Research note: Seismic attenuation due to wave‐induced fluid flow at microscopic and mesoscopic scales     

J. Germán Rubino  Klaus Holliger 《Geophysical Prospecting》2013,61(4):882-889

Wave‐induced fluid flow at microscopic and mesoscopic scales arguably constitutes the major cause of intrinsic seismic attenuation throughout the exploration seismic and sonic frequency ranges. The quantitative analysis of these phenomena is, however, complicated by the fact that the governing physical processes may be dependent. The reason for this is that the presence of microscopic heterogeneities, such as micro‐cracks or broken grain contacts, causes the stiffness of the so‐called modified dry frame to be complex‐valued and frequency‐dependent, which in turn may affect the viscoelastic behaviour in response to fluid flow at mesoscopic scales. In this work, we propose a simple but effective procedure to estimate the seismic attenuation and velocity dispersion behaviour associated with wave‐induced fluid flow due to both microscopic and mesoscopic heterogeneities and discuss the results obtained for a range of pertinent scenarios.  相似文献   

Multi-stage Ag–Bi–Co–Ni–U and Cu–Bi vein mineralization at Wittichen,Schwarzwald, SW Germany: geological setting,ore mineralogy,and fluid evolution     

Sebastian?Staude  Wolfgang?Werner  Teresa?Mordhorst  Klaus?Wemmer  Dorrit?E.?Jacob  Gregor?MarklEmail author 《Mineralium Deposita》2012,47(3):251-276

The Wittichen Co–Ag–Bi–U mining area (Schwarzwald ore district, SW Germany) hosts several unconformity-related vein-type mineralizations within Variscan leucogranite and Permian to Triassic redbeds. The multistage mineralization formed at the intersection of two fault systems in the last 250 Ma. A Permo-Triassic ore stage I with minor U–Bi–quartz–fluorite mineralization is followed by a Jurassic to Cretaceous ore stage II with the main Ag and Co mineralization consisting of several generations of gangue minerals that host the sub-stages of U–Bi, Bi–Ag, Ni–As–Bi and Co–As–Bi. Important ore minerals are native elements, Co and Ni arsenides, and pitchblende; sulphides are absent. The Miocene ore stage III comprises barite with the Cu–Bi sulfosalts emplectite, wittichenite and aikinite, and the sulphides anilite and djurleite besides native Bi, chalcopyrite, sphalerite, galena and tennantite. The mineral-forming fluid system changed from low salinity (<5 wt.% NaCl) at high temperature (around 300°C) in Permian to highly saline (around 25 wt.% NaCl + CaCl₂) at lower temperatures (50–150°C) in Triassic to Cretaceous times. Thermodynamic calculations and comparison with similar mineralizations worldwide show that the Mesozoic ore-forming fluid was alkaline with redox conditions above the hematite–magnetite buffer. We suggest that the precipitation mechanism for native elements, pitchblende and arsenides is a decrease in pH during fluid mixing processes. REE patterns in fluorite and the occurrence of Bi in all stages suggest a granitic source of some ore-forming elements, whereas, e.g. Ag, Co and Ni probably have been leached from the redbeds. The greater importance of Cu and isotope data indicates that the Miocene ore stage III is more influenced by fluids from the overlying redbeds and limestones than the earlier mineralization stages.  相似文献   

Origin and extent of fresh groundwater, salty paleowaters and recent saltwater intrusions in Red River flood plain aquifers, Vietnam   总被引：1，自引：0，他引：1  

Luu T. Tran  Flemming Larsen  Nhan Q. Pham  Anders V. Christiansen  Nghi Tran  Hung V. Vu  Long V. Tran  Hoan V. Hoang  Klaus Hinsby 《Hydrogeology Journal》2012,20(7):1295-1313

A model has been established on the origin and extent of fresh groundwater, salty paleowaters and saltwater from recent seawater intrusions in the Red River flood plain in Vietnam. This was done with geological observations, geophysical borehole logging and transient electromagnetic methods. Salt paleowater is present up to 50–75?km from the coastline, with occurrence controlled by the Holocene transgression. A density-driven leaching of salty porewater has occurred from high-permeability Holocene sediments into underlying Pleistocene deposits, whereas diffusion has dominated in low-permeability layers. In the Pleistocene aquifer, the highest content of dissolved solids is found below two intrinsic valleys with Holocene marine sediments and along the coastline. Recent intrusion of saltwater from the South China Sea is observed in shallow groundwater 35?km inland, probably a result of transport of salty water inland in rivers or leaching of paleowaters from very young near-coast marine sediments. The observed inverted salinity profile, with high saline water overlying fresher groundwater, has been formed due to the global eustatic sea-level changes during the last 8,000–9,000?years. The proposed model may therefore be applicable to other coastal aquifers, with a proper incorporation of the local geological environments.  相似文献   

Geostandards and Geoanalytical Research Bibliographic Review 2011     

Klaus Peter Jochum  Uwe Nohl  Nadja Rothbarth  Beate Schwager  Brigitte Stoll  Ulrike Weis 《Geostandards and Geoanalytical Research》2012,36(4):415-419

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Lu–Hf garnet systematics of a polymetamorphic basement unit: new evidence for coherent exhumation of the Adula Nappe (Central Alps) from eclogite-facies conditions     

Sascha?SandmannEmail author  Thorsten?J.?Nagel  Daniel?Herwartz  Raúl?O.?C.?Fonseca  Robert?M.?Kurzawski  Carsten?Münker  Nikolaus?Froitzheim 《Contributions to Mineralogy and Petrology》2014,168(5):1075

