Blind prediction of the site effects at Ashigara Valley,Japan, and its comparison with reality     

J. Zahradník  P. Moczo  F. Hron 《Natural Hazards》1994,10(1-2):149-170

Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s^–2) was not predicted qualitatively worse than the weak motion (8 cm s^–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.  相似文献   

The emplacement of intermediate volume ignimbrites: A case study from Roccamonfina Volcano,Southern Italy     

P. D. Cole  J. E. Guest  A. M. Duncan 《Bulletin of Volcanology》1993,55(7):467-480

A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km³ volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front.We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement.  相似文献   

The arrangement in mean elements space of the periodic orbits close to that of the Moon     

G. B. Valsecchi  E. Perozzi  A. E. Roy  B. A. Steves 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):373-380

In a simplified model of the Earth-Moon-Sun system based on the restricted circular 3-dimensional 3-body problem, it is possible to find numerically a set of 8 periodic orbits whose time evolutions closely resemble that of the Moon's orbit. These orbits have a period of 223 synodic months (i.e. the period of the Saros cycle known for more than two millennia as a means of predicting eclipses), and are characterized by a secular rotation of the argument of perigee . Periodic orbits of longer durations exhibiting this last feature are very abundant in Earth-Moon-Sun dynamical models. Their arrangement in the space of the mean orbital elements- for various values of the lunar mean motion is presented.  相似文献   

Generalized Lyapunov exponents indicators in Hamiltonian dynamics: An application to a double star system     

E. Lohinger  C. Froeschlé  R. Dvorak 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):315-322

The Lyapunov characteristic numbers (LCNs) which are defined as the mean value of the distribution of the local variations of the tangent vectors to the flow (=ln _k ⁱ ) (see Froeschlé, 1984) have been found to be sensitive indicators of stochasticity. So we computed the distribution of these local variations and determined the moments of higher order for the integrable and stochastic regions in a binary star system with =0.5.  相似文献   

Asteroid motion near the 3 : 1 resonance     

John D. Hadjidemetriou 《Celestial Mechanics and Dynamical Astronomy》1993,56(4):563-599

A mapping model is constructed to describe asteroid motion near the 3 : 1 mean motion resonance with Jupiter, in the plane. The topology of the phase space of this mapping coincides with that of the real system, which is considered to be the elliptic restricted three body problem with the Sun and Jupiter as primaries. This model is valid for all values of the eccentricity. This is achieved by the introduction of a correcting term to the averaged Hamiltonian which is valid for small values of the ecentricity.We start with a two dimensional mapping which represents the circular restricted three body problem. This provides the basic framework for the complete model, but cannot explain the generation of a gap in the distribution of the asteroids at this resonance. The next approximation is a four dimensional mapping, corresponding to the elliptic restricted problem. It is found that chaotic regions exist near the 3 : 1 resonance, due to the interaction between the two degrees of freedom, for initial conditions close to a critical curve of the circular model. As a consequence of the chaotic motion, the eccentricity of the asteroid jumps to high values and close encounters with Mars and even Earth may occur, thus generating a gap. It is found that the generation of chaos depends also on the phase (i.e. the angles andv) and as a consequence, there exist islands of ordered motion inside the sea of chaotic motion near the 3 : 1 resonance. Thus, the model of the elliptic restricted three body problem cannot explain completely the generation of a gap, although the density in the distribution of the asteroids will be much less than far from the resonance. Finally, we take into account the effect of the gravitational attraction of Saturn on Jupiter's orbit, and in particular the variation of the eccentricity and the argument of perihelion. This generates a mixing of the phases and as a consequence the whole phase space near the 3 : 1 resonance becomes chaotic. This chaotic zone is in good agreement with the observations.  相似文献   

施工顺序对软土地坪复合地基的影响探讨     

魏海涛  蔡智 《岩土工程技术》2021,(1)

