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91.
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
92.
Yuta Yamanoi Shingo Takeuchi Satoshi Okumura Satoru Nakashima Tadashi Yokoyama 《Journal of Volcanology and Geothermal Research》2008
We measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity (Strombolian activity, Vulcanian explosions and continuous ash venting activity) at Sakurajima volcano from 1974 to 1985. Colors of Strombolian ash samples have larger yellow components of their visible spectra (b? values) than those of explosion and continuous venting ash samples. Colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra (a? and b? values, respectively), while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples. Colors of components with lower densities than 3.1 g/cm3 (groundmass and phenocrystic plagioclase) obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples. This result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass. The particles can be classified into three different types of particles with different vesicularity and crystallinity (vesicular particle [VP], dense particle with vesicles [DPV] and dense particle without vesicles [DP]). Analytical results of component proportions, chemical compositions of groundmass glasses, ferrous iron contents and surface ferric materials show that (1) VP has larger yellow components of the visible spectrum (b? values) and high ferrous iron content, and is less crystallized than the DP and DPV, (2) DP has larger red and yellow components of its visible spectrum (a? and b? values, respectively) and involves ferric materials on the surfaces produced by oxidation process, and (3) DPV has smaller red and yellow components of its visible spectrum (a? and b? values, respectively) and involves less ferric materials on the ash surfaces. Color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of VP, DPV and DP. During the Strombolian activity, the VP is a main component in the ash, which is formed from relatively less degassed and crystallized magma. In the Vulcanian explosion and continuous ash venting activity, the proportions of DPV and DP in ash are larger than that in the Strombolian activity. The highly crystallized DP may correspond to a vent cap, and DPV to a magma below the cap. The color measurements of ash deposits provide information on the pre-eruptive processes at the shallower levels of a conduit. 相似文献
93.
Satoshi Yamamoto 《Mathematical Geology》1993,25(7):867-879
Modern marine sediments can be classified into terrigenous, hemipelagic, and pelagic types according to the distances from the land for the sites recovered and in terms of lithological characteristics of sediments. Ancient cherts are the best sedimentary rocks to reconstruct ancient depositional environments and hemipelagic and pelagic cherts can be identified in terms of lithologic and stratigraphic characteristics. However, geochemical characteristics of modern sediments and ancient cherts can discriminate them into these three types. Particularly, the degree of correlation between Fe and Mg in clay minerals is the most effective criterion for the classification, because the concentration of pelagic clay minerals in which the Fe/Mg ratio is constant may become indices for the classification into the three types. The correlation coefficient and goodness-of-fit to a certain regression line were used as indices of the classification and calculated for several sets of modern sediments and ancient cherts totalling to more than 400 samples. The correlation coefficients and the student-t values for the coefficients become better classification indices than the goodness-of-fit andF-values of the analysis of variance. Goodness-of-fit andF-values can be only used as subsidiary indices for the main classification indices of the correlation coefficients. The classification on the basis of the degree of correlation between Fe and Mg is effective and this approach can be used for other major chemical elements such as Al, K, and Na, if some sequential values of chemical analyses are available. 相似文献
94.
Bernhard Schnetger Yasuyuki Muramatsu Satoshi Yoshida 《Geostandards and Geoanalytical Research》1998,22(2):181-186
Analytical results for iodine in twenty six geological reference materials (RM) are presented. Bromine, fluorine and chlorine were also determined in some samples. Pyrohydrolysis in a heated quartz tube under a wet oxygen flow was used for the separation of the halogens from the matrix and the evolved gas was absorbed in a trap solution. The halogens were measured by ICP-MS and ion chromatography (IC). All four halogens can be collected in the trap solution from one combustion procedure. The analysed samples range in type from igneous rocks to terrestrial and marine sediments. Precision, detection limits, and accuracy are also presented. 相似文献
95.
Satoshi Hinata 《Astrophysics and Space Science》1977,51(2):303-318
The possibility of radio emission is considered within a model which produces the beam-plasma system near the pulsar. A longitudinal instability develops near the light cylinder for a particular choice of parameters adopted in the paper. The excited wave strongly oscillates the beam particles perpendicular to its average velocity on one hand, and forms bunches of them on the other hand. Consequently, coherent radiation is expected. The frequency of the emission falls within the radio band, but the intensity turns out to be too low to explain observations. An appreciable enhancement of the beam number density over the Goldreich-Julian value (n
bB/2ec) is needed if the mechanism discussed in the present paper is responsible for the pulsar radio emission. 相似文献
96.
Hiroshi Kuroda Yutaka Isoda Hidetaka Takeoka Satoshi Honda 《Journal of Oceanography》2006,62(5):731-744
In order to examine seasonal variation in a coastal current and the dynamics of the current, we carried out a mooring current
measurement near the coast on the eastern shelf of Hidaka Bay from December 2002 to July 2003. There seemed to be two current
regimes during the observed period; one a southeastward current from December to March, and the other a northwestward current
after April. Arrested topographic wave dynamics was used to understand along-shore steady momentum balance at the mooring
site. It was found that the friction term was negligible during the former regime, that is, the wind stress term roughly counterbalanced
the pressure gradient term. On the other hand, the contribution of each term to the momentum balance was sensitive to the
resistance coefficient value during the latter regime. A numerical study showed that wind forcing alone could not reproduce
the observed current velocity and momentum balance during the former regime. One possible interpretation of the observed results
is superposition of the arrested topographic waves forced by the along-shore wind stress and downstream extension of the Coastal
Oyashio. Numerical experiments using combined forcing of the wind stress and an inflow associated with the Coastal Oyashio
supported the expected dynamics. 相似文献
97.
