Search

PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell–Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log10 scale) for a peak ground acceleration of 5 m=s2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

Compressional and shear wave seismic measurements were performed in an old railway tunnel and in galleries excavated in a 250-m-thick Toarcian claystone formation in the Tournemire experimental station (France). Three component (3C) geophones and three orthogonal orientations of the vibroseismic force source were used. Additionally, vertical seismic profiling (VSP) measurements were recorded with a 3C borehole geophone, a hydrophone and a microphone in a 159 m deep borehole (ID180) in the tunnel. The seismic data show that Toarcian claystone has strong transverse isotropy (TI) with a vertical symmetry axis. The qP, SH and qSV wave propagation velocities in horizontal directions--the plane of isotropy of the TI medium--are measured as 3550, 1850 and 1290 m s-1, respectively. The zero-offset VSP reveals that only one shear wave propagates in the vertical (depth) direction and the P- and S-wave velocities are 3100 and 1375 m s-1, respectively. Four elastic moduli of the TI medium are determined from the seismic velocities and from the bulk density of 2.53 g cm-3: c11 = 31.9 GPa, c33 = 24.3 GPa, c44 = 4.5 GPa and c66 = 8.7 GPa. A walkaway VSP with the borehole geophone at 50 m depth in borehole ID180 and shot points in the galleries leads to oblique seismic ray paths which allow us to determine the fifth elastic modulus of the TI medium to c13 = 16 GPa. The tube wave recorded by a hydrophone in the water filled lower part of the borehole propagates with 1350 m s-1, which confirms the estimate of the elastic constant c66. The analysis of body wave and surface wave data from a seismic experiment in Galerie Est shows reflections from several fracture zones in the gallery floor. The thickness of the excavation damaged zone (EDZ) in the floor of Galerie Est is estimated to 0.7 m. [ABSTRACT FROM AUTHOR]

Knowledge of the acceleration spectral shape is crucial to various applications in engineering seismology. Spectral amplitude decays rapidly at high frequencies. Anderson and Hough (1984) introduced the empirical factor κ to model this attenuation. This is the first time κ is studied in a vertical array consisting of more than two stations. We use 180 earthquakes recorded at a downhole array with five stations in soils and rock to investigate the effect of soil conditions on κ. Given that κ computation processes vary across literature when following the classic AndersonHough method, we investigate its variability with the different assumptions that can be made when applying the method. The estimates of κ0 range between 0.0 17 and 0.031 s at the surface and between 0.004 and 0.024 s at rock. This variability due to the assumptions made is larger than the error of each estimate and larger than the average difference in values between sediment and rock. For this data set, part of it can be attributed to the type of distance used. Given this variability, κ0 values across literature may not always be comparable; this may bias the results of applications using κ0 as an input parameter, such as ground-motion prediction equations. We suggest ways to render the process more homogeneous. We also find that κ at rock level is not well approximated by surface records from which we deconvolved the geotechnical transfer function. Finally, we compute κ on the vertical component and find a dependence of the vertical-to-horizontal κ ratio on site conditions. [ABSTRACT FROM AUTHOR]

A method is proposed for accurately describing arbitrary-shaped free boundaries in finite-difference schemes for elastodynamics, in a time-domain velocity–stress framework. The basic idea is as follows: fictitious values of the solution are built in vacuum, and injected into the numerical integration scheme near boundaries. The most original feature of this method is the way in which these fictitious values are calculated. They are based on boundary conditions and compatibility conditions satisfied by the successive spatial derivatives of the solution, up to a given order that depends on the spatial accuracy of the integration scheme adopted. Since the work is mostly done during the pre-processing step, the extra computational cost is negligible. Stress-free conditions can be designed at any arbitrary order without any numerical instability, as numerically checked. Using 10 grid nodes per minimal S-wavelength with a propagation distance of 50 wavelengths yields highly accurate results. With 5 grid nodes per minimal S-wavelength, the solution is less accurate but still acceptable. A subcell resolution of the boundary inside the Cartesian meshing is obtained, and the spurious diffractions induced by staircase descriptions of boundaries are avoided. Contrary to what occurs with the vacuum method, the quality of the numerical solution obtained with this method is almost independent of the angle between the free boundary and the Cartesian meshing. [ABSTRACT FROM AUTHOR]

