Predicting seiche hazard for coastal harbours along the northern and western coasts of France

Natural Hazards - Long-period waves propagating inside harbours can lead to the generation of seiche that can affect and significantly disrupt port operations. This study is based on the analysis...     

An EPR study of native radiation-induced paramagnetic defects in sudoite (di–trioctahedral Al–Mg chlorite) from the alteration halo related to unconformity-type uranium deposits

Natural radiation-induced defects were identified in specimens of sudoite (Al–Mg di-trioctahedral chlorite) related to unconformity-type uranium deposits at the base of the Athabasca Group (Saskatchewan, Canada), using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. X-band spectra indicate the presence of a main native defect, named the A_s-center, whose EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g _// = 2,051 and g _⊥ = 2,005, and a secondary defect with apparent component g = 2,025. The study of oriented specimens shows that the main defect has its g _// component perpendicular to the (ab) plane of sudoite. The A_s-center corresponds to an electron hole located on oxygen atoms of the structure and is likely associated with Si, according to the lack of hyperfine structure. The A_s-center in sudoite has EPR parameters similar to the A-center in kaolinite and dickite, and the A_i-center in illite. The saturation behavior of EPR spectra as a function of power demonstrates that native defects of sudoite are different from those known in other clays, such as kaolinite, dickite or smectite, but are similar to those of illite. The isochronal annealing data suggest that the main defect in sudoite is stable to more than 300°C. The corresponding defects characterized in sudoite may have the potential for tracing past radionuclide migration around unconformity-type uranium deposits.     

Numerical simulation of waves generated by landslides using a multiple-fluid Navier–Stokes model

This work reports on the application and experimental validation, for idealized geometries, of a multiple-fluid Navier–Stokes model of waves generated by rigid and deforming slides, with the purpose of improving predictive simulations of landslide tsunamis. In such simulations, the computational domain is divided into water, air, and slide regions, all treated as Newtonian fluids. For rigid slides, a penalty method allows for parts of the fluid domain to behave as a solid. With the latter method, the coupling between a rigid slide and water is implicitly computed (rather than specifying a known slide kinematics). Two different Volume of Fluid algorithms are tested for tracking interfaces between actual fluid regions. The simulated kinematics of a semi-elliptical block, moving down a water covered plane slope, is first compared to an earlier analytical solution. Results for the vertical fall of a rectangular block in water are then compared to earlier experimental results. Finally, more realistic simulations of two- and three-dimensional wedges sliding down an incline are compared to earlier experiments. Overall, in all cases, solid block velocities and free surface deformations are accurately reproduced in the model, provided that a sufficiently resolved discretization is used. The potential of the model is then illustrated on more complex scenarios involving waves caused by multi-block or deformable slides.     

Evidence of native radiation-induced paramagnetic defects in natural illites from unconformity-type uranium deposits

This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic illites related to unconformity-type uranium deposits of Canada and Australia were studied using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g _∥ = 2.032 and g _⊥ = 1.993. The corresponding defect is named as A_i center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g _∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The A_i center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of the A_i center requires additional work.