Shallow velocity structure of the Luoyang basin derived from dense array observations of urban ambient noise

Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He'nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional (3D) shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region, while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.