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731.
732.
The Jason microwave radiometer (JMR) provides a crucial correction due to water vapor in the troposphere, and a much smaller correction due to liquid water, to the travel time of the Jason-1 altimeter radar pulse. An error of any size in the radiometer's measurement of wet path delay translates as an error of equal size in the measurement of sea surface height, the ultimate quantity that the altimetric system should yield. The estimate of globally-averaged sea surface height change associated with climate change, requires that uncertainties in the trends in such a global average be accurate to much better than the signal of 1-2 mm/yr. We first compare the JMR observations to those from the TOPEX/Poseidon radiometer (TMR) over approximately six months, since the intent of Jason is to continue the 10-year time series of precision ocean surface topography initiated by T/P. We then assess the stability of the JMR measurement by comparing its wet path delay to those of other orbiting radiometers over 22 months, specifically the Special Sensor Microwave Imager aboard the Defense Meteorological Satellite Program (DMSP-SSM/I) series of satellites, and the Tropical Rainfall Mapping Mission's Microwave Imager (TMI), as well as the European Center for Medium Range Weather Forecasting's (ECMWF) atmospheric numerical model estimate of water vapor. From the combined set, we obtain a robust assessment of the stability of JMR measurements. We find, that JMR is in remarkable agreement with TMR, only 2.5 mm longer, and 6-7 mm standard deviation on their difference in 0.5 degree averages; that JMR has experienced a globally-averaged step-function change, yielding an apparent shortening in wet path delay estimates of 4-5 mm around October 2002 (Jason cycles 28-32); that this step-function is visible only in the 23.8 GHz channel; and that the 34 GHz channel appears to drift at a rate of -0.4K/year. In addition, we find that, while in 2002 there was no evidence of sensitivity to the Jason satellite's attitude (a correlation of the wet path delay with yaw state), in 2003 there are strong (2-3 mm, up to 7 mm globally averaged) changes associated with such yaw state. These JMR issues were all found in the first 22 months of Jason's geophysical data records (GDR) data, and thus they apply to any investigations that use such data without further corrections. 相似文献
733.
Abdelkarim Yelles Jacques Déverchère Rabah Bracène Pierre Strzerzynski Guillaume Bertrand Thierry Winter Pascal Le Roy Hamou Djellit 《Tectonophysics》2009,475(1):98-116
The Algiers region, northern Algeria, is known to be seismically active, with recurrent large (M>6) earthquakes. Because of the lack of high-resolution bathymetry, the offshore structures remained for a long time poorly known. Thanks to a new marine data base (MARADJA 2003 cruise), the offshore part of the margin is accurately mapped, and new active and recent structures are described. West of the bay of Algiers, the margin enlarges, forming the Khayr al Din bank, interpreted as a tilted block of the passive margin born during the opening of the Algero-Provençal basin. At the slope break, a 80 km-long fault-tip Quaternary fold, namely the Khayr al Din fault, extends at the foot of the margin off NW Algiers and represents the largest active structure of the coastal area, together with the Sahel anticline. We also map for the first time a set of overlapping, en echelon active folds in the upper part of the Khayr al Din bank, located off previously known active structures on land. Most of these faults represent actually a threat for the Algiers region in terms of seismic hazard but also geological hazards, such as tsunamis, as most of them depicts significant dimensions and slip rates. The highest long-term horizontal shortening rate is found on the Khayr al Din fault and is estimated at 0.5 ± 0.1 mm/yr, with a maximal magnitude of 7.3, which provides one of the highest seismogenic potential in the region.A new tectonic framework for the Algiers region is proposed, in which the main south-dipping offshore structure, of opposite vergence relative to most thrusts on land, appears to be nowadays the main driving fault system, as also found further east in the Boumerdès (M 6.8) 2003 rupture zone. The overall apparent pop-up structure of the recent and active faults may result from a progressive migration of the plate limit from the Late Miocene, north-dipping suture zone on land, to the Quaternary, south-dipping main Khayr al Din fault at sea, suggesting a process of subduction inception. 相似文献
734.
This study aims at understanding the physico-chemical interactions between the saturated brine and the rocks enclosing the
underground salt workings in Lorraine (eastern France). These anhydrite-rich and argillaceous rocks were characterized in
terms of mineralogy, micro-texture and connected porosity. Then, the two main lithofacies, massive anhydrite and anhydrite-rich
argillite, were immersed in brine during more than 1 year. During this batch experiment, the argillites were affected by macroscopic
splitting, contrarily to the massive anhydrite. Micro-texture and brine chemical analyses clearly show the swelling due to
the hydration of anhydrite into gypsum inside the argillites, whereas hydration occurs superficially on the massive anhydrite,
due to its very low permeability. Anhydrite–gypsum transformation is promoted by the presence of dissolved strontium and potassium
in saturated brine. The low activity of water in saturated brine does not allow the clay fraction to swell significantly during
the experiment. Thus, the expansion resulting from the hydration of anhydrite into gypsum might be responsible of the splitting
of argillite in a saturated brine environment. The superficial anhydrite hydration on massive anhydrite can be explained by
the low amount of connected porosity (less than 1%). 相似文献
735.
