Abstract
Surface wave analysis generally neglects amplitude information, instead using phase information to delineate near-surface S-wave velocity structures. To effectively characterize subsurface heterogeneities from amplitude information, we propose a method of estimating lateral variation of attenuation coefficients of surface waves from multichannel–multishot (multifold) seismic data. We extend the concept of the common midpoint cross-correlation method, used for phase velocity estimation, to the analysis of attenuation coefficients. Our numerical experiments demonstrated that when used together, attenuation coefficients and phase velocities could characterize a lithological boundary as well as fracture zone. We applied the proposed method to multifold seismic reflection data acquired in Shikoku Island, Japan. We clearly observed abrupt changes in lateral variation of estimated attenuation coefficients around fault locations associated with a lithological boundary and with well-developed fractures, whereas phase velocity results could detect only the lithological boundary. Our study demonstrated that simultaneous interpretation of attenuation coefficients and phase velocities has the potential to distinguish localized fractures from lithological boundaries.
Highlights
Surface wave analysis is a technique for estimating shallow S-wave velocity structures (e.g., Xia et al 2009; Socco et al 2010)
The estimated attenuation coefficients increased near the MTL active fault system (MTLAFS) (Fig. 7a) as the simulation study showed (Fig. 4d–f ), whereas the effect of scattering and amplification at the lithological boundary was indicated near the MBMTL from the opposing trends in the α estimated from positive- and negative-offset data (Figs. 3e, f, 7a–c)
Like the common midpoint cross-correlation (CMPCC) analysis proposed by Hayashi and Suzuki (2004), this method retains high lateral resolution while estimating attenuation coefficients at each common midpoints (CMPs)
Summary
Surface wave analysis is a technique for estimating shallow S-wave velocity structures (e.g., Xia et al 2009; Socco et al 2010). To overcome the assumption of one-dimensional velocity structures in surface wave analysis, several workers have proposed methods to estimate quasi-two-dimensional dispersion curves with high. The S-wave velocity structure derived from surface wave analysis is frequently used to characterize shallow lithology. It is difficult to detect localized nearsurface fractures from phase velocity of surface waves derived from conventional surface seismic data. The detection of such fractures is important in various engineering applications (e.g., CO2 storage)
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