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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.

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.

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.

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.
Sea Technology | Year: 2012

A submarine cabled observation system can provide wide- band communications and electric power to deep-sea observatories, making it possible to carry out long-term, real-time monitoring with several kinds of sensors. JAMSTEC has been operating a 125-kilometer-long cabled observation system off Cape Muroto since 1997. The system has two ocean-bottom seismometers and two tsunami meter pressure gauges. At the end of the cable, the deep-sea observatory is equipped with a current meter, CTD sensor, TV camera, sub-bottom thermometer and acoustic Doppler current profiler (ADCP). The terrestrial station is powered by a constant current of 437 volts. Tests were carried out to confirm the curing of the resin in cold seawater and check insulation resistance. All equipment and seawater were cooled in a thermostatic chamber at 3° C. The insulator of the submarine cable was removed to simulate electrical fault, and the resistance between seawater and the copper tube in the cable was 0 ohms.

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.

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