The Study On The Syngenetic Mechanism Of Ground Fissures

Ground fissures are widely distributed in the whole world, which are most concentrated in China’s Fenwei basin. Fenwei basin is a rift sedimentary basin, in which each basin producing multiple ground fissures with different size and different attitude seems to have a certain syngenetic relationship of ground fissures. Studying basin syngenetic mechanism of ground fissure plays a significance role in revealing the formation mechanism of global ground fissures.This article is based on the research project "the comprehensive study of Fenwei regional ground fissures and disaster reduction ". Through the extensive collection of the geological background data of the Weihe basin, we understand the geological background and the regional tectonic framework. Then through the detailed field geological survey, we tidy the plane distribution of ground fissures in Weihe basin. By the means of the drilling and trenching adopted in typical areas, we analyze the profile features of ground fissures in Weihe basin. By probability statistics we summarize the time features of ground fissures in Weihe basin. On the basis of overview of the basin tectonic framework, the present situation of the ground fissures and syngenetic characteristic of ground fissures, we analyze the syngentic conditions and simulate the syngenetic process of ground fissures. Finally we generalize basin syngentic mechanism of ground fissures. The main work and results are as follows:(1) Through field geological survey and the collection of data, we analyze the geological background and the basin tectonic framework and summarize the present situation and syngenetic characteristics: 1) the similarity of the direction of the plane distribution; 2) the similarity of the profile structure; 3) the universal relevance with fracture; 4) activities on time synchronization.(2) The group of ground fissures in the Weihe basin is a kind of surface rupture system with syngenetic characteristics. The four floors of the model controlling the surface rupture system is the upper mantle uplift, upper and middle crustal flow extending, the different movement between the basement fault blocks, the stretching of the fault under the background of tectonic tensile stress.(3) Through the three-dimensional surface of the mohorovicic of the Weihe basin and its adjacent area constructed by Sufer11.0 and Ansys11.0, we understand the fluctuation of the upper mantle. We analyze the progress that the uplift of the upper mantle promotes the flow extending of the upper and middle crustal.(4) By Flac3 D we analyze the progress that basal stretching causes the different movement of the fault blocks under the condition of the flow extending of the upper and middle crustal.(5) By using the finite element software Ansys11.0 and Flac3 D, we analyze the progress that the tensile stress and the shear stress produced by the different movement of the fault block affect the fracture system of the cap rock.(6) By using mechanical analysis, we analyze the progress that the local stress field produced by the stretching of the fault causes surface ground fissures near the fault zone. Thereby, ground fissure grow, accompany, derive along the fault zone.(7) On the basis of the above results, we summarize the syngenetic mechanism of ground fissures in the Weihe basin. The uplift of the upper mantle promotes the flow extending of the upper and middle crustal. The basal stretching causes the different movement of the fault blocks under the condition of the flow extending of the upper and middle crustal. The tensile stress and the shear stress produced by the different movement of the fault block affect the fracture system of the cap rock. The local stress field produced by the stretching of the fault produces surface ground fissures near the fault zone. Thereby, ground fissure grow, accompany, derive along the fault zone.