Application of active and passive-sourced seismic surface wave exploration to the detecting of shallow overburden karst area

The active and passive-sourced seismic surface wave exploration was carried out to study the three-dimensional geological structure of the typical shallow overburden area in Xing'an County, Guilin City.The dispersion curve extracted from active and passive surface wave data broadened the frequency band and improved the resolution of low-frequency signals.The experimental results show that the shear wave velocity of underground medium ranges from 161.5 m/s to 519.5 m/s in the survey area.According to the difference of velocity value, the underground medium in the experimental area is roughly divided into four layers.The velocity of the first layer ranges from 161.5 m/s to 281 m/s, the second from 281 m/s to 360.5 m/s, the third from 360.5 m/s to 400.2 m/s, and the fourth from 400.2 m/s to 519.5 m/s.Combined with the drilling data, the lithology of the above-mentioned four layers corresponds to clay, silty clay, sand to glutenite, and limestone, respectively; and some local structures such as soil caves and karst caves are locally developed.The research results show that the Rayleigh surface wave exploration method can more precisely describe the soil thickness, structure distribution and the undulating shape of the contact between the soil layer and the bedrock.