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771.
I. Anastasopoulos A. Callerio M. F. Bransby M. C. R. Davies A. El Nahas E. Faccioli G. Gazetas A. Masella R. Paolucci A. Pecker E. Rossignol 《Bulletin of Earthquake Engineering》2008,6(4):645-675
Field evidence from recent earthquakes has shown that structures can be designed to survive major surface dislocations. This
paper: (i) Describes three different finite element (FE) methods of analysis, that were developed to simulate dip slip fault
rupture propagation through soil and its interaction with foundation–structure systems; (ii) Validates the developed FE methodologies
against centrifuge model tests that were conducted at the University of Dundee, Scotland; and (iii) Utilises one of these
analysis methods to conduct a short parametric study on the interaction of idealised 2- and 5-story residential structures
lying on slab foundations subjected to normal fault rupture. The comparison between numerical and centrifuge model test results
shows that reliable predictions can be achieved with reasonably sophisticated constitutive soil models that take account of
soil softening after failure. A prerequisite is an adequately refined FE mesh, combined with interface elements with tension
cut-off between the soil and the structure. The results of the parametric study reveal that the increase of the surcharge
load q of the structure leads to larger fault rupture diversion and “smoothing” of the settlement profile, allowing reduction of
its stressing. Soil compliance is shown to be beneficial to the stressing of a structure. For a given soil depth H and imposed dislocation h, the rotation Δθ of the structure is shown to be a function of: (a) its location relative to the fault rupture; (b) the surcharge load q; and (c) soil compliance. 相似文献
772.
A cross-sectional model of an idealised constant depth gulf with a sill at its entrance, connected to a deep ocean, is used
to examine the barotropic and baroclinic response of the region to wind forcing. The role of the oceanic boundary condition
is also considered. Calculations show that in the case of a tall sill, where the pycnocline intersects the sill, the baroclinic
response of the gulf is similar to that of a lake, and internal waves cannot radiate energy out of the gulf. The barotropic
response shows free surface oscillations, with nodes located close to the centre of the oceanic basin and entrance to the
gulf, with associated barotropic resonant periods. As the sill height is reduced, baroclinic wave energy is radiated from
the gulf into the ocean, and the form of the baroclinic response changes from a standing wave (tall sill) as in a lake to
a progressive wave (no sill). The location of sea surface elevation nodes and resonant periods changes as the sill height
is reduced. Calculations of the barotropic resonant periods with and without stratification could not determine if they were
influenced by the presence of stratification, although published analytical theory suggests that they should be able to when
energy is lost from the gulf by internal wave radiation. This inability to detect changes in barotropic resonant period due
to stratification effects is due to the small change in resonant frequency produced by baroclinic effects, as shown by analytical
results, and the broad peak nature of the computed resonant frequency. In the case of a closed offshore boundary (an offshore
island), there is a stronger and narrower energy peak at the resonant frequency than when a barotropic radiation condition
is applied. However, the influence of stratification upon the resonant frequency could not be accurately determined. Although
the offshore boundary was well removed from the gulf to such an extent that any baroclinic waves reflected from it could not
reach the gulf within the integration period, it did, however, slightly influence the gulf baroclinic response due to its
influence on the barotropic response. 相似文献
773.
A cross-sectional nonhydrostatic model using idealized sill topography is used to examine the influence of bottom friction
upon unsteady lee wave generation and flow in the region of a sill. The implications of changes in shear and lee wave intensity
in terms of local mixing are also considered. Motion is induced by a barotropic tidal flow which produces a hydraulic transition,
associated with which are convective overturning cells, wave breaking, and unsteady lee waves that give rise to mixing on
the lee side of the sill. Calculations show that, as bottom friction is increased, current profiles on the shallow sill crest
develop a highly sheared bottom boundary layer. This enhanced current shear changes the downwelling of isotherms downstream
of the sill with an associated increase in the hydraulic transition, wave breaking, and convective mixing in the upper part
of the water column. Both short and longer time calculations with wide and narrow sills for a number of sill depths and buoyancy
frequencies confirm that increasing bottom friction modifies the flow and unsteady lee wave distribution on the downstream
side of a sill. Associated with this increase in bottom friction coefficient, there is increased mixing in the upper part
of the water column with an associated decrease in the vertical temperature gradient. However, this increase in mixing and
decrease in temperature gradient in the upper part of the water column is very different from the conventional change in near-bed
temperature gradient produced by increased bottom mixing that occurs in shallow sea regions as the bottom drag coefficient
is increased. 相似文献
774.