场地回填土与搅拌桩施工顺序将直接影响软土地坪复合地基的处理效果,其中沉降控制是影响地坪安全运行的关键。以近海软土地区工业厂房水泥土搅拌桩复合地基工程为例,探讨了复合地基水泥土搅拌桩、回填土两种不同施工顺序的影响因素及相应处理效果;通过数值模拟试验,计算分析了不同填土厚度下两种工况的地基固结总沉降、施工沉降、工后沉降。结果表明,采用“先土后桩”的施工顺序的施工期沉降大于“先桩后土”,但工后沉降大大减小,提高了软土地坪地基处理效果,有利于处理后地坪的安全运行,验证了前述分析结论,为合理设计方案的确定提供了重要的参考依据。  相似文献   

Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)     

F. Bella  P. F. Biagi  M. Caputo  G. Della Monica  A. Ermini  P. V. Manjgaladze  V. Sgrigna  D. O. Zilpimiani 《Pure and Applied Geophysics》1995,144(2):277-300

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper  相似文献   

突发性地面增温与临震前兆——以1988年澜沧、耿马7.6,7.2级地震为例   总被引：6，自引：0，他引：6       下载免费PDF全文

徐秀登  强祖基  赁常恭 《地震地质》1990,12(3):243

本文通过较多的地面温度资料分析,认为1988年11月6日澜沧、耿马地震前几天,震区及其周围大范围的突发性地面增温异常是一种临震前兆,总结了增温异常的时空演变规律与地震活动的关系,并对其形成机制提出初步想法  相似文献   

Boron isotopic geochemistry of karst groundwater in Guiyang City, China     

Wei ZHANG Congqiang LIU Zhiqi ZHAO 《中国地球化学学报》2006,25(B08):172-172

Boron has two stable isotopes （^10B and ^11B） with relative abundances of about 20% and 80%, respectively. Boron isotopic ratios in natural materials show a huge range of variations, from -70‰ to ＋60‰, when expressed with the classical δ^11B notation. Most of these isotopic variations occur at the surface of the Earth. Hence, boron isotopic composition can be used as a sensitive tracer in geochemical study, for instance, to identify the different sources of contamination and factors controlling the salinity of groundwater. During the last decade, boron isotopes have been used to discriminate between the influences of seawater intrusion and anthropogenic discharge. But few of those researches can precisely identify the different sources of contamination. We measured the boron concentrations and boron isotopic ratios of groundwater samples collected in Guiyang City, as well as the major ions. The results indicate that the major ion composition of the groundwater in the investigated area is mainly controlled by the interactions between water and the dominant rock i.e. carbonates. All the water compositions are characterized by high concentrations of Ca^2＋, Mg^2＋, HCO3^-, SO4^2-, and NO3^-, which are the dominant contaminants. Both dissolved boron concentrations and isotopic ratios show large variations among the ground waters, from 2 μg/L to 90 μg/L and from -6‰ to ＋26‰, respectively. The boron concentrations and isotopic ratios indicate that the river across the studied city has been seriously contaminated by urban discharge. Boron concentrations of fiver water samples varied from 20 μg/L to 140 μg/L, with an average δ^11B value of ＋2.0‰. Using boron isotopic compositions and different geochemical indices allowed us to clearly identify and distinguish the two major sources of contamination, agricultural activity and urban wastewater. Both of the two sources are characterized by high boron concentrations but their boron isotopic compositions significantly differ.  相似文献   

Analysis of a rigid footing lying on three-layered soil using the finite difference method     

Priti Maheshwari  M. R. Madhav 《Geotechnical and Geological Engineering》2006,24(4):851-869

A numerical procedure is described for the analysis of the vertical deformation and the stress distribution of the strip footings on layered soil media. Three layers of soil with different stiffness are considered with the middle soil layer the thinnest and most stiff layer. The soil media is discretized and using the theory of elasticity, the governing differential equations are obtained in terms of vertical and horizontal displacements. These equations along with appropriate boundary and continuity conditions are solved by using the finite difference method. The vertical and horizontal displacements, strains and stresses are found at various nodes in the soil media. Parametric studies are carried out to study the effect of the placement depth of the middle soil layer, the relative ratios of the moduli of deformation of the soil layers on the vertical displacement of the footing and the vertical stress distribution. These studies reveal that the middle thin but very stiff layer acts like a plate and redistributes the stresses on the lower soft soil layer uniformly. The displacement on the top and bottom of the middle soil layer is almost the same showing that the compression of the middle layer is negligible as it is very stiff.  相似文献