The　Early　Summer　Seasonal　Change　of　Large－scale　Circulation　over　East　Asia　and　Its　Relation　to　Change　of　The　Frontal　Features　and　Frontal　Rainfall　Environment　During　1991　Summer   总被引：5，自引：0，他引：5  

Gong-Wang Si  Kuranoshin Kato  Takao Takeda 《大气科学进展》1995,12(2):151-176

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Free oscillations of a laterally heterogenous and anelastic earth   总被引：1，自引：0，他引：1  

Seiji Tsuboi 《Pure and Applied Geophysics》1995,145(3-4):445-457

We calculate normal modes of the laterally heterogeneous and anelastic earth model by using the variational method to include the coupling of the modes due to the asphericity of the earth. If the aspherical anelasticity correlates with the heterogeneity of elastic velocity structure, the quality factorQ of the split singlets has a correlation with the eigenfrequency. This can cause a center frequency shift of the spectral peak with time. We perform a synthetic experiment to examine whether the magnitude of the shift can become an observable for the realistic lateral heterogeneity model of anelasticity. The result of the experiment reveals that the shift of the center frequency is consistent with the initial estimate for the fundamental spheroidal modes used in the experiment. We then examine the actual seismograms of the June 9, 1994, Bolivian earthquake to determine if this shift of center frequency can be observed. Although the amount of the center frequency shift of each multiplet is large, there is no consistent shift of the center frequency that is predicted in the synthetic experiment.  相似文献   

Crustal movements in the tohoku district, Japan, during the period 1900–1975, and their tectonic implications     

Teruyuki Kato 《Tectonophysics》1979,60(3-4):141-167

Vertical crustal movements in the Tohoku district in the past 75 years are discussed with reference to their tectonic implications.

For this purpose, the author first compiled a map of accumulated vertical movement in the past 75 years, by making proper correction for closure. In addition, a new presentation technique utilizing a time-space domain representation of elevation changes is applied to the data. These contour maps provide an informative summary of the vertical crustal movement history in this district. From them, we see that the northeastern part of the district has subsided continuously and aseismically, with an area of significant subsidence inland at a distance about 300 km or more from the trench axis.

In order to explain the mechanism of the remarkable extension of the subsiding area, the finite element method is applied to model the elastic strain field in the district. It is shown that a simple model of uniform dragging at the interface of a sinking slab does not provide a good interpretation of the inland distribution of subsidence. A modification of the conventional model is proposed which hypothesizes vertical movement of the subducting lithospheric slab under the Tohoku district.  相似文献   

The Dependence of Constitutive Properties on Temperature and Effective Normal Stress in Seismogenic Environments     

Aitaro Kato  Shingo Yoshida  Mitiyasu Ohnaka  Hiromine Mochizuki 《Pure and Applied Geophysics》2004,161(9-10):1895-1913

— We have evaluated how the parameters prescribing the slip-dependent constitutive law are affected by temperature and effective normal stress, by conducting the triaxial fracture experiments on Tsukuba-granite samples in seismogenic environments, which correspond to a depth range to 15 km. The normalized critical slip displacement D _c almost remains constant below 300^oC (insensitive to both temperature and effective normal stress σ _n ^eff); D _c increases with increasing temperature above 300 °C, and the rate of D _c increase with temperature tends to be largest at higher σ _n ^eff. The breakdown stress drop Δτ _b for the granite at constant σ _n ^eff is roughly 80 MPa below 300 °C, and does not depend on σ _n ^eff. Above 300 °C, Δτ _b decreases gradually with increasing temperature, and the rate of Δτ _b reduction with temperature increases at higher σ _n ^eff. The peak shear strength τ _p increases nearly linearly with increasing σ _n ^eff below 300 °C. However, τ _p becomes lower above 300 °C, deviating from the linear relation extrapolated from below 300 °C. This is consistent with the onset of crystal plastic deformation mechanisms of Tsukuba granite.  相似文献   

Fault system of the 2004 Mid Niigata Prefecture Earthquake and its aftershocks     

Naoshi Hirata  Hiroshi Sato  Shin’ichi Sakai  Aitaro Kato  Eiji Kurashimo 《Landslides》2005,2(2):153-157

Data recorded by a seismic network deployed the day after the 2004 Mid Niigata Prefecture Earthquake (M6.8) in central Japan are used to determine the major source faults responsible for the mainshock and major aftershocks. Using this high-resolution seismic data, three major source faults are identified: two parallel faults dipping steeply to the west located 5 km apart, and the other dipping eastward and oriented perpendicular to the west-dipping faults. The analysis also reveals that the lateral variation in seismic velocity observed at the surface extends to a depth of 15 km, encompassing the source area of the mainshock. This strong heterogeneity of the crust, related to the complex geological and tectonic evolution of the area, is considered to be responsible for the prominent aftershock activity following the 2004 Niigata event.  相似文献   

Behavior of polycyclic aromatic hydrocarbons at impact shock: Its implication for survival of organic materials delivered to the early Earth     

