A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan   总被引：1，自引：0，他引：1  

Shuzo Takemoto  Akito Araya  Junpei Akamatsu  Wataru Morii  Hideo Momose  Masatake Ohashi  Ichiro Kawasaki  Toshihiro Higashi  Yoichi Fukuda  Shinji Miyoki  Takashi Uchiyama  Daisuke Tatsumi  Hideo Hanada  Isao Naito  Souichi Telada  Nobuo Ichikawa  Kensuke Onoue  Yasuo Wada 《Journal of Geodynamics》2004,38(3-5):477

We have installed a laser strainmeter system in a deep tunnel about 1,000 m below the ground surface at Kamioka, Gifu, Japan. The system consists of three types of independent interferometers: (1) an EW linear strainmeter of the Michelson type with unequal arms, (2) an NS-EW differential strainmeter of the Michelson type with equal arms and (3) a NS absolute strainmeter of the Fabry–Perot type. These are configured in L-shaped vacuum pipes, each of which has a length of 100 m. (1) and (2) are highly sensitive (order of 10⁻¹³ strain) and have wide dynamical range (10⁻¹³–10⁻⁶). Observations with strainmeters (1) and (2) started on June 11, 2003. (3) is a new device for absolute-length measurements of the order of 10⁻⁹ of a long-baseline (100 m) Fabry–Perot cavity by the use of phase-modulated light. This third strainmeter will be ready for operation before the end of 2004. The laser source of strainmeters (1) and (2) is a frequency-doubled YAG laser with a wavelength of 532 nm. The laser frequency is locked onto an iodine absorption line and a stability of 2 × 10⁻¹³ is attained. The light paths of the laser strainmeter system are enclosed in SUS304 stainless steel pipes. The inside pressure is kept to be 10⁻⁴ Pa. Consequently, quantitative measurement of crustal strains of the order of 10⁻¹³ can be attained by employing the laser strainmeter system of (1) and (2) at Kamioka. This resolving power corresponds to that of a superconducting gravimeter. Using the laser strainmeter system, we expect to determine parameters related to fluid core resonance, core modes and core undertone as well as other geodynamic signals such as slow strain changes caused by silent earthquakes or slow earthquakes.  相似文献   

Counter-clockwise rotation of the eastern part of the Mongolia block: Early Cretaceous palaeomagnetic results from Bikin, Far Eastern Russia     

Yo-ichiro Otofuji  Daisuke Miura  Koichi Takaba  Kazuhiro Takemoto  Kazutoshi Narumoto  Haider Zaman  Hiroo Inokuchi  Ruslan G. Kulinich  Petr S. Zimin  Vladimir G. Sakhno 《Geophysical Journal International》2006,164(1):15-24

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Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation   总被引：3，自引：5，他引：3  

Masafumi Kamachi  Tsurane Kuragano  Hiroshi Ichikawa  Hirohiko Nakamura  Ayako Nishina  Atsuhiko Isobe  Daisuke Ambe  Masazumi Arai  Noriaki Gohda  Satoshi Sugimoto  Kumi Yoshita  Toshiyuki Sakurai  Francesco Uboldi 《Journal of Oceanography》2004,60(2):303-312

We describe an operational ocean data assimilation system for the Kuroshio and its validation using a nine-year reanalysis (historical run from 1993 to 2001) dataset of upper-ocean state estimation in the North Pacific. The horizontal structure of volume transport of the Ryukyu Current System (RCS) is shown from the reanalysis: The RCS is connected to the flow of the subtropical gyre, and its volume transport gradually increases from south-east of Okinawa (5–10 Sv) to the east of Amami-Ohshima Island (20 Sv). Comparing the reanalysis with independent observations on the southeast slope of the Amami-Ohshima Island indicates that the root mean square differences (RMSDs) are 0.076 (0.037) m/s in the period of December 1998 to November 1999 (November 1999 to November 2000) respectively. The reanalysis field has a bias (3.1 Sv) of the volume transport of the RCS and the RMSD (3.5 Sv) which is larger than the observed variability (2.81 Sv). Surface velocity and the Kuroshio axis south of Japan are also examined. Comparison of the reanalysis and ADCP data gave maximum RMSD of 0.749 (0.271) m/s in the strong (weak) current regions, respectively. The annual mean value of the axis error is 19 km in 1998. The RMSD of the error is at most 50 km, in 294 cases in the observation period, which is smaller than the observed root mean square variability of the axis (64 km). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Could tsunami risk be underestimated using core‐based reconstructions? Lessons from ground penetrating radar          下载免费PDF全文

