The Regional Crustal Stability In Hebei Plain And Its Fuzzy Mathematics Comprehensive Assessment

The structure in Hebei plain is complex, the seism is frequent, and the engineering geology problem is many, but how stability of its whole crust is, up to now still no one do the research specially. With looking after other factors and following the principle that the tectonic stability research is the focus of the assessment and research of regional crustal stability, this thesis has quantitatively evaluated the crustal stability of Hebei plain applying the fuzzy mathematics comprehensive assessment method.In the factors that influence the crustal stability, this thesis takes tectonic stability as the key, researchs and explores systemically the faults of the Hebei plain, and has drawn conclusions that the Pirdmont Fault of Taihang Mountain is a active fault in Quaternary , the seismic belt along Xingtai-Tangshan line is a deep fault, and initially defines that there are 27 main faults in Hebei plain. Based on this, the paper also researchs systemically about the deep crustal structure, Cenozoic and recent tectonic activity, the crustal surface structure and rock-soil mechanical property, and seismic activity and its risk. After having scientifically analyzed the main factors that influence the crustal stability, taking the main faults that control the framework of Hebei plain as the key, the thesis divides the crust into five first order areas, then, with taking the second order faults as the key, divides the crust into 28 fault zones, 24 districts between different faults. So, in Hebei plain there are 52 areas to be evaluated applying the fuzzy mathematics comprehensive assessment method. The result shows that there are 11 relatively instable belts, and their position is corresponding to the Xingtai-Tangshan fault, except for this, in Niudong fault and Daxing-Xiadian fault zones of the north section of the Pirdmont Fault of Taihang Mountain., and in Cixian-Daming fault in the south of Hebei plain, there are relatively instable belts either. All these relatively instable fault belts are deep or active fault, so, this shows that deep fault and active fault plays a key role in influencing the crustal stability of Hebei plain. Moreover, The result of comparing the map of the fuzzy mathematics assessment of regional crustal stability in Hebei plain with the seismic risk zoning map of the Hebei province shows that the most of the relatively instable and less instable belts are within the risk areas of earthquake in Hebei plain forecasted by Hebei Earthquke Department. This shows that strong seismic activity and seimic risk area is a very impritant factor to the crustal stability of Hebei plian.The suface of Hebei plain is 72172.5km2, the result of evaluation shows that the area of relatively instable, less instablre belts, and the sum of the two is respectively 11.48, 33.22, and 44.7 percent of Hebei plain, and the area of the relatively less stable, stable,and the sum of the two is repectively 51.95, 3.36, 55.3 percent of Hebei palin .So, generally speaking, half of the crust of Hebei plain is relatively stable,and half of the crust of Hebei plain is relatively instable,and the fore gains advantage slightly, but, the later shuld not be neglected also.