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismicity. We recorded more than 500 microearthquakes, among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months. We performed an absolute location of all of the events and calculated the magnitudes. Then we applied a cross-correlation technique to gather similar events and to relocate relatively few of them. This method revealed a very clear alignment of 19 events in a direction N120° oblique to the N20° general trend of seismicity. Focal mechanisms were determined for the four largest events and composite solutions for 32 smaller ones. Both the alignments of the earthquakes and the focal solutions revealed that two oblique segments of the fault were activated during the crisis. The main segment (8 km long) that was oriented NNE with a left-lateral strike slip movement is called the Blausasc fault. Taking into account the tectonic evolution and the relationships between surface structures and the distribution of earthquakes, and through a paleaoreconstruction of the tectonic evolution, we propose that the Blausasc fault is the hidden root of the Peille-Laghet fault, which has a mapped length of at least 15 km. The smaller segment (0.6 km long) that was activated during the crisis could be interpreted as an antithetic Riedel fracture. The active Blausasc fault is located in a densely populated zone, at only 10 km from the crowded cities of Monaco and Nice. It is thus particularly interesting to analyse it for hazard assessment. In the last section, we present a simulation that is aimed at predicting what the ground motion in the city of Nice would be like if an earthquake of magnitude 5.7 occurs on this fault. For this, we used the recordings of the largest event of the seismic sequence ( Ml= 3.2) and an empirical Green's function summation scheme to simulate the ground motion at two stations situated in urban environments. The values obtained show that especially on soft soil sites, the effects of such an earthquake would be considerable in the city of Nice. [ABSTRACT FROM AUTHOR]

We perform the full elastic waveform inversion in the frequency domain in a 2-D geometry. This method allows imaging of two physical seismic parameters, using vertical and horizontal field components. The forward problem is discretized using finite difference, allowing to simulate the full elastic wavefield propagation. Moreover, it is solved in the frequency domain, a fast approach for multisource and multireceiver acquisition. The non-linear inversion is based on a pre-conditioned gradient method, where Born and Rytov formulations are used to compute Fréchet derivatives. Parameter perturbations linearly depend on fields perturbations in the Born kernel, and on the generalized complex phases of fields in the Rytov kernel, giving different Fréchet derivatives. The gradient is pre-conditioned with the diagonal part of the inverse Hessian matrix, allowing to better estimate the stepping in the optimization direction. Non-linearity is taken into account by updating parameters at each iteration and proceeding from low to high frequencies. The latter allows as well to progressively introduce smaller wavelengths in parameter images. On a very simple synthetic example, we examine the way the inversion determines the ( P-wave velocity) and V s ( S-wave velocity) images. We highlight that, with a transmission acquisition, final parameter images weakly depend on the chosen formulation to compute Fréchet derivatives and on the inverted parameters choice. Of course, convergence strongly depends on the medium wavenumber illumination which is related somehow to the acquisition geometry. With a reflection acquisition, the Born formulation allows to better recover scatterers. Moreover, the medium anomalies are not well reconstructed when surface waves propagate in the medium. This may be due to the evanescent nature of surface waves. By selecting first body waves and then surface waves, we improve the convergence and properly reconstruct anomalies. This shows us that preparation of the seismic data before the inversion is as critical as the initial model selection. [ABSTRACT FROM AUTHOR]

Solar or UVA (ultraviolet A) irradiation of the skin causes biological damage, including apoptosis, which is evident in the form of sunburn cells and the overexpression of p53. These two parameters, as well as the measurement of cellular viability, were used to evaluate the effects of UV irradiation on a reconstructed human epidermis (RHE) model, with and without the photoprotection of a broad spectrum sunblock. Reconstructed epidermis models were irradiated by solar spectrum (420 mJ cm–2) or UVA (20 J cm–2). In the absence of irradiation, and with irradiation doses of 420 mJ cm–2 and 20 J cm–2, viability was estimated at 95, 12 and 70% respectively. Sunburn cells per cm were evaluated at 0, 41 and 22, respectively under these same conditions. The apoptotic response was studied through the expression of p53, which increased at first and was then followed by a specific cleavage, 24 h after irradiation at 420 mJ cm–2. However, in the presence of a broad spectrum sunblock preparation (a combination of OMC, MBTBP, TiO2 and ZnO) and after irradiation at 420 mJ cm–2 and 20 J cm–2, viability increased to 40 and 85% respectively. The number of sunburn cells (SBC) per cm fell to 12 and nine respectively. The photoprotection provided by the sunblock limited the increase in the expression of p53 and resulted in the total disappearance of the cleavage. This study shows that human reconstructed epidermis is a valid skin model for use in the evaluation of the effects of solar and UVA irradiation, as well as in the testing of the efficacy of sunfilters. [ABSTRACT FROM AUTHOR]