Koichi Mimura  Seiji Toyama 《Geochimica et cosmochimica acta》2005,69(1):201-209

Polycyclic aromatic hydrocarbons (PAHs) with a hydrous or an unhydrous mineral matrix were impacted and analyzed, to study the behavior of PAHs against shock. Results of the shock experiments suggested that volatiles discharged from the hydrous mineral did not influence the behavior of PAHs against shock. The shocked samples contained unreacted starting PAHs, soot-like materials insoluble in dichloromethane, and secondarily formed PAHs with molecular weights ranging from 128 to 404. Approximately 95% of starting PAHs decomposed at ∼30 GPa and the dominant product was the soot-like materials. Formation mechanisms of the shock products were explained by reaction processes under static high pressure-temperature conditions (e.g., carbonization, radical addition reaction, ring cross linking, and methylation).We applied these results to estimate the survival degree of organic matter delivered by carbonaceous asteroids against their impact pressures at the accretion stage of early Earth. If we use a simplified homogeneous accretion model without atmosphere to represent the stage, the radius of Earth causing 30 GPa, the pressure at which PAHs almost decompose, was calculated as 2270 km (4.0 km s⁻¹ of impact velocity) for the impact of carbonaceous asteroids. In the case of impactors striking not land but oceans on the early Earth, the impact velocity for the decomposition of PAHs was estimated to be 6.0 km s⁻¹. These impact velocities should have been commonly realized on the early Earth, due to the airburst and the aerobreak of impactors in the dense atmosphere. The early Earth should have been a favorable environment for obtaining and maintaining a large quantity of prebiotic organic materials leading to life.  相似文献   

K-Ar dating studies of Ashigawa and Tokuwa granodiorite bodies and plutonic geochronology in the South Fossa Magna, central Japan     

Kazuo  Salto Koichi  Kato Shunji  Sugi 《Island Arc》1997,6(2):158-167

Abstract K-Ar age studies in the Ashigawa and the southern part of the Tokuwa granodioritic bodies, which consist of the southern part of the Kofu plutonic complex, revealed that they formed between 12 and 9 Ma. Quite a narrow range of ages obtained from the Ashigawa southernmost part of the Tokuwa pluton implies that they cooled rapidly. The southern part of the Tokuwa pluton, as a whole, shows a systematic age distribution with a decrease in age to the north. Compilation of currently available plutonic ages in the South Fossa Magna suggests that the plutonic activities occurred three times in this region. Episodic activity like this could be argued in relation to the tectonic development of this region.  相似文献   

Lake Suwa — Eutrophication and its partial recent recovery     

T. Okino Dr.  K. Kato Dr. 《GeoJournal》1987,14(3):373-375

Lake Suwa, located in the center of the largest Japanese island of Honshu was a typical hypertrophic lake with a dense scum Microcystis species in summer during the 1970's. However, due to the introduction of a sewage treatment plant and the awareness of environmental pollution by local residents, a decrease in the concentration of nutrients in lake water since 1981 has been observed (from 1600 g l^–1 and 160 g l^–1 in 1977 to 990 g l^–1 and 110 g l^–1 in 1984 for total nitrogen and phosphorus respectively).  相似文献   

Wind fluctuations near a cold vortex-tropopause funnel system observed by the MU radar     

Shoichiro Fukao  Manabu D. Yamanaka  Hiromasa Matsumoto  Toru Sato  Toshitaka Tsuda  Susumu Kato 《Pure and Applied Geophysics》1989,130(2-3):463-479

Vertical and temporal variations of three-dimensional wind velocity associated with an upper-tropospheric cold vortex-tropopause funnel system were observed by an MST radar in Japan (the MU radar). Marked changes of vertical velocity and horizontal wind direction were found between the inside and outside of the cold vortex. The vertical velocity activity outside the vortex was asymmetric; it was most active in a sector before the vortex. Unsaturated internal gravity waves in their generation stage contribute predominantly to the vertical velocity activity, suggesting that tropospheric occluded cyclones may be a possible source of middle-atmospheric gravity waves through the geostrophic adjustment process.  相似文献   

Internal gravity wave selection in the upper troposphere and lower stratosphere observed by the MU radar: Preliminary results     

Manabu D. Yamanaka  Shoichiro Fukao  Hiromasa Matsumoto  Toru Sato  Toshitaka Tsuda  Susumu Kato 《Pure and Applied Geophysics》1989,130(2-3):481-495

Marked wavelike variations of the lower stratospheric wind observed on 7–10 May, 1985 by an MST radar in Japan (by the MU radar) are analyzed assuming that they are induced by monochromatic internal inertio-gravity waves. These variations are mainly composed of two modes (periods: 22 and 24 hours), both of which have zonal phase velocities (C _X ) slower than the mean westerly wind (). A statistical analysis of the zonal phase velocity shows thatC _X above andC _X below the tropopause jet stream, which is considered to be a vivid proof of wave selection due to the tropospheric mean flow and upward wave emission from the tropopause jet. A comparison between the MU radar results and routine meteorological observations leads to the conclusion that the marked waves appear when the jet stream takes a maximum wind speed.  相似文献