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Stochastic Descriptions of Basin Velocity Structure from Analyses of Sonic Logs and the SCEC Community Velocity Model (CVM-H)

John H. Shaw, Andreas Plesch, & Thomas H. Jordan

Published September 2013, SCEC Contribution #1890

A trend of numerical wave propagation studies to shorter periods (> 2 Hz) has been facilitated by sustained increases in computational power, and has created a demand for higher resolution velocity models (e.g., Olsen and Jacobsen, 2011). Building such models is challenging, in part because geologic and seismologic data indicate that fine-scale elastic inhomogeneities can be strong in sedimentary basins and have spatially anisotropic statistical distributions (Magistrale et al., 1996; Süss and Shaw, 2003; Brocher, 2005). While we have local measures of fine-scale velocity structure (down to meter scales) along boreholes with sonic logs, there is not a sufficient density of such samples to facilitate the development of a deterministic regional model. Thus, we propose to develop a statistical description of fine-scale velocity structure, informed by these local observations, to enhance the community models so that they can support higher-frequency simulations. This past year, we analyzed wells in the Los Angeles basin and characterized the fine-scale velocity structure that is not represented in the current community velocity model (CVMH 11.9). We examined 103 wells with sonic logs in the basin extending to depths of 6.5 km. Moreover, we have assessed vertical and horizontal correlations of this fine-scale velocity (Vp) structure using a closely spaced subset of these wells. Most recently, we have analyzed a larger subset of closely spaced wells in an area covered by 3D seismic reflection data to explore further the horizontal correlation lengths of velocity structure. Our goal is to use these measure to develop stochastic representation of fine-scale velocity structure that can be incorporated into new versions of the CVMH.

Shaw, J. H., Plesch, A., & Jordan, T. H. (2013, 9). Stochastic Descriptions of Basin Velocity Structure from Analyses of Sonic Logs and the SCEC Community Velocity Model (CVM-H). Poster Presentation at SCEC Annual Meeting 2013.