排序方式： 共有21条查询结果，搜索用时 843 毫秒
11.
Grevemeyer Ingo Weigel Wilfried Dehghani G. Ali Whitmarsh Robert B. Avedik Felix 《Marine Geophysical Researches》1997,19(1):1-23
Two seismic refraction and gravity lines were obtained along and normal to the axis of the Aegir Rift, an extinct spreading centre in the Norway Basin. Velocity-depth solutions and crustal structure models are derived from ocean-bottom records using two-dimensional ray tracing and synthetic seismogram modelling techniques. Gravity data are used to generate models consistent with the lateral variations in thickness of the layers in the crustal models. The resulting models require considerable degree of lateral inhomogeneity along and perpendicular to the rift axis. Crust within the extinct spreading centre is found to be thinner and of low P-wave velocity when compared with the crust sampled off-axis. To explain reduced velocities of the lower crust we suggest that, due to the relationship between fracturing and seismic velocity, the decreasing spreading rate leading up to extinction let the mechanically strong layer thicken, so that faulting and fracturing extended to greater depths . Low velocities are also observed in the uppermost mantle underlying the extinct spreading ridge. This zone is attributed to hydrothermal alteration of upper mantle peridotites. Furthermore, after spreading ceased 32-26 my ago, ongoing passive hydrothermal circulation was accompanied by the precipitation of alteration products in open void spaces, thereby decreasing the porosity and increasing the velocity. Consequently the typical low velocities of layer 2 found at active mid-ocean ridges have been replaced by values typical of mature oceanic crust. 相似文献
12.
Jeremy B. Faden Robert S. Weigel Jan Merka Reiner H. W. Friedel 《Earth Science Informatics》2010,3(1-2):41-49
Autoplot is software developed for the Virtual Observatories in Heliophysics to provide intelligent and automated plotting capabilities for many typical data products that are stored in a variety of file formats or databases. Autoplot has proven to be a flexible tool for exploring, accessing, and viewing data resources as typically found on the web, usually in the form of a directory containing data files with multiple parameters contained in each file. Data from a data source is abstracted into a common internal data model called QDataSet. Autoplot is built from individually useful components, and can be extended and reused to create specialized data handling and analysis applications and is being used in a variety of science visualization and analysis applications. Although originally developed for viewing heliophysics-related time series and spectrograms, its flexible and generic data representation model makes it potentially useful for the Earth sciences. 相似文献
13.
Kostelecký J. Kostelecký J. Pešek I. Šimek J. Švábenský O. Weigel J. Zeman A. 《Studia Geophysica et Geodaetica》2004,48(3):503-518
Several quasigeoid models for the Czech Republic have been developed for different purposes since mid-seventies using different data sources: gravimetric, astronomical and GPS/levelling observations, as well as data gained from the territories of neighbouring countries. Two of the recent solutions, namely the VUGTK96 quasigeoid obtained from heterogeneous data and gravimetric quasigeoid CR2000 are described and compared. Accuracies of the models were estimated with the help of accuracy characteristics resulting from the processing, by comparison with GPS/levelling results available for most of the territory, and, finally, tested on a special GPS/levelling profile across the steepest slope of the quasigeoid surface in the south-eastern part of the territory. It is shown that the CR2000 gravimetric quasigeoid is suitable for transformation of ellipsoidal GPS heights to the gravity related heights with an accuracy of 3 cm. 相似文献
14.
Christoph Schaab Manfred K. Weigel 《Monthly notices of the Royal Astronomical Society》1999,308(3):718-730
Recently discovered quasi-periodic oscillations in the X-ray brightness of low-mass X-ray binaries are used to derive constraints on the mass of the neutron star component and the equation of state of neutron star matter. The observations are compared with models of rapidly rotating neutron stars which are calculated by means of an exact numerical method in full relativity. For the equations of state we select a broad collection of models representing different assumptions about the many-body structure and the complexity of the composition of superdense matter. The mass constraints differ from their values in the approximate treatment by ∼10 per cent. Under the assumption that the maximum frequency of the quasi-periodic oscillations originates from the innermost stable orbit, the mass of the neutron star is in the range M ∼1.92–2.25 M⊙ . The quasi-periodic oscillation in the Atoll-source 4U 1820−30 in particular is only consistent with equations of state that are rather stiff at high densities, which is explainable, so far, only with pure nucleonic/leptonic composition. This interpretation contradicts the hypothesis that the protoneutron star formed in SN 1987A collapsed to a black hole, since this would demand a maximum neutron star mass below 1.6 M⊙ . The recently suggested identification of quasi-periodic oscillations with frequencies of about 10 Hz with the Lense–Thirring precession of the accretion disc is found to be inconsistent with the models studied in this work, unless it is assumed that the first overtone of the precession is observed. 相似文献
15.
