Experimental investigation of three-dimensional propagation process from surface fault

Experimental study of the formation and propagation of three-dimensional (3D) faults is of great significance in the understanding of the propagation process developing from initial natural faults. In the study described in this paper, experimental investigations of 3D propagation processes of a type of surface fault are carried out under biaxial compression. The strain field near the surface fault is dynamically measured and fully analyzed with a high-density Multi-Channel Digital Strain Gauge (MCDSG) and Digital Speckle Correlation Method (DSCM) based on the white-light image analysis. Simultaneously the micro-fracture process involved in fault formation is observed by a 3D acoustic emission (AE) location system with a set of multi-channel whole-wave record equipment. The experimental results show that the 3D propagation process of surface fault differs greatly from that of the two-dimensional (2D) state and that a new more complicated type of 3D morphological characters and deformation mechanisms are produced. The 3D propagation process of surface faults may be divided into three stages: 1) the first stage of crack propagation initiated by wing cracks; 2) the conversion stage propagated by petal cracks; and 3) the second stage of crack propagation formed by shell-shaped fracture surface. The primary propagation patterns of the three stages are different. The corresponding deformation fields and micro-fracture distributions are likewise different. The fracture activities from petal cracks especially are of vital importance during surface fault propagation. This is also a key conversion state and marks an intrinsic difference between 2D-like and the 3D state in fault development.