This work is a multidisciplinary approach from geological and geophysical surveys to build a 3D geological model of Argostoli Basin (Cephalonia Island, Greece) aiming to be used for computational 3D simulation of seismic motion. Cephalonia Island is located at the north-western end of the Aegean subduction frontal thrust that is linked to the dextral Cephalonia Transform Fault (west of Cephalonia) where the seismic hazard is high in terms of earthquake frequency and magnitude. The Plio-Quaternary Koutavos-Argostoli basin site was selected within the French Research Agency PIA SINAPS@ project (www.institut-seism.fr/projets/sinaps/ - last accessed on November 25th 2019) to host a vertical accelerometer array. The long-term goal is to validate three-dimensional nonlinear numerical simulation codes to assess the site-specific amplification and nonlinearity. Herein the geological and geophysical surveys carried out from 2011 to 2017 are presented and in particular the complementary investigations that led to the identification of the main stratigraphic units and their structures. In addition, coral debris sampled from the vertical array deep borehole cores were used for Th-230/U-234 measurements, which confirmed the Pleistocene age of the Koutavos basin. The characterization of the three-dimensional structure of the stratigraphic units was achieved by coupling geological cross-sections (i.e., depth geometry) and geophysical surveys based of surface wave analysis.

Data provided by accelerometric networks are important for seismic hazard assessment. The correct use of accelerometric signals is conditioned by the station site metadata quality (i.e., soil class, VS30, velocity profiles, and other relevant information that can help to quantify site effects). In France, the permanent accelerometric network consists of about 150 stations. Thirty-three of these stations in the southern half of France have been characterized, using surface-wave-based methods that allow derivation of velocity profiles from dispersion curves of surface waves. The computation of dispersion curves and their subsequent inversion in terms of shear-wave velocity profiles has allowed estimation of VS30 values and designation of soil classes, which include the corresponding uncertainties. From a methodological point of view, this survey leads to the following recommendations: (1) perform both active (multi-analysis surface waves) and passive (ambient vibration arrays) measurements to derive dispersion curves in a broadband frequency range; (2) perform active acquisitions for both vertical (Rayleigh wave) and horizontal (Love wave) polarities. Even when the logistic contexts are sometimes difficult, the use of surface-wave-based methods is suitable for station-site characterization, even on rock sites. In comparison with previous studies that have mainly estimated VS30 indirectly, the new values here are globally lower, but the EC8-A class sites remain numerous. However, even on rock sites, high frequency amplifications may affect accelerometric records, due to the shallow relatively softer layers.

Determination of the site component of kappa(kappa(0)) is important in the implementation of host-to-target adjustments for estimation of seismic hazard at hard-rock sites. Its evaluation through the classical approach of Anderson and Hough (1984), kappa(0_AS), faces specific difficulties in low-to-moderate seismicity areas because the quantity and bandwidth of the usable data are generally limited. In such a context, measurements might have higher sensitivity to site amplification, frequency-dependent attenuation, the earthquake source, and the instrumental equipment. Here, the kappa(DS) displacement spectrum) approach of Biasi and Smith (2001) is compared with the kappa(AS) (acceleration spectrum) approach for three sites in an industrial area in Provence (southeastern France). A semiautomatic procedure is developed to measure individual values of kappa(r) that reduce interoperator variability and provide the associated uncertainty. We show that this uncertainty is mainly dependent on the bandwidth used to determine kappa(r). A good agreement is found between kappa(0_AS) and kappa(0_DS) for the two hard-rock sites, which yield similar to 30 ms. This highlights the kappa(DS) approach that is well adapted to low-magnitude events recorded at rock sites, and the use of velocimeters in low-tomoderate seismicity areas. The comparisons between these approaches are also used to infer the reliability of kappa measurements by addressing their sensitivity to site amplification, frequency-dependent attenuation, and the earthquake source. First, the impact of site amplification on kappa(0) estimates is shown to be very important and strongly frequency-dependent for stiff-soil sites, and non-negligible for hard-rock sites. Second, frequency-dependent attenuation cannot be ruled out for kappa, as indicated by comparison with the literature quality factor (Q) for the Alps. Finally, a source component for kappa(AS) is questionable from the comparison of kappa(r_AS) evaluated for a cluster of events that shared the same path and site components.

