title: Tsunami: ocean dynamo generator.
abstract: Secondary magnetic fields are induced by the flow of electrically conducting seawater through the Earth's primary magnetic field ('ocean dynamo effect'), and hence it has long been speculated that tsunami flows should produce measurable magnetic field perturbations, although the signal-to-noise ratio would be small because of the influence of the solar magnetic fields. Here, we report on the detection of deep-seafloor electromagnetic perturbations of 10-micron-order induced by a tsunami, which propagated through a seafloor electromagnetometer array network. The observed data extracted tsunami characteristics, including the direction and velocity of propagation as well as sea-level change, first to verify the induction theory. Presently, offshore observation systems for the early forecasting of tsunami are based on the sea-level measurement by seafloor pressure gauges. In terms of tsunami forecasting accuracy, the integration of vectored electromagnetic measurements into existing scalar observation systems would represent a substantial improvement in the performance of tsunami early-warning systems.
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Sugioka
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors.forename: Yozo
authors.initials: Y
authors.lastname: Hamano
authors.affiliation: Earthquake Research Institute, University of Tokyo, Tokyo, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Baba
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Kasaya
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Tada
authors.affiliation: Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Suetsugu