Study On The Three-dimensional Geometry Model Of Brittle Fault

Study on the Three-dimensionalGeometry Model of Brittle FaultThe brittle fault is one of basic structure in the upper earth. How to forecast the extension of brittle fault in three-dimensional space by existent structural form, lithologic character, stress field and experimental data is a problem to ore-prospecting, earthquake forecast and project construction. To this problem, based on summarizing the previous research, three-dimensional geometry of brittle fault is studied by follows in this dissertation.1.Based on the similar theory, the experiment on formation of brittle fault has been done by model material that is synthesized by quartz-sand, cement and gypsum. For the model having pre-crack or not, the formation of brittle fault goes through three stages:initial breach, extension and rupture of crack, their major difference lies in the pattern and stress value of initial breach. In the center of model with no pre-crack, cracks, parallel to axial stress, are formed. The initial breach with a smaller angle to axial stress occurs at the tip of pre-crack in the model having pre-crack, the pre-crack does not extends, and its stress value of initial breach is smaller obviously than that of the model with no pre-crack.2.The qualitative and quantitative study on three-dimensional geometry of brittle fault at different parts and forming stages have been done by section observation at different time and fractal geometry method. Experimental brittle fault is composite of central part with simple and bigger scale cracks; tail part with complicated secondary cracks and damaged part with en echelon cracks. During the course of brittle fault formation, fractal dimensional number of brittle cracks increases gradually from the initial breach, extension to rupture. The fractal dimensional number of brittle fault in different section plan reflects its complicated degree and better self-similar character.3.The formation of brittle fault is a progressive coalescence course that is from micro-crack, network crack to macro-fault. The interaction of focus elastic stress andIll(Doctoral DissertationABSTRACTmirror image force make the initial extending cracks into en echelon in the plastic deformation area. And that the angle between extending crack and principal axial stress decreases gradually is caused by the variation of tensile and shear stress focuses in the course of brittle formation.4.The three-dimensional geometry and strain field are simulated systematic by molecular dynamic method, discrete element and grid method. In the numerical model, both the width and shear strain intensity are bigger at the center of brittle fault, and smaller at the tail and tip parts. The extension of crack and shear strain intensity in the across section vary with that in the vertical section.5.The experimental model and numerical model are conformed by field examples. Last an intact three-dimensional geometry model of brittle fault is founded by experimental result, numerical simulation result and field examples. From center to tip, a brittle fault is composite of main fault, branch cracks with horsetail, en echelon cracks and intact rock. By the geometry model, combining with the factual condition of studying area, the position of existent fault in the whole fault and extension of brittle fault in three-dimensional space can be forecasted accurately, and the ore-prospecting, earthquake forecast and project construction will be guided better.