Seismic analysis in the context of nuclear safety in France is currently guided by a pure deterministic approach based on Basic Safety Rule (Règle Fondamentale de Sûreté) RFS 2001-01 for seismic hazard assessment, and on the ASN/2/01 Guide that provides design rules for nuclear civil engineering structures. After the 2011 Tohohu earthquake, nuclear operators worldwide were asked to estimate the ability of their facilities to sustain extreme seismic loads. The French licensees then defined the 'hard core seismic levels', which are higher than those considered for design or re-assessment of the safety of a facility. These were initially established on a deterministic basis, and they have been finally justified through state-of-the-art probabilistic seismic hazard assessments. The appreciation and propagation of uncertainties when assessing seismic hazard in France have changed considerably over the past 15 years. This evolution provided the motivation for the present article, the objectives of which are threefold: (1) to provide a description of the current practices in France to assess seismic hazard in terms of nuclear safety; (2) to discuss and highlight the sources of uncertainties and their treatment; and (3) to use a specific case study to illustrate how extended source modeling can help to constrain the key assumptions or parameters that impact upon seismic hazard assessment. This article discusses in particular seismic source characterization, strong ground motion prediction, and maximal magnitude constraints, according to the practice of the French Atomic Energy Commission. Due to increases in strong motion databases in terms of the number and quality of the records in their metadata and the uncertainty characterization, several recently published empirical ground motion prediction models are eligible for seismic hazard assessment in France. We show that propagation of epistemic and aleatory uncertainties is feasible in a deterministic approach, as in a probabilistic way. Assessment of seismic hazard in France in the framework of the safety of nuclear facilities should consider these recent advances. In this sense, the opening of discussions with all of the stakeholders in France to update the reference documents (i.e., RFS 2001-01; ASN/2/01 Guide) appears appropriate in the short term.

We compare different methods to estimate frequency-domain amplification and duration lengthening of earthquake ground motion in the Mygdonian basin (Greece). Amplification is measured by standard spectral ratios (SSRs) of horizontal component or by single-station earthquake horizontal-to-vertical ratios (EHVRs). Duration lengthening is measured either by the group delay method (Beauval et al., 2003) and labeled GDDL, or based on the significant duration (Trifunac and Brady, 1975) and labeled TBDL. The methods are applied both to high-quality recordings of the European experimental site EUROSEISTEST array and to a large set of 3D synthetics computed in a new basin model for 1260 sources regularly distributed in depth, distance, and azimuth from the center of the array.The analysis of the recordings in the center of the basin shows an anticorrelation between amplification and duration lengthening, that is, maxima (resp. minima) of GDDL correspond to minima (resp. maxima) of SSR. The maxima of GDDL are also found to coincide with those of SSR variability. This is confirmed by the analysis of the synthetics, which also reveals a pronounced north-south asymmetry of both amplification and duration lengthening caused by nonisotropic excitation of surface waves at the basin edges. We find that all estimates of site response depend on source location and that EHVR is also strongly sensitive to energy partitioning in the analyzed wavefield. We quantify the source-related variability of each estimate, discuss the biases in site response estimation using incomplete source catalogs, and investigate whether the azimuthal dependence of site response can be identified in the recordings.

The Tohoku earthquake and associated tsunami in March 2011 caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant, where level 7 (International Atomic Energy Agency (IAEA) INES scale) meltdown at three reactors occurred. The underestimation of the seismic and tsunami hazards has been recognized and the seismic margins assessment of the nuclear plants remains a priority for the whole nuclear community. In this framework a five-year research project called SINAPS@(Earthquake and Nuclear Installations: Ensuring and Sustaining Safety) is currently on-going in France. A reliable estimate of seismic margins is possible only if all uncertainties, epistemic and aleatory, are effectively identified, quantified and integrated in the seismic risk analysis. SINAPS@brings together a multidisciplinary community of researchers and engineers from the academic and the nuclear world. SINAPS@ aims at exploring the uncertainties associated to databases, physical processes and methods used at each stage of seismic hazard, site effects, soil and structure interaction, structural and nuclear components vulnerability assessments, in a safety approach: the main objective is ultimately to identify the sources of potential seismic margins resulting from assumptions or when selecting the seismic design level or the design strategy. The whole project is built around an "integrating" work package enabling to test state-of-the-art practices and to challenge new methodologies for seismic risk assessment: the real case of Kashiwazaki-Kariwa Japanese nuclear plant, shocked by the severe earthquake in 2007 provided a rich dataset which will be used to compare with the predictions. The present paper proposes for each step of the seismic risk analysis a review of the state of practice in France in the nuclear field and then precise the objectives and research strategy of SINAPS@ to overcome identified limitations or weaknesses. Scientific issues are illustrated through preliminary results of the project. (C) 2016 Elsevier B.V. All rights reserved.

