The French Institute for Radiation Protection and Nuclear Safety (IRSN), with the support of the Ministry of Environment, compiled a database (BDFA) to define and characterize known potentially active faults of metropolitan France. The general structure of BDFA is presented in this paper. BDFA reports to date 136 faults and represents a first step toward the implementation of seismic source models that would be used for both deterministic and probabilistic seismic hazard calculations. A robustness index was introduced, highlighting that less than 15 % of the database is controlled by reasonably complete data sets. An example of transposing BDFA into a fault source model for PSHA (probabilistic seismic hazard analysis) calculation is presented for the Upper Rhine Graben (eastern France) and exploited in the companion paper (Chartier et al., 2017, hereafter Part 2) in order to illustrate ongoing challenges for probabilistic fault-based seismic hazard calculations.
The practice acquired in nuclear regulation over the last
decade as well as the feedback arisen from recent earthquake consequences on
nuclear power plants (e.g. Kashiwazaki-Kariwa in 2007, Fukushima and
North Anna in 2011) have challenged the expertise of the IRSN (French Institute
for Radiation Protection and Nuclear Safety). Hence, IRSN's research
related to the geological aspects of seismic hazard analysis (SHA) has been
focused on three principal axes: (1) updating national seismotectonic zoning
pattern (Baize et al., 2013), (2) performing and publishing collaborative
studies on specific French active faults (see Cushing et al., 2008; Baize et
al., 2011; García-Moreno et al., 2015; De La Taille et al., 2015) and
(3) implementing the BDFA (from the French term
The above-mentioned third axis started in 2009 and consists of the ongoing
BDFA project (Palumbo et al., 2013). It represents a first step to supporting
SHA calculation, which needs a collection of geological information in order to
characterize seismic sources. This new database compiles available data on
faults with post-Late Miocene activity evidence in metropolitan France,
including geometrical properties, kinematics, slip rates, etc. All this
information is made available as a fault map and in related tables for further
application. Currently, the project focuses on faults that are longer than
10
BDFA aims to represent a first step towards the constitution of a seismic sources catalogue that can be later used in SHA as well as in PFDHA (probabilistic fault displacement hazard analyses) calculations. An outlook of BDFA in the Upper Rhine Graben and its transcription into a source model for PSHA calculation is presented in Sect. 4 of this paper.
Map of BDFA (Google Earth kml file provided in the Supplement) at the scale of metropolitan France. Faults coloured by the age of the last known movements. Black circles represent a 50 km perimeter around each nuclear facility. The black dashed rectangle represents the geographical imprint of Fig. 5. In the top left is a simplified structural sketch of France (modified from Baize et al., 2013): crystalline basement outcrops are defined in light red, major basement faults in black, and minor faults in grey.
Despite its distance to active plate boundaries and relatively low to moderate seismotectonic activity (intraplate domain), both significant earthquakes (e.g. historical catalogue, SISFRANCE, 2016) and surface faulting (e.g. Sébrier et al., 1997; Chardon et al., 2005) have occurred in metropolitan France during historical and pre-historical times.
The starting point for building the BDFA relied on previous research, namely
(1) the seismotectonic map released by Grellet et al. (1993) and the active
fault database of south-eastern France (Terrier, 2004), (2) the IRSN catalogue
of faulting evidence affecting Quaternary deposits (Baize et al., 2002), and
(3) the French catalogue of neotectonic evidence (available online at
BDFA aims to reflect the available data sets as much as possible, either for the establishment of fault mapping or for the description of the fault activity. Because various opinions may have been proposed by different authors at different times and at different scales, we compiled their interpretations/data in a specific form for each fault complementing the BDFA traces and tables. Our own choices of fault parameters and associated uncertainties are therefore tracked and referenced to the aforementioned form. These forms and the neotectonic and structural syntheses compiled at regional scales (i.e. Alps, Britany, Jura Mountains, etc.) are written in French and are available upon request.
Among the parameters compiled in the database, we focused on the two following critical points.
The main cartographic reference for the BDFA is that of Grellet et
al. (1993), who, following Fourniguet (1978), first attempted to synthesize
neotectonic and active faults across France at the
This task represents a key point of the database which is, however, not straightforward to determine, because of both scientific and regulatory issues.
From a scientific point of view, when no sign of current activity is recorded along a fault (from seismicity and geodesy), which is often the case in intraplate domains, determining whether a fault is active or not is based upon the age of the youngest observed deformation, with particular attention to multiple movements occurring over the last thousands to hundreds of thousands of years.
