Transversal Seismicity Action

Over the last ten years or so, the French seismological, geodetic and gravimetric communities have been structured within Résif (French Seismological and Geodetic Network). After carrying out a lot of work on the development of new seismological networks, in particular the RLBP (Permanent Broadband Network), and on the modernization of data management and distribution, clearly it was necessary to develop a Résif transversal action centred on French seismicity.

The purpose of the Transversal Seismicity Action (ATS in French) is to coordinate all work on seismicity within a single structure to enhance the effectiveness of that work and increase its visibility. This includes the production and distribution of products based on Resif data, focusing on the knowledge of French seismicity and associated hazards.

ATS Contact

Frédéric Masson, Eost

Six thematic sections

The ATS is currently subdivided into six sections which work on the following themes:

• the construction of a multi-origin seismicity bulletin in France,
• the construction of a reference catalogue of seismicity in France,
• collection and analysis of macro-seismic data – historical and contemporary seismicity in France,
• the implementation of ShakeMap at the national level integrating both macro-seismic and instrumental (accelerometric and velocimetric) data,
• the study of faults that produced earthquakes with surface ruptures in metropolitan France during Quaternary
• the study and characterization of seismic hazards at the national level.

Sections 1 and 2: the multi-origin bulletin and reference catalogue

The objective of these 2 sections is to produce a multi-origin bulletin and a reference catalogue of seismicity in France, based on collaborative work by the different actors involved in monitoring and analysis of seismicity at the national and regional levels.

The bulletin contains, all the information (hypocentres, phase arrival time, magnitude, etc.) for each seismic event resulting from analysis of data acquired by the Résif seismological networks and other French or foreign networks. These parameters are provided by the members of Résif whose work mainly at the national level (CEA, BCSF-Rénass), and also by members who carry out regional seismicity analyses (OCA, OMP, Osug, etc.). The bulletin is constantly updated whenever additional information becomes available and can, for example, include later specific works (theses, seismicity of temporary networks, etc.). The bulletin is essentially a tool for the seismological community.

The catalogue includes the solutions deemed the most relevant, for each incident in the multi-origin bulletin. It is limited to location parameters (time of origin, latitude, longitude, depth), magnitude and associated uncertainties. The catalogue will be examined, approved and updated annually by the members who construct the bulletin. Several studies will be carried out for the construction of the bulletin and the catalogue, namely:

1. assessing the uncertainties associated with each event,
2. distinguishing natural earthquakes from other seismic events (quarry blasts, induced earthquakes, etc.)
3. possibly associating a mechanism to the event’s centre,
4. estimating the Mw magnitude if this is not provided directly.

This catalogue is the reference catalogue for French seismicity. It is intended for all persons concerned by seismicity.

Bulletin contacts

Marc Grunberg (Eost), Gilles Mazet-Roux (CEA)

Catalogue contacts

Sophie Lambotte (Eost), Bruno Hernandez (CEA)

Section 3: Macro-seismic data, historical and contemporary seismicity

Section 3 of this ATS involves the collection and analysis of historical and contemporary seismicity macroseismic data and includes all work on the acquisition and management of macroseismic data and intensity assessment. The data collected and produced in this section will be linked to the multi-origin bulletin (section 1) so that all data available for an event are easily accessible and usable. The exchange of intensity data with cross-border regions will be integrated into this project to acquire a broad, overall view of an event. Historical macro-seismic data is also a development theme for section 3, the aim being for the data managers involved to enhance such data and associate it with contemporary data. Macro-seismic intensity data must be available, understandable and usable for a large academic or non-academic community.

Contacts

Christophe Sira (Eost), Ludmila Provost (IRSN)

Section 4: Shakemap

The objective of section 4, ShakeMap, is to generate a nationwide map of earthquake tremors, in mainland France and other countries. This mapping is based on numerical modelling from source data (characteristics of the event) and earthquake propagation models (regional and local characteristics such as mitigation, site effects) while integrating all available instrumental and macro-seismic measures.

The resulting Shakemap can be made rapidly available to any users (scientists, general public, authorities) and is also a tool for seismic risk research and applications. This ShakeMap section 4 builds on the results of sections 1, 2 and 3 while also contributing to section 6. It is a collaborative project linked to regional ShakeMap initiatives – one covering the Pyrenees (SisPyr and Pocrisc projects) and the other the South-East (Cassat and Risval projects).

A major challenge in the development of shakemaps lies in the rapid estimation (a few minutes) of seismic movements generated in the area affected by the event. These maps can then be used in tools for estimating the impact of the earthquake (SEISAID and Vigirisks projects), in order to propose a first projection of possible damages and losses.

Contacts

Antoine Schlupp (Eost), Didier Bertil (BRGM)

Section 5: Active faults France (FACT)

From a seismotectonic point of view, metropolitan France like its Western European neighbors can be defined nowadays as a stable continental region (SCR) with a strong structural inheritance undergoing low strain rates. The “Active faults France” axis aims to better understand the seismicity associated with active faults in France and the processes at the origin of this seismicity, by building upthe most complete possible database of active faults for the Quaternary period.

To do this, two approaches are implemented:

• the critical and objective reassessment (contradictory debates, field visits if necessary) of the potentially active faults in France “BDFA” (IRSN, 2017) and “Neopal” (BRGM) databases. These two databases are available on the site : https://data.oreme.org/observation/fact
• the launching of new investigations using the most appropriate methods and techniques in morphotectonics and paleoseismology to detect and characterize the active faults in this SCR context (e.g. very high resolution DTM, sub-surface geophysics type UHRS, all Quaternary dating: 14C, OSL, ERS, cosmogenic isotopes) and thus to characterize their most recent seismic activity (i.e. 10 Ka- 1Ma)

The FACT axis gathers a large number of academic and institutional geoscientists, experts in active tectonics and/or associated methods, whose works are distributed over 9 regions on the metropolitan territory.

Contacts

Jean-François Ritz (Géosciences Montpellier) et Stéphane Baize (IRSN) – Suppléante L. Audin (Isterre)

Referrals in Regions and Institutions of the Active faults France (FACT) Section of Resif-ATS

Section 6: Hazard

The ‘hazard’ section 5 aims to encourage interaction between all actors working on the definition of seismic hazards (university and CNRS laboratories, organisations such as BRGM, IRSN or CEA, public and private companies) to:

1. bring together all the databases required to assess the seismogenic potential of seismic sources in France;
2. promote the development of new seismotectonic and seismic hazard models integrating the latest research results.

To achieve this, section 5 uses data and products both from Résif (seismicity, geodesy) and from other disciplines in the fields of geology, geophysics and numerical modelling. Current efforts are therefore focused on the construction of reference seismotectonic models providing a basis for the development of future seismotectonic zoning which can be used for both research projects and seismic hazard calculations.

Contacts

Stéphane Mazzotti (Géosciences Montpellier), Hervé Jomard (IRSN)