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111.
Marcos E. Machado Boris V. Somov Marta G. Rovira Cornelis De Jager 《Solar physics》1983,85(1):157-184
We discuss the spatial and temporal characteristics of X-ray flares occurring in the active region NOAA2372 from April 6 to 13, 1980. The flares are seen to extend in most cases across the whole active complex, involving several magnetic features. They originate in an intermediate bipole, between the two main sunspots of the active region, where high magnetic shear was detected. A rapid expansion is seen in some cases, in conjunction with the start of the impulsive hard X-ray bursts. We also detect, in the late phases of some of the events, a large soft X-ray structure overlying the whole active region, which also shows up as a noise storm region at metric wavelengths. These large loops cool by heat conduction but, in some cases, Hα condensations seem to appear, probably as a result of magnetic compression and a condensation mode of the thermal instability. The topological aspects of the field configuration are discussed, in the context of flare models invoking magnetic reconnection at the site of the primary energy release. In such a model, the intermediate bipole is the natural site of initial magnetic reconnection, particle acceleration and heating. In one particular case of a flare observed at the limb, we find possible evidence of particle acceleration in a neutral sheet at the boundary between two clearly defined magnetic structures. 相似文献
112.
Lluís Casas Boutheina Fouzai Marta Prevosti Nejia Laridhi‐Ouazaa Ramon Jrrega Siwar Baklouti 《Geoarchaeology》2016,31(6):564-576
Two isolated kilns of unknown age and three well‐dated artifacts from Tunisia have been investigated using archaeomagnetic techniques. Dating has been attempted for the kilns and archaeomagnetic intensities have been obtained for the artifacts. The kilns lack datable artifacts although one of them (Sidi Zahruni) could be related to a nearby late Roman site. Comparison with the SCHA.DIF.3K regional geomagnetic model suggests for both kilns two possible periods of last use, either Roman or Medieval. Three archaeomagnetic intensities were obtained for the well‐dated ceramic artifacts adding to scarce archaeomagnetic data from Africa. The new data along with recently published archaeointensities from other Tunisian sites have been compared with the regional model SCHA.DIF.3K, its updated version, and the global ARCH3k.1 geomagnetic model. The models show relatively good agreement with the new archaeointensities and with previously published intensities. The uncertainty of the experimental data tends to increase for older artifacts, and their agreement with the geomagnetic models diminishes. The observed trend of the intensity models to underestimate values in the Tunisian area for the Roman period could be overcome by adding new data from well‐dated artifacts from North African, particularly from pre‐Roman and Roman sites. 相似文献
113.
Vojtěch Janoušek Jaroslav Aichler Pavel Hanžl Axel Gerdes Vojtěch Erban Vladimír Žáček Vratislav Pecina Marta Pudilová Kristýna Hrdličková Petr Mixa Eliška Žáčková 《International Journal of Earth Sciences》2014,103(2):455-483
The low-grade metavolcanic/volcanosedimentary complex of the Devonian Vrbno Group (Silesicum, NE Bohemian Massif, Czech Republic) occurs in two ~NE–SW trending belts, separated by tectonic slices of Cadomian metagranitic paraautochton. (1) The basic–intermediate lavas of the calc-alkaline Western Volcanic Belt came from a moderately depleted mantle $ \left( {\varepsilon_{\text{Nd}}^{370} \sim + 3} \right) $ . Rare rhyolites (374.0 ± 1.7 Ma: 2σ, LA–ICP–MS U–Pb Zrn) were derived most likely from immature crust or by extensive fractionation of primary basaltic melts. The rock association is interpreted as a vestige of a deeply dissected continental arc. (2) The Eastern Volcanic Belt consists mainly of (nearly) contemporaneous (371.0 ± 1.4 Ma) felsic alkaline lavas with high HFSE contents, as well as high Ga/Al and Fe/Mg ratios, typical of within-plate igneous setting. The petrology and Nd–Sr isotopic data point to a high-T anatexis of a young metagranitic crust, resembling the Cadomian (Brunovistulian) basement, in a back-arc setting. The attenuated Brunovistulian lithosphere could have partially melted by the heat provided by the upwelling asthenosphere and/or underplating basic magma. (3) Finally, the region was penetrated by numerous subalkaline, MORB/EMORB-like dolerite sheets—a hallmark of the considerable crustal thinning. 相似文献
114.
