The ultra-low-frequency magnetic disturbances associated with earthquakes          下载免费PDF全文

Masashi Hayakawa  Yasuhide Hobara  Kenji Ohta  Katsumi Hattori 《地震科学（英文版）》2011,24(6):523-534

The ultra-low-frequency (ULF) electromagnetic emission is recently recognized as one of the most promising candidates for short-term earthquake (EQ) prediction. This paper reviews previous convincing evidence on the presence of ULF emissions before three major EQs. Then, we present further statistical study on the ULF occurrence, our networks of ULF monitoring in different spatial scales in Japan and finally we present several signal processings to identify the seismogenic emissions by showing latest results for recent large EQs.  相似文献   

Production and transport of long-chain alkenones and alkyl alkenoates in a sea water column in the northwestern Pacific off central Japan     

Ken Sawada  Nobuhiko Handa  Takeshi Nakatsuka 《Marine Chemistry》1998,59(3-4)

Sinking particles collected from year-long time-series sediment traps at 1674, 4180, 5687 and 8688 m depths, the underlying bottom sediment at 9200 m depth, and suspended particles from surface and subsurface waters in the northwestern North Pacific off Japan were analyzed for long-chain alkenones and alkyl alkenoates (A&A) which are derived mainly from Gephyrocapsacean algae, especially Emiliania huxleyi and Gephyrocapsa oceanica. Alkenone temperature records in sediment trap samples at 1674 m were almost similar to observed sea surface temperatures (SST) with a time delay of one half to one full month. However, alkenone temperatures in trap samples were about slightly lower than measured SST in late spring to early fall. The lowering might be caused by formation of the seasonal thermocline. Nevertheless, these temperature drops observed in trap samples were smaller than those actually observed in a subsurface layer off central Japan. Vertical profiles of A&A concentrations and alkenone temperatures in suspended particles collected from the subsurface waters in early fall indicated that these compounds were produced mostly in a surface mixed layer above the depth of the chlorophyll maximum even in warm seasons. These results suggested that alkenone temperatures strongly reflected SST rather than the temperatures of thermocline waters in these study areas even in such a warm season. Pronounced maxima in A&A fluxes found in sediment trap samples at 1674 m in late spring to summer showed that A&A productions were highest during the periods of spring bloom, according to a time delay between alkenone temperatures and observed SST. Seasonal patterns of alkenone records in trap samples at 4180 and 5687 m could also preserve SST signals well, suggesting that A&A in deep sea waters were mainly derived from primary products in the surface layer. A&A fluxes tended to decrease with water depth, and the ratios of A&A to particulate organic carbon (POC) rapidly decreased in underlying bottom sediment. This clearly indicates that A&A were decomposed and diluted by other refractory organic materials in either the water column or the sediment–water interface. However, A&A compositions were consistently uniform between the trap samples and the underlying bottom sediments, so that A&A could not qualitatively alter during early diagenetic processes.  相似文献   

    

Takeshi Arakaki  Alfonso Mucci 《Aquatic Geochemistry》1999,5(2):225

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Characteristics of crustal structures in the Yamato Basin,sea of Japan,deduced from seismic explorations     

Takeshi Sato  Tetsuo No  Shuichi Kodaira 《Island Arc》2023,32(1):e12474

Crustal structures around the Yamato Basin in the southeastern Sea of Japan, inferred from recent ocean bottom seismography (OBS) and active-source seismological studies, are reviewed to elucidate various stages of crustal modification involved from rifting in the crust of the surrounding continental arc to the production of oceanic crust in the Yamato Basin of the back-arc basin. The northern, central, and southern areas of the Yamato Basin have crustal thicknesses of approximately 12–16 km, and lowermost crusts with P-wave velocities greater than 7.2 km/s. Very few units have P-wave velocities in the range 5.4–6.0 km/s, which corresponds to the continental upper crust. These findings, combined with previous geochemical analysis of basalt samples, are interpreted to indicate that a thick oceanic crust has been formed in these areas of the basin, and that this oceanic crust has been underplated by mantle-derived magma. In the central Yamato Basin, the original continental crust has been fully breached and oceanic crust has been formed. Conversely, the presence of a unit corresponding to the continental upper crust and the absence of a high-velocity part in the lower crust implies that the southwestern edge of the Yamato Basin has a rifted crust without significant intrusion. The Oki Trough has a crust that is 17–19 km thick with a high-velocity lower crust and a unit corresponding to the continental upper crust. The formation of the Oki Trough resulted from rifting with magmatic intrusion and/or underplating. We interpret these variations in the crustal characteristics of the Yamato Basin area as reflecting various instances of crustal modification by thinning and magmatic intrusion due to back-arc extension, resulting in the production of a thick oceanic crust in the basin.  相似文献   

