云南地区上部地壳结构和地震构造环境的层析成像研究

利用4条DSS丰富的测深资料，对云南地区上部地壳结构和地震构造环境进行了层析成像研究．成像结果显示，得到的速度模型与地表盆地、隆起与断裂有很好的对应关系，显示了与地表火山岩系相应的低速异常体．云南地区上部地壳横向不均匀性显著．结晶基底的深度一般为0~5 km．局部基底高于海平面，基岩直接出露地表，同时在一些大的坳陷处沉积厚度可达8~12 km．作为一级构造单元的昌宁-双江断裂可能切割不深，而红河断裂作为板块缝合线切割较深，有延伸到中下地壳的迹象．云南地区历史上的广泛的火山活动与现今中强地震的发生有紧密联系．有的地方尽管现今地表已不再有火山活动，但中下地壳活动并未停止，存在较大的应力作用．由于地表火山活动停止，来自中下地壳和上地幔的大部分能量得不到释放，而在有利的构造部位积聚，以及盆地水的渗透、其它流体的作用和外动力作用，可能是云南地区经常诱发中强地震的重要原因．

TOMOGRAPHIC INVESTIGATION OF THE UPPER CRUSTAL STRUCTURE AND SEISMOTECTONIC ENVIRO-NMENTS IN YUNNAN PROVINCE

Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province by using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the exposed basins, uplifts and faults, and the low velocities anomaly corresponding to the volcanoes also has been revealed. There exits a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrock are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust however maybe shallow. On the other hand, known as the plates' seam, the Honghe fault has a distinct evidence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a closed relationship with the earthquake's occurrence up-to-date. Despite of the stop of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. For the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and upper mantle cannot be released, therefore it accumulates at some beneficial tectonic locations. Moreover, saturation of the water from the basin and the action of other fluids, and the affection of outer stress maybe another direct reason account for the strong earthquakes' occurrence in Yunnan region.