From a regulatory point of view, national and international definitions of
when a fault should be considered active may differ when it comes to deciding
on the temporal limits that should be taken into account. Concerning the
determination of ground motion at sites, the French Nuclear Safety Authority
rules (ASN, 2001) recommend, for example, that the hazard related to an active
fault should be taken into account when defining the ground motion related to a
potential event whose return period is of the order of a few tens of
thousands of years. Concerning the fault displacement hazard, the
international nuclear safety guideline (IAEA, 2010) indicates that for
intraplate domains, fault capability (i.e. capacity of a fault to rupture the
surface during an earthquake) should be assessed by collecting geological
information covering the Plio-Quaternary period (the temporal threshold to
account for should then be 5.3
At the metropolitan France scale, the orientation of the tectonic stress field has not experienced dramatic changes since the end of Miocene, with the persistence of the convergence between Africa and Eurasia. In parallel, the age of Plio-Quaternary sediments that may attest for deformation along faults are often absent or poorly constrained. In this context, we regarded the re-activation of past structures as possible and build the BDFA as a potentially active fault database, thus including the late Miocene to Quaternary structures as considered in a previous compilation by Baize et al. (2013) (Fig. 1).
The database structure (see the Supplement) was inspired by other databases developed in the world, such as the ones from the USA (QFAULT; Haller et al., 2004), New Zealand (NZAFD; Langridge et al., 2016), Japan (Active Fault Database of Japan; AIST, 2016), Italy (ITHACA; Michetti et al., 2000) and Iberia (QAFI; García-Mayordomo et al., 2012). The proposed map for metropolitan France is associated with a relational database describing the state of knowledge for each fault segment. This database is composed of several thematic tables (designed in Microsoft Excel spreadsheets) linked together with an identification key.
The identification key for each fault described in BDFA (ID_Fault – IDF)
corresponds to the one referenced in the French Geological survey (BRGM)
fault database related to the The main table contains all gathered fault parameters with associated
uncertainties when available (i.e. map characteristics, geometry,
neotectonics, ages and kinematics, calculation of a robustness index, editing
notes and release date). The index-ref and reference tables list the publications used to
characterize the faults. The index-evidence table includes all neotectonic evidence reported in
the NEOPAL and IRSN databases (respectively NEOPAL, 2009 and Baize et
al., 2002). The index-seismic table reports the largest earthquakes, essentially events
described in the historical archives (SISFRANCE) for which magnitude values
are proposed by Baumont and Scotti (2011).
All fields are described in the BDFA table enclosed in the Supplement. Most of
them are manually implemented, but we took advantage of GIS capabilities to
implement cartographic parameters such as length, azimuth, tips coordinates.
When a field cannot be filled because of a lack of data, a numerical code of
Fault segmentation and location are key parameters in seismic hazard assessment (Wesnousky, 1986; Field et al., 2015; Biasi and Wesnousky, 2016). While building up the BDFA, we mapped fault traces and associated segmentations directly as they were defined in the literature. Where several references were available for a single fault or fault segment, we decided to report the traces proposed from the most recent or reliable references. These principles have largely been applied for faults in eastern, northern, and southern France, because most of them have been studied for many years. However, the age of some publications led us to propose an alternative mapping in light of more recent cartographic documents (see the second point below).
In parallel, few active or potentially active faults have been studied in
detail in central and north-eastern France. It may also happen, in
particular for long faults (e.g. the south Armorican shear zone is longer
than 500 As defined earlier, the basic unit filled in the database is the fault
segment (UID), grouped into a fault (IDF), forming a discontinuous trace at
the surface. In order to propose a surficial trace of the fault segments, we relied on
the available map documents with a cartographic scaled approach. Priority was
given to large-scale geological maps from the French geological survey
( Fault segments were archived into four typologies (major: M, parallel: P,
oblique: OB and orthogonal: OX). This term was introduced to differentiate
what is considered to be the main fault trace (major) from satellite or
conjugate systems. This is especially useful for inherited faults in hard
rocks (e.g. Armorican shear zones) for which geologists have mapped all
brittle structures and where it is not possible to reject the potentiality of
faulting due to the activation of the main structure. This distinction
accounts for the relative strike of the subordinate segments with respect to
the major fault trace (M): between 0 and 15 The unique identification number (UID) of each fault segment is obtained by
concatenating IDF, the segment typology (M, P, OB, OX) and the number of the
segment (SNB). As an example (Table 1), the second major segment of the Vuache
fault (IDF
BDFA parameters concerning the 5317_2_M segment of the Vuache fault. Data derived from Baize et al. (2011).