H. Sugai R. I. Davies M. Ishii M. J. Ward 《Monthly notices of the Royal Astronomical Society》2000,317(2):447-452
We have obtained an H2 v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H2 emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging. 相似文献
775.
Russell J. Smith John R. Lucey Michael J. Hudson David J. Schlegel Roger L. Davies 《Monthly notices of the Royal Astronomical Society》2000,313(3):469-490
We present new spectroscopic data for 532 early-type galaxies, predominantly Abell cluster members with cz <12 000 km s−1 . We tabulate 919 individual measurements, from six observing runs, for recession velocity, cz , central velocity dispersion, σ , and magnesium line-strength indices, Mg2 and Mg b . The median estimated error, per measurement, in σ is 5 per cent. The Mg2 line-strength data have median errors of 0.009 mag. The observed scatter between repeat measurements is largely accounted for by photon-counting errors. These data will be employed in forthcoming papers, where they will form part of a merged and standardized catalogue of Fundamental Plane data for use in cluster distance estimates and peculiar velocity analyses. 相似文献
776.
Giovanni Leone Ashley Gerard Davies Lionel Wilson David A. Williams Laszlo P. Keszthelyi Windy L. Jaeger Elizabeth P. Turtle 《Journal of Volcanology and Geothermal Research》2009,187(1-2):93-105
Data from Jupiter's moon Io returned by the Galileo spacecraft have been used to create a geologic map of Prometheus Patera, its associated flow field, and nearby features. We have identified the location of the vent that fed the Prometheus flow field during the Galileo epoch in the north-eastern portion of the main Prometheus flow field. This vent is the probable source of a small sulphur-rich plume. Previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault. It is plausible that, in the past, magma exploited the fault to reach the surface at Prometheus Patera, but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the Prometheus flow field. We also speculate on how a new Prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle. 相似文献
777.
Marc K. Reichow M.S. Pringle A.I. Al'Mukhamedov M.B. Allen V.L. Andreichev M.M. Buslov C.E. Davies G.S. Fedoseev J.G. Fitton S. Inger A.Ya. Medvedev C. Mitchell V.N. Puchkov I.Yu. Safonova R.A. Scott A.D. Saunders 《Earth and Planetary Science Letters》2009,277(1-2):9-20
We present new high-precision 40Ar/39Ar ages on feldspar and biotite separates to establish the age, duration and extent of the larger Siberian Traps volcanic province. Samples include basalts and gabbros from Noril'sk, the Lower Tunguska area on the Siberian craton, the Taimyr Peninsula, the Kuznetsk Basin, Vorkuta in the Polar Urals, and from Chelyabinsk in the southern Urals. Most of the ages, except for those from Chelyabinsk, are indistinguishable from those found at Noril'sk. Cessation of activity at Noril'sk is constrained by a 40Ar/39Ar age of 250.3 ± 1.1 Ma for the uppermost Kumginsky Suite.The new 40Ar/39Ar data confirm that the bulk of Siberian volcanism occurred at 250 Ma during a period of less than 2 Ma, extending over an area of up to 5 million km2. The resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates, or is synchronous with, the end-Permian mass extinction, further strengthening an association between volcanism and the end-Permian crisis. A sanidine age of 249.25 ± 0.14 Ma from Bed 28 tuff at the global section and stratotype at Meishan, China, allows us to bracket the P–Tr boundary to 0.58 ± 0.21 myr, and enables a direct comparison between the 40Ar/39Ar age of the Traps and the Permo–Triassic boundary section.Younger ages (243 Ma) obtained for basalts from Chelyabinsk indicate that volcanism in at least the southern part of the province continued into the Triassic. 相似文献
778.
