2013 Fiscal Year Final Research Report

A new model for seismotectonics beneath Kanto, Japan: Tectonic implications for role of serpentinized mantle

Research Project

Project/Area Number	24740300
Research Category	Grant-in-Aid for Young Scientists (B)
Allocation Type	Multi-year Fund
Research Field	Solid earth and planetary physics
Research Institution	Tohoku University
Principal Investigator	NAKAJIMA Junichi 東北大学, 理学(系)研究科(研究院), 准教授 (30361067)
Project Period (FY)	2012-04-01 – 2014-03-31
Keywords	地震波減衰 / フィリピン海プレート / マグマ活動 / 流体
Research Abstract	I developed an inversion technique to estimate attenuation term, site responses, and source parameters, and applied the method to waveform data recorded at Tohoku and Kanto. The results show that an inclined high-attenuation zone is clearly imaged in the mantle wedge of Tohoku and it probably represents a mantle upwelling flow associated with arc magmatism. The lower crust shows high attenuation only beneath volcanic clusters, suggesting that magmatic fluids are concentrated beneath volcanoes. For Kanto, I imaged a prominent high-attenuation region in the mantle of the subducting Philippine Sea slab beneath eastern Kanto, where serpentinization of the mantle has been proposed on the basis of the distribution of low-velocity anomalies. Two historical M~7 earthquakes occurred along the western boundary of the serpentinized mantle, suggesting that intraslab earthquakes likely occur associated with the structural heterogeneity in the subducting slab.