Mid- and far-infrared extinction coefficients of hydrous silicate minerals     

Chiyoe Koike  Hiroichi Hasegawa  Takeshi Hattori 《Astrophysics and Space Science》1982,88(1):89-98

Extinction coefficients were measured for three kind of hydrous silicate minerals, montmorillonite, chlorite and serpentine, from 7 to 140 m. The infrared extinction coefficients of these minerals show (1) a few broad bands in the mid-infrared region and (2) a less steep wavelength-dependence in the far-infrared region, in contrast to those of high-temperature magnesium silicates. In the far-infrared region, montmorillonite shows a ^–0.8±0.1 dependence (, the wavelength) without any band structure, chlorite has a double maxima structure around 80 m, and serpentine shows a rather steep dependence with a small peak at 77 m.The changes of mid-infrared spectra by heating were measured. Change in chlorite spectrum is the most significant. Many fine features appear by heating and then they disappear. Above 900°C one broad feature remains around 10 m. Fine features of the montmorillonite spectrum disappear by heating. For serpentine, many new peaks appear and the spectrum resembles the spectrum of olivin. In near-infrared a band around 2.72 m disappears by heating.Extinction coefficients at very low temperatures were measured in the far-infrared region. For montmorillonite and serpentine, the spectrum is the same as that at room temperature. The double peaks of chlorite around 80 m become higher.  相似文献   

Phase equilibria and the pressure-temperature path of the highest-grade Ryoke metamorphic rocks in the Yanai district, SW Japan     

Takeshi Ikeda 《Contributions to Mineralogy and Petrology》1998,132(4):321-335

The garnet-cordierite zone, the highest-grade zone of the Ryoke metamorphic rocks in the Yanai district, SW Japan, is defined by the coexistence of garnet and cordierite in pelitic rocks. Three assemblages in this zone are studied in detail, i.e. spinel + cordierite + biotite, garnet + cordierite + biotite and garnet + biotite, all of which contain quartz, K-feldspar and plagioclase. The Mg/(Fe + Mg) in the coexisting minerals decreases in the following order: cordierite, biotite, garnet and spinel. Two facts described below are inconsistent with the paragenetic relation in the K₂OFeOMgOAl₂O₃SiO₂H₂O (KFMASH) system in terms of an isophysical variation. First, garnet and biotite in the last assemblage have Mg/(Fe + Mg) higher than those in the second. Second, the first two assemblages are described by the reaction, while they occur in a single outcrop. The addition of MnO, ZnO and TiO₂ to the system can resolve the inconsistencies as follows. The assemblage garnet + biotite can consist of garnet and biotite higher in Mg/(Fe + Mg) than those in garnet + cordierite + biotite as long as they are enriched in spessartine and depleted in Al, respectively. The assemblage garnet + cordierite + biotite becomes stable relative to spinel + cordierite + biotite with increasing spessartine content or decreasing gahnite content and the Ti content of biotite. The constituent minerals of the assemblages, spinel + cordierite + biotite and garnet + cordierite + biotite, preserve several reaction microstructures indicative of prograde reactions, and together with retrograde reactions, and This suggests that the pressure-temperature path of the rocks includes an isobaric heating and an isobaric or decompressional cooling. The high-grade areas consisting of the K-feldspar-cordierite zone, sillimanite-K-feldspar zone and garnet-cordierite zone have prograde paths involving isobaric heating and show a southwards increase in pressure with a thermal maximum in the middle. These high-grade zones are closely associated with the gneissose granitic rocks, suggesting that the Ryoke metamorphism, one of the typical low-pressure type, is caused by the heat supply from the syn-tectonic granitic rocks that emplaced at the middle level of the crust. Received: 22 August 1997 / Accepted: 11 May 1998  相似文献   

