On the Testing of Ground--Motion Prediction Equations against Small--Magnitude Data

Ground-motion prediction equations (GMPE) are essential in probabilistic seismic hazard studies for estimating the ground motions generated by the seismic sources. In low seismicity regions, only weak motions are available in the lifetime of accelerometric networks, and the equations selected for the probabilistic studies are usually models established from foreign data. Although most ground-motion prediction equations have been developed for magnitudes 5 and above, the minimum magnitude often used in probabilistic studies in low seismicity regions is smaller. Desaggregations have shown that, at return periods of engineering interest, magnitudes lower than 5 can be contributing to the hazard. This paper presents the testing of several GMPEs selected in current international and national probabilistic projects against weak motions recorded in France (191 recordings with source-site distances up to 300km, 3.8\leqMw\leq4.5). The method is based on the loglikelihood value proposed by Scherbaum et al. (2009). The best fitting models (approximately 2.5\leqLLH\leq3.5) over the whole frequency range are the Cauzzi and Faccioli (2008), Akkar and Bommer (2010) and Abrahamson and Silva (2008) models. No significant regional variation of ground motions is highlighted, and the magnitude scaling could be predominant in the control of ground-motion amplitudes. Furthermore, we take advantage of a rich Japanese dataset to run tests on randomly selected low-magnitude subsets, and check that a dataset of ~190 observations, same size as the French dataset, is large enough to obtain stable LLH estimates. Additionally we perform the tests against larger magnitudes (5-7) from the Japanese dataset. The ranking of models is partially modified, indicating a magnitude scaling effect for some of the models, and showing that extrapolating testing results obtained from low magnitude ranges to higher magnitude ranges is not straightforward

Selection of ground motion prediction equations for the global earthquake model

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. From many available GMPEs, we select those models recommended for use in seismic hazard assessments in the Global Earthquake Model. We present a GMPE selection procedure that evaluates multidimensional ground motion trends (e.g., with respect to magnitude, distance, and structural period), examines functional forms, and evaluates published quantitative tests of GMPE performance against independent data. Our recommendations include: four models, based principally on simulations, for stable continental regions; three empirical models for interface and in-slab subduction zone events; and three empirical models for active shallow crustal regions. To approximately incorporate epistemic uncertainties, the selection process accounts for alternate representations of key GMPE attributes, such as the rate of distance attenuation, which are defensible from available data. Recommended models for each domain will change over time as additional GMPEs are developed

Toward a ground-motion logic tree for probabilistic seismic hazard assessment in Europe

The Seismic Hazard Harmonization in Europe (SHARE) project, which began in June 2009, aims at establishing new standards for probabilistic seismic hazard assessment in the Euro-Mediterranean region. In this context, a logic tree for ground-motion prediction in Europe has been constructed. Ground-motion prediction equations (GMPEs) and weights have been determined so that the logic tree captures epistemic uncertainty in ground-motion prediction for six different tectonic regimes in Europe. Here we present the strategy that we adopted to build such a logic tree. This strategy has the particularity of combining two complementary and independent approaches: expert judgment and data testing. A set of six experts was asked to weight pre-selected GMPEs while the ability of these GMPEs to predict available data was evaluated with the method of Scherbaum et al. (Bull Seismol Soc Am 99:3234-3247, 2009). Results of both approaches were taken into account to commonly select the smallest set of GMPEs to capture the uncertainty in ground-motion prediction in Europe. For stable continental regions, two models, both from eastern North America, have been selected for shields, and three GMPEs from active shallow crustal regions have been added for continental crust. For subduction zones, four models, all non-European, have been chosen. Finally, for active shallow crustal regions, we selected four models, each of them from a different host region but only two of them were kept for long periods. In most cases, a common agreement has been also reached for the weights. In case of divergence, a sensitivity analysis of the weights on the seismic hazard has been conducted, showing that once the GMPEs have been selected, the associated set of weights has a smaller influence on the hazar

