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Nishi-Tokyo-shi, Japan

Arndt J.E.,Alfred Wegener Institute for Polar and Marine Research | Schenke H.W.,Alfred Wegener Institute for Polar and Marine Research | Jakobsson M.,University of Stockholm | Nitsche F.O.,Lamont Doherty Earth Observatory | And 12 more authors.
Geophysical Research Letters | Year: 2013

The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60°S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 × 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at http://dx.doi.org/10.1594/PANGAEA.805736. Key Points The first regional bathymetric compilation covering the entire Southern Ocean A new keystone dataset for Antarctic research The southern equivalent to IBCAO is now released ©2013. American Geophysical Union. All Rights Reserved. Source

Nishimura T.,Kyoto University | Sato M.,Japan Coast Guard | Sagiya T.,Nagoya University
Annual Review of Earth and Planetary Sciences | Year: 2014

The global positioning system (GPS) is one of the most powerful tools available for observation of Earth's surface deformation. In particular, coseismic, postseismic, slow transient, and interseismic deformation have all been observed globally by GPS over the past two decades, especially in subduction zones. Moreover, GPS-acoustic techniques have been developed for practical use in the past decade, allowing observation of offshore deformation immediately above slip regions. Here, we describe the application of GPS and GPS-acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around Japan, where geodetic data coverage is particularly dense. The data demonstrate temporally variable strain accumulation in the source region of the 2011 Mw 9.0 Tohoku-oki earthquake, and observation of the huge slip of the Tohoku-oki earthquake near the trench using GPS-acoustic methods has considerably advanced our knowledge of stress release and accumulation in this subduction zone. © 2014 by Annual Reviews. All rights reserved. Source

Watanabe S.-I.,Japan Coast Guard | Ishikawa T.,Japan Coast Guard | Yokota Y.,Japan Coast Guard
Earth, Planets and Space | Year: 2015

Repeatedly performing the GPS-acoustic seafloor positioning, we first succeeded in detecting non-volcanic seafloor movements on the Philippine Sea plate (PHS) subducting along the Sagami Trough. At a seafloor geodetic site on the northernmost part of the PHS off the Boso Peninsula, we detected significant eastward motion with respect to the central part of the PHS. This is unaccountable by the coupling between the Pacific plate and the PHS along the Izu-Bonin (Ogasawara) Trench because it would cause the westward elastic deformation at BOSS. It is rather consistent with the rigid motion of the tectonic block in the fore-arc along the Izu-Bonin Trench, associated with the back-arc rift. The other site on the western side of the Sagami Bay had moved toward the north relative to the Izu Peninsula. It suggests that the Izu microplate obviously moves relative to the northern PHS. The difference between the velocities of the Sagami Bay and the Izu Peninsula indicates the coupling on the boundary fault as well. © 2015 Watanabe et al. Source

Nishizawa A.,Japan Coast Guard | Kaneda K.,Japan Coast Guard | Oikawa M.,Japan Coast Guard
Earth, Planets and Space | Year: 2011

Seismic refraction and reflection measurements were made along three profiles across the Shikoku Basin, one of the three backarc basins on the Philippine Sea plate. The P-wave velocity models show the presence of a very large horizontal irregularity related to the seamounts on the extinct spreading center, transition zones from the Shikoku Basin to Kyushu-Palau Ridge, and from the Shikoku Basin to the Izu-Ogasawara Island arc. However, the other areas were found to have features similar to those of a normal oceanic crustal model composed of oceanic Layer 2 with a high velocity gradient and Layer 3 with a small velocity gradient. The Shikoku backarc basin oceanic crust was found to be characterized by a thinner igneous crust, especially in Layer 3, and the azimuthal anisotropy in the uppermost mantle expected from the seafloor spreading was not detected. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS). Source

Nagano A.,University of Tokyo | Michida Y.,University of Tokyo | Odamaki M.,Japan Coast Guard | Suzuki K.,Japan Coast Guard | Ogata J.,Japan Coast Guard
Polar Science | Year: 2010

Sea-level oscillations induced by Sumatran earthquakes on 26 December 2004 and 28 March 2005 were analyzed using tide gauge data recorded in Lützow-Holm Bay, Antarctica. The oscillations continued for more than 2 days, with principal periods of about 1 and 3 h. The 3-h component was repeatedly excited by the 1-h component, resulting in alternations of the dominant period of oscillation. The dynamical modes of sea-level oscillations were calculated based on topographic data for Lützow-Holm Bay. The predominant periods of the long-lived sea-level oscillations were found to be similar to those of the waves of topographically constrained modes. The alternations in the dominant period of the oscillations may be interpreted as disturbances that were initially localized in a shallow region of the basin and subsequently expanded to the entire basin. © 2010 Elsevier B.V. and NIPR. Source

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