The p53 protein accumulates in human skin cells in vitro and in vivo when UV-irradiated. The transient stability of p53 requires a decrease in the activity of the ubiquitin ligase murine double minute 2 (Mdm2). Solar light irradiation (52.5, 105 and 405 mJ/cm2) of reconstructed human epidermis caused cutaneous damage. Specifically, UV-B induced the formation of sunburn cells and at first, an increase in the accumulation of p53 protein. Unexpectedly, 24 h after irradiation, a specific proteolytic cleavage of p53 resulted in the formation of a 40 kDa fragment. Both the accumulation of p53 and the proteolytic cleavage increased, commensurate with the UV dose. In contrast to p53, the level of expression of Mdm2 decreased drastically with the UV dose. It is important to note that calpastatin (20 microM), a specific inhibitor of calpains, decreased the formation of sunburn cells, inhibited the cleavage of p53 and induced an accumulation of Mdm2. The apoptotic process is strongly repressed. This demonstrates for the first time that calpains can participate in the down-regulation of Mdm2 in the epidermis very rapidly after UV irradiation, and that they contribute to a specific cleavage of p53 protein. All of these processes may be involved in the apoptotic response of the skin to UV stimulation.

UV irradiation can cause cutaneous damage that may be specific according to the wavelength of UV rays. For example, damage from UVB irradiation manifests itself in the form of sunburn cells and enhancement of the expression of p53, while damage from UVA exposure results in an increase in the expression of vimentin. These reactions to UV irradiation were used in this work to evaluate the photoprotective capacities of two sunblock preparations that were applied to the surface of the skin. One sunblock preparation is a UVB absorber containing zinc oxide (ZnO) and titanium oxide (TiO2) exclusively. The other sunblock preparation is a new organo-mineral sunblock containing Tinosorb M, OCM, ZnO and TiO2. Evaluation of the photoprotective capacities of both preparations on hairless rat skin and on in vitro reconstructed human epidermis revealed that they were effective in preventing UVB-induced damage. In contrast, only the organo-mineral sunblock was effective in the prevention of UVA-specific damage such as dermal alterations characterized by the expression of vimentin. Furthermore, our data support the fact that hairless rat skin and in vitro reconstructed human epidermis are a reliable basis for the evaluation of the photoprotective capacities of various sunscreens against UVB and UVA damage.

The effect of solar irradiation on ex vivo dermatomed hairless rat skin samples maintained in culture on flow-through diffusion cells for at least 24 h was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and by histological observations. Transepidermal water loss (TEWL) measurements and kinetic analysis of the permeation of both tritiated water and 14C caffeine through the skin were performed after full-spectrum solar exposure involving the use of a xenon arc solar simulator. After a UV exposure of less than 420 mJ/cm2, skin integrity and permeation of both water and caffeine did not change significantly. In contrast, after a 420 mJ/cm2 UV exposure, the epidermis appeared more contracted, associated with an increase of 55% of TEWL and 220% of the skin permeation of tritiated water after 6 h. The data suggested a dramatic alteration of the skin barrier integrity. Moreover, the flux of 14C caffeine increased rapidly by 338% of the absorption of water 12 h after irradiation. These results reveal the presence of a threshold UV exposure that would not modify skin penetration.

For a long time hearing aids were the only solution for the deaf to perceive speech and sounds. Today, among the new deaf-aids, acoustic amplification still offers the easiest and most versatile means of combatting the majority of such handicaps. However, due to the fundamental inadequacy of amplification in compensating frequency selectivity, audiologist are obliged to pay particular attention to the improvement of the signal/noise ratio and to observe a rigourous procedure in choosing and fittings hearing aids to the user. In the future, signal processing in digital devices should contribute to enhancing the efficacy of the prosthesis.