Short-Range Prediction Experiments with Operational Data Assimilation System for the Kuroshio South of Japan 总被引:3,自引:3,他引:3
Masafumi Kamachi Tsurane Kuragano Satoshi Sugimoto Kumi Yoshita Toshiyuki Sakurai Toshiya Nakano Norihisa Usui Francesco Uboldi 《Journal of Oceanography》2004,60(2):269-282
The short-range (one month) variability of the Kuroshio path was predicted in 84 experiments (90-day predictions) using a
model in an operational data assimilation system based on data from 1993 to 1999. The predictions started from an initial
condition or members of a set of initial conditions, obtained in a reanalysis experiment. The predictions represent the transition
from straight to meander of the Kuroshio path, and the results have been analyzed according to previously proposed mechanisms
of the transition with eddy propagation and interaction acting as a trigger of the meander and self-sustained oscillation.
The reanalysis shows that the meander evolves due to eddy activity. Simulation (no assimilation) shows no meander state, even
with the same atmospheric forcing as the prediction. It is suggested therefore that the initial condition contains information
on the meander and the system can represent the evolution. Mean (standard deviation) values of the axis error for all 84 cases
are 13, 17, and 20 (10, 10, and 12) km, in 138.5°E, in the 30-, 60-, and 90-day predictions respectively. The observed mean
deviation from seasonal variation is 30 km. The predictive limit of the system is thus about 80 days. The time scale of the
limit depends on which stage in the transition is adopted as the initial condition. The gradual decrease of the amplitude
in a stage from meander to straight paths is also predicted. The predictive limit is about 20 days, which is shorter than
the prediction of the opposite transition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Seasonal variation of the current in the Tsushima Strait deduced from ADCP data of ship-of-opportunity 总被引:1,自引:0,他引:1
The ADCP data obtained in the Tsushima Strait in the period from February 1987 to November 1990 on board twelve patrol vessels and one research vessel belonging to Maritime Safety Agency was analyzed. Total amount of the data is 200,053, but after quality check, we used 158,401 data for the analysis of the current field and its variability in the strait. The seasonal variation of the currents had been believed to be large. However, no direct current observation throughout the season had been made, and the knowledge on the seasonal variation was derived indirectly from the data of the sea level difference across the strait and of the density field given by hydrographic observations. ADCP data indicates that the seasonal variation of the current field is considerably small in all sub-regions. In the relatively strong current region to the west of the Tsushima Island, the northeast current component has maximum value in the early winter season. 相似文献
99.
Sinking particulate matter were obtained from twelve depths using free-drifting sediment trap arrays which were deployed in the upper 2,000 m water column of the Izu Trench, northwest Pacific Ocean. The largest flux of 146 mgC m–2 day–1 was observed at 150 m depth. The flux generally decreased with depth below the maximum, however, minor flux peaks occurred at 1,000 and 1,250 m depth (>30 mgC m–2 day–1). Sinking large particles (>100 µm) were composed of fecal pellets typical of crustaceans, macroscopic aggregates, and planktonic organisms and their fragments. Three major components constituted 19%, 20% and 29%, respectively, of the total carbon flux (averaged from the fluxes at five depths; 50, 100, 150, 1,000 and 2,000 m). Among them, fecal pellet flux and large organism flux were well correlated with the total flux. The close correspondence between the fecal flux and the total carbon flux suggests that the latter is derived from a group of variables including other biogenic matter, among which fecal pellet is one of the leading factors controlling total flux, though the latter is only a minor covariable in quantity. Vertical flux profiles of fecal pellets and their internal constituents revealed some new inputs of feces occurring through the water column. This phenomenon implies that downward transportation of organic material is characterized by feeding and egestion activities of zooplankton, including overlapping processes of sinking and dispersion of large fecal particles and repackaging of dispersed small particles. 相似文献
100.
Importance of feeding on regenerable parts of prey for juvenile stone flounder Platichthys bicoloratus in estuarine habitats 总被引:3,自引:0,他引:3
Takeshi Tomiyama Satoshi Katayama Michio Omori Hitoshi Honda 《Journal of Sea Research》2005,53(4):297-308
Prey availability is one of the most important factors affecting the quality of nursery grounds. Estuaries play an important role as nursery grounds for juvenile stone flounder, but the mechanism behind the consistently high availability of prey has never been examined. This study investigates which prey is mainly selected by juvenile stone flounder (15–55 mm standard length) in the estuary of the Natori River, northern Japan. In a cage experiment, juveniles showed positive selection for the palps of the spionid polychaete Pseudopolydora kempi in March, and for the siphons of the bivalve Nuttallia olivacea in April, May and June in both sandy and muddy-sand habitats. This selective predation showed that sublethal predation on regenerable parts of invertebrates is important for stone flounder. Nuttallia olivacea, the dominant bivalve in the estuary, was more abundant and in better somatic condition in the sandy area in spite of the stronger siphon-cropping pressure by juvenile stone flounder. These results confirm that sublethal predation on highly abundant benthos plays an important role in forming estuarine habitats into areas of high prey availability for juvenile stone flounder, which leads to their high growth rate. 相似文献