Characteristics of seismic wave attenuation in rock with velocity fluctuation based on deep borehole array observation

PreviousNext No AccessProceedings of the 12th SEGJ International Symposium, Tokyo, Japan, 18-20 November 2015Characteristics of seismic wave attenuation in rock with velocity fluctuation based on deep borehole array observationAuthors: Hiroaki SatoNaoki NishizakaShunsuke SuzukiKozo OhnishiYoshihiko IshikawaShinichi MatsuzakiHiroaki SatoCentral research Institute of Electric Power Industry ()Search for more papers by this authorEmail the author at [email protected], Naoki NishizakaShikoku Electric Power Co.Inc.Search for more papers by this author, Shunsuke SuzukiShikoku Electric Power Co.Inc.Search for more papers by this author, Kozo OhnishiShikoku Electric Power Co.Inc.Search for more papers by this author, Yoshihiko IshikawaShikoku Electric Power Co.Inc.Search for more papers by this author, and Shinichi MatsuzakiShikoku Electric Power Co.Inc.Search for more papers by this authorhttps://doi.org/10.1190/segj122015-065 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract The 2000 m deep borehole array earthquake observation is conducted by Shikoku Electric Power Co. Inc., Japan. By using array observation records at deep borehole between GL -500 m and GL -2000 m, the seismic wave attenuation in deep underground is estimated to be Q=118 from the least-squared fitting of the spectral-ratio decay model of direct upgoing S wave. The result is consistent with the previous Q estimated from rock core samples (psammitic schist) deeper than GL -500 m at this borehole station. It is suggested that the seismic wave attenuation between GL -500 m and GL -2000 m is mainly caused by intrinsic absorption in rock, and that the additional attenuation effect by heterogeneity is very small. The heterogeneity strength at the borehole station is also investigated by using S wave logging data between GL -500 m and GL -2000 m. As a result, it is found that the standard deviation of 1D velocity fluctuation at this borehole station is smaller than the ones at the other near-surface rock sites (