LI B C，SUN S H，LI G P. Application of SPAC method in dividing strata of the Quaternary strata [J]. Journal of Henan Polytechnic University( Natural Science), doi:10.16186/j.cnki.1673- 9787. 2023120033.  

Received：2023-12-13

Revised：2024-04-08

Online：2024-05-21

Application of SPAC method in dividing strata of the Quaternary strata (Online)

LI Baochun^1，2，3，SUN Shaohuai^1，2，LI Guoping^1，2

（1.School of Resources and Environmental Engineering，Inner Mongolia University of Technology，Hohhot 010051，Inner Mongolia，China；2.Inner Mongolia Engineering Research Center of Geological Technology and Geotechnical Engineering，Inner Mongolia University of Technology，Hohhot 010051，Inner Mongolia，China；3.School of Geophysics and Information Technology，China University of Geosciences，Beijing 100083，China）

Abstract: The SPAC method is the most effective method to extract phase velocity from environmental noise.The calculation of S-wave velocity structure by the SPAC method has important scientific significance for studying velocity structure. Objectives To verify the reliability of the SPAC method in dividing strata of the Quaternary strata, Methods this study used a multi-observation array to collect microtremor signals within 2 to 40 Hz.It calculated the spatial autocorrelation coefficients between Stations A,B,and C groups and the central station.Furthermore,zero-order Bessel functions were used to fit the spatial autocorrelation coefficients.It extracted the phase velocity-frequency relationship from the Rayleigh surface wave to obtain the phase velocity dispersion curve.Contrasting the Forking Genetic Algorithm fGA,the Low-Velocity Soft Layer Model,the High-Velocity Hard Layer Model,and the Velocity-Increasing Model,the Forking Genetic Algorithm fGA exhibits the advantage of inverting the dispersion curve without relying on an initial model. Results We used the SPAC,transient Rayleigh surface wave,and wave velocity logging methods to invert the S-wave velocity structure in the northern margin of the North China Craton.It is found that within the depth of 6.7 to 9.0 m,the fully weathered gneiss exhibits S-wave velocities as low as 305 m/s,whereas the strongly weathered plagioclase gneiss shows higher S-wave velocities ranging from 430 to 540 m/s below 9.0 m. Conclusions Based on the SPAC,transient Rayleigh surface wave,wave velocity logging methods and drilling data,it can be seen that the accuracy of stratigraphic stratification and S-wave velocity value of the SPAC method are consistent with other results,which verifies the reliability of the SPAC method.

Key words：SPAC method;microtremor signal;S-wave velocity structure;dispersion curve; Rayleigh surface wave

CLC: P315