Mass-transport deposits on the Algerian margin (Algiers area) : morphology, lithology and sedimentary processes

International audienceOn 21st May 2003, a damaging earthquake of Mw: 6.9 struck the region of Boumerdès 40 km east of Algiers in northern Algeria. The seismic shocks had devastating effects in the offshore area between the cities of Algiers and Dellys, where numerous cable breaks were observed. The submarine area encompassing the 2003 Boumerdès epicenter (central Algerian margin) was recently investigated using geophysical and sampling tools. It has been observed that small-size slides and mass-transport deposits occur across this area. Thus, a detailed analysis was performed on 25 submarine slides identified in water depth from 500 m to 2700 m, by measuring different morphological parameters (i.e. surface, head-scarp height, slope in the source area and in adjacent areas).Various deposits consisting of matrix supported mud-clast, distorted stratified sediments and sandturbidite beds were observed in gravity cores near and within the most significant-size slide. Based on this work and previous studies it can be presumed that the recurrent seismic activity can be considered as the main triggering factor for failure in the central Algerian margin

Permeability changes in Boom clay with temperature

International audienceIn the framework of research into radioactive waste disposal, this paper presents some tests carried out to investigate the effects of temperature on the changes in permeability of Boom between 20 and 90°C. Constant head permeability tests were carried out in a high pressure isotropic compression tests at various temperature and isotropic stresses. The results show that the changes in permeability of Boom clay with temperature are only due to the changes in viscosity of free water with temperaure. This demonstrates on the one hand that the water involved in transfer at various temperatures is free water and on the other hand that there is apparently only few changes in the status of adsorbed water with respect to temperature between 20 and 90°C

Boundedness of some operators on grand Herz spaces with variable exponent

Our aim in this paper is to prove boundedness of an intrinsic square function and higher order commutators of fractional integrals on grand Herz spaces with variable exponent ${\dot{K} ^{a(\cdot), u), \theta}_{ s(\cdot)}(\mathbb{R}^n)}$ by applying some properties of variable exponent

Thermodynamic analysis of porphyrin binding to Momordica charantia (bitter gourd) lectin

Owing to the use of porphyrins in photodynamic therapy for the treatment of malignant tumors, and the preferential interaction of lectins with tumor cells, studies on lectin-porphyrin interaction are of significant interest. In this study, the interaction of several free-base and metalloporphyrins with Momordica charantia (bitter gourd) lectin (MCL) was investigated by absorption spectroscopy. Difference absorp-tion spectra revealed that significant changes occur in the Soret band region of the porphyrins on binding to MCL. These changes were monitored to obtain association constants (Ka) and stoichiometry of binding. The tetrameric MCL binds four porphyrin molecules, and the stoichiometry was unaffected by the presence of the specific sugar, lactose. In addition, the agglutination activity of MCL was unaffected by the presence of the porphyrins used in this study, clearly indicating that porphyrin and carbohydrate ligands bind at different sites. Both cationic and anionic porphyrins bind to the lectin with comparable affinity (Ka =103-105 m-1). The thermodynamic parameters associated with the interaction of several porphyrins, obtained from the temperature dependence of the Ka values, were found to be in the range: Δ H° = -98.1 to -54.4 kJ·mol-1 and Δ S° =-243.9 to -90.8 J·mol-1·K-1. These results indicate that porphyrin binding to MCL is governed by enthalpic forces and that the contribution from binding entropy is negative. Enthalpy-entropy compensation was observed in the interaction of different porphyrins with MCL, underscoring the role of water structure in the overall binding process. Analysis of CD spectra of MCL indicates that this protein contains about 13%α-helix, 36%β-sheet, 21%β-turn, and the rest unordered structures. Binding of porphyrins does not significantly alter the secondary and tertiary structures of MCL

Boundedness of Hardy operators on grand variable weighted Herz spaces

In this paper, we will introduce the idea of grand variable weighted Herz spaces ${{\dot{K} ^{\alpha(\cdot), \epsilon), \theta}_{ q(\cdot)}(\tau)}}$ in which $\alpha$ is also a variable. Our main purpose in this paper is to prove the boundedness of Hardy operators on grand variable weighted Herz spaces

Impact of tides and sea-level on deep-sea Arctic methane emissions

Sub-sea Arctic methane and gas hydrate reservoirs are expected to be severely impacted by ocean temperature increase and sea-level rise. Our understanding of the gas emission phenomenon in the Arctic is however partial, especially in deep environments where the access is difficult and hydro-acoustic surveys are sporadic. Here, we report on the first continuous pore-pressure and temperature measurements over 4 days in shallow sediments along the west-Svalbard margin. Our data from sites where gas emissions have not been previously identified in hydro-acoustic profiles show that tides significantly affect the intensity and periodicity of gas emissions. These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume. Hence, the question remains as to whether sea-level rise may partially counterbalance the potential threat of submarine gas emissions caused by a warmer Arctic Ocean

Microevents produced by gas migration and expulsion at the seabed: A study based on sea bottom recordings from the Sea of Marmara

International audienceDifferent types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of ∼400 very similar microevents (based on principal component analysis) was recorded in less than one day by an OBS located in the close vicinity of an active, gas-prone fault cutting through the upper sedimentary layers. The presence of gas in superficial sediments, together with analogies with laboratory experiments, suggest that gas migration followed by the collapse of fluid-filled cavities or conduits could be the source of the observed microevents. This work shows that OBSs may provide valuable information to improve our understanding of natural degassing processes from the seafloor