Beryllium-7 Deposition and Its Relation to Sulfate Deposition   总被引：2，自引：0，他引：2  

Yasuhito Igarashi  Katsumi Hirose  Makiko Otsuji-Hatori 《Journal of Atmospheric Chemistry》1998,29(3):217-231

Deposition of ⁷Be, a cosmogenic radionuclide, was observed at the Meteorological Research Institute in Tsukuba, Japan from 1986 to 1993 and compared with those of several chemical species observed in Tsukuba over the same period. We found a correlation between the monthly depositions of ⁷ Be and SO ₄ ² -, a major acidic species. The correlation was especially strong for late spring and fall, when both species had high depositional fluxes. This correlation was also observed in precipitation samples collected daily in 1992 at the same site. The cause of this correlation is discussed in connection with the fact that the stratospheric aerosol is composed largely of SO ₄ ² -. ⁷ Be is produced in the upper atmosphere, and detection of ⁷Be, especially in spring and fall in Japan, can be regarded as detection of stratospheric aerosol. However, we conclude that the bulk of the SO ₄ ² - observed did not have a stratospheric or an upper tropospheric origin. The correlation, therefore, may present a new question regarding acidic deposition: Why does the deposition of stratospheric aerosol in Japan coincide with that of nss-SO ₄ ² - originally from anthropogenic sources on the Earth's surface?  相似文献   

Laboratory experiment and digital simulation of multiple fill-cut terrace formation     

Takeshi Mizutani 《Geomorphology》1998,24(4):353-361

The formation mechanism of multiple erosional terraces which develop in the dissection process of sedimentary valley fills was investigated by laboratory experiments and computer simulations. Sequences of unpaired terraces were produced on experimental fan-like deposits under conditions of constant water discharge, no base-level change, and no sediment supply. The terraces developed as a result of the repetition of lateral shifting and stillstand of the stream channel at each cross-section during continuous downcutting. This mode of channel migration was caused by meander growth during which amplitude and wavelength increased with time. The terrace formation process was well-reproduced by computer simulations using a meander model having a similar wave mode.  相似文献   

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods     

Katsumi Hirose  Yukio Sugimura 《Marine Chemistry》1985,16(3):239-247

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.  相似文献   

Seasonal differences in catches of leptocephali in the East China Sea and Suruga Bay, Japan   总被引：2，自引：0，他引：2  

Gen Minagawa  Michael J. Miller  Yobuo Kimura  Shun Watanabe  Akira Shinoda  Jun Aoyama  Katsumi Tsukamoto 《Estuarine, Coastal and Shelf Science》2007,71(3-4):730-740

The species composition, distribution, and size of eel larvae, or leptocephali, caught near the continental shelf in subtropical and temperate regions of East Asia were compared between two seasons (May–Jun and Oct–Dec) to learn about the seasonality of reproduction of marine eels. There was greater species richness and evidence of spawning by more species of marine eels during the late autumn surveys in both the East China Sea (ECS) and in Suruga Bay along the east coast of Japan. Small leptocephali <10 mm TL and a wide range of sizes of various taxa were collected during both seasons along the outer edge of the continental shelf in the ECS, indicating that some marine eels may spawn there all year. The lack of small leptocephali during the spring survey in Suruga Bay suggested that most eels have a clear seasonal cycle of summer or autumn spawning at the higher latitudes of coastal Japan where there is much greater fluctuation of water temperature throughout the year than in the ECS. At lower latitudes such as in the ECS, and in tropical areas where water temperatures are higher and more constant, some marine eels may spawn all year round.  相似文献