西藏高原札木、当雄地区的平均应力场

根据西藏札木和当雄地区区域地震观测资料,用平滑小震初动的方法得到了这两个地区的平均应力场,结果是: 1.当雄地区及札木的A区主压应力方向大体上为南北向,仰角较小,分别为23°和14°,说明两板块之间以水平挤压为主。 2.在札木的B区,主压应力方向为东西向,仰角为51°,说明和俯冲的情况相对应。 这一结果与印度板块和欧亚板块互相挤压碰撞的模式基本上一致,说明了此地区无论大震小震郁受板块构造力的控制。

THE AVERAGE STRESS FIELDS OF ZHAMO AND DAMXUNG REGIONS IN THE XIZANG PLATEAU

The average stress fields of Zhamo and Damxung regions in Xizang Plateau are obtained by smoothing the first motion patterns from the regional seismological ob-servation data. The results are as follows:1. The compressional axes in Damxung region and part A of Zhamo region are roughly in the north-south direction. The angles of elevation of these axes are small, being 23 degrees and 14 degrees respectively. This indicates that the interaction be-tween two plates is dominantly compression.2. In part B of Zhamo region, the compressional axis is in the east-west direc-tion with an angle of elevation about 51 degrees. This seems to correspond to the underthrusting condition.Such a result is basically in accord with the model of collision between the Indian plate and the Eurasian plate and agrees with the fault plane solutions of the major earthquakes which occurred in that region. This implies that all earthquakes whether large or small are all controlled by the- plate movement.