This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather
summertime conditions. The Riviera Valley in southern Switzerland was chosen for a detailed case study, in which the evaluation
of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350-m
horizontal grid spacing) large-eddy simulations using the numerical model ARPS. The simulations verify what has already been
observed on the basis of measurements: TKE profiles scale surprisingly well if the convective velocity scale w
* is obtained from the sun-exposed eastern slope rather than from the surface directly beneath the profiles considered. ARPS
is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production
mechanism. Therefore, the surface heat flux (and thus w
*) on the eastern slope does not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction
of thermally-driven cross-valley and along-valley flows. Excellent correlation between w
* and the up-valley wind speed solidifies this hypothesis. 相似文献
16.
Soil exploration, collection of hydrologic and meteorologic data, and sequential comparative photography were used to investigate erosion/deposition on alluvial banks of an island in the Ohio River from April 1980 through April 1982. Major erosion episodes coincided with flood events and were caused primarily by exit of bank recharge waters from pervious bank soil layers after flood recession. Waves created by wind and/or vessel passage were of little significance in causing bank failure. Floodwater tractive forces, runout of precipitation-derived waters, and wave action were effective only in removing soft sediments or loose debris from upper bank failures. Sediments deposited by spring floods, if allowed to dry for two to three months, strongly resisted subsequent wave attack. 相似文献
17.
Herber R. Grevemeyer I. Exner O. Villinger H. Weigel W. 《Marine Geophysical Researches》1998,20(3):239-247
Bottom shots have been used for a number of years in seismic studies on the ocean floor. Most experiments utilized explosives as the energy source, though researchers have recognized the usefulness of collapsing water voids to produce seismoacoustic signals. Implosive sources, however, suffered generally from a lack of control of source depth. We present a new experimental tool, called SEEBOSEIS, to carry out seismic experiments on the seafloor utilizing hollow glass spheres as controlled implosive sources. The source is a 10-inch BENTHOS float with penetrator. Inside the sphere we place a small explosive charge (two detonators) to destabilize the glass wall. The time of detonation is controlled by an external shooting device. Test measurements on the Ninetyeast Ridge, Indian Ocean, show that the implosive sources can be used in seismic refraction experiments to image the subbottom P-wave velocity structure in detail beyond that possible with traditional marine seismic techniques. Additionally, the implosions permit the efficient generation of dispersed Scholte waves, revealing upper crustal S-wave velocities. The frequency band of seismic energy ranges from less than 1 Hz for Scholte modes up to 1000 Hz for diving P-waves. Therefore, broadband recording units with sampling rates >2000 Hz are recommended to sample the entire wave field radiated by implosive sources. 相似文献
18.
Seismic velocities of the uppermost igneous crust versus age 总被引：1，自引：0，他引：1
19.
M. W. Pedersen A. Kokkalis H. Bardarson S. Bonanomi W. J. Boonstra W. E. Butler F. K. Diekert N. Fouzai M. Holma R. E. Holt K. Ø. Kvile E. Nieminen K. M. Ottosen A. Richter L. A. Rogers G. Romagnoni M. Snickars A. Törnroos B. Weigel J. D. Whittington P. Woods J. Yletyinen A. S. A. Ferreira 《Climatic change》2016,134(1-2):147-161
20.
A simple, low cost, deep-towed system for high-resolution reflection seismic profiling is described. It consists of a vertical array with two hydrophones having a separation of 2.2 m and rigidly mounted onto streamlined tow bodies. Improvement of the signal-to-noise ratio is attained by simple stacking of the hydrophone outputs after signal conditioning and travel time corrections. The suppression of side echoes and surface reflections is achieved by an analog procedure which in effect improves the directional characteristics of the array. A circuit for automatic gain control is included to enhance weak signals as well as to suppress ringing.Results in Kiel Bay and over the crest of the Jan Mayen Ridge (northern Atlantic) suggest that this simple vertical array may supplement air gun systems better than conventional, surface pinger-type equipment.Institute of Geophysics 相似文献