A pilot project of ambient noise tomography on a dense seismic array in Ji’nan urban area

In this study, we conducted ambient noise tomography (ANT), with 33-day data, to investigate the near-surface shear-velocity structure in downtown Ji’nan, Shandong Province, China. The cross-correlation functions with quiet clear Rayleigh waves are obtained with more symmetrical energy distribution which indicates that strong human activities, such as moving vehicles and municipal engineering construction, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surface-wave tomographic method with period-dependent ray-tracing is used to invert all surface-wave dispersion data in the period band 0.2–1.5 s simultaneously for 3D variations of shear-velocity structure. The study result can help us better understand the local geologic structures, evaluate the distribution and geometry of the fracture-karst media, and assess hazards of the concealed active fault and its effect on the springs in the future.