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11.
P. R. Vogt J. Gardner K. Crane E. Sundvor F. Bowles G. Cherkashev 《Geo-Marine Letters》1999,19(1-2):97-110
Numerous small (50- to 300-m-diameter) strong-backscatter objects were imaged on the 1200- to 1350-m deep crest of Vestnesa
Ridge (Fram Strait) and along the 900- to 1000-m deep northeast margin of the Storegga slide valley. Ground-truthing identified
most of these objects as 2- to 10-m-deep pockmarks, developed within soft, acoustically stratified silty clays (typical wet
bulk density: 1400–1600 kg m-3; sound speed: 1480– 1505 m s-1; porosity, 65–75%; shear strength: 5–10 kPa; water content: 80–120%; and thermal conductivity: 0.8–0.9 W m-1 deg C-1 in the top 3 m). Gas wipeouts, enhanced reflectors, and reflector discontinuities indicate recent or ongoing activity, but
the absence of local heat flow anomalies suggests that any upward fluid flows are modest and/or local. 相似文献
12.
Heat flow taken between Svalbard and Greenland reveal three thermal provinces:
- 1. (1) the Molloy Ridge within the Spitsbergen Transform,
- 2. (2) the Yermak Plateau
- 3. (3) the northeastern margin of Svalbard (Nordaustlandet).
13.
Recent geophysical measurements, including multi-channel seismic reflection, on the Svalbard passive margin have revealed that it has undergone a complex geological history which largely reflects the plate tectonic evolution of the Greenland Sea and the Arctic Ocean. The western margin (75–80°N) is of a sheared-rifted type, along which the rifted margin developed subsequent to a change in the pole of plate rotation about 36 m.y. B.P. The north-trending Hornsund Fault on the central shelf and the eastern escarpment of the Knipovich Ridge naturally divide the margin into three structural units. These main marginal structures strike north, paralleling the regional onshore fault trends. This trend also parallels the direction of Early Tertiary plate motion between Svalbard and Greenland. Thus, the western Svalbard margin was initially a zone of shear, and the shear movements have affected the adjacent continental crust. Although, the nature and location of the continent—ocean crustal transition is somewhat uncertain, it is unlikely to lie east of the Hornsund Fault. The northern margin, including the Yermak marginal plateau, is terminated to the west by the Spitsbergen Fracture Zone system. This margin is of a rifted type and the preliminary analysis indicates that the main part of the investigated area is underlain by continental crust. 相似文献
14.
Numerical ocean modelling is computationally very demanding. Traditionally, the hydrostatic approximation has been applied to reduce the computational burden. This approximation is valid in large scale studies with coarse grid resolution. With faster computers and gradually smaller grid sizes, we may expect that more studies will be performed with non-hydrostatic ocean models. In recent papers several methods for including non-hydrostatic pressure in σ-coordinate models have been suggested. In this paper the sensitivity of the non-hydrostatic pressure field, the velocity fields, and the density fields to changes in the method for computing non-hydrostatic pressure in σ-coordinate ocean models is addressed.The first test case used involves the propagation and breaking of an internal wave at an incline in a tank. The other test case concerns tidally driven flow over a sill in a stratified fjord. The results from our numerical exercises suggest that the velocity and density fields are very robust to the model choices investigated here. The differences between the model results are of the same order as the uncertainty due to the internal pressure gradient error, and they are smaller than an estimate of the uncertainty due to subgrid scale closure. 相似文献
15.
Flow in a porous medium can be described by a set of non-linear partial differential equations. The pressure variable satisfies
a maximum principle, which guarantees that the solution will have no oscillations. A discretisation of the pressure equation
should preserve this monotonicity property. Whether a numerical method is monotone will depend both on the medium and on the
grid. We study monotonicity of Multi-point Flux Approximation methods on triangular grids. We derive necessary conditions
for monotonicity on uniform grids. Further, we study the robustness of the methods on rough grids, and quantify the violations
of the maximum principle. These investigations are done for single phase flow, however, they are supported by two-phase simulations. 相似文献
16.
Anna Nissen Eirik Keilegavlen Tor Harald Sandve Inga Berre Jan Martin Nordbotten 《Computational Geosciences》2018,22(2):451-467
In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks. 相似文献
17.
In coronal holes the electron (proton) density is low, and heating of the proton gas produces a rapidly increasing proton temperature in the inner corona. In models with a reasonable electron density in the upper transition region the proton gas becomes collisionless some 0.2 to 0.3 solar radii into the corona. In the collisionless region the proton heat flux is outwards, along the temperature gradient. The thermal coupling to electrons is weak in coronal holes, so the heat flux into the transition region is too small to supply the energy needed to heat the solar wind plasma to coronal temperatures. Our model studies indicate that in models with proton heating the inward heat conduction may be so inefficient that some of the energy flux must be deposited in the transition region to produce the proton fluxes that are observed in the solar wind. If we allow for coronal electron heating, the energy that is needed in the transition region to heat the solar wind to coronal temperatures, may be supplied by heat conduction from the corona. 相似文献
18.
