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Arai K.,Chiba University | Naruse H.,Kyoto University | Miura R.,Nippon Marine Enterprises Ltd. | Kawamura K.,Yamaguchi University | And 7 more authors.
Geology | Year: 2013

We show the first real-time record of a turbidity current associated with a great earthquake, the Mw 9.0, 2011 Tohoku-Oki event offshore Japan. Turbidity current deposits (turbidites) have been used to estimate earthquake recurrence intervals from geologic records. Until now, however, there has been no direct evidence for large-scale earthquakes in subduction plate margins. After the 2011 Tohoku-Oki earthquake and tsunami, an anomalous event on the seafloor consistent with a turbidity current was recorded by ocean-bottom pressure recorders and seismometers deployed offSendai, Japan. Freshly emplaced turbidites were collected from a wide area of seafloor offthe Tohoku coastal region. We analyzed these measurements and sedimentary records to determine conditions of the modern tsunamigenic turbidity current. We anticipate our discovery to be a starting point for more detailed characterization of modern tsunamigenic turbidites, and for the identification of tsunamigenic turbidites in geologic records. © 2013 Geological Society of America.


Kawaguchi Y.,Japan Agency for Marine - Earth Science and Technology | Nishino S.,Japan Agency for Marine - Earth Science and Technology | Inoue J.,Japan Agency for Marine - Earth Science and Technology | Inoue J.,Japan National Institute of Polar Research | And 6 more authors.
Journal of Physical Oceanography | Year: 2016

The Arctic Ocean is known to be quiescent in terms of turbulent kinetic energy (TKE) associated with internal waves. To investigate the current state of TKE in the seasonally ice-free Chukchi Plateau, Arctic Ocean, this study performed a 3-week, fixed-point observation (FPO) using repeated microstructure, hydrographic, and current measurements in September 2014. During the FPO program, the microstructure observation detected noticeable peaks of TKE dissipation rate ε during the transect of an anticyclonic eddy moving across the FPO station. Particularly, ε had a significant elevation in the lower halocline layer, near the critical level, reaching the order of 10-8 W kg-1. The ADCP-measured current displayed energetic near-inertial internal waves (NIWs) propagating via the stratification at the top and bottom of the anticyclone. According to spectral analyses of horizontal velocity, the waves had almost downward energy propagation, and its current amplitude reached ~10 cm s-1. The WKB scaling, incorporating vertical variations of relative vorticity, suggests that increased wave energy near the two pycnoclines was associated with diminishing group velocity at the corresponding depths. The finescale parameterization using observed near-inertial velocity and buoyancy frequency successfully reproduced the characteristics of observed e, supporting that the near-inertial kinetic energy can be effectively dissipated into turbulence near the critical layer. According to a mixed layer slab model, a rapidly moving storm that has passed over in the first week likely delivered the bulk of NIW kinetic energy, eventually captured by the vortex, into the surface water. © 2016 American Meteorological Society.


Asakawa K.,Japan Agency for Marine - Earth Science and Technology | Hyakudome T.,Japan Agency for Marine - Earth Science and Technology | Yoshida M.,Kyocera Corporation | Okubo N.,Kyocera Corporation | And 2 more authors.
IEEE Journal of Oceanic Engineering | Year: 2012

Ceramics have some outstanding features that are necessary for pressure-tight housings, such as higher compressive strength, lower specific gravity, and higher resistance against corrosion. One promising application is pressure-tight housings for a free-fall popup ocean-bottom seismometer (OBS). Ceramic pressure-tight housings can provide sufficient strength and buoyancy even at 11-km water depth. Nevertheless, tensile and bending strengths of ceramics are only a fraction of their compressive strength. For metals, they are almost equal. Therefore, common design methods for pressure-tight housings are not directly applicable to ceramic pressure-tight housings. As described herein, we propose a new design method for ceramic pressure-tight housings, particularly a method of reinforcement of through-holes for underwater connectors. We also present detailed data that support the proposed design method. © 1976-2012 IEEE.


