Source inversion for estimating the continuous slip distribution on a fault—introduction of Green's functions convolved with a correction function to give moving dislocation effects in subfaults     

Haruko Sekiguchi  Kojiro Irikura  Tomotaka Iwata 《Geophysical Journal International》2002,150(2):377-391

  相似文献   

Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada     

Takaki Iwata  R. Paul Young 《Pure and Applied Geophysics》2005,162(6-7):1291-1308

The correlation between the b-values of acoustic emissions (AEs) and the phase of the moon was investigated at the Underground Research Laboratory (URL) in Canada. The same data as those used in Iwata (2002) were examined, which showed that the occurrence of AEs is correlated with the phase of the moon. It was expected, therefore, that the b-value of the AEs would also be sensitive to tidal stress/strain fluctuations. We investigated the variation of the b-values as a function of the phase of the moon. Results show that b-values immediately following the times of full/new moon are higher than those at other times. Using AIC (Akaike Information Criterion) and random (Monte Carlo) simulations, it was confirmed that this feature is statistically significant. We also investigated whether or not there was a change in the b-values immediately before the times of full/new moon, but no statistically significant change was observed. The results suggest that the effect of stress/strain fluctuations on AE occurrences at the URL is asymmetric to the times of full/new moon.All authors are members of the Academic Robotics Group. In listing The Academic Robotics Group, the authors are endeavoring to place each of the participant institutions on an equal footing in terms of effort and authorship. M. A. Talamini is serving as presenter.  相似文献   

Monitoring over‐winter soil water dynamics in a freezing and snow‐covered environment using a thermally insulated tensiometer     

Yukiyoshi Iwata  Tomoyoshi Hirota 《水文研究》2005,19(15):3013-3019

Water potential below a frozen soil layer was continuously monitored over an entire winter period (using thermally insulated tensiometers sheltered in a heated chamber) along with other soil, snow and atmospheric variables. In early winter, the freezing front advanced under a thin snow cover, inducing upward soil water flow in the underlying unfrozen soil. The freezing front started to retreat when the snow cover became thick enough to insulate the soil, resulting in the reversal of the flow direction in the unfrozen zone. These data provide a clear illustration of soil water dynamics, which have rarely been monitored with a tensiometer. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Accidents due to oxygen deficiency and methane gas blow-off in Tokyo area,Japan     

Hisato Hayashi  Motomu Ishii 《Environmental Geology》1989,13(2):167-177

The groundwater leve in the Tokyo area had declined to about 60 m below the surface because of excess withdrawal of groundwater from various aquifers. Many construction workers died due to oxygen deficiency at construction sites from 1960 to 1980, the period of decreasing groundwater level. The compressed air in pneumatic foundation construction sites passed easily through the aquifer, and the oxygen in it was consumed by ferrous ions oxidizing to ferric ions. During periods of high barometric pressure, atmospheric air penetrates into the strata and it is deoxygenated there. Suffocation occurred not only at construction sites in underground excavations, but also in residences in Tokyo. Such acidents have become less frequent with recovery of the pore-water pressure in aquifers, which has accompanied the recovery of the groundwater level since 1972.With the recovery of the pore-water pressure and the groundwater level in the aquifer, fires and explosions resulting from gushes of methane have occurred in Tokyo lowlands since 1973. These blow-off gases are classified into two types: Kameido and Asakusa.The gas of the Kameido type originates from the Kazusa Group and migrates into upper alluvial deposits or Pleistocene sediments because of the recovery of pore-water pressure in the Kazusa Group. The gas of the Asakusa type formed from the air that penetrated the aquifers during the period of low groundwater level. Methane was produced by the depletion of oxygen accumulated in alluvial deposits and Pleistocene sediments. This gas blows off through wells in alluvial deposits and Pleistocene sediments at times of low barometric pressure. Accidents of the Asakusa type will not happen when the groundwater level and pore-water pressure in alluvial and Pleistocene sediments is restored to previous levels.  相似文献   

Persistent organochlorine residues in sediments from the Chukchi Sea, Bering Sea and Gulf of Alaska   总被引：14，自引：0，他引：14  

Hisato Iwata  Shinsuke Tanabe  Mari Aramoto  Norio Sakai  Ryo Tatsukawa 《Marine pollution bulletin》1994,28(12):746-753

Three surface sediments and two sediment cores were collected from the Gulf of Alaska, Bering Sea and Chukchi Sea, and analysed for persistent organochlorines (OCs). The geographical distributions of OCs showed different patterns according to their physicochemical properties. The concentrations of HCHs and HCB revealed rather uniform distribution, suggesting their more transportable nature in long-range atmospheric transport. On the other hand, DDTs and PCBs were predicted to be less transportable via the atmosphere due to the decreasing trends of residue levels in sediments from south to north. The OC profiles in the sediment core from the Gulf of Alaska which seemed to be preserved without turbation revealed the elevated residue levels from bottom to surface layers. This implies that the aerial inputs of OCs in the cold ocean are still continuing significantly. The accumulation rates of OCs into sediments were rather smaller than the atmospheric inputs, indicating that the residue levels in water bodies are unlikely to decrease rapidly in the near future.  相似文献   

Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan     

Koji  Kameo  Makoto  Okada  Moamen  El-Masry  Toshio  Hisamitsu  Saneatsu  Saito  Hiroomi  Nakazato  Naohiko  Ohkouchi  Minoru  Ikehara  Hisato  Yasuda  Hiroshi  Kitazato  Asahiko  Taira 《Island Arc》2006,15(3):366-377

Abstract   A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ¹⁸O and δ¹³C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area.  相似文献   

Influence of fine sediment on the fluidity of debris flows     

Norifumi Hotta  Takahiro Kaneko  Tomoyuki Iwata  Haruo Nishimoto 《山地科学学报》2013,10(2):233-238

Debris flows include a great diversity of grain sizes with inherent features such as inverse grading, particle size segregation, and liquefaction of fine sediment. The liquefaction of fine sediment affects the fluidity of debris flows, although the behavior and influence of fine sediment in debris flows have not been examined sufficiently. This study used flume tests to detect the effect of fine sediment on the fluidity of laboratory debris flows consisting of particles with various diameters. From the experiments, the greatest sediment concentration and flow depth were observed in the debris flows mixed with fine sediment indicating increased flow resistance. The experimental friction coefficient was then compared with the theoretical friction coefficient derived by substituting the experimental values into the constitutive equations for debris flow. The theoretical friction coefficient was obtained from two models with different fine-sediment treatments: assuming that all of the fine sediments were solid particles or that the particles consisted of a fluid phase involving pore water liquefaction. From the comparison of the friction coefficients, a fully liquefaction state was detected for the fine particle mixture. When the mixing ratio and particle size of the fine sediment were different, some other cases were considered to be in a partially liquefied transition state. These results imply that the liquefaction of fine sediment in debris flows was induced not only by the geometric conditions such as particle sizes, but also by the flow conditions.  相似文献   

Lunar gravity field determination using SELENE same-beam differential VLBI tracking data   总被引：2，自引：0，他引：2  

S. Goossens  K. Matsumoto  Q. Liu  F. Kikuchi  K. Sato  H. Hanada  Y. Ishihara  H. Noda  N. Kawano  N. Namiki  T. Iwata  F. G. Lemoine  D. D. Rowlands  Y. Harada  M. Chen 《Journal of Geodesy》2011,85(4):205-228

A lunar gravity field model up to degree and order 100 in spherical harmonics, named SGM100i, has been determined from SELENE and historical tracking data, with an emphasis on using same-beam S-band differential VLBI data obtained in the SELENE mission between January 2008 and February 2009. Orbit consistency throughout the entire mission period of SELENE as determined from orbit overlaps for the two sub-satellites of SELENE involved in the VLBI tracking improved consistently from several hundreds of metres to several tens of metres by including differential VLBI data. Through orbits that are better determined, the gravity field model is also improved by including these data. Orbit determination performance for the new model shows improvements over earlier 100th degree and order models, especially for edge-on orbits over the deep far side. Lunar Prospector orbit determination shows an improvement of orbit consistency from 1-day predictions for 2-day arcs of 6 m in a total sense, with most improvement in the along and cross-track directions. Data fit for the types and satellites involved is also improved. Formal errors for the lower degrees are smaller, and the new model also shows increased correlations with topography over the far side. The estimated value for the lunar GM for this model equals 4902.80080±0.0009 km³/s² (10 sigma). The lunar degree 2 potential Love number k ₂ was also estimated, and has a value of 0.0255 ± 0.0016 (10 sigma as well).  相似文献   

Geodynamics and Tectonics of Central Asia: Continental Growth in Vendian-Paleozoic Time     

M.M. Buslov  T. Watanabe  Y. Fujiwara  K. Iwata  Yu.I. Saphonova  O.T. Obut  Y. Sugai 《Gondwana Research》2001,4(4):587

  相似文献   

Biological significance of effects of phytophagous fishes on phytoplankton     

T. Miura  K. Iwata  Zhang Zongshe 《中国海洋湖沼学报》1989,7(4):335-338

The effects of phytophagous fishes on phytoplankton primary productivity in a freshwater pond, the importance of recycling of algae in fish feces, and the species specific interaction with phytoplanktons were studied. Phaeopigment amounts in pond water and in feces of fish were compared. The reduction of chlorophylla into phaeopigments in the process of passing through the phytophagous fish intestines was analyzed, and used for a direct comparison of the production rates of phytoplanktons before and after intestinal passage.  相似文献