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91.
92.
Quantification of strain rate in the Western Alps using geodesy: comparisons with seismotectonics 总被引:1,自引:0,他引:1
Bastien Delacou Christian Sue Jean-Mathieu Nocquet Jean-Daniel Champagnac Cécile Allanic Martin Burkhard 《Swiss Journal of Geoscience》2008,101(2):377-385
The contrasted seismotectonic regime of the Western Alps is characterized by radial extension in the high chain, combined with local compressive areas at the foothill of the belt, and everywhere occurrence of transcurrent tectonics. Here, we compare this seismotectonic regime to a large-scale compilation of GPS measurements in the Western Alpine realm. Our analysis is based on the raw GPS database, which give the measured velocity field with respect to the so called “stable Europe”, and an interpolated velocity field, in order to smooth the database on a more regular mesh. Both strain rate and rotational components of the deformation are investigated. The strain rate field shows patch-like structure, with extensional areas located in the core and to the North of the belt and compressional areas located in its periphery. Although the GPS deformation fields (both raw and interpolated) are more spatially variable than the seismotectonic field, a good qualitative correlation is established with the seismotectonic regionalization of the deformation. The rotation rate fields (both raw and interpolated) present counterclockwise rotations in the innermost part of the belt and a surprising continuous zone of clockwise rotations following the arc-shape geometry of the Western Alps along their external border. We interpret this new result in term of a counterclockwise rotation of the Apulia plate with respect to the stable Europe. This tectonic scheme may induce clockwise rotations of crustal block along the large strike-slip fault system, which runs in the outer part of the belt, from the Rhône-Simplon fault to the Belledonne fault and Southeastward, to the High-Durance and Argentera fault. 相似文献
93.
Merged remotely sensed data for geomorphological investigations in deserts: examples from central Saudi Arabia 总被引:1,自引:0,他引:1
Image merging has gained acceptance in geological remote sensing, however it has rarely been applied in geomorphology. We report on the usefulness of principal components substitution (PCS) to merge IRS panchromatic data with multispectral Thematic Mapper (TM) imagery, to map commonly encountered desert geomorphological features, and in relative age dating of alluvial surfaces. The merged data were applied to the identification and mapping of geomorphological features along two geolo-gically different mountain fronts in central Saudi Arabia. Two types of geomorphological maps have been created. A morphogenetic map that distinguishes between aeolian landforms, fluvial landforms, desert pavements, and gypsum crusts. Second, a morphochronological map, which shows the relative age of four geomorphic surfaces developed on an alluvial fan. The construction of the two maps is supported by field observations and laboratory measurements. Using the optimum index factor (OIF), a TM band 1, 5 and 7 image (of 20 merged composites) was found to be the optimum colour composite image for the geomorphological features in this arid environment. We discuss our findings in the context of the spatial and spectral properties required for applied geomorphological remote sensing. 相似文献
94.
Sue Bowler 《Astronomy& Geophysics》2003,44(3):3.08-3.12
Sue Bowler draws together some of the NAM scientific sessions, to capture the flavour of this lively and popular meeting. 相似文献
95.
96.
Complexation of europium (III) and UO22+ by humic acid was found to be very fast (< 1 m). However, passage through ion exchange resin removed a fraction which decreased as the contact time increased over a 2–3 day period. The dissociation kinetics for UO22+-humate were described by an equation with five first order terms with rate constants ranging from 40.6 m−1 to 5.64×10−3 m−1. The percentage of UO22+ dissociating by the slower paths, comparable to that eluting with the humic acid through the ion exchange resin is assigned to internal site-bound cations (strong binding). The faster dissociating fraction corresponded roughly to the UO22+ removed by the cation exchange resin (weak binding). The time dependence of the weak to strong binding ratio was associated with change in the conformation of the macromolecular humic acid as the cations neutralized the charge repulsions of the anionic humate. 相似文献
97.
