排序方式： 共有26条查询结果，搜索用时 15 毫秒
11.
The mechanical behaviour of a rock mass is strongly affected by discontinuities such as faults and joints. In this paper, a damage mechanics theory is proposed which deals with some sets of discontinuities distributed in a rock mass, for example, joint systems. In this theory, the distributed discontinuities are characterized by a second-order symmetric tensor, called the damage tensor. By introducing the damage concept, the deformation and fracturing behaviour of the rock mass can be reated in a framework of continuum mechanics. A numerical procedure is developed in order to implement the damage mechanics model by using the finite element method. The theory and numerical analysis are applied to several laboratory tests and a practical underground opening problem. Numerical results are compared with measured data. 相似文献
12.
Sixiong Han Yasuaki Ichikawa Toshikazu Kawamoto 《Soil Dynamics and Earthquake Engineering》1991,10(6)
In this paper, a new model to treat the problem of elastic wave travelling in rock mass that embeds cracks is proposed, in which, instead of modelling the crack directly the mechanical effects of discontinuities are translated into the equivalent nodal forces on a numerical procedure. Thus the response is physically obtained as the superposition of the incident wave field and the scattering wave field produced by the radiation of the reflected waves from the crack surfaces. Finally, a numerical example is carried out and it shows that the results by the proposed method have a very good agreement with those of the exact ones. 相似文献
13.
The coda Q has been calculated for Nevado del Ruiz Volcano, Colombia (NRV) from 1985 to 1999 by using a single scattering model. During this period, the inverse of Q (Q-1 proportional to attenuation) exhibited a long-term decrease with time, as well as shorter-term variations related to the volcanic activity. Q-1 increased prior to volcanic crises and decreased afterward. Based on these observations, a seismic warning criterion has been developed. The parameters (frequency band, size of moving average window, and threshold levels) necessary to evidence clear and significant short-term changes in Q-1 have been investigated and appropriated values are proposed. We suggest a phenomenological model with three stages for the short-term temporal changes in Q-1 at NRV. Firstly, Q-1 increases before a volcanic crises because of accumulation of gas and/or liquid, which decreases the aspect ratio of fluid pockets and increases the fractional volume of fluid in the rocks and the pore aspect ratio. Secondly, Q-1 starts to decrease during the crises by the discharging of fluids such as gas, water, etc. from the volcano. Finally, Q-1 becomes more stable after the crisis at a lower value because of the degassing and/or increasing of rigidity of the medium because of the long-term crystallization and cooling processes. Q-1 seems to be a promising monitoring tool at NRV. It is possible that the observed temporal changes of Q-1, combined with other parameters, may help to predict with greater accuracy a volcanic crisis at NRV. 相似文献
14.
Kuju Volcano lies near Aso Caldera at the center of Kyushu Island, western Japan. After a few hundred years of dormancy,
a phreatic explosion accompanied by a small ash eruption occurred on 11 October 1995. This study was undertaken to determine
the subsurface seismic velocity structure associated with the active magmatic regime in the Kuju volcanic region. The three-dimensional,
upper crustal, P-wave velocity structure beneath Kuju Volcano was determined using methods for the simultaneous inversion
of P-wave arrival times from local earthquakes in and around the Kuju volcanic region for velocities and hypocentral parameters.
Results reveal two shallower low-velocity anomalies located in the northern and southern parts of Kuju Volcano, consistent
with the presence of significant negative Bouguer gravity anomalies. In addition, a high-velocity anomaly is located approximately
5 km northwest of Mt. Kuju, one of the domes in Kuju Volcano. Beneath this high-velocity anomaly, a low-velocity anomaly is
present. This velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a
chamber of partially molten material.
Received: 23 September 1997 / Accepted: 20 June 1998 相似文献
15.
Measurements of the Turbulent Energy Dissipation Rate around the Shelf Break in the East China Sea 总被引：1，自引：0，他引：1
Takeshi?MatsunoEmail author Manabu?Shimizu Yasuhiro?Morii Hideaki?Nishida Yasuaki?Takaki 《Journal of Oceanography》2005,61(6):1029-1037
Using the micro-structure profiler, TurboMAP, large values for the turbulent energy dissipation rate ε were found just above the bottom of the shelf and around the thermocline near the continental shelf break in the East China
Sea. The values found above the bottom are produced by the bottom stress due to tidal currents, resulting in a distinct bottom
mixed layer where the vertical eddy diffusivity Kz is also large. Distinct maxima in the values of ε detected around the thermocline are located at the depth of the fine-scale shear maxima detected with the moored ADCP. The
vertical profiles of ε were compared with those of the current velocity, and it was found that the maxima in ε appear to correspond to those of the shear with fine scale. The magnitude of the observed ε coincided approximately with the ε calculated from the fine-scale shear and the buoyancy frequency according to the parameterization proposed by Gregg (1989),
if the large-scale mean shear caused by the Kuroshio is subtracted. However, it is not clear whether the parameterization
for the internal wave fields in the open ocean is applicable to the estimation of ε in the shelf break. Whereas the most predominant value of ε was found just above the bottom and around the thermocline, the maxima of ε could be found in the internal area. They could have been caused by the propagation of the vertically high wave number internal
tides along the characteristic ray. 相似文献
16.