Ishida H.,National Institute of Technology, Toyama College | Yasue Y.,Nippon Marine Enterprises Ltd. | Hachiga T.,National Institute of Technology, Toyama College | Andoh T.,University of Toyama | And 3 more authors.
Optical Review | Year: 2014

We developed a micro multipoint laser Doppler velocimeter (μ-MLDV) for noninvasive in-vivo measurements of blood flow and we presented the results of demonstrations performed on experimental animals. In this paper, we investigate the validity of power spectrum analysis for determining the flow velocity and the minimum power of the semiconductor laser in the μ-MLDV. Although average velocity is generally estimated from a peak position (f peak) in the power spectrum, the power spectrum of blood flow included an additional component in the high-frequency region. The conventional method for determining the average velocity of flows of transparent artificial fluids, which involves determining the average velocity from f peak, is unsuitable for in-vivo measurements of blood flow. The laser power was reduced from 140 to 30mW since 30mW was the minimum power at which images of blood flow velocity in microvessels could be obtained. About 30mW (power density of 15mW/mm2) is the maximum power which can be irradiated to humans. Further reduction in the laser power is necessary before this technique can be applied to humans. © 2014 The Optical Society of Japan.


Baba T.,Japan Agency for Marine - Earth Science and Technology | Matsumoto H.,Japan Agency for Marine - Earth Science and Technology | Kashiwase K.,Japan Agency for Marine - Earth Science and Technology | Hyakudome T.,Japan Agency for Marine - Earth Science and Technology | And 2 more authors.
Submarine Mass Movements and Their Consequences - 5th International Symposium | Year: 2012

A moderate earthquake (Mw 6.4) caused a submarine mass movement in Suruga Bay, Japan on 11th August, 2009. The earthquake was also accompanied by a tsunami, which was observed at various observatories around Suruga Bay. A micro-bathymetric map was obtained from an autonomous underwater vehicle (AUV) survey of Urashima in the area where the submarine mass movement occurred. The Urashima cruised close to the seafloor and collected very high resolution bathymetric data as a raster graphic image with pixels arranged in a 1 m by 1 m square grid. The 3D seafloor image obtained clearly shows an escarpment (450 m wide and 10-15 m deep) approximately 5 km off the coast. Bedforms which were considered to have been formed due to earthquake-induced turbidity currents, spread wide in the survey area. The bedforms appear at about 20-30 m interval, and are lower than 1 m in height. A numerical simulation of the tsunami assuming that the fault motion and submarine mass movement occurred simultaneously provided a better match with the tsunami observation records at Yaizu tidal station and other stations than a simulation based on fault motion alone. © Springer Science+Business Media B.V. 2012.


Yamashita M.,Japan Agency for Marine - Earth Science and Technology | Kasaya T.,Japan Agency for Marine - Earth Science and Technology | Takahashi N.,Japan Agency for Marine - Earth Science and Technology | Takizawa K.,Japan Agency for Marine - Earth Science and Technology | And 2 more authors.
Earth, Planets and Space | Year: 2015