In any case, whether the retained geometries derive from publications or maps, fault segments are always defined on the basis of static geologic criteria or at least long-term morphological evidence of deformations. This is mainly due to the fact that, in metropolitan France, dynamic criteria (surface ruptures, fault source models, etc.) cannot be derived from the analyses of major earthquakes, the last surface-rupturing event probably being the Lambesc earthquake in 1909 (Chardon et al., 2005).
Segmentation typologies (TYP) used to define the identity code of each segment (UID).
The age of the youngest deformed geological horizon will condition whether the causative fault/fault segment is considered in hazard calculations or not (French RFS 2001-01; IAEA, 2010; U.S. NRC, 2017). A second time, once a fault or a fault segment is considered, the associated slip rate will be the most influencing parameter in quantifying its seismogenic activity.
Consequently, we designed the database to provide the necessary parameters to
(1) assess the age of the last movement along a fault or fault segment, and
(2) calculate slip rates or understand how they were derived. Concerning the
age of the last movement, we defined the following parameters to be filled in
the database for each fault segment:
The DCHR (deformed chronostratigraphic unit) field indicates the local
terminology of the most recent chronostratigraphic unit involved in faulting.
These may refer to epochs (e.g. Pliocene, Quaternary) or to more precise
stages (e.g. Riss, Würm) due to the fact that Plio-Quaternary deposits
are often poorly dated, Depending on the age defined in DCHR, a generic field
called neotectonic age (NA) is provided in addition and used for mapping.
Four predefined terms were adopted to fill the NA field: Quaternary, Pliocene
(i.e. syn- to post-Pliocene), Miocene (i.e. syn to post-Late Miocene), and
Undetermined. As a consequence, it may happen, because of missing sediments
or datings along specific fault segments, that different ages are attributed
to segments of a single fault. In this case, it is up to the user to decide
whether the considered fault is active or not. DCHRT and DCHRB (DCHR top and base, in years) inform the
numerical age of the top and the base of the youngest unit (DCHR) involved in
the faulting. It may happen that one, both, or none of these ages are
available. DM (dating method) refers to the dating method used to establish
DCHRT and DCHRB. We rely on three predefined terms: (1) radiometric,
when numerical ages are available; (2) relative, when ages of
movement can be constrained by stratigraphic or biostratigraphic information
and (3) indirect when only facies correlations are
available at regional scales. NWEU (north-west European chronostratigraphic stages) – because the
terminology of Quaternary glaciations used over time in the French
bibliography often refers to Alpine regional stages, we introduced a field
referring to their corresponding north-western European stages. UCHR (undeformed CHRonostratigraphic unit) indicates the
local terminology of the oldest chronostratigraphic units not involved in the
faulting. As mentioned previously, DCHR may cover a wide variety of terms. NEOF (neotectonic offset). It informs the minimum and maximum offset
values of the marker used to estimate slip rates and associated
uncertainties. In general, it corresponds to the amount of slip registered by
the youngest available dated and faulted marker. OST (offset span time, in years).
It reports the time span used to calculate slip rates. It could be either a
single value or a bracket depending on the presence or absence of dated
deformation markers. AR (age used for rate). It mentions the name of the chronostratigraphic
units constraining OST. It may happen that OST does not correspond to DCHR
because the amount of slip (i.e. NEOF) in the youngest affected sediments can
not be quantified. In this case, longer-term slip rates may be derived from
older stratigraphic/morphologic markers.
Concerning slip rates, we were rarely able to extract from the consulted
references direct information concerning fault slip rates. Published slip
rate values were controlled before integration into the database, when
chronological and/or stratigraphical issues arose because of either
ambiguous, vague, or even inconsistent information. When reliable
constraints in terms of chronology and amount of slip can be extracted from
the consulted references (scientific papers, maps, etc.), then we propose
slip rates based on these observations. The following parameters are filled
in the database:
Slip rate ranges are finally calculated by dividing NEOF with OST. When
sufficient data are available, they may be decomposed in vertical slip rate
(VSR) and/or horizontal slip rate (HSR).
Conceptual example illustrating the different chronological terms used in BDFA to determine the age of deformations and slip rates.
In Fig. 3, we illustrate a theoretical case in which we reported the different fields informed in the database. This corresponds to an ideal case in which stratigraphic markers with absolute ages are available within the youngest deformed unit, which will allow for the recovery of a range of slip rates related to the most recent deformed horizon.
