发生的地点进行了预测。

Based on the subplate division of Chinese mainland and its surrounding areas, we study the spatio-temporal evolution characteristics of strong earthquakes with M≥7.0 in Qinghai-Tibet subplate from 1900 to 2005. The result shows we can distinguish five seismic active periods and quiet periods in time sequence respectively. The average duration of the active periods is （ 12 ± 3 ） years, the average frequency is 8.5, and the maximum magni- tude is larger than 8 in 80 percent active periods. The average duration of the quiet periods is 7 years; the durations of the three anterior quiet periods are only 4-7 years. According to their spatial evolution characteristics, we think that there exist two kinds of quiet regions, A-type and B-type, during the active periods. Besides, we find a strong earthquake migration response region near 35°N and the transformation of strong earthquakes with M≥ 7.0 from south to north in the area south of 26°N of Yunnan. We divide studied area into three sections from east to west and three segments from north to south, and find main active area of strong earthquakes has transmigration features. It transfers from east section to west section and then to central section, finally transfers to east section again. As well as it transfers from north segment to central segment and then to south segment, finally transfers to north segment again. According above features, the start time and main active area of next active period and the location of first strong earthquake have been forecasted.