Simulation numérique de la propagation d'ondes en milieu géologique complexe (application à l'évaluation de la réponse sismique du bassin de Caracas (Venezuela))

Ce travail de thèse est consacré au développement d'un outil numérique capable de modéliser la propagation 3D d'ondes sismiques dans les milieux géologiques complexes caractérisés par des effets de site. La méthode des éléments spectraux (SEM) est particulièrement adaptée à la problématique de la réponse sismique dans de tels milieux: estimation précise des ondes de surface, capacité à prendre en compte des géométries compliquées (topographie des surfaces libres, interfaces) et possibilité d'ajuster la résolution des longueurs d'ondes sismiques dans des conditions de milieux hétérogènes par des maillages non-structurés. Des extensions numériques de la SEM liées à la réponse de bassin ont été développées: Perfectly Matched Layers filtrantes et introduction efficace d'un champ incident. La principale limitation actuelle des SEM reste cependant liée au manque de flexibilité des maillages hexaédriques malgré l'utilisation de ces maillages non-structurés dont la génération constitue une tâche complexe. Ce travail de thèse souligne ainsi les difficultés associées à la prise en compte de telles structures et décrit le processus complet qu'implique la modélisation de la réponse sismique dans des milieux géologiques complexes, de l'élaboration du modèle physique et numérique à l'analyse des résultats.Je présente des simulations 3D de la réponse sismique dans la région de Caracas (Venezuela), incluant la géométrie 3D du bassin et la chaîne de montagnes Ávila qui borde la ville. L'importance des effets liés à ces deux types de structures est évaluée, par différents scénarios d'excitation par une onde plane. Ces effets géométriques 3D révèlent des phénomènes complexes d'amplification associés à la réflexion et à la focalisation d'ondes se propageant dans toutes les directions, ainsi qu'à la génération d'ondes de surface au niveau des bords et des zones de rétrécissement du remplissage sédimentaire. Une comparaison avec des simulations 2D montre l'intérêt d'une modélisation 3D, de nettes différences en terme de temps de résidence et de niveau d'énergie et d'amplification ayant été constatéesPARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

3D Spectral Element Method Simulations of the Seismic Response in the Caracas Basin

International audienceThis paper presents the first results of 3D simulations of the seismic response in the Caracas basin using the spectral element method. The seismic response of the basin is obtained by the excitation of an incident plane wave which is efficiently implemented via its traction and velocity at the rock sediments interface. A generalized filtering perfectly matched layer allows for a better absorption of surface waves in elongated basins. Our simulations clearly show combined effects from the topography and the basin, with diffracted waves coming from the mountains, and low frequency energy trapped in the deepest part of the basin. Spectral ratio exhibits focalization and 3D amplification effects

3D Spectral Element Method simulations of the seismic response in complex media: application to the Caracas valley

International audienc

3D Spectral Element Method simulations of the seismic response of Caracas (Venezuela) basin

International audienc

Spectral element modeling of seismic wave propagation in visco-elastoplastic media including excess-pore pressure development

Numerical modelling of seismic wave propagation, considering soil nonlinearity, has becomea major topic in seismic hazard studies when strong shaking is involved under particular soilconditions. Indeed, when strong ground motion propagates in saturated soils, pore pressureis another important parameter to take into account when successive phases of contractiveand dilatant soil behaviour are expected. Here, we model 1-D seismic wave propagation inlinear and nonlinear media using the spectral element numerical method. The study usesa three-component (3C) nonlinear rheology and includes pore-pressure excess. The 1-D-3C model is used to study the 1987 Superstition Hills earthquake (ML 6.6), which wasrecorded at the Wildlife Refuge Liquefaction Array, USA. The data of this event presentstrong soil nonlinearity involving pore-pressure effects. The ground motion is numericallymodelled for different assumptions on soil rheology and input motion (1C versus 3C), usingthe recorded borehole signals as input motion. The computed acceleration-time histories showlow-frequency amplification and strong high-frequency damping due to the development ofpore pressure in one of the soil layers. Furthermore, the soil is found to be more nonlinearand more dilatant under triaxial loading compared to the classical 1C analysis, and significantdifferences in surface displacements are observed between the 1C and 3C approaches. Thisstudy contributes to identify and understand the dominant phenomena occurring in superficiallayers, depending on local soil properties and input motions, conditions relevant for sitespecificstudies