The Bayonnaise Knoll caldera is a conical silicic caldera located on the eastern part of the back-arc rift zone of the Izu-Ogasawara arc. Many geological and geophysical surveys have shown that the Bayonnaise Knoll caldera contains hydrothermal sulfide deposits. The Japan Agency for Marine-Earth Science and Technology conducted high-resolution multi-channel seismic reflection surveys across the Bayonnaise Knoll caldera to ascertain details of the crustal structure, such as the configuration of faults around the caldera. A reflection profile of excellent quality was obtained by high-density velocity analysis at about 150-m intervals. We applied prestack depth migration by using the results of the high-density velocity analysis and further analyzed this region. The depth-migrated profile shows many faults, which correspond to bathymetric lineations, on the eastern side of the Bayonnaise Knoll caldera. The velocity structure of the Bayonnaise Knoll caldera resembles that of the Myojin Knoll caldera, which has been well surveyed and is associated with the hydrothermal deposit. The depth-migrated profile shows a clear reflective zone that is distributed asymmetrically to the Bayonnaise Knoll caldera center. These data suggest that caldera formation was controlled by back-arc rifting activity in the Izu-Ogasawara arc. The hydrothermal fluid migration path in the Bayonnaise Knoll caldera is estimated to be the result of faulting and magmatic intrusion on the eastern side of the structure. It is assumed that these fluids formed the Kuroko-type sulfide deposit in the eastern part of the caldera structure. © 2015 Yamashita et al.; licensee Springer.


Yokobiki T.,Japan Agency for Marine - Earth Science and Technology | Iwase R.,Japan Agency for Marine - Earth Science and Technology | Momma H.,Nippon Marine Enterprises Ltd.
OCEANS'11 - MTS/IEEE Kona, Program Book | Year: 2011

Underwater repair method for insulator of the optical submarine cable has been developed and test samples were successfully repaired in deep-sea field tests. In this paper, the detail of the new repair method, equipment, trial test in a laboratory and the deep-sea field experiments are described. © 2011 MTS.


Patent
Japan Agency for Marine - Earth Science, Technology and Nippon Marine Enterprises Ltd. | Date: 2013-05-21

An underwater observation apparatus includes an observation apparatus body, a weight structure, a coupling device, and a fusion cutting device. The observation apparatus body is configured to house at least a power source, a communication circuit for a communication device, and a signal processing device. The coupling device couples the observation apparatus body with the weight structure via a remote-controlled release structure capable of releasing the observation apparatus body from the weight structure. The underwater observation apparatus also includes a power feeding coil located inside of a glass sphere to generate magnetic flux, and a power receiving coil located outside of the glass sphere. The power receiving coil generates an induced voltage when interlinked by the magnetic flux generated by the power feeding coil. The power receiving coil is configured to supply drive power to the fusion cutting device.


Maeda Y.,Japan Agency for Marine - Earth Science and Technology | Asakawa K.,Japan Agency for Marine - Earth Science and Technology | Obana K.,Japan Agency for Marine - Earth Science and Technology | Terada I.,Nippon Marine Enterprises Ltd.
2013 IEEE International Underwater Technology Symposium, UT 2013 | Year: 2013

We developed a new ocean bottom seismometer (OBS) that can be deployed to the ocean floor to 9,000 m depth. We conducted the first observations using the device. Conducting seismic observations in waters deeper than 6,000 m had been difficult because the maximum applicable depth of conventional ocean bottom seismometers is 6,000 m. The Japan Trench, where the Great East Japan Earthquake occurred, is included in those areas which are difficult to observe. To increase the applicable depth, we used newly developed ceramic pressure-tight spheres for the housing in place of 17-inch glass spheres. Although the rated maximum depth is 11,000 m, its size and the weight are almost equal to those of 17-inch glass spheres. We have also refurbished acoustic transponders, radio beacons, and flashers for application to 9,000 m water depth. We have deployed six Super-deep-sea OBS (SDOBS) in the Japan Trench deeper than 6,000 m, and have succeeded in observations. Herein, we present an outline of the SDOBS. © 2013 IEEE.


Yokobiki T.,Japan Agency for Marine - Earth Science and Technology | Iwase R.,Japan Agency for Marine - Earth Science and Technology | Takahashi Y.,Japan Agency for Marine - Earth Science and Technology | Momma H.,Nippon Marine Enterprises Ltd.
2013 IEEE International Underwater Technology Symposium, UT 2013 | Year: 2013

Underwater repair method for insulator of the optical submarine cable has been developed and test samples were successfully repaired in deep-sea field tests. © 2013 IEEE.

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