Advances in the Study of Moving Sediments and Evolving Seabeds 总被引:1,自引:0,他引:1
Sands and mud are continually being transported around the world’s coastal seas due to the action of tides, wind and waves.
The transport of these sediments modifies the boundary between the land and the sea, changing and reshaping its form. Sometimes
the nearshore bathymetry evolves slowly over long time periods, at other times more rapidly due to natural episodic events
or the introduction of manmade structures at the shoreline. For over half a century we have been trying to understand the
physics of sediment transport processes and formulate predictive models. Although significant progress has been made, our
capability to forecast the future behaviour of the coastal zone from basic principles is still relatively poor. However, innovative
acoustic techniques for studying the fundamentals of sediment movement experimentally are now providing new insights, and
it is expected that such observations, coupled with developing theoretical works, will allow us to take further steps towards
the goal of predicting the evolution of coastlines and coastal bathymetry. This paper presents an overview of our existing
predictive capabilities, primarily in the field of non-cohesive sediment transport, and highlights how new acoustic techniques
are enabling our modelling efforts to achieve greater sophistication and accuracy. The paper is aimed at coastal scientists
and managers seeking to understand how detailed physical studies can contribute to the improvement of coastal area models
and, hence, inform coastal zone management strategies. 相似文献
779.
During August 1998, the UK EISCAT special programme SP-UK-CSUB, which combines operation of both the mainland VHF and Svalbard UHF incoherent scatter radars, was run for several hours around magnetic midnight on four consecutive days. The CUTLASS Finland HF coherent scatter radar was, at these times, operating in a discretionary mode, sounding on all 16 beams, one at high-time resolution. This study presents a comparison of the velocities measured by coherent and incoherent techniques during the SP-UK-CSUB experiments. Agreement, particularly between the ion velocities measured by the EISCAT Svalbard radar and irregularity drift measurements by the Finland radar, is remarkable, thereby validating the scientific integrity of both data sets. This work highlights the substantive contribution to our understanding of the solar-terrestrial environment which can be made by use in concert of incoherent and HF coherent scatter radars. 相似文献
780.
Soft-sediment deformation during thawing of ice-rich frozen soils: results of scaled centrifuge modelling experiments 总被引:2,自引:0,他引:2
The origin of periglacial involutions remains uncertain, largely because of the difficulties of field monitoring in modern permafrost regions. This paper describes an alternative approach, in which process studies are based on scaled centrifuge modelling of thawing ice-rich soils. Centrifuge scaling laws allow similitude in self-weight stresses between the model scale and the prototype (field) scale to be achieved. In these experiments, 120- to 130-mm-thick frozen models comprising a sand unit overlying ice-rich kaolinite clay (three models) or ice-rich silt (one model) were thawed under an acceleration of 20 gravities. The models were therefore equivalent to 2·4–2·6 m of frozen sediments (permafrost) at the prototype scale. Temperature profiles and porewater pressures during the thawing of each model are described. Porewater pressures significantly in excess of hydrostatic were not observed in the sand/silt model. In the sand/clay models, however, excess pressures developed rapidly after thawing, and observed fluctuations in pressure were interpreted as water-escape events. After thawing, careful sectioning of the models revealed small-scale deformation structures at the clay–sand interface, resulting from loading of the upper sand layer into very soft fluid-like clay and injection of clay upwards into the base of the sand. It is concluded that these experiments provide analogues for some Pleistocene involutions. Such involutions therefore mark phases of permafrost degradation when high porewater pressures caused loading and injection along sedimentary boundaries. 相似文献