排序方式： 共有8条查询结果，搜索用时 46 毫秒
1
1.
2.
The linear oscillations of a stratified atmosphere embedded in a uniform vertical magnetic field are studied here. We use
a simple theoretical model, formed by the superposition of two isothermal layers, representing, respectively, i) the photosphere
and the chromosphere, and ii) the corona. The bottom layer behaves, for some modes, as a resonant cavity where MAG waves are
semi-trapped. We find the existence of two types of modes: 1) Fast modes which are trapped below the transition layer, 2)
Mixed modes which are resonant modes in the first layer and leak part of the energy to the corona. These mixed modes have
been found to be damped in the horizontal direction and can explain the observed slow modes in the corona. 相似文献
3.
Merzouk Ouyed Mouloud Idres Amar Bourmatte Mohamed Salah Boughacha Sadek Samai Abdelkrim Yelles Abderrahmene Haned Chafik Aidi 《Journal of Seismology》2011,15(2):173-189
In order to try to identify the seismogenic sources in the epicentral area, we interpreted data collected from gravity and
aftershocks in the eastern part of the Mitidja basin after the occurrence of the 21 May 2003 Boumerdes earthquake (Mw = 6.8).
The residual gravity anomaly and the horizontal gradient maps revealed the basement shape and density discontinuities. A seismotectonic
model obtained from the aftershocks distribution and gravity data is proposed. This model highlights three active faults:
one offshore and two onshore. The offshore reverse fault striking NE-SW, parallel to the coast, is consistent with the USGS
focal mechanism of the main event, which is assumed to have the most moment release. The two onshore dipping blind active
faults are postulated at crossing angles near the SW tip of the main fault. The interpretation is based mainly on the re-location
and distribution of aftershocks, and their focal solutions. It is also supported by the basin structures obtained from the
inversion and interpretation of residual gravity anomalies, as well as by additional compiled information such as the pattern
of coastal co-seismic uplift. This configuration puts forward the failure mode complexity during the main shock. The topography
of the basement obtained from 3D gravity inversion shows that all the onshore located aftershocks occurred in the basement,
and the area between the two onshore faults rose as a consequence of their sliding. 相似文献
4.
Khadhar Samia Charef Abdelkarim Hidri Yassin Higashi Teruo 《Arabian Journal of Geosciences》2013,6(11):4337-4346
Irrigation by treated wastewater (TWW) can pollute the soil by different organic and inorganic compounds. The pollution level can depend on the irrigation period, soil nature, and wastewater characteristics. Since 1989, the Zaouit Sousse area (central Tunisian) has been irrigated by treated wastewater. The irrigation period and the mineralogy of soil composition change from one locality to another in Zaouit Sousse area. In this work, we are interested in organic compounds, polycyclic aromatic hydrocarbons (PAHs), and heavy metals (HMs) evolution. One control soil (S1) and four irrigated areas soil (S2, S3, S4, and S5) were chosen. The soil samples differ by the irrigation period and soil characteristics. Total PAHs content in control soil was 66.2 ng?g?1 and in irrigated areas were between 46.23 and 129.51 ng?g?1. The PAHs content in irrigated soil, except S5 which has been irrigated with wastewater for 20 years and contains the highest clay fraction percent, decreased with the irrigation period (from 0 to 20 years). The microbial degradation may decrease the PAHs concentrations in the soil thanks to bacterium brought by TWW and the important soil permeability. Concentration of heavy metals ranged from 24 to 1,320 μg?L?1. The HMs (Cu, Cr, Zn, Fe, Ni, Pb, and Cd) contents decreased with the irrigation period (from 10 to 20 years). So, following the PAHs aerobic bio-degradation, this organic compound discharges their absorbed heavy metals which leached to deeper levels. The Cr, Cu, Al, Zn, and Cd mobility depend on the clay yield too. However, the PAHs and Pb mobility are also related to humic substance quantities. Cr and Cu have affinities both to clay and humic substance quantities. 相似文献
5.
A. Domzig V. Gaullier P. Giresse H. Pauc J. Déverchère K. Yelles 《Marine and Petroleum Geology》2009,26(5):673-694
The westernmost Algerian margin (south Algero-Provençal basin) depicts a few offshore active faults, moderate to rare seismicity, and generally very steep slopes (>16°). We classified and mapped 12 echo types according to their sub-bottom acoustic facies observed on this margin on 2–5.2 kHz Chirp echo-sounder data (MARADJA 2003 cruise). The echo-character maps are interpreted in terms of sedimentary processes: the B1 echo type (parallel to subparallel high- to low-amplitude sub-bottom reflections), mainly in the deep basin, corresponds to hemipelagic sedimentation; R1 (prolonged single echo with no sub-bottoms) and R2 (small irregular overlapping hyperbolae) echo types, generally near or in canyon systems, are associated with turbidity currents or more rarely to contour currents or mass-transport deposits such as slumps, slides and debris flows; the transparent echo types (T1–T5) and R3 (chaotic lens of low-amplitude reflections on top of higher amplitude), often located at the foot of the slope or canyons walls, typically indicate mass-transport deposits (like slides) or turbidites. Large zones that display a large variety of echo types are evidenced in the study area and are generally associated with turbidity currents, but could also be associated with bottom currents. It appears that active tectonics plays a significant role in this part of the margin which presents a few active faults offshore but also a strong and relatively frequent seismicity onland. The general pattern of the distribution of mass-transport deposits is particular – i.e. many but small slides all along the margin – and suggests a probable triggering by recurrent earthquake shakings. However, active tectonics is not the only factor influencing the deposition pattern, as some zones seem characterized by predominant strong turbidity currents transporting sediments far away from the foot of the margin, whereas others depict retrogressive erosion features on the slope, i.e. small slides scarps in gullies rather than transport by turbidity currents. In particular, the rivers sediment discharge fluxes and the geomorphologic characteristics of the margin seem to be very important factors too. 相似文献
6.
Gabriela Dan Nabil Sultan Bruno Savoye Jacques Deverchere Karim Yelles 《International Journal of Earth Sciences》2009,98(4):769-789
The Algerian margin is a seismically active region, where during the last century, several large magnitude earthquakes took
place. This study combines geotechnical and sedimentological data with numerical modelling to quantitatively assess the present-day
slope stability of the Algerian margin. Geotechnical laboratory tests, such as cyclic triaxial tests, oedometric tests and
vane shear tests were carried out on sediment cores collected on the study area. The liquefaction potential of a sediment
column located about 30 km from the Boumerdès earthquake epicentre of 21st May 2003 was evaluated theoretically for an earthquake
of M
w
= 6.8. We show that thin sand and silt beds such as those described on recovered sediment cores are the main cause of sediment
deformation and liquefaction during earthquakes. Numerical calculations showed that the slope failure may occur during an
earthquake characterised by a PGA in excess of 0.1g, and also that, under a PGA of 0.2g liquefaction could be triggered in shallow silty–sandy deposits. Moreover, comparison of the predicted slope failure with
failure geometries inferred from seafloor morphology showed that earthquakes and subsequent mass movements could explain the
present-day morphology of the study area. 相似文献
7.
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
8.
1