MODEL EXPERIMENTAL STUDY ON BEHAVIOR OF DEFORMATION AND ACOUSTIC EMISSION NEAR THE INTERSECTIONS OF FAULTS
MA JIN ZHANG BOTAO Xu XIUQIN WANG BAOSHENG (Institute of Geology, State Seismological Bureau)
More than 20 kinds of models, each with two intersecting faults are made from the Changping granite. Gypsum used to simulate the fault material is of thickness 2 mm. The models are loaded under uniaxial stress.Four types of fracture combinations are obtained during the experiments:(1). Shearing and slipping In this case, the model contains two faults dipping in opposite directions, one at an angle of more than 45° to σ1 and the other at an angle less than 45° toσ1. When gypsum in the fault zones has a moisture content of 10-15% the shearing fracture occurred along the fault starts at. larger angles and then a terminal frictional slip along the fault at smaller angles, takes place. There are two stress drops on the stress-displacement curve. When the gypsum in fault zones has a moisture content of less than 5%, a frictional slip occurs only along the surface of the fault at small angles. There is one stress-drop on the stress-displacement curve.(2). Wedge by compression This happens when the two sets of faults make angles larger than 45° with σ1. Its stress-displacement curve rises in the form of steps. The direction of fault dislocation may vary repeatedly.(3). Wedge by tension This happens when the sets of faults make angles less than 30 ° withσ1 There is only one stress drop on the stress-displacement curve.(4). Bi-shearing or Bi-slipping This happens when the two sets of faults make angles of 30° to 45° with σ1. There appear two succesive stress drops on the stress-displacement curve.Based on the facts of similarity between the stress-displacement curve and the stress-accumulative number of acoustic emission curve and that between the accumulative acoustic emission number before the principal fracture and the peak stress value during it as well as the relation between acoustic emission and faults, it can be seen that the process of acoustic emission is sensitive to structural conditions.Earthquake precursors possibly appear in the case of different combinations of faults have also been discussed in this paper.