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Yokohama-shi, Japan

Aoyama Y.,Japan National Institute of Polar Research | Doi K.,Japan National Institute of Polar Research | Shibuya K.,Japan National Institute of Polar Research | Ohta H.,51St Japanese Antarctic Research Expedition | And 3 more authors.
Earth, Planets and Space | Year: 2013

The horizontal velocity vector of ice flow on the floating ice tongue of the Shirase Glacier, East Antarctica, was determined using two GPS buoys located on its east and west sides. The GPS buoys consisted of a singlefrequency GPS receiver module and an Iridium satellite communication system. The instantaneous horizontal position of each GPS buoy was automatically obtained every 30 minutes, and the data were immediately transmitted to the National Institute of Polar Research (NIPR), Tokyo, Japan, via a satellite link. The location data demonstrated that the floating ice tongue moved primarily in a linear manner during the monitoring period between February and April, 2010. The speed and azimuth of the eastern buoy were (5.779 ± 0.004 m/day, N1.4°E ± 0.5°), respectively, while for the western buoy the speed and azimuth were (7.005 ± 0.006 m/day, N13.1°W ± 0.6°), respectively. Short-term variations about the mean speed and azimuth of the ice flow, with a period of 3-10 days, were also identified. © The Society of Geomagnetism and Earth Planetary and Space Sciences (SGEPSS) The Seismological Society of Japan The Volcanological Society of Japan The Geodetic Society of Japan The Japanese Society for Planetary Sciences TERRAPUB.

Kazama T.,Kyoto University | Hayakawa H.,Japan National Institute of Polar Research | Higashi T.,TerraGrav LLC | Ohsono S.,GNSS Technologies Inc. | And 8 more authors.
Polar Science | Year: 2013

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2±0.7μgal (1 [μgal]=1×10-8[m/s2]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection. © 2013 Elsevier B.V. and NIPR.

Matsumoto T.,University of Ryukyus | Mori A.,Global Ocean Development Inc. | Kise S.,University of Ryukyus | Abe N.,Japan Agency for Marine - Earth Science and Technology
Geochemical Journal | Year: 2013

The Chile Triple Junction (CTJ), an RTT-type triple junction located at 46° 13' S, 75°48' W off the western coast of Chile, is characterized by the subducting Chile Ridge, which is the constructive plate boundary that generates both the Nazca Plate and the Antarctic Plate. The ridge subduction mechanism and the regional tectonics around the CTJ were investigated primarily using marine geophysical data (topography, gravity, geomagnetic field and single-channel seismics) collected during the SORA2009 cruise (Cruise ID = MR08-06) by R/V MIRAI together with other cruise data from the National Geophysical Data Center. The segment of the ridge axis just before the subduction around the CTJ is associated with an axial deep covered with thick sediment unlike that seen in typical ridge crests. The profiles of both topography and the free air anomaly around the CTJ show quite different patterns from those of ordinary subduction zones. However, topographic features typical of a slow-spreading type ridge, including a median valley and both flanks, remain in the seaward side of the trench. Even after the subduction of the eastern flank, the topographic features of the western flank remain. A slight Outer Rise and an Outer Gravity High, which are common in the western Pacific area, were observed in an area far away from the CTJ on both Nazca and Antarctic plate sides. The geomagnetic anomaly pattern around the Chile Ridge near the CTJ shows that the estimated spreading rate decreases gradually towards the ridge crest. This suggests that volcanic activity diminishes gradually towards the subducting ridge axis. The lithosphere under the Chile Ridge might have amalgamated with the surrounding oceanic lithosphere due to heat loss after the cessation of volcanic activity. The oceanic lithosphere towards the trench also thickens rapidly due to heat loss. Consequently, shallow-angle subduction of the youngest and most immature oceanic plate occurs smoothly via slab-pull force without any resistance along the interface between the South American continental plates. © 2013 by the Geochemical Society of Japan.

Goto S.,Japan National Institute of Advanced Industrial Science and Technology | Mizoguchi T.,System Intech Co. | Kimura R.,Global Ocean Development Inc. | Kinoshita M.,Japan Agency for Marine - Earth Science and Technology | And 2 more authors.
Marine Geophysical Research | Year: 2012

We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1 W/m K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (≥1.0 W/m K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (<0.9 W/m K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9 W/m K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features. © 2012 Springer Science+Business Media B.V.

Nakano I.,Global Ocean Development Inc. | Ishida H.,Kobe University
2013 IEEE International Underwater Technology Symposium, UT 2013 | Year: 2013

In order to measure the velocity of rip current, we have developed an acoustic monitoring system consisting of two transducers and several sound reflectors. The two transducers are connected to a modified two-frequency fish-finder which can alternatively transmit and receive the preset sound signals of 50kHz or 200kHz at an interval of several seconds. Sound reflectors were composed of commercial steel rods. The sea trial of this system was carried out in the Uradome Beach in early September 2012. The transducers were placed at a height of 0.5m over the sea floor at a depth of 1m to 1.5m and horizontally separated at a distance of 30m offshore. Six reflectors were placed at a distance of 15m, 30m, 45m, 60m, 75m and 90m along the shoreline. The sound signal of 50 kHz burst waves were transmitted by one transducer and received by the other, and vice versa. The SNR's of the signals through the direct base line and through reflective paths of the 30m, 45m and 60m reflectors were sufficient for the analysis as expected. The preliminary result suggested to be able to reconstruct a current velocity distribution in the beach based on passive reciprocal sound transmissions. © 2013 IEEE.

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