Mary Sue Bell 《Meteoritics & planetary science》2016,51(4):619-646
A study of pure, single crystal calcite shocked to pressures from 9.0 to 60.8 GPa was conducted to address contradictory data for carbonate shock behavior. The recovered materials were analyzed optically and by transmission electron microscopy (TEM), as well as by thermogravimetry (TGA), X‐ray diffraction (XRD), and Raman‐spectroscopy. In thin section, progressive comminution of calcite is observed although grains remain birefringent to at least 60.8 GPa. TGA analysis reveals a positive correlation between percent of mass loss due to shock and increasing shock pressure (R = 0.77) and suggests that shock loading leads to the modest removal of structural volatiles in this pressure range. XRD patterns of shocked Iceland spar samples produce peaks that are qualitatively and quantitatively less intense, more diffuse, and shift to lower o2θ. However, the regularity observed in these shocked powder patterns suggests that structures with very uniform unit cell separations persist to shock pressures as high as 60.8 GPa. Raman spectral analyses indicate no band asymmetry and no systematic peak shifting or broadening. TEM micrographs display progressively diminishing crystallite domain sizes. Selected area electron diffraction (SAED) patterns reveal no signatures of amorphous material. These data show that essentially intact calcite is recovered at shock pressures up to 60.8 GPa with only slight mass loss (~7%). This work suggests that the amount of CO2 gas derived from shock devolatilization of carbonate by large meteorite impacts into carbonate targets has been (substantially) overestimated. 相似文献
98.
Rivers transport both organic and inorganic carbon from their sources to the sea. Results of ~800 organic and inorganic analyses from various British rivers of contrasting size and land use are presented here: (1) the headwater River Tern, a rural river of 852 km2 catchment; (2) the Ouseburn, a small urban 55 km2 catchment; (3) the River Tyne, a larger river system of ~3000 km2 catchment; (4) a spatial survey from 205 sample sites on ~60 rivers from SW England. We found that, with the exception of peat-rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO3 − , with DIC concentrations highest in highly urbanised catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognised anthropogenic inorganic carbon input to urban rivers. 相似文献
99.
Late Weichselian relative sea-level changes and ice sheet history in southeast Greenland 总被引:1,自引:0,他引:1
Antony J. Long David H. Roberts Matthew J.R. Simpson Sue Dawson Glenn A. Milne Philippe Huybrechts 《Earth and Planetary Science Letters》2008,272(1-2):8-18
Relative sea-level (RSL) observations from the margins of the Greenland Ice Sheet (GIS) provide information regarding the timing and rate of deglaciation and constraints on geophysical models of ice sheet evolution. In this paper we present the first RSL record for the southeast sector of the GIS based on field observations completed close to Ammassalik. The local marine limit is c. 69 m above sea-level (asl) and is dated to c. 11 k cal. yrs BP (thousand calibrated years before present) and is a minimum date for ice free conditions at the study site. RSL fell to c. 24 m asl by 9.5 k cal. yrs BP and continued to fall at a decreasing rate to reach close to present by 6.5 k cal. yrs BP. Our chronology agrees with radiocarbon dates from offshore cores that indicate ice free conditions on the adjacent mid-shelf by 15 k cal. yrs BP. We compare the new RSL data with predictions generated using two recently published glaciological models of the GIS that differ in the amount and timing of ice loading and unloading over our study area. These two GIS models are coupled to the same Earth viscosity model and background (global) ice model to aid in the data-model comparison. Neither model provides a close fit to the RSL observations. Based on a preliminary sensitivity study using a suite of Earth viscosity models, we conclude that the poor data-model fit is most likely due to an underestimate of the local ice unloading. An improved fit could be achieved by delaying the retreat of a thicker ice sheet across the continental shelf. A thick ice sheet extending well onto the continental shelf is in agreement with other recent observations elsewhere in east and south Greenland. 相似文献
100.
This is the text of a letter sent by the President of the RAS to Lord Sainsbury of Turville, Parliamentary Under Secretary of State for Science, following the Discussion Meeting on ESO. 相似文献