Theoretical Investigations on the Nakamura\u27s Technique

We use synthetic calculations to investigate the spectral ratio between horizontal and vertical components (H/V ratio), derived from noise simulation, in order to appreciate the reliability of the so-called Nakamura\u27s method for site effects applications. This ratio shows a peak whose position generally coincides with the fundamental resonance frequency. We show that this position is independent of the source function, whereas it is characteristic of the geological structure. We also compare these results with those obtained for vertical S waves and Rayleigh waves, in order to better understand the significance of this HIV peak. Finally, we show that the amplitude of the H/V ratio cannot be used directly to derive the amplification for body waves, as suggested by Nakamura (1989), since it is very sensitive to parameters such as the Poisson\u27s ratio and the source-receiver distance

Optimization of a new interatomic potential to investigate the thermodynamic properties of hypo-stoichiometric mixed oxide fuel U1−yPuyO2−x

International audienceThe behaviour of stoichiometric U1−yPuyO2 compounds used as nuclear fuel is relatively well understood. Conversely, the effects of stoichiometry deviation on fuel performance and fuel stability are intricate and poorly studied. In order to investigate what affect these have on the thermophysical properties of hypo-stoichiometric U1−yPuyO2−x mixed oxide fuel, new interaction parameters based on the many-body CRG (Cooper–Rushton–Grimes) potential formalism were optimized. The new potential has been fitted to match experimental lattice parameters of U0.70Pu0.30O1.99 (O/M = 1.99) and U0.70Pu0.30O1.97 (O/M = 1.97), where M represents the total amount of metallic cations, through a rigorous procedure combining classical molecular dynamic and classical molecular Monte Carlo simulation methods. This new potential provides an excellent description of the U1−yPuyO2−x system. Concerning lattice parameter, although fitted on only one Pu content (30%) and two stoichiometries (1.99 and 1.97), our potential allows good predictions compared to available experimental results as well as to available recommendations in wide ranges of O/M ratio, Pu content and temperature. For the U0.70Pu0.30O2−x hypo-stoichiometric system (30% Pu content and O/M ratio ranging from 1.94 to 2.00), some direct properties (lattice parameter and enthalpy) and some derivative properties (linear thermal expansion coefficient and specific heat) were systematically investigated from room temperature up to the expected melting temperatures and a good agreement with experiments is found. Moreover, our potential shows good transferability to the plutonium sesquioxide Pu2O3 system

2D equivalent linear site effect simulation: example applications to two deep valleys

International audienceIn the framework of the Sismovalp European project, an equivalent linear 2D code was developed to compute the response of a valley to SH waves, using the discrete wave-number method proposed by Aki and Larner (Aki K, Larner KL (1970) J Geophys Res 75:5). To overcome the frequency upper bound limitation, the Aki and Larner's method is combined with a one-dimensional computation using a classical multi-layer method (Aki K, Richards PG (1980) Quantitative Seismology: Theory and Methods, vols. 1 & 2. W.H. Freeman & Co, San Francisco). The so-called “Aki–Larner extended method” is associated to an iterative algorithm, as proposed by Seed and Idriss (Seed HB, Idriss IM (1969) Report No. EERC 70–10, Earthquake Research Center, University of California, Berkeley, California) which accounts for the modulus and damping degradation using a linear visco-elastic model. A comparison of the results in the linear and the equivalent linear cases, for a magnitude 6.0 earthquake, shows that the account for the equivalent linear behaviour of the soil significantly reduces the amplification level, especially at frequencies higher than the fundamental resonance frequency of the site. In the case of site effects or microzonation studies devoted to produce design spectra for engineering structures, this can have a major impact on the associated results and costs, depending on the frequency of interest for the considered structure. As a first application of the developed technique, 2D equivalent linear Aki–Larner computations are used to perform the seismic microzonation study of the upper Rhone valley, in the Visp area (Switzerland), a typical 2D alpine valley. These investigations made it possible to determine site specific spectra, associated with different zones, to be used instead of the code spectra that do not take into account the local 2D amplification

H/V technique for site response analysis synthesis of data from various surveys

International audienceH/V" techniques are very attractive tools for estimating local site effect characteristics. They consist in computing the spectral ratio between the horizontal and the vertical components of a signal. For the "receiver function", or RF method, the signal is an earthquake, whereas it is composed of ambient noise for the NN method. The classical transfer function method, called SR here, is based on the spectral ratio of an earthquake recording between one site and a reference. The aim of this paper is to collect experimental results (44 sites) and compare values worthy of note obtained from the H/V and the SR techniques. For several typical sites, we first illustrate that, when a clear peak arises on an SR curve, it also exists, at the same frequency for RF or NN curves. But there is no correlation between the two kinds of curves except for the low frequency part (below the first peak) where a fuzzy relationship seems to exist. Finally,we show that NN and RF techniques determine, very accurately, the fundamental frequency of alluvial sites, below which there is no amplification. In most cases, they also provide a lower bound (in amplitude) and bandwidth (in frequency) estimates for peak amplification

H/V technique for site response analysis synthesis of data from various surveys

International audienceH/V" techniques are very attractive tools for estimating local site effect characteristics. They consist in computing the spectral ratio between the horizontal and the vertical components of a signal. For the "receiver function", or RF method, the signal is an earthquake, whereas it is composed of ambient noise for the NN method. The classical transfer function method, called SR here, is based on the spectral ratio of an earthquake recording between one site and a reference. The aim of this paper is to collect experimental results (44 sites) and compare values worthy of note obtained from the H/V and the SR techniques. For several typical sites, we first illustrate that, when a clear peak arises on an SR curve, it also exists, at the same frequency for RF or NN curves. But there is no correlation between the two kinds of curves except for the low frequency part (below the first peak) where a fuzzy relationship seems to exist. Finally,we show that NN and RF techniques determine, very accurately, the fundamental frequency of alluvial sites, below which there is no amplification. In most cases, they also provide a lower bound (in amplitude) and bandwidth (in frequency) estimates for peak amplification