Earthquake Nucleation on Faults with a Revised Rate- and State-Dependent Friction Law     

Nobuki Kame  Satoshi Fujita  Masao Nakatani  Tetsuya Kusakabe 《Pure and Applied Geophysics》2015,172(8):2237-2246

Recently Nagata et al. (J Geophys Res 117:B02314, 2012) have proposed a new version of rate- and state-dependent friction law (RSF) that seems to have eventually resolved all the previously known discrepancies in the existing RSFs from laboratory observations. The values of a and b, empirical RSF parameters determined by fitting the same laboratory experiments, have been revised to be five times greater and a newly noticed weakening effect by shear stress with a coefficient c has been introduced. By using this revised RSF, we reinvestigated a problem of 2D quasi-static nucleation on faults. A crack-like nucleation-zone expansion known for the ‘aging’ version of RSF is not sustainable with the ‘Nagata’ law, which is understandable as the Nagata law does not produce a slip-weakening distance proportional to the involved strength reduction, an aging law’s feature that contradicts laboratory observations. The later stage of Nagata-law nucleation shows localization of quasi-static slip within a limited spatial extent, but the localization is much milder than that predicted by the ‘slip’ version of RSF. With an appropriate c parameter of the Nagata law, the nucleation size seems to be reduced only by a factor from that of the aging law.  相似文献   

Simulation of tides in hydrocarbon lakes on Saturn’s moon Titan   总被引：1，自引：1，他引：0  

Tetsuya Tokano 《Ocean Dynamics》2010,60(4):803-817

Numerous hydrocarbon lakes have recently been detected on Saturn’s largest moon Titan, representing the only known large bodies of liquids on a planetary surface outside the Earth. In the context of comparative oceanography, tides and tidal currents in two representative lakes on Titan (Kraken Mare and Ontario Lacus) are simulated by a three-dimensional baroclinic ocean circulation model. Since the tide-generating force on Titan is an order of magnitude larger than on Earth and the gravitational acceleration is small, tides and currents are substantially larger than in Earth’s lakes and are more comparable with those in Earth’s oceans. The predicted maximum tidal range in Kraken Mare is 4 m. The tidal wave propagates around the basin of Kraken Mare, while a nearly standing tidal wave is excited in Ontario Lacus. Titan’s rotation is too slow to affect the tidal flow in any Titan’s lake. The tidal current velocity in Kraken Mare amounts to a few centimeters per second except in the vicinity of a narrow strait, where it is enhanced by an order of magnitude. In summer, when the lake is stratified, internal tides can develop. Seiches cannot be caused by tide. In the largest lakes, atmospheric tide may cause additional lake surface displacements.  相似文献   

Provenance identification based on EPMA analyses of heavy minerals: Case study of the Toki Sand and Gravel Formation,central Japan     

Mayuko Shimizu  Naomi Sano  Tadamasa Ueki  Tetsuya Komatsu  Ken‐ichi Yasue  Masakazu Niwa 《Island Arc》2019,28(2)

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Recent and historical tsunami deposits from Lake Tokotan,eastern Hokkaido,Japan, inferred from nondestructive,grain size,and radioactive cesium analyses     

Shinozaki  Tetsuya  Sawai  Yuki  Ito  Kazumi  Hara  Junko  Matsumoto  Dan  Tanigawa  Koichiro  Pilarczyk  Jessica E. 《Natural Hazards》2020,103(1):713-730

Geological evidence of recent tsunamis from sediment samples collected from Lake Tokotan, a coastal lagoon in eastern Hokkaido, northern Japan, was detected using computed tomography (CT) and soft X-ray images, grain size, and radionuclide profiles. Initial field observations revealed that sediments had no discernable sedimentary structures at the top of the core. However, results of CT imaging, soft X-ray, and grain size analyses show evidence for three invisible sand layers that are intercalated with mud layers. These sand layers exhibit trends of landward fining and thinning. Furthermore, the distribution of sand layers was limited to the center and seaward parts of the lake. Vertical profiles of cesium and lead concentrations in combination with recent eyewitness accounts indicated that these sand layers are correlated with the 1973 Nemuro-oki, 1960 Chilean, and 1952 Tokachi-oki tsunami events. The deeper part of the sediment cores includes three volcanic ash layers and three prehistoric coarse sand layers. The prehistoric layers are correlated with unusually large tsunamis that were geologically identified in previous studies from eastern Hokkaido. These findings suggest that nondestructive techniques, in combination with radionuclide analysis, allow for detection of frequent but faint tsunami deposits. This technique allows for an improved understanding of the history of tsunami inundation in Lake Tokotan and of other locations for which stratigraphic evidence for faint tsunamis layers is not readily apparent from field assessments.

