653 research outputs found
Interplay of seismic and aseismic deformations during earthquake swarms: An experimental approach
Observations of earthquake swarms and slow propagating ruptures on related faults suggest a close relation between the two phenomena. Earthquakes are the signature of fast unstable ruptures initiated on localized asperities while slow aseismic deformations are experienced on large stable segments of the fault plane. The spatial proximity and the temporal coincidence of both fault mechanical responses highlight the variability of fault rheology. However, the mechanism relating earthquakes and aseismic processes is still elusive due to the difficulty of imaging these phenomena of large spatiotemporal variability at depth. Here we present laboratory experiments that explore, in great detail, the deformation processes of heterogeneous interfaces in the brittle-creep regime. We track the evolution of an interfacial crack over 7 orders of magnitude in time and 5 orders of magnitude in space using optical and acoustic sensors. We explore the response of the system to slow transient loads and show that slow deformation episodes are systematically accompanied by acoustic emissions due to local fracture energy disorder. Features of acoustic emission activities and deformation rate distributions of our experimental system are similar to those in natural faults. On the basis of an activation energy model, we link our results to the Rate and State friction model and suggest an active role of local creep deformation in driving the seismic activity of earthquake swarms
Terahertz multispectral imaging by thermo-conversion using MIM antenna
International audienceConversion of terahertz radiation into thermal radiation is a low-cost approach for terahertz detection by standard infrared camera. In this work, THzâIR thermo-conversion is performed by the combination of a THz absorber made of MIM antenna and an emissive layer made of carbon nanotubes. Structural and optical characterizations of the membrane are done, and multispectral imaging in the terahertz range is demonstrated
Numerical analysis of seismic wave amplification in Nice (France) and comparisons with experiments
The analysis of site effects is very important since the amplification of
seismic motion in some specific areas can be very strong. In this paper, the
site considered is located in the centre of Nice on the French Riviera. Site
effects are investigated considering a numerical approach (Boundary Element
Method) and are compared to experimental results (weak motion and
microtremors). The investigation of seismic site effects through numerical
approaches is interesting because it shows the dependency of the amplification
level on such parameters as wave velocity in surface soil layers, velocity
contrast with deep layers, seismic wave type, incidence and damping. In this
specific area of Nice, a one-dimensional (1D) analytical analysis of
amplification does not give a satisfactory estimation of the maximum reached
levels. A boundary element model is then proposed considering different wave
types (SH, P, SV) as the seismic loading. The alluvial basin is successively
assumed as an isotropic linear elastic medium and an isotropic linear
viscoelastic solid (standard solid). The thickness of the surface layer, its
mechanical properties, its general shape as well as the seismic wave type
involved have a great influence on the maximum amplification and the frequency
for which it occurs. For real earthquakes, the numerical results are in very
good agreement with experimental measurements for each motion component.
Two-dimensional basin effects are found to be very strong and are well
reproduced numerically
Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media
To analyze seismic wave propagation in geological structures, it is possible
to consider various numerical approaches: the finite difference method, the
spectral element method, the boundary element method, the finite element
method, the finite volume method, etc. All these methods have various
advantages and drawbacks. The amplification of seismic waves in surface soil
layers is mainly due to the velocity contrast between these layers and,
possibly, to topographic effects around crests and hills. The influence of the
geometry of alluvial basins on the amplification process is also know to be
large. Nevertheless, strong heterogeneities and complex geometries are not easy
to take into account with all numerical methods. 2D/3D models are needed in
many situations and the efficiency/accuracy of the numerical methods in such
cases is in question. Furthermore, the radiation conditions at infinity are not
easy to handle with finite differences or finite/spectral elements whereas it
is explicitely accounted in the Boundary Element Method. Various absorbing
layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the
spurious wave reflections especially in some difficult cases such as shallow
numerical models or grazing incidences. Finally, strong earthquakes involve
nonlinear effects in surficial soil layers. To model strong ground motion, it
is thus necessary to consider the nonlinear dynamic behaviour of soils and
simultaneously investigate seismic wave propagation in complex 2D/3D geological
structures! Recent advances in numerical formulations and constitutive models
in such complex situations are presented and discussed in this paper. A crucial
issue is the availability of the field/laboratory data to feed and validate
such models.Comment: of International Journal Geomechanics (2010) 1-1
Finite Fault Analysis and Near Field Dynamic Strains and Rotations due to the 11/05/2011 (Mw5.2) Lorca Earthquake, South-Eastern Spain
The 11/5/2011 Lorca, Spain earthquake (Mw5.2) and related seismicity produced
extensive damage in the town of Lorca and vicinity. During these earthquakes,
evidence of rotations and permanent deformations in structures were observed.
To analyze these aspects and study the source properties from the near field,
the displacement time histories were obtained including the static component at
Lorca station. Displacement time histories were computed by an appropriate
double time integration procedure of accelerograms. Using these data, the
foreshock and mainshock slip distributions were calculated by means of a
complete waveform kinematic inversion. To study the dynamic deformations, the
3D tensor of displacement gradients at Lorca station was first estimated by a
single station method. Using the finite fault inversion results and by means of
a first order finite difference approach, the dynamic deformations tensor at
surface was calculated at the recording site. In order to estimate the
distribution of the peak dynamic deformations, the calculation was extended to
the close neighboring area of the town. The possible influence of the
near-field deformations on the surface structures was analyzed.Comment: 29 pages, 8 figure
Widespread Wolbachia infection in terrestrial isopods and other crustaceans
Wolbachia bacteria are obligate intracellular alpha-Proteobacteria of arthropods and nematodes. Although widespread among isopod crustaceans, they have seldom been found in non-isopod crustacean species. Here, we report Wolbachia infection in fourteen new crustacean species. Our results extend the range of Wolbachia infections in terrestrial isopods and amphipods (class Malacostraca). We report the occurrence of two different Wolbachia strains in two host species (a terrestrial isopod and an amphipod). Moreover, the discovery of Wolbachia in the goose barnacle Lepas anatifera (subclass Thecostraca) establishes Wolbachia infection in class Maxillopoda. The new bacterial strains are closely related to B-supergroup Wolbachia strains previously reported from crustacean hosts. Our results suggest that Wolbachia infection may be much more widespread in crustaceans than previously thought. The presence of related Wolbachia strains in highly divergent crustacean hosts suggests that Wolbachia endosymbionts can naturally adapt to a wide range of crustacean hosts. Given the ability of isopod Wolbachia strains to induce feminization of genetic males or cytoplasmic incompatibility, we speculate that manipulation of crustacean-borne Wolbachia bacteria might represent potential tools for controlling crustacean species of commercial interest and crustacean or insect disease vectors.This research was funded by a European Research Council Starting Grant (FP7/2007-2013 grant 260729 EndoSexDet) to RC and a Comité Mixte de Coopération Universitaire Franco-Tunisien grant to DB and FCC
Compact planar lenses based on a pinhole and an array of single mode metallic slits
Plasmonic lenses are based on complex combinations of nanoscale high aspect ratio slits. We show that their design can be greatly simplified, keeping similar performance while releasing technological constraints. The simplified system, called Huygens lens, consists in a central aperture surrounded by several identical single mode slits in a thin gold layer that does not rely anymore on surface plasmons. The focusing behaviour with respect to the position and number of slits is investigated, and we demonstrate the interest of this design to get compact array of lenses
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