Imaging urban near-surface structure with passive surface waves method: A case study in Guangzhou, southern China

Investigating geological structures has fundamental significance in engineering construction and the develop-ment of the urban economy. Limited by the circumstance related to human activities including the poor signal-to-noise ratio, buildings restricting accessibility, and surface conditions weakening sensor coupling, conventional geophysical methods are difficult to acquire high-precision geological structures, which is the premise and foundation of subway construction. The Passive surface waves method shows its preponderance in urban area surveys compared to conventional geophysical methods, especially in complex urbanized environments. Ambient noise caused by human activities can be considered as satisfying signals to perform surface wave dispersion energy calculation and explore shear wave velocity structure. In this study, 218 short-period seismometers were deployed as a four-line array crossing the planning subway of Line 22 in Guangzhou, Guangdong Province, south China. The spatial autocorrelation (SPAC) method, one of the passive surface-wave methods that can extract the dispersion curves from ambient noise data, is used to explore the distribution of the Guangsan Fault across the study area. The inverted velocity structure reveals that the linear array applied in the SPAC method with long-time seismic ambient noise record can retrieve reliable dispersion information to image subsurface geological structure. The three-dimensional result illustrated the distribution and characteristics of the Guangsan Fault matching well with previous geological references and revealed the Enping-Xinfeng Fault across the study area. The passive surface waves method has great potential for urban near-surface hidden fault investigation and can meet the demands of three-dimensional geological structure imaging with high precision.