Maria F. Gazulla Marta Rodrigo Monica Orduña Carmen M. Gómez 《Geostandards and Geoanalytical Research》2012,36(2):201-217
This article describes a series of methods developed for the determination of total carbon (CTotal), organic carbon (Corg), hydrogen, nitrogen and sulfur. The following elemental analysers were used: LECO model RC‐412 for the determination of organic carbon, total carbon and hydrogen; LECO model CS‐200 for the determination of total carbon and sulfur; LECO model TN‐400 for the determination of nitrogen; and LECO model TruSpec CHNS for the determination of organic carbon, total carbon, hydrogen, nitrogen and sulfur. Uncertainty and limits of detection and quantification were calculated for each method, as well as the running costs to define the most effective instrument for each material and each analyte. Accuracy was checked by the application of the Sutarno–Steger test. Finally, a compilation of the results obtained in the determination of CTotal, Corg, H, N and S in forty‐nine reference materials is presented. 相似文献
115.
In southern Poland, Miocene deposits have been recognised both in the Outer Carpathians and the Carpathian Foredeep (PCF). In the Outer Carpathians, the Early Miocene deposits represent the youngest part of the flysch sequence, while in the Polish Carpathian Foredeep they are developed on the basement platform. The inner foredeep (beneath the Carpathians) is composed of Early to Middle Miocene deposits, while the outer foredeep is filled up with the Middle Miocene (Badenian and Sarmatian) strata, up to 3,000mthick. The Early Miocene strata are mainly terrestrial in origin, whereas the Badenian and Sarmatian strata are marine. The Carpathian Foredeep developed as a peripheral foreland basin related to the moving Carpathian front. The main episodes of intensive subsidence in the PCF correspond to the period of progressive emplacement of the Western Carpathians onto the foreland plate. The important driving force of tectonic subsidence was the emplacement of the nappe load related to subduction roll-back. During that time the loading effect of the thickening of the Carpathian accretionary wedge on the foreland plate increased and was followed by progressive acceleration of total subsidence. The mean rate of the Carpathian overthrusting, and north to north-east migration of the axes of depocentres reached 12 mm/yr at that time. During the Late Badenian-Sarmatian, the rate of advance of the Carpathian accretionary wedge was lower than that of pinch-out migration and, as a result, the basin widened. The Miocene convergence of the Carpathian wedge resulted in the migration of depocentres and onlap of successively younger deposits onto the foreland plate. 相似文献
116.
Slope instability induced by volcano-tectonics as an additional source of hazard in active volcanic areas: the case of Ischia island (Italy) 总被引:1,自引:0,他引:1
Marta Della Seta Enrica Marotta Giovanni Orsi Sandro de Vita Fabio Sansivero Paola Fredi 《Bulletin of Volcanology》2012,74(1):79-106
Ischia is an active volcanic island in the Gulf of Naples whose history has been dominated by a caldera-forming eruption (ca.
55 ka) and resurgence phenomena that have affected the caldera floor and generated a net uplift of about 900 m since 33 ka.
The results of new geomorphological, stratigraphical and textural investigations of the products of gravitational movements
triggered by volcano-tectonic events have been combined with the information arising from a reinterpretation of historical
chronicles on natural phenomena such as earthquakes, ground deformation, gravitational movements and volcanic eruptions. The
combined interpretation of all these data shows that gravitational movements, coeval to volcanic activity and uplift events
related to the long-lasting resurgence, have affected the highly fractured marginal portions of the most uplifted Mt. Epomeo
blocks. Such movements, mostly occurring since 3 ka, include debris avalanches; large debris flows (lahars); smaller mass
movements (rock falls, slumps, debris and rock slides, and small debris flows); and deep-seated gravitational slope deformation.
The occurrence of submarine deposits linked with subaerial deposits of the most voluminous mass movements clearly shows that
the debris avalanches impacted on the sea. The obtained results corroborate the hypothesis that the behaviour of the Ischia
volcano is based on an intimate interplay among magmatism, resurgence dynamics, fault generation, seismicity, slope oversteepening
and instability, and eruptions. They also highlight that volcano-tectonically triggered mass movements are a potentially hazardous
phenomena that have to be taken into account in any attempt to assess volcanic and related hazards at Ischia. Furthermore,
the largest mass movements could also flow into the sea, generating tsunami waves that could impact on the island’s coast
as well as on the neighbouring and densely inhabited coast of the Neapolitan area. 相似文献
117.
Marta Tárraga Servando De La Cruz-Reyna Ana T. Mendoza-Rosas Roberto Carniel Alicia Martínez-Bringas Alicia García Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681
The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report
the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous
seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals
recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External
visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We
briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters
in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers
away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic
alert levels. 相似文献
118.
119.
Non‐Metabolic Uptake of Al3+ by Dead Leaves of Rubus ulmifolius: Comparison With Metabolic Bioaccumulation Data
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120.
Michael Tsimplis Marta Marcos Samuel Somot Bernard Barnier 《Global and Planetary Change》2008,63(4):325-332
Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975. 相似文献