The Mechanism Of Loess Landslide Caused By Earthquake In Haiyuan Of Ningxia

As part of the northwestern loess region, the loess hill country is situated on the northwestern rim of the Qingzang plateau with an area of about 17,000km2 and general altitude of about 2,000m. It demonstrates typical triphibian climate with little rainfall, strong wind and heavy sand. It is not only the important borderline between the east and the west of China' s landforms, but the noticeable earthquake country in the Euro-Asian Continent. During the 400 years since the 16th century, intense earthquakes above magnitude 7 on the Richter scale have happened 10 times in its middle part and neighbourhood. The Haiyuan Earthquake of magnitude 8.5 on the Richter scale is among them. Control with the Liupan Mountain The new tectonics movement and seismic activities are frequent.On the 16th of December, 1920, an earthquake of magnitude 8. 5 on the Richter scale occurred in Haiyuan Country of Ningxia, China, which damaged innumerable houses and took the life of 230, 000 persons. The astonishing world-wide earthquake resulted in intense surface deformation around the breakdown belt and the extreme earthquake country. the large-scale failures and loess seismic landslides occurred over 600 times with the earthquake intensity ranging from eleven to twelve degrees and nine to ten degrees respectively within the extreme earthquake country. Forty-one earthquake barrier lakes took shaped, among which 27 still exist today, and the destroy area of the whose intensity is above eight degrees amounts to 50X103km2. In the meantime, the kind of landslides are so various that the district is referred to as the museum of loess seismic landslide. This article target at the mechanism of loess seismic landslide in Haiyuan . Research mainly expend from two respects: The microstructure property of the late Pleistocene loess in the landslide-attacked country, the coupling effect between earthquake waves and site soil.Intensity area is smaller in scope than in low intensity. The loess' s microstructure property make the earthquake vibration The yellowish-brown late Pleistocene loess reveals with loosen structure and porous. Property, the concrete research include of microstructure property expending from loess' s arrangement mode of grain shape, pore feature, state of binding materials and structure type. Those special property affect and control the extent and intensity of loess landslides, which unfolds the difference that landslide in high feature exerts influence on the damage result, such as the phenomenon demonstrated by strength loose in an instant, have more intense loess which caused the deadweight collapsible property, low intensity and other engineering geological property, and other strong earthquake effects. Those property are very different from other area in loess plateau.The magnifying and basin effect for earthquake waves mainly researched from terrain factor which distributed among incised ravines and the tops of loess yuan, liang and mao. with its special topography and geomorphologic. The slopes of abrupt ravine walls range from 80 to 90 degrees and the general slopes of liang and mao from 25 to 30 degrees, and the dissected reduction degrees are more than 15, which are covered with deep ravines in large numbers, lead to frequent earthquake catastrophe and causes the unbalance of loess under the seismic force. So the mechanism of large-scale loess seismic landslide is connected with thicker burden soil, loess' s microstructure, topography factor, and basin effect. All of above reflects certain coupling relation between loess site condition and earthquake dynamic effect, which the possibility to become the fundamental reason such as why the loess in the south of Ningxia is more easy to leads to large-scale seismic loess landslides and make the earthquake disaster' s condition worsened than other types of site soil.The paper providing scientific basis for earthquake disaster prediction and control, and construction site safety evaluation of non-saturation loess site country with low moisture in the arid and half-arid areas.