| In recent years, the application of shallow seismic exploration has become more and more widely in the field of hydrology, engineering, and environment, which provided a greater application platform for the development of shallow seismic exploration. Meanwhile, the breakthrough of deep seismic exploration technology in the field of oil and gas provided many valuable lessons for the development of shallow seismic exploration. Shallow seismic exploration has gradually developed and perfected under such context. However, due to the different application fields, there was a great different between shallow seismic exploration and deep seismic exploration in the geological environmental conditions, which required that the shallow seismic exploration needed not only to inherit the method and technique of deep seismic exploration, but also to take full account of the basis of shallow geological conditions to establish and improve the method and technique with its own characteristics, even to make a clear distinction to deep seismic exploration on the individual concepts and exploration ideas.In order to analyze the application effects of shallow seismic exploration under different conditions and to better explore the method and technique of shallow seismic exploration, on the basis of summing up the actual geological features of shallow seismic, this paper conducted researches from the aspects of data collection, processing, and interpretations of shallow seismic by means of numerical simulation. The research work of this paper focused on the following aspects:(1) It studied the wave equation in different media, and from the basic theory of the Hooke’s Law, Cauchy equations, and Navier equation, it derived the acoustic wave equation, elastic wave equation, visco-elastic wave equation, and anisotropic elastic wave equation, which analyzed and studied the physical and structural differences of media described by different wave equations. On this basis, it studied the numerical simulation of seismic waves, and conducted systematic studies of it from the aspects of difference discrete format, definite condition, stability, numerical dispersion and so on, selecting the finite difference method as the core algorithm.(2) It reached numerical simulation of the wave equation’s finite difference method by using Visual C/C++ language. Starting from the simplest acoustic wave equation, using the finite difference method to achieve its numerical simulation, there was a preliminary understanding for the wave field characteristics of seismic waves. On this basis, it achieved the numerical simulation of elastic wave equation and was compared with the wave field characteristics of acoustic wave equation. While using the wave field separation technique, it studied the multi-wave and multi-component wave field characteristics of elastic waves. Further considering the absorption and attenuation of earth towards seismic waves, it achieved a numerical simulation of Kelvin body visco-elastic wave, which analyzed the difference between the elastic wave equation from the characteristics of amplitude and frequency response. Further considering the anisotropy of media, it analyzed the impact of anisotropic parameters on the anisotropy of P and S waves. Numerical simulation of wave equation is an important way to correctly recognize different difference formats, different wave equations and different media properties, and is the basis of numerical simulation application studies.(3) Combining with the actual situation, it analyzed and summarized the geological conditions of shallow seismic and technical characteristics of reflected wave method. This paper, on one hand, analyzed the physical characteristics such as shallow rocks, soil velocity, visco-elasticity, anisotropy and Poisson’s ratio, geological features of near-surface earthquake such as covering layer, water table, and topography, and the underground geological formation features such as bedrock weathering zone, concealed structural fracture zones, high-speed layer shielding, weak intercalated layer in the settled layer, aquifer and leakage belt; on the other hand, conducted comparatively analysis between deep seismic exploration from the aspects of source characteristics, arranged features, background noise characteristics and single shot records, which summarized the method and technique characteristics of shallow seismic reflected wave method in the above aspects. Thus it can be seen that due to there were big differences of geological conditions between the near surface and deep part, and there were great differences of construction environment, objectives, tasks and detection objects between shallow seismic exploration and deep seismic exploration, the shallow seismic exploration is not the "scaled-down version" of deep seismic exploration.(4) Through studying and analyzing the characteristics of shallow seismic exploration, it established and selected geological simulation and forward simulation parameter which is more in line with the characteristics of shallow seismic exploration, and specifically carried out numerical simulation studies of shallow seismic exploration. In terms of data collection, this paper firstly considered the different impacts of different permutations of length, shot point locations, minimum offset towards the original records, and secondly considered the impact of seismic exploration resolution. On this basis, it summarized the standard of selection for the best time window of shallow seismic exploration. In data processing, aiming at the overlay processing, it proposed a two-dimensional weighted stack algorithm based on the SNR and statistical properties, and tested the performance advantages of this two-dimensional weight, which comparatively analyzed the overlay effects of weighted superposition algorithm and traditional superposition algorithm, and simulated the application effects of weighted superposition algorithm in the multiple detection technique and multiple coverage technique. In the data interpretation, firstly by means of numerical simulation, from the aspects of seismic reflection interface and geological interface, seismic time profile and depth profile, seismic profile and geological structure, it analyzed the relationship between seismic profile and geological profile; secondly, aiming at the typical geologic body of shallow layer, it established the interlayer model of high-speed layer and low-speed layer, fault and fault cutting model, and aqueous and non-aqueous cavity model, which analyzed and summarized the wave field characteristics of above models in the single shot records and post stack profile; finally, combining with the measured data, it conducted numerical simulation studies, which fully illustrated that it can provide references and evidence for the actual shallow seismic exploration by means of numerical simulation.In this paper, aiming at the geological characteristics of shallow seismic exploration and technical characteristics of the reflected wave method, it carried out a more comprehensive study, in order to provide a way for the theory guiding practice, and to form some general conclusions for the reference of actual work. |
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