The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7km to 8km around the main segment of the fault zone.

The Euroseistest Verification and Validation Proje ct (E2VP) aimed at a quantitative analysis of accuracy of the current, most-advanced numerical me thods applied to realistic 3D models of sedimentary basins (verification), and a quantitati ve comparison of the recorded and numericallysimulated ground motions (validation). The target s ite, located within the Mygdonian basin near Thessaloniki, Greece, has been thoroughly investiga ted for two decades and a detailed, realistic 3D model has been derived from geological, geophysi cal and geotechnical investigations, while a dedicated instrumentation provided a significant nu mber of surface and borehole recordings. Verification and validation tests up to a frequency of 4 Hz, much beyond the 0.7 Hz fundamental frequency, have been performed for a set of local, small to moderate magnitude events. For careful and accurate enough computations, the model-to-mode l diff rences are smaller than the model-toobservations differences, controlled by uncertainti es primarily in the crustal propagation model and source properties, and secondarily in the shall ow structure.

n a low‐seismicity context, the use of numerical simulations becomes essential due to the lack of representative earthquakes for empirical approaches. The goals of the EUROSEISTEST Verification and Validation Project (E2VP) are to provide (1) a quantitative analysis of accuracy of the current, most advanced numerical methods applied to realistic 3D models of sedimentary basins (verification) and (2) a quantitative comparison of the recorded ground motions with their numerical predictions (validation). The target is the EUROSEISTEST site located within the Mygdonian basin, Greece. The site is instrumented with surface and borehole accelerometers, and a 3D model of the medium is available. The simulations are performed up to 4 Hz, beyond the 0.7 Hz fundamental frequency, thus covering a frequency range at which ground motion undergoes significant amplification. The discrete representation of material heterogeneities, the attenuation model, the approximation of the free surface, and nonreflecting boundaries are identified as the main sources of differences among the numerical predictions. The predictions well reproduce some, but not all, features of the actual site effect. The differences between real and predicted ground motions have multiple origins: the accuracy of source parameters (location, hypocentral depth, and focal mechanism), the uncertainties in the description of the geological medium (damping, internal sediment layering structure, and shape of the sediment‐basement interface). Overall, the agreement reached among synthetics up to 4 Hz despite the complexity of the basin model, with code‐to‐code differences much smaller than predictions‐to‐observations differences, makes it possible to include the numerical simulations in site‐specific analysis in the 3D linear case and low‐to‐intermediate frequency range.

In order to quantify low amplitude deformations in sedimentary basins, fault offsets are modelled, restored and quantified in 3D. We studied a field example where such faults where blanketed by a small angular unconformity between Upper and Lower Cretaceous in the central area of the Allauch Massif (SE Provence, France) to which we applied sub-surface structural modelling techniques (Gocad). We gathered mapping, structural and sedimentologic data in the field. Fault and stratigraphic surfaces were interpolated with gOcad for constructing a 3D structural model of the Allauch Massif. In order to restore the original geometry of the erosional wedge and low amplitude fault offsets, we restored the post-unconformity Pyrenean-Alpine deformation. We obtained a 3D structural model of the angular unconformity at the pre-Upper Turonian times.The angular unconformity was due to a 5 degrees fault-induced tilting of the Lower Cretaceous and underlying layers, which implied a 3 degrees erosion wedge and a differential erosion of similar to 140 m over 4 km in the Valanginian and Hauterivian layers. Bauxites were deposited during the time interval between Early and Late Cretaceous. The restored geometry suggests that the bauxite was preserved in topographic steps aligned parallel to the strike (similar to NNW-SSE) of the Lower Cretaceous. This strike is due to tilting synchronous with normal faults. (C) 2010 Elsevier Ltd. All rights reserved.