Context and research themes
In accordance with safety requirements, all nuclear facilities (reactors, plants, disposal facilities and research centers) must be adequately protected against seismic hazards. Seismic risk must be taken into account in facility design, which entails assessing the characteristics of potential seismic activity and estimating any ground motion that may occur as a result at sites where facilities are to be built. Ground motion used to define seismic risk is taken as the seismic load used to analyze how engineering structures and equipment are likely to behave in the event of earthquake.
The Tohoku earthquake that occurred in Japan in March 2011 triggered a tsunami that hit the coast in the region around Sendai, causing a major nuclear accident at Fukushima-Daiichi nuclear power plant. This accident raised questions regarding established practices, applied in France and worldwide, for taking seismic hazard into account when building nuclear facilities. In this field, IRSN has been involved in establishing new measures that take account of hazards that may occur more rarely than at the levels factored into the original design basis for nuclear facilities. Introducing a probabilistic approach in assessing seismic risk in France, in addition to the deterministic approaches employed since the 1970s as the main baseline in assessing nuclear facility safety, is another of the recent changes introduced to improve practice.
There is broad international consensus regarding the need to improve our knowledge and understanding of natural hazards liable to cause severe damage at nuclear facility sites. To address this need, the BERSSIN is tasked with:
Assessing seismic hazard as part of the examination of safety analysis reports on nuclear facilities. In France, these safety analysis reports are examined within the framework of technical support provided to the French Nuclear Safety Authority (ASN). The BERSSIN also carries out these examinations in other countries where different regulatory guidelines apply (national, IAEA, or US NRC regulations)
Contributing to the review of national and international regulations relative to seismic risk for nuclear facilities. The BERSSIN also provides technical support to the French Ministry for the Ecological and Inclusive Transition, for example for the review of seismic protection regulations applicable to standard buildings and to facilities classified for environmental protection (ICPEs)
Conducting fundamental and applied research related to seismic hazard assessment
Providing training through research for students and engineers (Masters, PhD, post-doc, ENSTTI)
Setting up seismological and geodetic measurement stations in partnership with national monitoring networks brought together under the RESIF
Assessing seismic risk, for any type of facility, nuclear or non-nuclear, entails:
- characterizing faults or, at least, zones in which seismic activity is likely, in particular, estimating the magnitude (measures energy) and frequency of possible earthquakes,
- describing how seismic waves propagate from source to site of interest, factoring in the geological features of the ground beneath the facility ("site effects"),
- taking account, at every stage, of the random variability inherent in seismic processes and of uncertainties due to a lack of data or scientific knowledge,
- providing structural engineers with seismic signals mapping predicted hazards at the site of interest, enabling them to make dynamic calculations of a facility's earthquake resistance.
To improve the assessment of seismic hazard and induced stress on facilities, BERSSIN conducts studies and research, usually in collaboration with national or international scientific organizations.Characterizing faults and seismic zones
The aim is to characterize faults or, when these are not known, zones that are sources of seismic activity in terms of seismogenic potential (magnitude and location of associated seismic events) based on sufficiently well-consolidated data. Studies conducted in this area cover the following subjects:
- conducting studies of active faults in France and worldwide, including studies based on surface traces of rupture left by seismic events. Particular interest is given to contemporary seismic events in order to establish causal links between surface ruptures observed and the magnitude of seismic events. This information can be used to estimate the characteristics of past earthquakes based on traces of displacement left in geological layers, and thus have a better understanding of the geological activity in a fault. Such studies use a combination of different techniques and tools (geomorphology, satellite imaging, geological field survey, paleoseismic trenching studies and geophysical survey).
- building a database on potentially active faults (BDFA) in mainland France, primarily focused on nuclear sites;
- developing a database on fault-generated surface ruptures (the Surface Rupture Database: SURE, a worldwide data collection) with a view to establishing empirical relationships for use in calculating displacement hazard and ground motion hazard;
- it is not always possible to ascertain the relationship between a moderate earthquake and a clearly identified fault: for this reason, IRSN is developing sheet lines systems of the Earth's crust, divided into 'diffuse' and ' homogeneous' seismic blocks (known as seismotectonic zoning schemes) based on available data (seismicity, nature and amplitude of deformation, geological characteristics of the crust, etc.);
- playing an active role in French national networks through Résif - the French seismological and geodetic network (encompassing seismological measurement stations, GPS stations and periodic geodetic measurement stations) to contribute to national data acquisition and interpretation initiatives;
- working with EDF and the BRGM to develop a database on the seismic history of mainland France (SisFrance), to document all the seismic events observed in the past and assess the effects felt and damage in terms of macroseismic intensity;
- estimating the magnitude and depth of earthquakes that occurred in the past, based on macroseismic intensity (effects of seismic events on terms of effects felt or damage suffered) to develop catalogues of seismic events.
Evaluating seismic wave propagation
The aim here is to develop a complete computer code package for representing fault rupture, long-range seismic wave propagation between faults and sites of interest, and the propagation/modification of seismic waves in the local geological context of a specific site (site effects). Studies conducted in this area cover the following subjects:
- numerical modeling of rupture propagation along a fault, including taking account of the physical parameters of rupture at depth;
- adapting predictive models of seismic motion to mainland France (database of seismic records, measuring high-frequency attenuation of seismic vibration (Kappa);
- characterizing the properties of geological layers using geophysical and geological investigation methods (to measure vibrations associated with ambient noise, and seismic and electrical geophysical measurements);
- taking in-situ seismological measurements of variations in the amplitude and duration of seismic waves associated with site effects;
- developing digital models of seismic wave propagation in complex geological environments – site effects.
