Forward Modelling Research On Excitation In Thick Loess Area

As the unique landscape of central and western regions in China, loess plateau, which contains a whealth of coal, oil and gas and coal bed methane, is an important energy base.Seismic exploration is an important means of investigation of coal, oil, nature gas, as well as solid resources. Based on the differences in elasticity and density of subsurface, the properties and shapes of underground rock strata are infered by observing and analyzing earth response to seismic waves created artificially. The loess plateau seismic exploration, especially the selection of excitation parameters, is recognized as a difficult problem in geophysics, because there are too many limiting factors in the area overlaid with loess, including:thickness varies significantly; landform undulation is remarkable; the loess is characterized by dry, porous, low density and high porosity and has strong attenuation of absorption of seismic waves; in seismic exploration, excitation is difficult, signal-to-noise ratio is too low and interference of surface waves is serious. In order to obtain high resolution, fidelity and signal-to-noise ratio of seismic data, in this study, the seletion of excitation parameters from both theoretical and practical aspects were discussed in-depth. The results given here served as basis for solving the problem of loess plateau seismic exploration.At first, this article stated systematically the difficulty in selection of excitation parameters and loess plateau seismic exploration and the basic principles of forward modeling of seismic wave field. Then the model of geological structure of thick loess plateau was established and selection of shotpoint horizon and excitation frequency was simulated. Finally, different fold number of time section of seismic response was analyzed and results obtained from excitation parameters tests of three-dimensional seismic exploration in loess plateau of coal mining area of Xiangfen were compared with the conclusion deduced from theoretical modeling. Besides, the research on survey of shallow strata and wave field characteristics related to excitation parameters was also conducted. The results in this study had some theoretical and practical significance in future investigation of the selection of excitation parameters in loess plateau seismic exploration.