In the dynamic response analysis of extremely complex structural systems in which the damping characteristics of each element are independent, the damping matrix is not always diagonalized by the use of undamped free vibration mode shapes. In the present paper, a mode-superposition method by the use of damped free vibration mode shapes is developed for such structural systems. It is also shown that the Fast Fourier Transform (FFT) procedures, that are available for the dynamic response analysis of linear structural systems, are used effectively in this mode-superposition method with good accuracy. 相似文献
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
— 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 Dc almost remains constant below 300oC (insensitive to both temperature and effective normal stress σneff); Dc increases with increasing temperature above 300 °C, and the rate of Dc increase with temperature tends to be largest at higher σneff. The breakdown stress drop Δτb for the granite at constant σneff is roughly 80 MPa below 300 °C, and does not depend on σneff. Above 300 °C, Δτb decreases gradually with increasing temperature, and the rate of Δτb reduction with temperature increases at higher σneff. The peak shear strength τp increases nearly linearly with increasing σneff below 300 °C. However, τp 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
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
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, 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
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
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 (CX) slower than the mean westerly wind (). A statistical analysis of the zonal phase velocity shows thatCX above andCX 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
A 3729-m-deep geothermal research well, WD-1a, provides us with a unique opportunity to study initial petrographic features of a high-temperature granite just after solidification of magma. The well succeeded in collecting three spot-cores of the Kakkonda Granite that is a pluton emplaced at a shallow depth and regarded as a heat source of the active Kakkonda geothermal system. The core samples were collected at the present formation temperatures of 370, 410 and over 500°C. These samples are granodiorite to tonalite consisting mainly of plagioclase, quartz, hornblende, biotite and K-feldspar. A sample collected at a formation temperature of over 500°C possesses the following remarkable petrographic features compared to the other two samples. Interstitial spaces are not completely sealed. K-feldspar exhibits no perthite by the exsolution of albite lamella. Quartz includes glassy melt inclusions without devitrification. Hornblende is less intensively altered to actinolite, and biotite is not altered. This study directly confirmed that perthite in K-feldspar is a recrystallization texture formed at 410–500°C based on a comparison of the in situ temperatures of the samples. Chemical compositions of minerals were analyzed to compare temperatures determined from geothermometers in several publications to the in situ temperatures of the samples. 相似文献