Modelling of scattering of seismic waves from a corrugated rough sea surface: a comparison of three methods

International audienceWe compare three numerical methods to model the sea surface interaction in a marine seismic reflection experiment (the frequencies considered are in the band 10-100 Hz): the finite-difference method (FDM), the spectral element method (SEM) and the Kirchhoff method (KM). A plane wave is incident at angles of 0° and 30° with respect to the vertical on a rough Pierson-Moskowitz surface with 2 m significant wave height and the response is synthesized at 6, 10 and 50 m below the average height of the sea surface. All three methods display an excellent agreement for the main reflected arrival. The FDM and SEM also agree very well all through the scattered coda. The KM shows some discrepancies, particularly in terms of amplitudes

Rapport BCSF (2014) - Séisme de Barcelonnette (Alpes-de-Haute-Provence) du 7 avril 2014

This report is based on data provided by the services responsible for seismic monitoring in France (RéNaSS for the CNRS and the Universities, the ISTerre and Géoazur laboratories for the Universe Science Observatories, LDG for the CEA).The earthquake of April 7, 2014 occurred at 19:27 UT (21:26:59 local time) in the Alpes-de-Haute-Provence. Its epicentre is located approximately 6 km west southwest of the commune of Saint-Paul-sur-Ubaye and 11 km north of Barcelonnette, near the border of the departments of Alpes-de-Haute-Provence and Hautes-Alpes (Figure 1). The initiation of the rupture (hypocentre) is estimated at a depth of 11km below sea level (about 13km below the surface).This earthquake had an impact on the south-eastern quarter of France, i.e. 18 departments plus the Principality of Monaco. It has been noted by many residents as the strongest felt in the region in many years. At La Motte-en-Champsaur (yet 55 km from the epicentre) or Puy-Saint-Eusebe (22km) all the inhabitants went out to the village square to comment on this event, also fearing a more important replica.The mission of the French Central Seismological Office is to collect data on earthquakes felt in France, to collect useful information and to facilitate its dissemination to stakeholders concerned by seismic risk or conducting studies or research requiring the use of these observations.Ce rapport s'appuie sur les données communiquées par les services chargés de la surveillance sismique du territoire français (RéNaSS pour le CNRS et les Universités, les laboratoires ISTerre et Géoazur pour les observatoires des Sciences de l’Univers, LDG pour le CEA).Le séisme du 7 avril 2014 s’est produit à 19h27 TU (21h 26min 59sec heure locale) dans les Alpes- de-Haute-Provence. Son épicentre est situé à environ 6 km à l’Ouest Sud-Ouest de la commune de Saint-Paul-sur-Ubaye et 11km au Nord de Barcelonnette, à proximité de la limite des départements des Alpes-de-Haute-Provence et des Hautes-Alpes (figure 1). L’initiation de la rupture (hypocentre) est estimée à une profondeur de 11km sous le niveau de la mer (environ à 13 km de profondeur sous la surface du sol).Ce séisme a impacté par ses effets le quart sud-est de la France, soit 18 départements plus la Principauté de Monaco. Il a été noté par de nombreux habitant comme étant le plus fort jamais ressenti dans la région depuis de nombreuses années. À La Motte-en-Champsaur (pourtant à 55 km de l’épicentre) ou encore à Puy-Saint-Eusebe (22km) l’ensemble des habitants est sorti sur la place du village pour commenter cet événement, craignant aussi une réplique plus importante.Le Bureau Central Sismologique Français a pour mission de collecter les données sur les séismes ressentis en France, de rassembler les informations utiles et de faciliter leur diffusion vers les acteurs concernés par le risque sismique ou menant des études ou recherches nécessitant l’usage de ces observations