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S wave attenuation structure on the western side of the Nankai subduction zone: Implications for fluid distribution and dynamics
Author(s) -
Takahashi Tsutomu,
Obana Koichiro,
Yamamoto Yojiro,
Nakanishi Ayako,
Kodaira Shuichi,
Kaneda Yoshiyuki
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011103
Subject(s) - attenuation , geology , seismology , subduction , amplitude , slab , scattering , trough (economics) , seismic wave , tectonics , geophysics , physics , optics , macroeconomics , economics
We estimated the S wave attenuation structure in southwestern Japan and the western Nankai Trough by analyzing maximum S wave amplitudes at 4–8, 8–16, and 16–32 Hz with a correction term for apparent amplitude attenuation due to multiple forward scattering. Because the estimated attenuation ( Q −1 ) in our tomographic study was much larger than Q −1 due to wide‐angle scattering, our estimated Q −1 was composed mainly of intrinsic attenuation. High‐attenuation areas ( Q −1 > 1/300 at 4–8 Hz) were imaged beneath Quaternary volcanoes and south off Shikoku. Low (<1/1500 at 4–8 Hz) or moderate Q −1 (1/500–1/1000 at 4–8 Hz) was imaged beneath Shikoku and nonvolcanic areas of Chugoku. High and moderate Q −1 in and around Shikoku are located near the top of subducting Philippine Sea Plate. This correspondence implies that these high and moderate Q −1 reflect fluid in the subducting slab. By applying a theoretical model of attenuation in water‐saturated porous random media, we examined wave‐induced fluid flow induced by lower frequency (<1 Hz) seismic waves that may be related with triggering of nonvolcanic tremor by surface waves. Even though Q −1 structure in this study cannot fully explain the tremor triggering by wave‐induced fluid flow, large uncertainties of Q −1 in tremor zone suggest that high resolution imaging of Q −1 and random inhomogeneities would give some constraints for the spatial variation of permeability and other medium properties.