平面P波在饱和半空间中洞室周围的散射(I):解析解

利用波函数展开法给出了入射平面P波在饱和半空间中圆形洞室周围散射问题的一个解析解。半空间假定为无粘性流体饱和介质,满足Biot理论。采用一种基于实验数据的孔隙率和模量之间的线性关系来确定Biot模型中的介质参数。解答考虑了透水边界和非透水边界两种情况。对边界条件进行了数值检验,结果表明,随着级数截断项数的增大,边界残量衰减很快。解答为进一步研究入射波频率和角度、边界渗透条件、孔隙率、泊松比等参数对散射的影响奠定了基础。     

Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica

Ice exposed in ablation zones of ice sheets can be a valuable source of samples for paleoclimate studies and information about long-term ice dynamics. We report a 28-km long stable isotope sampling transect along a flowline on lower Taylor Glacier, Antarctica, and show that ice from the last glacial period is exposed here over tens of kilometers. Gas isotope analyses on a small number of samples confirm our age hypothesis. These chronostratigraphic data contain information about past ice dynamics and in particular should be sensitive to the longitudinal strain rate on the north flank of Taylor Dome, averaged over millennia. The imprint of climatic changes on ice dynamics may be discernible in these data.     

Limit state model for R.C. bridge joints under seismic loading

Most of the available models of monolithic reinforced concrete joints under seismic action focus on estimation of cracking and ultimate shear strengths. Very few studies have been directed towards developing expressions for the associated joint deformations at the milestone response points so as to compose a limit-state model for joints that would be compatible with the emerging framework of deformation based seismic assessment and design methods. This objective is pursued in the present paper with particular emphasis on monolithic bridge joints. Deformation capacity at yielding and failure of joints is derived by establishing equilibrium and geometric compatibility of smeared stresses and strains, and satisfying material constitutive relationships. Expressions and model parameters are calibrated with the database of published bridge joint tests assembled from International literature, using statistical evaluation. From the mean values of the design parameters simplified equations for shear strength and ultimate shear strain of bridge joints are proposed.     

Creep and rate of loading effects on geogrid- reinforced sand

This paper presents the results of studies of creep and rate of loading effects on geogrid-reinforced dune sand. Model plate load tests were conducted on reinforced sand beds under displacement and load controls. Displacement controlled set of plate load tests were carried out in the range 1–0.001 mm/min. Load controlled set of plate load tests were carried out in which the staged pressure was held constant for 6000 min. Results indicate that rate of displacement (strain rate) is very significant for potential improvement of geogrid-reinforced sand. Both stiffness and bearing capacity of geogrid-reinforced sand increases logarithmically with rate of displacement. Geogrid reduces the creep of sand especially in the working pressure range. A simple stiffness degradation and creep relationships were obtained for geogrid-reinforced dune sand. The results of the tests are reported, and the significance of each control variable is assessed.     

Deformation-enhanced metamorphic reactions and the rheology of high-pressure shear zones, Western Gneiss Region, Norway

Microstructural and petrological analysis of samples with increasing strain in high‐pressure (HP) shear zones from the Haram garnet corona gabbro give insights into the deformation mechanisms of minerals, rheological properties of the shear zone and the role of deformation in enhancing metamorphic reactions. Scanning electron microscopy with electron backscattering diffraction (SEM–EBSD), compositional mapping and petrographic analysis were used to evaluate the nature of deformation in both reactants and products associated with eclogitization. Plagioclase with a shape‐preferred orientation that occurs in the interior part of layers in the mylonitic sample deformed by intracrystalline glide on the (0 0 1)[1 0 0] slip system. In omphacite, crystallographic preferred orientations indicate slip on (1 0 0)[0 0 1] and (1 1 0)[0 0 1] during deformation. Fine‐grained garnet deformed by diffusion creep and grain‐boundary sliding. Ilmenite deformed by dislocation glide on the basal and, at higher strains, prism planes in the a direction. Relationships among the minerals present and petrological analysis indicate that deformation and metamorphism in the shear zones began at 500–650 °C and 0.5–1.4 GPa and continued during prograde metamorphism to ultra‐high‐pressure (UHP) conditions. Both products and reactants show evidence of syn‐ and post‐kinematic growth indicating that prograde reactions continued after strain was partitioned away. The restriction of post‐kinematic growth to narrow regions at the interface of garnet and plagioclase and preservation of earlier syn‐kinematic microstructures in older parts layers that were involved in reactions during deformation show that diffusion distances were significantly shortened when strain was partitioned away, demonstrating that deformation played an important role in enhancing metamorphic reactions. Two important consequences of deformation observed in these shear zones are: (i) the homogenization of chemical composition gradients occurred by mixing and grain‐boundary migration and (ii) composition changes in zoned metamorphic garnet by lengthening diffusion distances. The application of experimental flow laws to the main phases present in nearly monomineralic layers yield upper limits for stresses of 100–150 MPa and lower limits for strain rates of 10^?12 to 10^?13 s^?1 as deformation conditions for the shear zones in the Haram gabbro that were produced during subduction of the Baltica craton and resulted in the production of HP and UHP metamorphic rocks.     

Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms

Fault plane solutions for earthquakes in the central Hellenic arc are analysed to determine the deformation and stress regimes in the Hellenic subduction zone in the vicinity of Crete. Fault mechanisms for earthquakes recorded by various networks or contained in global catalogues are collected. In addition, 34 fault plane solutions are determined for events recorded by our own local temporary network on central Crete in 2000–2001. The entire data set of 264 source mechanisms is examined for types of faulting and spatial clustering of mechanisms. Eight regions with significantly varying characteristic types of faulting are identified of which the upper (Aegean) plate includes four. Three regions contain interplate seismicity along the Hellenic arc from west to east and all events below are identified to occur within the subducting African lithosphere. We perform stress tensor inversion to each of the subsets in order to determine the stress field. Results indicate a uniform N-NNE direction of relative plate motion between the Ionian Sea and Rhodes resulting in orthogonal convergence in the western forearc and oblique (40–50^∘) subduction in the eastern forearc. There, the plate boundary migrates towards the SE resulting in left-lateral strike-slip faulting that extends to onshore Eastern Crete. N110^∘E trending normal faulting in the Aegean plate at this part is in accordance with this model. Along-arc extension is observed on Western Crete. Fault plane solutions for earthquakes within the dipping African lithosphere indicate that slab pull is the dominant force within the subduction process and responsible for the roll-back of the Hellenic subduction zone.     

Analysis of State of Stress During The 1997 Earthquake Swarm In Western Bohemia

Focal mechanisms of 70 events of the January 1997 earthquake swarm were analysed using the Gephart and Forsyth method to determine the state of stress in the West Bohemia/Vogtland region and to reveal possible stress variations during the swarm activity. The method was applied to the whole set of 70 focal mechanisms and to several subsets distinguishing magnitudes of events and the spatial and temporal distribution of the swarm. The three representative stress models A ( ₁ ,A: 0/45 (az/dip), ₂ A: 134/35, ₃ A: 243/25), B ( ₁ ,B: 162/38, ₂ B: 263/14, ₃ B: 10/49), and C ( ₁ C: 135/30, ₂ C: 1/50, ₃ C: 239/23) which could characterise the state of stress in the region were found. Model C can be considered to be the most probable stress model because of its consistency with the European stress field. The results of the stress analysis applied to the individual subsets of focal mechanisms indicate that the state of stress was more uniform during the first phase of the swarm. To distinguish between the fault plane and the auxiliary plane of fault plane solutions a statistical approach was used. The results showed that the fault planes striking NW-SE and dipping 45° to NE were activated during the swarm.     

Artificial Neural Network Approach for Reconstruction of Event Arrival-Direction in Wide-Angle Atmospheric Cerenkov Detector Arrays: A Feasibility Study

A feasibility study has been carried out to assess the potentialof an Artificial Neural Network (ANN) for determiningthe direction of incidence of an Atmospheric Cerenkov Event(ACE) from the arrival-time information registered by aspaced-array of wide-angle Cerenkov detectors. Theresults obtained so far, using both, simulated and experimental data, indicate that a properly-trained net can yield a degree of accuracy which is comparable with what is achieved through the conventional ²-minimization, wavefront-fitting procedure.     

软化岩土介质的应变局部化研究进展--意义·现状·应变梯度

如何准确描述岩土的应变软化已是岩土力学研究的难题,而岩土介质的软化性状与应变局部化的产生和发展直接相关。阐述了研究岩土材料的软化性状的意义以及岩土材料的软化与应变局部化的关系。从实验研究、理论建模和数值模拟三方面综述应变局部化在岩土力学中的研究现状;说明应变局部化发生时考虑应变梯度的必要性;就应变局部化研究在岩土力学中的发展趋势提出初步看法。