Abstract
Rayleigh wave exploration is widely used in engineering investigation due to the advantages of speediness, small attenuation, and strong anti-interference ability. However, it is difficult to get accurate results since the Rayleigh wave inversion is a multi-parameter and high nonlinear problem. During the inversion, the strata over the target layer must be divided into many thin layers. The more thin layers are divided, the more parameters are needed to invert. Usually, the number of parameters is much larger than the actual data points, which makes the inversion an under-determined equation. Actually, the several adjacent thin layers will be the parts of a same geological unit. The paper therefore proposed a new method for Rayleigh wave inverting based on geological unit merging into a super unit. Simultaneously, the Bayesian estimation was introduced to determine if the adjacent thin layers could be merged into larger ones. The synthetic model testing demonstrated that the new method is feasible and can effectively improve the accuracy of the inversion.
Highlights
The Rayleigh wave is formed by the interference from P-wave and S-wave near the free surface and has the characteristics of strong energy and weak amplitude attenuation
The strata over the target layer must be divided into many thin layers according to the finite element method for simulating calculation[15]
In order to solve the problem, this paper proposes a new method based on geological unit merging
Summary
The Rayleigh wave is formed by the interference from P-wave and S-wave near the free surface and has the characteristics of strong energy and weak amplitude attenuation. The especial dispersion is an important inversion tool of geophysical prospecting, which is widely used in the research of near surface structure, continental internal structure, subgrade quality detection, etc[4,5,6]. There are several methods to calculate the dispersion curve of surface wave in horizontal layered media quickly and accurately, like Thomson Haskell algorithm[7,8], Knopoff algorithm[9,10], Abo-Zena algorithm[11], reflection and transmission matrix algorithm[12,13,14], which promoted surface wave exploration. The several adjacent thin layers can be merged into a larger one when their geophysical parameters belong to the predetermined threshold based on Bayesian estimation
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