Study On Multi-modes Surface Wave Dispersion Curves In Bedding Media

Surface wave has been looked as a "noise" for seismic exploration for a long time. But sine 1950's, Rayleigh surface wave was found to have the disperse characteristic in the bedding media. With the theoretical and applied studies going deeply, Rayleigh wave has been utilized widely in earthquake and inter structure, engineering exploration, losses detecting and so on. It involves three problems: the first is data collection; secondly, dispersion theory. Many studies are focused on the computation of dispersion function in the level bedding media, which concern two aspects: the stability of numerical value and the rapidity of computation. The third is inversion; It's impossible to avoid to use dispersion-forward theory in programming, The reliability and accuracy of dispersion formula affect the inversion directly. The numerations also affect the inversion's speed. So, how to get a rapid, steady and accurate numerical computation strategy in the level bedding media is no doubt to have comprehensive and profound influence in the Rayleigh wave exploration.The numerical computation of Rayleigh wave found there are many modes in dispersion curve in the bedding media. What's the character of the multi-mode dispersion curve and how to explain them is also a problem. In dispersion curve, multi-mode should represent multi-curves. But in fact, we always get only one curve from actual data. Which mode correspond to the curve, we have no answer still by now. How to make the multi-modes correspond with the only curve is an urgent question for Rayleigh wave inversion now.Doctor Jianghai Xia in American Kansas University combined the fundamental mode with the higher modes, carried out the dispersion curve inversion by using the damping least square method, and Acquired preferable result. Fan Youhua also studied the Rayleigh surface wave,taking the multi-modes into consideration. These studies all explain that with the dispersion curves higher modes have important meaning.Having reviewed the developments of Rayleigh wave, this paper has carried out the theoretical study on dispersion curves in horizontal bedding media, and numerically calculated them under the conditions of two and three layers. Also analyzed the dispersion curve character affected by the shear wave, density and depth of the media. The author specially calculated the media embed of low velocity and joints. With the exploration begin to extend from overland to lakes or shallow sea, the author numerically calculated the dispersion curve when the media of surface layer is liquid. And acquired some useful conclusions.