从昭通地震破坏实例看山区地震地面破坏特点
A DISCUSSION ON THE SEISMIC GROUND FAILURE IN MOUNTAIN REGION AS FROM THE ZHAO TONG EARTHQUAKE DAMAGE
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摘要: 1974年5月11日3时25分,东经104度,北纬28.2度我国云南省昭通境内发生M=7.1地震。宏观震中为大关县以北,木杆公社钟(杜)家坪附近。震中烈度为IX度。震区为拔海2000米的滇东北高原地区,地面经受强烈切刻,山高坡陡,尤其震区西部,地形尤显陡峻。地形的坡度一般均在30°以上,主要河流的坡降平均为2.53%。该区地质情况比较复杂。地层分布主要为二迭纪阳新统灰岩,峨眉山玄武岩,三迭纪飞仙关砂页岩等等。Abstract: From the ground failures caused by Zhao Tong earthquake (11, V, 1974, M = 7.1) in high mountain region may be distinguished many types: the main-the landslides and rock-falls in a wide area, the secondary-the debris flow, dumping, ground crack, ground collaps, the local subsidence in limestone area and so on. It is stressed that the degree of earthquake damage for the high mountain region depends on the stepness of surface slope. The remarkable fact is that the western part of Zhao Tong seismic region suffered to more serious ground failure is a deeply incised area with a steep surface slope (mostly slope > 30? and a greater gradient of river. And the eastern part, in spite of its position near by the epicentral area, has undergone the slighter ground failure due to the different geologic structures and petrologic characteristics as well as the even surface slope.After a stronger earthquake in the high mountain region exists chance of sudden fail triggered by some small earthquakes or other factors, as the broad landslides in Lao-zhai-bao.By comparing the earthquakes damage occurred in mountain regions of western China it is preliminarily recognized that the ground failure caused by earthquakes can be divided into two types, i.e. the seismo-tectonic failure and the seismo-gravita-tional failure. Therefore, the Zhao Tong earthquake damage should be belonging to the latter on account of its failure nature. The bad local topographic and geologic conditions must be taken into consideration in estimation of the Intensity of earthquakes for a certain region.
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