Factoring in uncertainties relating to the parameters used to describe seismic hazard
The aim of this is to have validated codes and relevant models that can be used, as part of a deterministic or a probabilistic approach, to factor in random uncertainty relating to the data and epistemic uncertainty relating to different interpretations made by the assessors. Studies conducted in this area cover the following subjects:
- implementing knowledge acquisition methods used by assessors;
- developing deterministic and probabilistic computer codes for seismic hazard integrating uncertainty;
- adapting methods used to gather geological data, model faults and factor them into probabilistic codes for seismic hazard at various levels of knowledge and seismicity (rupture propagation, Fault2SHA);
- drawing up deterministic and probabilistic studies on specific seismic hazards for sites of interest targeted according to needs for assessment, R&D or review of the regulations.
Selecting and characterizing seismic signals to analyze structures
The aim of this is to produce the knowledge and tools needed to define the appropriate seismic signals required to analyze the earthquake resistance of facilities. Studies conducted in this area cover the following subjects:
- analyzing techniques used to adjust seismic signal spectra and their effects on the seismological properties and signal responses of engineered structures;
- studying the harmfulness of seismic signals to identify which ground motion indicators correlate to the behavior of a structure;
- developing a methodology for the probabilistic evaluation of seismic safety.
Christophe Clément, head of section - seismology
Edward Marc Cushing, head of section's assistant - Geology
Stéphane Baize - geology
Élise Delavaud - seismology
Bérénice Froment - seismology
Céline Gélis - seismology
Sébastien Hok - seismology
Hervé Jomard - geology
Maria Lancieri - seismology
Ludmilla Provost - geophysics
Oona Scotti - sismotectonics
Aurore Laurendeau - seismology
Thomas Chartier, PhD student ENS (2016-2019)
Marguerite Mathey, PhD student U. Grenoble-IRSN (2017-2020)
Flomin Tchawe Nziaha, PhD student (2017-2020)
Arnaud Montabert, PhD student ENS (2017-2020)
Rihab Sassi, PhD student (2018-2021)
Fiia Nurminen, PhD student U. Chieti - IRSN (2018-2021)
Estelle Hannouz, PhD student U. Grenoble (2019-2022)
Mathilde Banjan, PhD student Isterre U. Chambery (2019-2022)
Marion Baques, PhD student Geoazur - CEA- IRSN (2019-2022)
Facilities and techniques
study seismic events and deformation in the region of the Moyenne Durance fault
system, the BERSSIN has developed an in-situ measurement network made up of
three accelerometric seismic monitoring stations and three permanent GPS
stations. Data is transmitted to the Résif national networks (RAP and RENAG) where they are made available to the community. The
BERSSIN also has a fleet of mobile seismological instrumentation stations used
to characterize the geophysical properties of sedimentary layers and to record
seismic activity during temporary measurement campaigns. The BERSSIN is also
equipped with subsurface electrical measurement instrumentation used to develop
sectional maps of electrical resistivity through faults and sedimentary basins.
This instrumentation can be used in combination with other instrumentation
networks in liaison with other institutes in order to take measurements on a
much larger scale.
Céline Gélis, engineer at the Seismic Risk Assessment Office for the Safety of Installations (IRSN/PRP-DGE/SCAN/BERSSIN), is setting up test of several seismic sensors before carrying out networked seismic noise measurements in Tricastin region (photo from the IRSN media library).
Partnerships and research networks
Partner of the consortium Résif
(French Seismological & Geodetic Network), RESIF-RAP
(Permanent Accelerometric Network) and RESIF-RENAG (Permanent National GNSS Network)
Partner of the SISFRANCE
consortium (BRGM, EdF, IRSN): Historical seismicity of Metropolitan France
Member of the AFPS
(French Association of Earthquake Engineering)
Universities and schools: CentraleSupelec, CEREGE, EOST, ENS, GéoAzur, IPGP, U. Grenoble, U. Besançon, U. Montpellier, U. Aachen, U. Chieti
Public or private organizations: AXA, BRGM, CEA, CEREMA, CNRS, EdF, IFSTTAR, IRD, Mines Paris, etc.
International research institutes: INGV (Italy), ORB (Belgium).
International organizations: EESS
Cross-functional thematic collaborations at IRSN on the following topics: geotechnics, liquefaction, tsunami, geological disposal (geophysical investigations), effects of earthquakes on fracture networks, seismic movement for engineers, seismic PSA
Collaborations framework: ANR projects (SubChile, DEBATE, ADN, SISCOR, AGIR, REMAKE
, PIA SINAPS@
), RESIF-RAP Kappa project, European projects (ASAMPSA_E) & specific conventions and collaboration agreements
Working groups: WG SHARE and WG Aléa of the AFPS, WG MoVing of the RESIF-RAP, INQUA, Fault2SHA, SURE, Vibris, EPOS