Hiraku Takeda  Kazuhisa Goto  James Goff  Hideaki Matsumoto  Daisuke Sugawara 《地球表面变化过程与地形》2018,43(4):808-816

Where should we take cores for palaeotsunami research? It is generally considered that local depressions with low energy environments such as wetlands are one of the best places. However, it is also recognized that the presence or absence of palaeotsunami deposits (and their relative thickness) is highly dependent upon subsoil microtopography. In the beach ridge system of Ishinomaki Plain, Japan, several palaeotsunami deposits linked to past Japan Trench earthquakes have been reported. However, the number of palaeotsunami deposits reported at individual sites varies considerably. This study used ground penetrating radar (GPR) combined with geological evidence to better understand the relationship between palaeotopography and palaeotsunami deposit characteristics. The subsurface topography of the ~3000–4000 bp beach ridge was reconstructed using GPR data coupled with core surveys of the underlying sediments. We noted that the number (and thickness) of the palaeotsunami deposits inferred from the cores was controlled by the palaeotopography. Namely, a larger number of events and thicker palaeotsunami deposits were observed in depressions in the subsurface microtopography. We noted a total of three palaeotsunami deposits dated to between 1700 and 3000 cal bp , but they were only observed together in 11% of the core sites. This result is important for tsunami risk assessments that use the sedimentary evidence of past events because we may well be underestimating the number of tsunamis that have occurred. We suggest that GPR is an efficient and invaluable tool to help researchers identify the most appropriate places to carry out geological fieldwork in order to provide a more comprehensive understanding of past tsunami activity. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Cosmic‐ray exposure age and heliocentric distance of the parent body of the Rumuruti chondrite PRE 95410     

Tomoya Obase  Daisuke Nakashima  Tomoki Nakamura  Keisuke Nagao 《Meteoritics & planetary science》2020,55(5):1031-1047

We measured concentrations and isotopic ratios of noble gases in the Rumuruti (R) chondrite Mount Prestrud (PRE) 95410, a regolith breccia exhibiting dark/light structures. The meteorite contains solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated a heliocentric distance of its parent body, a cosmic‐ray exposure age on the parent body regolith (parent body exposure age), and a cosmic‐ray exposure age in interplanetary space (space exposure age) of the meteorite. Assuming a constant solar wind flux, the estimated heliocentric distance was smaller than 1.4 ± 0.3 au, suggesting inward migration from the asteroid belt regions where the parent body formed. The largest known Mars Trojan 5261 Eureka is a potential parent body of PRE 95410. Alternatively, it is possible that the solar wind flux at the time of the parent body exposure was higher by a factor of 2–3 compared to the lunar regolith exposure. In this case, the estimated heliocentric distance is within the asteroid belt region. The parent body exposure age is longer than 19.1 Ma. This result indicates frequent impact events on the parent body like that recorded for other solar‐gas‐rich meteorites. Assuming single‐stage exposure after an ejection event from the parent body, the space exposure age is 11.0 ± 1.1 Ma, which is close to the peak of ~10 Ma in the exposure age distribution for the solar‐gas‐free R chondrites.  相似文献   

Basin-scale distribution of NH<Subscript>4</Subscript><Superscript>+</Superscript> and NO<Subscript>2</Subscript><Superscript>−</Superscript> in the Pacific Ocean     

Sayaka Yasunaka  Yukihiro Nojiri  Taketo Hashioka  Chisato Yoshikawa  Taketoshi Kodama  Shin-ichiro Nakaoka  Sanae Chiba  Fuminori Hashihama  Masahide Wakita  Ken Furuya  Daisuke Sasano  Akihiko Murata  Hiroshi Uchida  Michio Aoyama 《Journal of Oceanography》2018,74(1):1-11

We used more than 25,000 nutrient samples to elucidate for the first time basin-scale distributions and seasonal changes of surface ammonium (NH₄ ⁺) and nitrite (NO₂ ^?) concentrations in the Pacific Ocean. The highest NH₄ ⁺, NO₂ ^?, and nitrate (NO₃ ^?) concentrations were observed north of 40°N, in the coastal upwelling region off the coast of Mexico, and in the Tasman Sea. NH₄ ⁺ concentrations were elevated during May–October in the western subarctic North Pacific, May–December in the eastern subarctic North Pacific, and June–September in the subtropical South Pacific. NO₂ ^? concentrations were highest in winter in both hemispheres. The seasonal cycle of NH₄ ⁺ was synchronous with NO₂ ^?, NO₃ ^?, and satellite chlorophyll a concentrations in the western subtropical South Pacific, whereas it was synchronous with chlorophyll-a but out of phase with NO₂ ^? and NO₃ ^? in the subarctic regions.  相似文献   

