Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 119, Issue 8, Pages 6486-6511Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014JB011099
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Funding
- Japan Society for the Promotion of Science [23740329, 25800243]
- Grants-in-Aid for Scientific Research [22340126, 23740329, 25800243, 26109006] Funding Source: KAKEN
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In this study, we imaged a detailed seismic attenuation structure (frequency-independent Q(-1)) beneath Hokkaido, Japan, by merging waveform data from a dense permanent seismic network with those from a very dense temporary network. Corner frequency of each event used for t* estimation was determined by the S coda wave spectral ratio method. The seismic attenuation (Q(p)(-1)) structure is clearly imaged at depths down to about 120 km. For the fore-arc side of Hokkaido, high-Q(p) zones are imaged at depths of 10 to 80 km in the crust and mantle wedge above the Pacific slab. Low-Q(p) zones are clearly imaged in the mantle wedge beneath the back-arc areas of eastern and southern Hokkaido. These low-Q(p) zones, extending from deeper regions, extend to the Moho beneath volcanoes, the locations of which are consistent with those of seismic low-velocity regions. These results suggest that the mantle wedge upwelling flow occurs beneath Hokkaido, except in the area where there is a gap in the volcano chain. In contrast, an inhomogeneous seismic attenuation structure is clearly imaged beneath the Hokkaido corner. A broad low-Q(p) zone is located at depths of 0-60 km to the west of the Hidaka main thrust. The location almost corresponds to that of the seismic low-velocity zone in the collision zone. The fault planes of the 1970 M6.7 and 1982 M7.1 earthquakes are located at the edges of this broad low-Q(p) zone. Observations in this study indicate that our findings contribute to understanding the detailed arc-arc collision process, magmatism, and seismotectonics beneath Hokkaido.
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