title: Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.
abstract: It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Ryuta
authors.initials: R
authors.lastname: Arai
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Takahashi
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kodaira
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kaiho
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Nakanishi
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Gou
authors.initials: G
authors.lastname: Fujie
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ishihara
authors.affiliation: Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan.
authors.forename: Seiichi
authors.initials: S
authors.lastname: Miura
authors.affiliation: Institute of Education, Research and Regional Cooperation for Crisis Management Shikoku, Kagawa University, 1-1 Saiwai-cho, Takamatsu, Kagawa 760-8521, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kaneda