Common-midpoint spatial autocorrelation analysis of seismic ambient noise obtained from a spatially unaliased sensor distribution,Geophysics

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Common-midpoint spatial autocorrelation analysis of seismic ambient noise obtained from a spatially unaliased sensor distribution
Geophysics ( IF 3.0 ) Pub Date : 2021-07-08 , DOI: 10.1190/geo2020-0467.1
Koichi Hayashi ₁ , Mitchell Craig ₂ , Shunjia Tan ₃ , Chisato Konishi ₄ , Haruhiko Suzuki ₅ , Michitaka Tahara ₅ , Kent Falkenstein ₆ , Bin He ₇ , Daxiang Cheng ₇

Affiliation

We have introduced a passive surface-wave method using seismic ambient noise obtained from dozens of receivers forming spatially unaliased 2D arrays. The method delineates 2D or 3D S-wave velocity (

V_{S}

) models to depths of several hundreds of meters, without using any sources. Typical data acquisition uses 50–100 vertical-component 2 Hz geophones on the surface with 5–30 m receiver spacing. Cableless seismographs with GPS record 20–60 min of ambient noise. We establish a 2D grid covering the investigation area and use a common-midpoint spatial autocorrelation (CMP-SPAC) method to calculate phase velocities, resulting in a dispersion curve for each grid point. The method provides dozens of ispersion curves in the investigation area. We use a 1D nonlinear inversion to estimate a 1D

V_{S}

profile for each grid point, and then we construct pseudo-2D or pseudo-3D

V_{S}

models from the 1D

V_{S}

profiles. The precision and accuracy of the CMP-SPAC method were tested with a numerical simulation using a 3D finite-difference method. The results of the simulation demonstrated the applicability of the method to complex velocity structures. We applied the method to an active fault investigation in China. Sixty-four cableless seismographs were deployed in an investigation area of 330 × 660 m (217,800 m²) with 5 and 30 m receiver spacings for dense and sparse grids, respectively. A 3D