甘、宁、青地区地震孕育的力源环境

从3个方面讨论了甘、宁、青三省区地震孕育的力源环境。①从强震震源机制、地震形变带、断层滑移特征和现代形变、地应力实地测量等几个不同侧面，讨论了区域构适应力场的分布规律。指出，甘、宁、青现今区域构造应力场以水平为主，主压应力方向从地区的西部到东南部，由NNE逐渐转为近EW向，且在地壳的深部、浅部和地表，方向有较好的一致性。它是印度板块向青藏块体碰撞、挤压，使青藏块体向北东方向推济，同时向东蠕散的结果。②通过讨论发展断层的错动形式以及部分前兆资料所反映的应力特征，揭示了地震孕育过程中震源及周围地区处于一种更高的应力状态。这是该地区地震前兆具有普遍性的根本原因。③讨论了甘、宁、青现今地震的孕育方式。指出，6级以上地震基本上以先存断层重新活动或相互沟通为主要活动形式。

THE MECHANICAL ENVIRONMENT OF EARTHQUAKE PREPARATION IN GANSU-NINGXIA-QINGHAI REGION

The mechanical environment of earthquake preparation in Gansu-Ningxia-Qinghai region is discussed in the following aspects: (1) The distribution regularity of regionalstructural stress field is studied, by nleans of considering the seismic source mechanism ofstrong earthquakes, characteristics of deformation belts and sliding movement of active faultsand on-the-spot measuring results of modern ground deformation and stress. The study re-sult shows that in this region the direction of modern regional structural stress field is mainlyhorisontal, the direction of main compressional stress is gradually changing from west to near-ly south-east, from NNE to EW. Furthermore, such a stress direction on surface is identhalto that in shallow and deep crust. It is thought that such a regularity of stress direction is due tothe effects of block collision and compression of lndin plate to Qinghai- Tibet plateau, whichmake the latter push north-eastward and creep eastward at the same time. (2) Based on dis-cussion of dislocation types of earthquake-generating faults and some precursory data, the pa-per suggests that during earthquake preparation period the seismic source area and its neigh-bouring region are of high stress condition, which is the basic reason for the genertllity of pre-cursors in this region. (3) Modern earthquake preparation and development Pattern are alsodiscussed in this paper. It is concluded that the activity of earthquakes with magnitude greaterthan 6.0 is mainly attributed to or linking up between Faults.