Research On Rayleigh Wave Forward Modeling In Low Velocity Layer

With the acceleration of China’s industrialization,the demand for mineral resources is increasing.Scientific and reasonable mineral exploration methods can provide strong technical support for its mining work.When detecting the formation structure in the low velocity layer in the area with complex terrain,the conventional methods such as shallow seismic reflection exploration method and small refraction method sometimes have poor results.The Rayleigh wave exploration method has been widely used in the field of engineering geological exploration because of its advantages of economy,speed,high efficiency and high resolution,but to find out the response mechanism and propagation law of Rayleigh wave,It is still difficult to obtain the fine structural characteristics of the low velocity layer near the earth’s surface and the accurate parameter model.In order to solve this problem,this paper starts with the forward modeling of dispersion curve and wave field,and jointly carries out the forward simulation of Rayleigh wave.Dispersion curve forward modeling can simulate the dispersion characteristics of Rayleigh wave under layered geological model,and then analyze its variation characteristics.Wave field forward modeling can simulate the full wave field characteristics under non layered geological model.It is studied from many aspects of waveform characteristics,seismic records and dispersion curve.The combination of the two methods can better analyze the response characteristics of Rayleigh wave in low velocity layer.Firstly,this paper investigates the research status of Rayleigh wave forward modeling at home and abroad,deduces the Rayleigh wave dispersion equation in horizontal layered media based on the generalized reflection transmission coefficient algorithm,then carries out forward simulation research on many typical geological models including low-speed soft interlayer and high-speed hard interlayer,and analyzes the response mechanism of dispersion curve under different geological structures,The influence of changing different physical parameters on multi-order dispersion curve is deeply explored.Starting with the method theory of Rayleigh wave field simulation,the P-SV elastic wave equation on the two-dimensional xoz plane is deduced,and the staggered grid high-order finite difference scheme is deduced by using the staggered grid high-order finite difference method,and then several problems in the finite difference calculation of wave equation are systematically analyzed.Complex geological models such as near surface low velocity layer medium model,inclined fault medium model and vertical geological anomaly body medium model are established,and compared and analyzed by changing the formation thickness and physical parameters of the medium.The propagation characteristics of Rayleigh wave in near surface and low velocity layer under approximate real conditions are simulated,and the characteristics of waveform characteristics,seismic records and frequency dispersion energy spectrum are analyzed.The theoretical solution of Rayleigh wave exploration is based on the theoretical process of Rayleigh wave exploration and Rayleigh wave simulation.