The materials were obtained from the survey conducted in the Kuroshio area of the East China Sea to the Southwest of Kyushu in Japan (29°30'-32°00', 128°00'-130°'00'E) on board the R. V. Yoko Maru of Seikai Regional Fisheries Lab, Fisheries Agency, Japan in June 15~28, 1988 during China-Japan Joint Research on the Kuroshio. Zoo-plankton was collected by means of the North Pacific Net with model TSK flowmeter through vertical haul from 50 -Om. Temperature and salinity were measured with CTD. 134 species (including 4 spp. ) of planktonic copepods were preliminarily identified in the survey area. Most of them belonged to the tropical and subtropical species and a few of them were the warm-temperate species and eurytopic species. The main dominant species vteieOncaea venusta, Oithona plumifera, Clausocalanus furcatus, C. Arcuicornis, Paracaianus dculeatus, Oithona similis, Temara turbinata, Oncaea media, Undinula danvinii, Acartia negligent, Corycaeus speciosus, Scolecithrix danae, etc. The total number 相似文献
17.
Abstract The Miura Group (Miocene-Pliocene) of south-central Japan shows a number of unique lithological and structural features. The group is composed of volcanic arc-derived marine sediments, and those in the south of the Mineoka Tectonic Belt particularly show various kinds of complex structures such as layer-parallel faults, thrust duplexes, imbricate thrusts and vein structures, yet the degree of compaction of the sediments is still remarkably low. These structures involve deformations at a very early stage and at shallow depths. They arose shortly after sedimentation within the Izu fore arc, and continued during accretion to the Honshu fore arc. The deformational stages are classified here into three stages, the first comprises bedding-parallel faulting associated with gravitational sliding and sediment injection. The first vein structures formed during this stage in the Izu fore arc area. These structures are cut by features developed during the second and third stages: especially thrusting, including duplex and imbricate thrusts. This horizontal shortening occurred during the accretionary prism formation on the subduction plate boundary. The second vein structures formed during this stage in the accretionary prism formation. The origin of the vein structures was discussed both by field observation and laboratory experiments. The latter suggests earthquake origin and the formative process is explained in relation to the field evidence. 相似文献
18.
We investigated dam behaviours during high-flow events and their robustness against perturbations in meteorological conditions using the H08 global hydrological model. Differences in these behaviours were examined by comparing simulation runs, with and without dams and using multiple meteorological datasets, at a case-study site, Fort Peck Dam on the Missouri River, USA. The results demonstrated that dam-regulated river flow reduced temporal variability over large time periods and also dampened inter-forcing discrepancies in river discharge (smoothing effects). However, during wet years, differences in peak flow were accentuated downstream of the dam, resulting in divergence in simulated peak flow across the meteorological forcing (pulsing effect). The pulsing effect was detected at other major dams in global simulations. Depending upon the meteorological forcing, the dams act as a selective filter against high-flow events. Synergy between a generic dam scheme and differences in meteorological forcing data might introduce additional uncertainties in global hydrological simulations. 相似文献
19.
Emission scenario dependencies in climate change assessments of the hydrological cycle 总被引：1，自引：1，他引：0
Hideo Shiogama Naota Hanasaki Yuji Masutomi Tatsuya Nagashima Tomoo Ogura Kiyoshi Takahashi Yasuaki Hijioka Toshihiko Takemura Toru Nozawa Seita Emori 《Climatic change》2010,99(1-2):321-329
Anthropogenic global warming will lead to changes in the global hydrological cycle. The uncertainty in precipitation sensitivity per 1 K of global warming across coupled atmosphere-ocean general circulation models (AOGCMs) has been actively examined. On the other hand, the uncertainty in precipitation sensitivity in different emission scenarios of greenhouse gases (GHGs) and aerosols has received little attention. Here we show a robust emission-scenario dependency (ESD); smaller global precipitation sensitivities occur in higher GHG and aerosol emission scenarios. Although previous studies have applied this ESD to the multi-AOGCM mean, our surprising finding is that current AOGCMs all have the common ESD in the same direction. Different aerosol emissions lead to this ESD. The implications of the ESD of precipitation sensitivity extend far beyond climate analyses. As we show, the ESD potentially propagates into considerable biases in impact assessments of the hydrological cycle via a widely used technique, so-called pattern scaling. Since pattern scaling is essential to conducting parallel analyses across climate, impact, adaptation and mitigation scenarios in the next report from the Intergovernmental Panel on Climate Change, more attention should be paid to the ESD of precipitation sensitivity. 相似文献
20.
Yasuaki Sudo 《Bulletin of Volcanology》1991,53(2):99-111
The attenuation of amplitude is seen in seismic waves which pass through the central region of the Aso caldera, in Kyushu, Japan. It is also recognized from spectral analysis of seismic waves that the higher frequencies of the P-wave are reduced in the waves which pass through the central region of the caldera. It is shown that the relative attenuation increases remarkably for the frequency range of 5 to 10 Hz. The specific attenuation factor Q of the P-wave train is about 100. From the surface projection of the ray paths with low Q values through the Aso caldera to each station, the attenuating region is located beneath the center of the caldera, extending to the north of the central cones. In conjunction with the low Q value of the P-wave and the decreases of S-wave amplitudes, the relative P-wave residual times have comparatively large values for seismic waves passing through the central region beneath the caldera. In order to attempt to provide additional information on the depth configuration of the attenuating material, the ray paths of P-wave's first arrivals are located in three-dimensional space. It indicates that the low-velocity material is located beneath the center of the caldera at depths of about 6 to 9 km. However, lowvelocity anomalies above the depth of 6 km and below the depth of 15 km were not able to be detected, because most of the available seismic ray paths had crossed the caldera at depths of about 6 to 15 km. Furthermore, the relative residual times have numerous errors resulting from incorrect hypocenter locations, origin times, inhomogeneities in the structure and uncertainty of the velocity structure. At shallow depths in the Aso caldera, refraction or reflection studies are required for an accurate estimate of the structure and more detailed properties of the attenuating material. 相似文献