Estimation of Shallow Shear Velocity Structure in a Site with Weak Interlayer Based on Microtremor Array

A site condition survey is extremely important for the seismic fortification of major projects. The distribution of underlying weak interlayer in sites is extremely harmful to buildings. However, it is a technical problem to find out the distribution of weak interlayer in the overburden. The shallow velocity structure can directly reflect the change characteristics of a stratigraphic structure. In this paper, acquisition of background noise is conducted using a microtremor linear array method, and the distribution characteristics of two typical stratigraphic structures in Wuhan, Hubei Province, are obtained through an inversion of the apparent S-wave velocity; meanwhile, the equivalent shear-wave velocity and the overburden thickness are estimated, which provides a basis for site classification. The research results are as follows: (1) The two-dimensional profile of the apparent S-wave velocity obtained by the microtremor linear array method can be used for fine imaging of the stratum with weak interlayer, and its distribution form and velocity structure characteristics are highly consistent with those of the drilling data. (2) Compared to the borehole data obtained through in situ test, the error of the overburden thickness and the equivalent shear-wave velocity estimated by the inversion of the apparent S-wave velocity is only about 10%, and the estimated parameters can be directly used for site classification. These results can provide important parameters for seismic fortification of major projects, and also provide reference for the exploration of unfavorable geological bodies, such as weak interlayer in complex urban areas, in the future, which can have good scientific significance and popularization value.