Intracontinental subduction: a possible mechanism for the Early Palaeozoic Orogen of SE China 总被引:11,自引:0,他引:11
Michel Faure Liangshu Shu Bo Wang Jacques Charvet Flavien Choulet Patrick Monie 《地学学报》2009,21(5):360-368
The Early Palaeozoic Orogen of SE China consists of three litho-tectonic elements, from top to bottom: a sedimentary Upper Unit, a metamorphic Lower Unit and a gneissic basement. The boundaries between these units are flat lying, south directed, ductile decollements. The lower one is coeval with an amphibolite facies metamorphism (M1). The belt is reworked by migmatite–granite domes, high-temperature metamorphism (M2) and granitic plutons related to post-orogenic crustal melting. We date here the syn-M1 ductile shearing at 453 ± 7 Ma by U-Th/Pb method on monazite. Previous ages and our new 40 Ar/39 Ar ages of biotites and muscovites show that the metamorphic rocks experienced syn-M2 exhumation from 440 to 400 Ma. The Early Palaeozoic Orogen of SE China is an intracontinental belt in which decollements accommodated the north-directed subduction of the Cathaysian continent. This orogen is an example of intracontinental subduction that was not preceded by oceanic subduction. 相似文献
736.
Koen de Jong Bo Wang Michel Faure Liangshu Shu Dominique Cluzel Jacques Charvet Gilles Ruffet Yan Chen 《International Journal of Earth Sciences》2009,98(6):1239-1258
Laser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North
Tianshan domain’s southern margin yielded 40Ar/39Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation
in the Proterozoic basement of the Yili arcs’s southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous
metasediments overlying this basement yielded plateau ages (1σ) of 253.3 ± 0.3 (muscovite) and 252.3 ± 0.3 (biotite) Ma. The
Permian ages of mylonites date movement on these ductile, dextral strike-slip shear zones, whereas the mica ages are interpreted
by recrystallisation as a result of fluid flow around such transcurrent faults. We propose that the Tianshan’s Permian syn-tectonic
bimodal magmatism was created in a non-plume-related Yellowstone-like extensional–transtensional tectonic regime. Gold mineralisation,
tracing aqueous flow in the crust, peaked in Permian time and continued locally into the Triassic. The picture is emerging
that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an
elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages in the literature
for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation. 相似文献
737.
Southern India and Sri-Lanka are the places where "incipient charnockites",i.e.the local transformation of amphibolite-facies gneisses into orthopyroxene-bearing,igneous looking charnockites,have been discovered in the early sixties.The fact that some incipient charnockites occur along a network of brittle fractures,together with CO_2 remnants preserved in mineral inclusions,had called for the role of fluids during charnockite alteration.The present work presents new observations on fluid inclusions and microtextures of incipient charnockites from type localities in southern India.In addition to CO_2-rich fluid inclusions in quartz and feldspar,all of the occurrences have disrupted remnants of concentrated aqueous alkali chloride solutions.CO_2 inclusions are more abundant in paragneiss(Kerala)than in orthogneiss(Karnataka/Tamil Nadu).The finding of disrupted brine inclusions in the Kabbal charnockite is a key link between closely associated massive charnockites and Closepet Granite,both of which also share the brine remnants.All of the occurrences studied here have feldspar or feldspar-quartz microvein networks along grain boundaries of recrystallized quartz,feldspar and orthopyroxene.These metasomatic veins again indicate the action of alkali-exchanging fluids(i.e.,saline solutions).Feldspar microveins,which have been found in most "massive" charnockites,along with the CO_2-rich fluid inclusions,suggest a commonality of incipient charnockite and massive charnockite,both types differing in intensity of interaction with metasomatizing pore fluids. 相似文献
738.
Gregoire Broquet Pierre Brasseur David Rozier Jean-Michel Brankart Jacques Verron 《Ocean Dynamics》2008,58(1):1-17
The characterization of model errors is an essential step for effective data assimilation into open-ocean and shelf-seas models.
In this paper, we propose an experimental protocol to properly estimate the error statistics generated by imperfect atmospheric
forcings in a regional model of the Bay of Biscay, nested in a basin-scale North Atlantic configuration. The model used is
the Hybrid Coordinate Ocean Model (HYCOM), and the experimental protocol involves Monte Carlo (or ensemble) simulations. The
spatial structure of the model error is analyzed using the representer technique, which allows us to anticipate the subsequent
impact in data assimilation systems. The results show that the error is essentially anisotropic and inhomogeneous, affecting
mainly the model layers close to the surface. Even when the forcings errors are centered around zero, a divergence is observed
between the central forecast and the mean forecast of the Monte Carlo simulations as a result of nonlinearities. The 3D structure
of the representers characterizes the capacity of different types of measurement (sea level, sea surface temperature, surface
velocities, subsurface temperature, and salinity) to control the circulation. Finally, data assimilation experiments demonstrate
the superiority of the proposed methodology for the implementation of reduced-order Kalman filters. 相似文献
739.
To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussées. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on re... 相似文献
740.
Paleozoic accretionary terranes in Northern Tianslian, NW China 总被引:14,自引:2,他引:12
Liangshu Shu Yuntang Chen Huafu Lu Jacques Charvet Sebastie Laurent-Charvet Donghao Yin 《中国地球化学学报》2000,19(3):193-202
During the paleozoic,the Northern Tianshan region of China in Central Asia consists of 7 allochthonous terranes which were situated in the ancient sino-Mongolian Ocean as volcanic arcs and splitted continental fragments.The tectonic framework was similar to that of Southwest pacific today,In the Late Paleozoic,these terranes started mutual amalgamation to cause strong thrusting.At thd end of Carboniferous,the Sino-mongolian ocean including several inter-terrane small sea basins closed and these terranes accreted on the margins of the Siberian and Tarim continents,The 6 ophiolitic zones zomong the terranes recorded this collision event. 相似文献