Shelf edge and shoreline trajectories, a dynamic approach to stratigraphic analysis   总被引：1，自引：1，他引：0  

Sverre Henriksen  Gary J. Hampson†  William Helland-Hansen‡  Erik P. Johannessen§  Ron J. Steel¶ 《Basin Research》2009,21(5):445-453

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Experimental modelling of shallow magma emplacement: Application to saucer-shaped intrusions     

Olivier Galland  Sverre Planke  Else-Ragnhild Neumann  Anders Malthe-Sørenssen 《Earth and Planetary Science Letters》2009,277(3-4):373-383

Saucer-shaped dolerite and sandstone intrusions are common in sedimentary basins world-wide. We have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins, with particular attention on the formation of saucer-shaped sills. The model materials were (1) cohesive fine-grained silica flour, representing brittle crust; and (2) molten low-viscosity oil, representing magma. The experiments were performed in both homogeneous and layered models. In all the experiments, oil injection resulted in doming of the surface. In the homogeneous models, the injected oil formed cone sheets and sub-vertical dykes. Cone sheets formed for shallow injection (1–3 cm), and vertical dykes formed for deeper injection (4–5 cm). In layered models, the injected oil always formed saucer-shaped intrusions. Our experimental results show that (1) sill intrusion results in the formation of a dome, with melt erupting at the rim; (2) layering controls the formation of sills and saucer-shaped sills; (3) saucer-shaped sills are fed from the bottom and the fluid flows upward and outward; and (4) the diameter of saucer-shaped sills increase with increasing emplacement depth. The systematic relation between domes and sills and the depth-dependence of sill diameters show that saucer-shaped intrusions result from the interaction between a growing flat-lying shallow sill and doming of the free surface. We conclude that saucer-shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins.  相似文献   

Testing the ability of surface arrays to monitor microseismic activity   总被引：2，自引：0，他引：2  

Kit Chambers  J.‐Michael Kendall  Sverre Brandsberg‐Dahl  Jose Rueda 《Geophysical Prospecting》2010,58(5):821-830

Recently there has been much interest in the use of data from surface arrays in conjunction with migration‐based processing methods for passive seismic monitoring. In this study we use an example of this kind of data recorded whilst 18 perforation shots, with a variety of positions and propellant amounts, were detonated in the subsurface. As the perforation shots provide signals with known source positions and origin times, the analysis of these data is an invaluable opportunity to test the accuracy and ability of surface arrays to detect and locate seismic sources in the subsurface. In all but one case the signals from the perforation shots are not visible in the raw or preprocessed data. However, clear source images are produced for 12 of the perforation shots showing that arrays of surface sensors are capable of imaging microseismic events, even when the signals are not visible in individual traces. We find that point source locations are within typically 45 m (laterally) of the true shot location, however the depths are less well constrained (～150 m). We test the sensitivity of our imaging method to the signal‐to‐noise ratio in the data using signals embedded in realistic noise. We find that the position of the imaged shot location is quite insensitive to the level of added noise, the primary effect of increased noise being to defocus the source image. Given the migration approach, the array geometry and the nature of coherent noise during the experiment, signals embedded in noise with ratios ≥0.1 can be used to successfully image events. Furthermore, comparison of results from data and synthetic signals embedded in noise shows that, in this case, prestack corrections of traveltimes to account for near‐surface structure will not enhance event detectability. Although, the perforation shots have a largely isotropic radiation pattern the results presented here show the potential for the use of surface sensors in microseismic monitoring as a viable alternative to classical downhole methods.  相似文献   

The formation of a bound star cluster: from the Orion nebula cluster to the Pleiades     

Pavel Kroupa  Sverre Aarseth  Jarrod Hurley 《Monthly notices of the Royal Astronomical Society》2001,321(4):699-712

Direct N -body calculations are presented of the formation of Galactic clusters using GasEx , which is a variant of the code Nbody6 . The calculations focus on the possible evolution of the Orion nebula cluster (ONC) by assuming that the embedded OB stars explosively drove out 2/3 of its mass in the form of gas about 0.4 Myr ago. A bound cluster forms readily and survives for 150 Myr despite additional mass loss from the large number of massive stars, and the Galactic tidal field. This is the very first time that cluster formation is obtained under such realistic conditions. The cluster contains about 1/3 of the initial 10⁴ stars, and resembles the Pleiades cluster to a remarkable degree, implying that an ONC-like cluster may have been a precursor of the Pleiades. This scenario predicts the present expansion velocity of the ONC, which will be measurable by upcoming astrometric space missions. These missions should also detect the original Pleiades members as an associated expanding young Galactic-field subpopulation. The results arrived at here suggest that Galactic clusters form as the nuclei of expanding OB associations.
The results have wide implications, also for the formation of globular clusters and the Galactic-field and halo stellar populations. In view of this, the distribution of binary orbital periods and the mass function within and outside the model ONC and Pleiades is quantified, finding consistency with observational constraints. Advanced mass segregation is evident in one of the ONC models. The calculations show that the primordial binary population of both clusters could have been much the same as is observed in the Taurus–Auriga star-forming region. The computations also demonstrate that the binary proportion of brown dwarfs is depleted significantly for all periods, whereas massive stars attain a high binary fraction.  相似文献   

Formation of glauconie in foraminiferal shells on the continental shelf off Norway     

Kristian Bjerkli  Johan Sverre Östmo-Saeter 《Marine Geology》1973,14(3):169-178

Glauconie inside shells of foraminifers, assumed to be formed during the timespan from the Last Glaciation to the present, is reported. The process is thought to take place at water temperatures of 6–7°C. The nature of the infilling process is suggested to be neoformation of clay minerals rather than transformation of pre-infilled clay.  相似文献   

On the joint distribution of heights and periods of sea waves     

Sverre Haver 《Ocean Engineering》1987,14(5)

In the design of offshore structures, a consistent method of choosing the height and period for the adopted design wave may be crucial for a reliable design. With this objective, the joint probability density function for the height and period is considered in this paper. At first the adequacy of a simple theoretical model for the joint distribution under stationary conditions is investigated, using measurements achieved during storms in Northern North Sea. In a slightly modified form the model is found to be of a reasonable accuracy as far as the highest waves are of interest. Design curves regarding simultaneous values of heights and periods are estimated by means of this model and their possible impact for design is discussed.  相似文献