Time-distance Simulation Of P-wave Reflection From 3D Dipping Interface In Anisotropic Media

With rapid development of geophysics, three-dimensional seismic exploration and propagation of seismic waves in anisotropic media become hot study topics in recent years. In order to get clear images of underground structures, the stack migration as a traditional method needs exact velocity. Two factors that cause velocity errors are lateral heterogeneity and anisotropy of underground media. Current studies on anisotropy are based on the homogeneous media and have vertical or horizontal anisotropic symmetric axis, then the problem connected with three dimensional dipping interface is still unsolved. This thesis attempts to evaluate the effects of a 3D dipping interface within anisotropic media for the time-distance features of reflected P-wave.Three-dimensional exploration seismology uses net receiving on the surface for detecting three-dimensional structure under the ground. This requires three-dimensional explanation and data processing. As far as data analyses are concerned, the underground reflection interface is often three dimensional dipping resulted as the reflection path plane is dipping necessarily. The spatial orientation of the path plane will change with the shot and receiver. This includes some complexities that lead previous work carried out with various restrictions. As to past data processing and explanation, the fundamental assumption is the path plane being a vertical plane relative to the earth surface both for 2D and 3D reflections. On such assumption, the apparent dipping angle, corresponding velocity and position of reflector for each survey line is not the same, so there is the great departure of the inversion velocity and depth from exact.In the anisotropy medium, the velocity varied with the propagation direction. The difference between the supposed vertical plane and the true path plane causes the error between the theoretic and practical velocity of anisotropy. While due to the complexity of true three-dimensional path ray, the study anisotropy under the condition of three-dimensional dipping interface is very difficult, so the symmetricaxis of anisotropy parallel or vertical to surface is assumed by many authors until now.The underground media are appeared as eighth lateral heterogeneity or anisotropy. So the theoretic study the reflection from three dimensional plane including effects of anisotropy is very important to 3D seismic data explanation.In this study, the symmetric axes of parallel aligned crack induced anisotropy can have arbitrary orientation in space. The cracks are filled with either gas or water .The receiver array can be classified as x-direction and y-direction respectively indicating the lateral surrey line and the longitudinal surrey line. The method of hyperbolic time-distance for P-wave isotropic reflection is used to examine the anisotropic effects on travel time inversion. Since the velocity variation associated with water filled crack is usually small, the study is focused on the gas filled cracks with a great number of simulation.From our theoretical investigation, the following new understanding P-wave anisotropic reflection for 3D seismic survey has been obtained:1. The time-distance curve is a hyperbola when the P-wave is reflected from a 3D dipping interface in isotropic media .Under certain conditions, the time-distance curve of reflected P-wave in anisotropic media has similar feature compared with isotropic case.2. When the crack density is small, the difference between the arrival time in isotropic and anisotropic media is little .As such crack density is large, the difference becomes significant as to several tens ms (millisecond) even. When the survey lines are normal to the parallel crack, the difference is remarkable but small as the survey lines parallel to parallel crack.3. Within the offset range near the seismic explosion, the travel time of anisotropic reflection can also be fitted well using hyperbolic equation except the crack density is very larger.4. For anisotropic reflection, there is an equivalent isotropic...