The Adula Nappe in the Central Alps is a mixture of various pre-Mesozoic continental basement rocks, metabasics, ultrabasics, and Mesozoic cover rocks, which were pervasively deformed during Alpine orogeny. Metabasics, ultrabasics, and locally garnet–mica schists preserve eclogite-facies assemblages while the bulk of the nappe lacks such evidence. We provide garnet major-element data, Lu profiles, and Lu–Hf garnet geochronology from eclogites sampled along a north–south traverse. A southward increasing Alpine overprint over pre-Alpine garnets is observed throughout the nappe. Garnets in a sample from the northern Adula Nappe display a single growth cycle and yield a Variscan age of 323.8 ± 6.9 Ma. In contrast, a sample from Alpe Arami in the southernmost part contains unzoned garnets that fully equilibrated to Alpine high-pressure (HP) metamorphic conditions with temperatures exceeding 800 °C. We suggest that the respective Eocene Lu–Hf age of 34.1 ± 2.8 Ma is affected by partial re-equilibration after the Alpine pressure peak. A third sample from the central part of the nappe contains separable Alpine and Variscan garnet populations. The Alpine population yields a maximum age of 38.8 ± 4.3 Ma in line with a previously published garnet maximum age from the central nappe of 37.1 ± 0.9 Ma. The Adula Nappe represents a coherent basement unit, which preserves a continuous Alpine high-pressure metamorphic gradient. It was subducted as a whole in a single, short-lived event in the upper Eocene. Controversial HP ages and conditions in the Adula Nappe may result from partly preserved Variscan assemblages in Alpine metamorphic rocks.  相似文献   

Editorial: The Depositional Record     

Peter K. Swart  Paul A. Carling  Adrian M. Immenhauser  James S. Klaus 《Sedimentology》2014,61(6):1485-1485

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Superrotation of the thermosphere by global deposition of meteoroids?     

Peter W. Blum  David W. Hughes  Klaus G.H. Schuchardt 《Planetary and Space Science》1975,23(5):892-896

Mitra has suggested that the Superrotation of the upper atmosphere is caused by a deposition of meteoroids. The meteoroids are assumed to impart to the atmosphere the excess of their orbital angular momentum per unit mass over the Earth's angular momentum per unit mass. The process is to take place in the height region above 150 km. Only above this height is a Superrotation of the atmosphere observed. In this report the forces that tend to make the atmosphere corotate with the Earth are analysed. It is shown that the most important of these forces is ion drag, and not viscous drag as postulated by Mitra. As the net angular spin momentum imparted by the meteoroids seems to be less than Mitra's estimate and its main part is applied to the atmosphere at altitudes much lower than 150 km, the hypothesis that meteoroids provide a significant contribution to the Superrotation is rejected.  相似文献   

An impact model of Newton’s law of gravitation     

Klaus Wilhelm  Horst Wilhelm  Bhola N. Dwivedi 《Astrophysics and Space Science》2013,343(1):135-144

The far-reaching gravitational force—in the approximation of Newton’s law of gravitation—is described by a heuristic model with hypothetical massless particles propagating at the speed of light in vacuum and transferring momentum and energy between physical entities through interactions on a local basis. The model has some similarities with the impact theory presented by Nicolas Fatio de Duillier to the Royal Society in 1690. Objections raised against this idea are dispelled by invoking the Special Theory of Relativity, considering non-local interactions, and replacing the shielding concept by a secular mass increase of massive bodies. Some consequences and applications of the model are discussed.  相似文献   

Ejection behavior characteristics in experimental cratering in sandstone targets     

Frank SOMMER  Fiona REISER  Anja DUFRESNE  Michael H. POELCHAU  Tobias HOERTH  Alex DEUTSCH  Thomas KENKMANN  Klaus THOMA 《Meteoritics & planetary science》2013,48(1):33-49

Abstract– Within the frame of the MEMIN research unit (Multidisciplinary Experimental and Numerical Impact Research Network), impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass, velocity, and target water saturation on the cratering and ejection processes. The projectiles were accelerated with two‐stage light‐gas guns (Ernst‐Mach‐Institute) onto fine‐grained targets (Seeberger sandstone) with about 23% porosity. Collection of the ejecta on custom‐designed catchers allowed determination of particle shape, size distribution, ejection angle, and microstructures. Mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high‐speed videos. The increase in projectile mass from 0.067 to 7.1 g correlates with an increase in the total ejected mass; ejecta angles, however, are similar in range for all experiments. The increase in projectile velocity from 2.5 to 5.1 km s^?1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency, and a widening of the ejecta cone. A higher degree of water saturation of the target yields an increase in total ejecta mass up to 400% with respect to dry targets, higher ejecta velocity, and a steeper cone. These data, in turn, suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase, while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution.  相似文献   

World space observatory-ultraviolet among UV missions of the coming years     

Boris Shustov  Mikhail Sachkov  Ana I. Gómez?de?Castro  Klaus Werner  Norbert Kappelmann  Alexander Moisheev 《Astrophysics and Space Science》2011,335(1):273-282

Continuous access to the UV domain has been considered of importance to astrophysicists and planetary scientists since the mid-sixties. However, the future of UV missions for the post-HST era is believed by a significant part of astronomical community to be less encouraging. We argue that key science problems of the coming years will require further development of UV observational technologies. Among these hot astrophysical issues are: the search for missing baryons, revealing the nature of astronomical engines, properties of atmospheres of exoplanets as well as of the planets of the Solar System etc. We give a brief review of UV-missions both in the past and in the future. We conclude that UV astronomy has a great future but the epoch of very large and efficient space UV facilities seems to be a prospect for the next decades. As to the current state of the UV instrumentation we think that this decade will be dominated by the HST and coming World Space Observatory-Ultraviolet (WSO-UV) with a 1.7 m UV-telescope onboard. The international WSO-UV mission is briefly described. It will allow high resolution/high sensitivity imaging and high/low resolution spectroscopy from the middle of the decade.  相似文献