A multiphase model for the intracluster medium     

Daisuke Nagai  Martin E. Sulkanen  August E. Evrard 《Monthly notices of the Royal Astronomical Society》2000,316(1):120-128

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Movement of the Kuroshio axis to the northeast shelf of Taiwan during typhoon events     

Akihiko Morimoto  Shoichiro Kojima  Sen Jan  Daisuke Takahashi 《Estuarine, Coastal and Shelf Science》2009

We investigated the movement of the Kuroshio axis on the northeast shelf of Taiwan associated with the passage of typhoons, using sea surface current data observed by the ocean radar system on Yonaguni and Ishigaki islands. First, we examined daily Kuroshio axis variation on the northeast shelf of Taiwan during typhoon events. The ocean radar data showed that the Kuroshio axis moved onto the shelf after passages of typhoons. The Kuroshio moved onto the shelf and stayed there after the passage of Typhoon Hai-Tang; while the Kuroshio maintained this pattern, southerly wind blew continuously for 4 days. The mean current speed northeast of Taiwan after the typhoon's passage increased by 18 cm s⁻¹. In addition, the sea level difference between two satellite altimetry tracks east of Taiwan increased by 14.4 cm. These results suggest that coastal upwelling east of Taiwan caused by the southerly wind generated an east–west sea level difference that, in turn, generated a northward geostrophic current. This current could have enhanced the Kuroshio east of Taiwan, and pushed it onto the shelf.  相似文献   

Enrichment of alkanes within a phytoplankton bloom during an in situ iron enrichment experiment in the western subarctic Pacific     

Sohiko Kameyama  Urumu Tsunogai  Fumiko Nakagawa  Motoki Sasakawa  Daisuke D. Komatsu  Akira Ijiri  Junko Yamaguchi  Takeo Horiguchi  Hiroshi Kawamura  Aika Yamaguchi  Atsushi Tsuda 《Marine Chemistry》2009,115(1-2):92-101

During the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study ΙΙ (SEEDS-II), we monitored variations in the concentrations of non-methane hydrocarbons (NMHCs), CH₃Cl, N₂O, and CH₄ within a phytoplankton bloom. Stable isotopic compositions were also determined to evaluate the sources of the variations. Although there was little variation in either the concentrations or the stable isotopic compositions of alkenes, CH₃Cl, N₂O, and CH₄ during the 23-day observation period, alkane concentrations increased substantially as the phytoplankton bloomed. The column-integrated quantities of alkanes increased to 3 times pre-bloom levels for C₂H₆, 5 times for C₃H₈, and 20 times for n-C₄H₁₀. The δ¹³C values of both C₂H₆ and C₃H₈ remained almost constant while concentrations increased, whereas that of n-C₄H₁₀ increased by about 12‰. To evaluate the sources of the alkanes produced during the bloom, we compared their δ¹³C values with those of alkanes produced in axenic phytoplankton cultures in our laboratory. We concluded that during the SEEDS-ΙΙ experiment the major portions of C₂H₆ and C₃H₈ were produced during the autolysis of diatoms cells, whereas n-C₄H₁₀ was produced during autolysis of other phytoplankton cells such as cryptophytes and dinoflagellates.  相似文献   

Surface current structure of the Tsushima Warm Current region in the Japan Sea derived by satellite-tracked surface drifters     

Tatsuro Watanabe  Daisuke Simizu  Kou Nishiuchi  Toru Hasegawa  Osamu Katoh 《Journal of Oceanography》2009,65(6):791-801

We examined the surface current structure in the Tsushima Warm Current (TWC) region of the Japan Sea based on a dataset from satellite-tracked surface drifters, including our new deployments during 2004–2008. The gridded mean current velocity and mean kinetic energy (KE) fields calculated from all available drifter data revealed the structure and seasonality of the three branches of the TWC. By comparing the eddy kinetic energy (EKE) field to the KE field, we found four regions where the ratio of EKE to KE was high. In particular, this ratio became extremely high east of the Oki Islands located between the first branch of the TWC (FBTWC) and the second branch of the TWC (SBTWC). Our analysis suggests that the generation of alternate warm and cold eddies east of the Oki Island induced this high ratio. The occurrence of a warm or cold eddy was related to the route—either nearshore or offshore—of the SBTWC. When the offshore route of the SBTWC became dominant, a warm eddy was frequently generated east of the Oki Islands. In contrast, when the nearshore route of the SBTWC became dominant, a cold eddy was more likely to be generated.  相似文献