Abstract: The North-Soath Seismic Belt is one of the most seismically active belts in China. It stretches from the Yinchuan depression in the northern end through the Liupangshan Mts., Qinling Mt., Wenxian, Maowen and along the Hengduan Mts., and far beyond the frontier.In this paper a preliminary discussion is made on the structural features of the crust and upper mantle under the northern (Holangshan-Liupangshan seismic zone) and middle sections (Tianshui-Wudu, Wenxian-North-West-Sichuan seismic zones) of the North-South seismic belt through the geophysical data.The analysis and study of the materials and data available make enable us to recognize the main features of deep seismic environment in northern and middle sections of this seismic belt.1. Top surface of the upper mantle under this seismic belt appears to be in zonal uplift. The axial orientation of the zonal uplift of upper mantle is in NNE direction in the Yinchuan graben area and in NW direction in Xiji, Haiyuan and Guyuan areas, and in sublatitudinal direction in Tianshui-Wudu area.2. The strike of faults along which strong earthquakes occurred and direction of migration of epicenters are coincident with the orientation of isobaths of the top surface of the asthenosphere.3. Strong earthquakes usually took place in the conjunction portion of deep-seated structures with shallow-seated structures at depth in the earth, such as in Tianshui-Wudu area.4. The occurrence of strong earthquakes is related to the local uplifts and depression of the high conductivity layers in the crust and upper mantle.A tentative analysis is made on the relation of the deep-seated environment to preparation of earthquakes. At the end of this paper a discussion is made on the significance of the deep seismic environment in research on medium and long-term earthquake prediction and causes of earthquakes.

摘要： 本文从部分地球物理资料出发,初步探讨了中国南北地震带北段(贺兰山—六盘山地震带)、中段(天水—武都、文县—川西北地震带)地壳和上地慢的结构特征。 根据对有关资料的分析研究,初步得出中国南北地震带北段、中段深部地震环境的主要特点: 地震带下部的上地幔顶面呈带状隆起:银川地堑地区上地幔顶面带状隆起的轴向呈北北东向;西吉、海原、固原地区呈北西向;天水—武都地区呈近南北向。 强烈地震的断层走向、震中迁移方向与软流圈顶面等深线轴向方向一致。 强烈地震往往发生在深部构造与浅部构造在深部的交汇区,如天水、武都地区。 强烈地震与壳内高导层和上地幔高导层的局部隆起和拗陷有关。 进而尝试性的分析了深部环境与地震孕育发生的关系。最后文章讨论了深部地震环境对中长期地震预报和地震成因研究的意义。