title: Helium anomalies suggest a fluid pathway from mantle to trench during the 2011 Tohoku-Oki earthquake.
abstract: Geophysical evidence suggests that fluids along fault planes have an important role in generating earthquakes; however, the nature of these fluids has not been well defined. The 2011 magnitude 9.0 Tohoku-Oki earthquake ruptured the interface between the subducting Pacific plate and the overlying Okhotsk plate. Here we report a sharp increase in mantle-derived helium in bottom seawater near the rupture zone 1 month after the earthquake. The timing and location indicate that fluids were released from the mantle on the seafloor along the plate interface. The movement of the fluids was rapid, with a velocity of ~4 km per day and an uncertainty factor of four. This rate is much faster than what would be expected from pressure-gradient propagation, suggesting that over-pressurized fluid is discharged along the plate interface.
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa-noha, Chiba 277-8564, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sano
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa-noha, Chiba 277-8564, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hara
authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa-noha, Chiba 277-8564, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Takahata
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kawagucci
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Makio
authors.initials: M
authors.lastname: Honda
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan.
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Nishio
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Nankoku, Kochi 783-8502, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Tanikawa
authors.affiliation: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Hasegawa
authors.affiliation: Department of Earth Sciences, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: Keiko
authors.initials: K
authors.lastname: Hattori