青藏块体8级左右地震前中强地震 活动图像的相似性演化

2008年5月12日,四川汶川发生8.0级特大地震.汶川地震前,青藏块体曾出现与2001年11月昆仑山口西8.1级特大地震前相似的大规模中强地震活动图像.为了探讨8级左右地震前的中强地震活动规律,本文研究了1900年以来中国大陆地区8级左右地震前中强地震的时空分布特征,认为①青藏块体8级左右地震前一般会出现中强地震活动图像的两阶段演化,第一阶段主要表现为中强地震沿印度板块与青藏块体接触带附近分布、青藏块体内部平静,第二阶段主要表现为中强地震向青藏块体内部扩展,形成大规模中强地震条带,未来主震一般发生在大规模中强地震主条带或者多组条带的交汇处.②该演化规律可能反映了印度板块作用于欧亚板块(尤其是青藏块体)产生的大区域地壳运动与构造应力场的动态变化过程,对预测青藏块体8级左右地震(尤其是8级以上特大地震)有一定意义,对预测新疆块体8级左右地震有参考价值,但尚不适用于中国大陆东部地区.③从更大范围考察中强地震活动图像的演化,有可能发现大地震前的场兆信息,对分析、预测未来的8级左右地震是一个有意义而且可行的方向.本文还对汶川地震的孕震过程和大规模中强地震条带的形成机理作了初步的探讨.

The similar evolution of seismicity patterns of strong-moderate earthquakes before about Ms8 earthquakes of Qinghai-Tibet block

An M_s8.0 super-strong earthquake occurred in Wenchuan of Sichuan on May 12, 2008. Before the earthquake there appeared large-scale strong-moderate seismicity patterns in Qinghai-Tibet block similar with that before the M_s8.1 earthquake of Kunlun Mountain in November of 2001. According to the analysis and study of distribution and evolution of strong-moderate earthquakes before about M_s8 earthquakes in Chinese Mainland since 1900, we considered: ① There is always a two-stage evolution of seismicity pattern of strong-moderate earthquakes before the M_s8 earthquakes in Qinghai-Tibet block. In the first stage strong-moderate earthquakes occurred along the contact zone of Indian Plate and Qinghai-Tibet block while were calm in the Qinghai-Tibet block. In the second stage, the strong-moderate earthquakes extended into the Qinghai-Tibet block and formed large-scale strong-moderate earthquake belts. Subsequent main shock always occurred in the intersection of main or multi-group belts of strong-moderate earthquakes. ②The evolution maybe reflects the dynamic-change process of large-area crustal movement and tectonic stress field caused by the action of Indian Plate on Qinghai-Tibet block, which have important significance in M_s≥8 super-strong earthquakes prediction of Qinghai-Tiber block and reference value for prediction of M_s≥8 earthquakes in Xinjiang block, but not valid for earthquakes in the east of Chinese mainland. ③We may find the precursory information before strong earthquakes by studying large-scale evolution of seismicity patterns of strong-moderate earthquakes, which is meaningful and feasible to analyze and forecast future M_s8 earthquakes. In addition,we discussed preliminarily the seismogenic process of Wenchuan earthquake and formation mechanism of large-scale strong-moderate seismicity belts in this paper.