Ambient noise multimode surface wave tomography

Seismic techniques using earthquakes are powerful tools for exploring the Earth’s internal structure. However, the earthquake distribution limits the spatial resolution. In recent years, ambient noise surface wave tomography using ambient seismic wave field has resolved these limitations. A typical ambient seismic wave field is microseisms excited by ocean swell activities. Ambient noise surface wave tomography is a technique in seismic interferometry that extracts seismic wave propagation between pairs of stations by cross-correlating the seismic records. The cross-correlation function can be interpreted as an impulsive response at a station with a virtual source at the other station. This technique became standard with the development of modern dense seismic networks. This paper reviews a theory of seismic interferometry for ambient noise surface wave tomography and procedures for practical data processing to calculate cross-correlation functions. The tomographic method typically consists of four steps: (1) the construction of reference 1-D models, (2) phase velocity measurements for each path, (3) 2-D phase velocity inversions, and (4) the construction of a 3-D S-wave tomographic model obtained from series of local 1-D inversions at all the grids. This paper presents the feasibility of multimode surface wave dispersion measurements for improving depth resolution.