Seismic Velocity and Attenuation Structures around Active Volcanoes Beneath Tohoku: Linking Crustal Structure to Low-frequency Earthquakes and S-wave Reflectors (Special Issue: “Possible Effect of Mega Earthquake on Long-term Volcanic Activity” Part 2)
Seismological observations suggest that magmatism in subduction zones occurs as a result of flux melting in the mantle wedge and upward migrations of melt to the continental crust through a mantle upwelling flow. However, the fundamental volcanic processes determining how much melt is distributed in the lower crust and how melt ascends to the surface remain unknown. Seismological structures beneath active volcanoes in Tohoku, together with spatial distributions of low-frequency earthquakes and S-wave reflectors, are reviewed. Beneath each volcano or volcanic cluster, the lower crust shows marked low-velocity, high Vp/Vs, and high-attenuation anomalies, which are interpreted as the existence of partial melt with ~1 vol%. In contrast to the lower crust, the upper crust beneath volcanoes generally shows low-velocity and low-Vp/Vs anomalies. The low Vp/Vs in the upper crust can be attributed to the presence of fluids expelled by the solidification of magmas in the lower crust. Low-frequency earthquakes and S-wave reflectors are mostly distributed, respectively, at the edge of and above the low-velocity and high-attenuation zones in the middle to the lower crust. Seismological observations in Tohoku can provide the most reliable constraint on melt migration path and volcanic processes in the crust.
雑誌名
東京大学地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
92
号
2-4
ページ
49 - 62
発行年
2017
ISSN
00408972
書誌レコードID
AN00162258
著者版フラグ
publisher
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
東北地方の火山周辺の地震波速度・減衰構造 : 地殻構造と低周波地震・S波反射面との関係 (特集:「巨大地震と火山活動」Part 2)
IHO922402.pdf
(8.23MB)