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Separation of Heavy Lanthanoids by Flash Column Chromatography for Precise Determination of Er and Yb Isotope Compositions in Rock Samples     

Tetsuya Yokoyama  Ryota Fukai  Masaki Nakahara 《Geostandards and Geoanalytical Research》2020,44(2):265-285

We present a new column chemistry technique for the quantitative separation of heavy lanthanoids by an ultra‐fine‐grained LN resin (20–50 µm) with a specific emphasis on the purification of Er and Yb for their isotopic analysis. To achieve the quantitative separation of Er and Yb within a reasonable timescale, flash column chromatography was applied, where the column was attached to a newly designed vacuum box system, thus accelerating the elution speed by ten times compared with that of the normal column procedure operated by gravity flow. The recovery yields of Er and Yb were confirmed to be approximately 100%, which is important to suppress the effect of the mass‐independent fractionation of the Er and Yb isotopes during chromatography. Additionally, we have developed precise Er and Yb isotope measurements by thermal ionisation mass spectrometry (TIMS) using multistatic and/or dynamic methods. Moreover, in most cases, the Er and Yb isotope compositions of the measured four terrestrial rock samples were indistinguishable from those of the commercially available Er and Yb Alfa Aesar solutions. The new method presented in this work will be useful for future studies on heavy lanthanoids in various geological materials.  相似文献   

Preface     

Roussos Dimitrakopoulos  Richard B. McCammon  Tetsuya Shoji 《Mathematical Geology》1994,26(8):877-878

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Spatial relations between preflares and flares     

František Fárník  Hugh Hudson  Tetsuya Watanabe 《Solar physics》1996,165(1):169-179

We have conducted an initial search for discrete preflare brightenings as observed in soft X-radiation by Yohkoh. The Yohkoh images allow us to identify, to within a few arc seconds, the location of a preflare event relative to the succeeding flare. Our initial motivation in this study was to search for early coronal brightenings leading to flare effects, as had been suggested by earlier studies; thus we concentrated on Yohkoh limb events. We find no evidence for such early coronal brightenings. Between 15% and 41% of the 131 suitable events matched our criteria for preflare brightening: the same active region; brightening within one hour of the flare peak; preflare brightness less than 30% of the flare peak. In the great majority of the preflare cases, we found that physically separate nearby structures brightened initially. Often these structures appeared to share a common footpoint location with the flare brightening itself. In a few cases the preflare could have occurred in exactly the same structure as the flare.  相似文献   

Effects of the introduction of rice on evapotranspiration in seasonal wetlands          下载免费PDF全文

Tetsuji Suzuki  Takeshi Ohta  Tetsuya Hiyama  Yasuhiro Izumi  Osmund Mwandemele  Morio Iijima 《水文研究》2014,28(17):4780-4794

Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice‐cropping on evapotranspiration in seasonal wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime^?1) and NVF (1.8 mm daytime^?1) were greater than that in UF (1.0 mm daytime^?1). RF and NVF showed a slight difference in seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non‐vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Upwelling of oxygen-depleted water (Sumishio) in Omura Bay,Japan     

Tetsuya Takahashi  Hideaki Nakata  Keiji Hirano  Kazumi Matsuoka  Mitsunori Iwataki  Hitoshi Yamaguchi  Tomoyuki Kasuya 《Journal of Oceanography》2009,65(1):113-120

Wind-induced circulation and the distribution of hypoxia corresponding to the upwelling of oxygen-depleted water (called “Aoshio” in Japan and “Sumishio” locally in Omura Bay) in Omura Bay, Japan, was examined field observations and by three-dimensional modeling. During the calm weather in summer, well-mixed strait water, in rich oxygen at the mouth of the bay intruded into the middle layer of the bay, southward and northward along the west and east coast, respectively, forming basin-scale cyclonic circulation. A stagnant water mass was formed below the center of this cyclonic circulation, and it became hypoxic water. As a result of the prevailing strong southeast (northeast) wind, the bottom hypoxia moved in a southeasterly (northeasterly) direction. This induces the upwelling of hypoxic water, accompanied by mass mortality of marine organisms.  相似文献   

Contamination level of mercury in red meat products from cetaceans available from South Korea markets     

Endo T  Yong-Un M  Baker CS  Funahashi N  Lavery S  Dalebout ML  Lukoschek V  Haraguchi K 《Marine pollution bulletin》2007,54(6):669-677

Levels of total mercury (T-Hg) were surveyed in red meat (n=73) and liver (n=3) from toothed whales, dolphins and porpoises (odontocetes) sold for human consumption in the coastal cities of South Korea. High concentrations of T-Hg were found in the liver products of finless porpoises (18.7 and 156 microg/wet g) and common dolphins (13.2 microg/wet g). The T-Hg concentrations in red meat products were highest in the false killer whale (9.66+/-12.3 microg/wet g, n=9), bottlenose dolphin (10.6+/-12.6 microg/wet g, n=3) and killer whale (13.3 microg/wet g, n=1), and lowest in Cuvier's beaked whale and the harbour porpoise (0.4-0.5 microg/wet g). Thus, most of the products that originated from odontocetes exceeded the safety limit of 0.5 microg/wet g for T-Hg set by the South Korean health authorities for the fishery industry. Pregnant women and other vulnerable sectors of the population living in South Korea should therefore limit their consumption of odontocete products.  相似文献