Shallow shear wave velocity structure of the Dongshan sag area using surface wave data in a deep reflection profile of the Yuanmou area of Yunnan province, China

Abstract

Deep reflection seismic data contain abundant surface wave information for which the velocity structure in the near-surface shallow underground can be obtained using multichannel analysis of surface waves (MASW). This paper uses the MASW method to process deep reflection data in the Yuanmou area in Yunnan province, China. The MASW method uses the phase velocity spectral transformation of Rayleigh waves to obtain its dispersion curve. The initial model for different lithology classifications is established to invert the underground velocity structure. This study obtains a two-dimensional shear wave velocity structure profile to investigate the shear wave velocity structure. Generally, the study results have shown that the shear wave velocity structure obtained by the MASW method corresponds well with the surface conditions and accurately reflects faults' changes, folds, and lithology. Moreover, the formation sand content calculation shows a large difference in Dongshan sag's formation sand content. The sand contents of Cretaceous and Middle Jurassic strata are over 30% similar, and the sandstone content of underlying Early Jurassic strata is mostly 30% lower. The stratum buried depth of Early Jurassic strata is between 0– 800 m. The dip angle of LZJF at this location is 90°. The west side of the LZJF is based on Proterozoic uplift, and the Quaternary sedimentary thickness exceeds 300 m above the uplift stratum. Whereas on the east side of the LZJF, the stratum of the Dongshan sag section is mainly a synclinal structure.