The Bam Earthquake of 26 December 2003 总被引:3,自引:0,他引:3
Farrokh?NadimEmail author Masoud?Moghtaderi-Zadeh Conrad?Lindholm Arild?Andresen Svein?Remseth Mohammad?Javad?Bolourchi Mohammad?Mokhtari Eirik?Tvedt 《Bulletin of Earthquake Engineering》2004,2(2):119-153
The devastating earthquake of 26 December 2003 claimed more than 26,000 lives in the city of Bam and surrounding towns and villages in Southeast Iran, and left the majority of the Bam population homeless. The reason for this tragedy was an unfortunate combination of geological, social and human circumstances. The causative fault practically traversed the city of Bam and the earthquake occurred at a shallow depth. The residential buildings were completely inappropriate for a seismic region, being extremely vulnerable to earthquake shaking, and the earthquake occurred early in the morning when most people were still sleeping. The damage pattern was nearly symmetric about a line 3 km to the west of the surface expression of the Bam fault, and the damage attenuated rapidly with distance from this line. The industrial facilities and the lifelines performed relatively well and experienced slight to moderate damage, but this might have been due to their distance from the earthquake epicentre. However, many of the qanat (traditional subterranean irrigation channels) chains that served the twin cities of Bam and Baravat collapsed. Emergency facilities (hospitals, police and fire stations), schools and the university were destroyed and/or heavily damaged during the earthquake. The geotechnical effects of the earthquake were not significant. There was little evidence that site response effects played a major role in the damage pattern in the city. There were no reports of liquefaction and only minor sliding activity took place during the event. A unique set of strong motion acceleration recordings were obtained at the Bam accelerograph station. The highest peak ground acceleration (nearly 1g) was recorded for the vertical component of the motion. However, the longitudinal component (fault-parallel motion in N–S direction) clearly had the largest energy flux, as well as the largest maximum velocity and displacement. 相似文献
19.
The role of the Spitsbergen shear zone in determining morphology,segmentation and evolution of the Knipovich Ridge 总被引:1,自引:1,他引:1
Crane Kathleen Doss Hany Vogt Peter Sundvor Eirik Cherkashov Georgy Poroshina Irina Joseph Devorah 《Marine Geophysical Researches》2001,22(3):153-205
In 1989–1990 the SeaMARC II side-looking sonar and swath bathymetric system imaged more than 80 000 km2 of the seafloor in the Norwegian-Greenland Sea and southern Arctic Ocean. One of our main goals was to investigate the morphotectonic
evolution of the ultra-slow spreading Knipovich Ridge from its oblique (115° ) intersection with the Mohns Ridge in the south
to its boundary with the Molloy Transform Fault in the north, and to determine whether or not the ancient Spitsbergen Shear
Zone continued to play any involvement in the rise axis evolution and segmentation.
Structural evidence for ongoing northward rift propagation of the Mohns Ridge into the ancient Spitsbergen Shear Zone (forming
the Knipovich Ridge in the process) includes ancient deactivated and migrated transforms, subtle V-shaped-oriented flank faults
which have their apex at the present day Molloy Transform, and rift related faults that extend north of the present Molloy
Transform Fault. The Knipovich Ridge is segmented into distinct elongate basins; the bathymetric inverse of the very-slow
spreading Reykjanes Ridge to the south. Three major fault directions are detected: the N-S oriented rift walls, the highly
oblique en-echelon faults, which reside in the rift valley, and the structures, defining the orientation of many of the axial
highs, which are oblique to both the rift walls and the faults in the axial rift valley.
The segmentation of this slow spreading center is dominated by quasi stationary, focused magma centers creating (axial highs)
located between long oblique rift basins. Present day segment discontinuities on the Knipovich Ridge are aligned along highly
oblique, probably strike-slip faults, which could have been created in response to rotating shear couples within zones of
transtension across the multiple faults of the Spitsbergen Shear Zone. Fault interaction between major strike slip shears
may have lead to the formation of en-echelon pull apart basins. The curved stress trajectories create arcuate faults and subsiding
elongate basins while focusing most of the volcanism through the boundary faults. As a result, the Knipovich Ridge is characterized
by Underlapping magma centers, with long oblique rifts.
This style of basin-dominated segmentation probably evolved in a simple shear detachment fault environment which led to the
extreme morphotectonic and geophysical asymmetries across the rise axis. The influence of the Spitsbergen Shear Zone on the
evolution of the Knipovich Ridge is the primary reason that the segment discontinuities are predominantly volcanic.
Fault orientation data suggest that different extension directions along the Knipovich Ridge and Mohns Ridge (280° vs. 330°,
respectively) cause the crust on the western side of the intersection of these two ridges to buckle and uplift via compression
as is evidenced by the uplifted western wall province and the large 60 mGal free air gravity anomalies in this area.
In addition, the structural data suggest that the northwards propagation of the spreading center is ongoing and that a `normal'
pure shear spreading regime has not evolved along this ridge.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
20.