Determination of the contrast boundaries of the low velocity zone by analyzing the features of the dispersion curves of the Rayleigh wave velocities based on empirical dependencies

Abstract

An important application of the multichannel surface wave (MASW) method is seismic safety assessment. The key parameters in the calculation of increments in the input of seismic microzoning are the thickness and average velocity of the soil mass lying on the base of more rigid rocks. To determine these parameters, we propose a new method for constructing horizontally layered models of the upper part of the geological section using the features (positions of extrema of the second derivative) of the dispersion curves of phase velocities of the Rayleigh surface wave, which, as shown by numerical experiments, are associated with the position of contrasting boundaries in the medium under study. (e.g., the boundary between soils and rocks). This approach is much simpler than the problem of recovering a horizontally layered model traditionally solved in the MASW method from a set of phase velocities for a sequence of frequencies and does not require an initial approximation and/or any restrictions on the possible values of the model parameters. In the case of two-layer and three-layer media, our approach is reduced to a simple and fast application of explicit formulas.