A real example illustrating the use of long-term slip rates because of
missing quantified tectonic offsets in the most recent formations is given
for the Vuache fault and derived from the publication of Baize et al. (2011).
The parameters introduced in the database for the 5317_2_M segment are
reported in Table 1. Along this fault segment, faulted Quaternary deposits
were observed in a quarry and dated at the end of Riss
(
The current version of the database includes 136 faults with a total of 581
fault segments. Among these 581 segments, 118 are reported as active during
the Quaternary. We provide a robustness index (RI), estimated for each
segment. This index aims to provide a ranking of the fault population in
terms of reliability of their potential activity. RI (Eq. 1) follows the
empirical expression modified from Baize et al. (2012):
This index is subjective by nature. It gives a higher weight to dynamic
criteria like seismicity, because we consider that it is the most relevant
criterion to prove seismotectonic activity. The total population of the
database was classified within equally separated RI classes (Fig. 4). It
highlights that a relatively small part of BDFA fault segments are reliably
potentially active (82 segments with an RI
Robustness index (RI) distribution for all fault segments described in BDFA.
The southern part of the Upper Rhine Graben (URG) straddles the border
between France and Germany from northern Switzerland to Mainz in western
Germany. It presents significant seismic activity for an intraplate area
with, for instance, a magnitude 4 or greater earthquake shaking the area
every
Previous investigations have supported the hypotheses that the 1356
historical earthquake might be due either to the activity of west-trending
buried faults (e.g. Meyer et al., 1994), or to a north-trending Rhenish
structure (e.g. Meghraoui et al., 2001). Nivière et al. (2008)
investigated the north–south Rhenish structures (e.g. Rhine River fault; see
Fig. 5) and concluded from morphological and borehole data that these
structures are potentially able to generate earthquakes as large as
Because of their proximity to the French nuclear power plant (NPP) of
Fessenheim (
The three closest-to-NPP faults mapped in BDFA are the West Rhenish, the
Rhine River and the Black Forest faults ( Faults lengths: BDFA surficial traces are taken into account and
digitized in PSHA CRISIS 2014 (Ordaz et al., 2014, Fig. 5). Lengths may
slightly differ due to a rough digitization in the PSHA software. In BDFA,
surficial fault traces (Fig. 5c) of the three considered faults were directly
derived from the literature. Faults depths: in BDFA, we gave priority to fault depths characterized
through geophysical prospections. Concerning the West Rhenish fault, for
example, segment depths in BDFA are derived from the interpretation of
reprocessed high-resolution industrial seismic profiles published by Rotstein
and Schaming (2008). For the PSHA fault source model, we retain depths
derived from the analysis of regional seismicity (Edel et al., 2006) and the
interpretation of a crustal-scale seismic profile (DEKORP-ECORS, Brun and
Wenzel, 1991). Two depth values will be tested for PSHA calculations: 15 and
20 Faults dips: we mainly relied on the BDFA values, except for the Black
Forest fault for which a higher angle equal to the Rhine River fault was
preferred ( Faults slip rates: we considered slip rates contained in the BDFA (lower
and upper bounds). For the Rhine River and the Black Forest faults,
slip rates are available in the literature for only one segment of each
fault; we then attributed coherent values to all segments for which no value
were proposed in the literature. Slip rates along these fault segments were
deduced from the analysis of post-Pliocene geological markers (Nivière et
al., 2008). For the West Rhenish Fault, considered in BDFA as active during
the Pliocene and possibly during the Quaternary, no slip rates were found in the
literature. To this model we then attribute an upper bound of slip rate
equal to the lower slip rate determined for both the Rhine River and Black
Forest faults and a lower bound of slip rate coherent with lower fault-slip
rates determined in the Lower Rhine Graben following Vanneste et al. (2013).
It is important to mention that in this part of the Rhine Graben, all fault slip rates that are available in the literature are given as vertical slip rates, considering that the long-term normal activity observed along these faults is representative of the ongoing deformation processes. However, data from seismicity (Edel et al., 2006), geodesy (Tesauro et al., 2005) as well as long-term regional stresses (Rotstein and Schaming, 2011) suggest a possible strike-slip component along faults in the Fessenheim area. To date, field data along faults are missing to confirm and quantify this strike-slip component (possibly dominant), but it is clear that such a hypothesis should be explored in future hazard assessments.
This exercise of converting the database into a fault source model shows that this transcription is not straightforward. Concerning the area we considered for this exercise, which is among the most studied in France, only five segments over nine present robustness indexes over 10, which means that the basic data we need to build a fault source model are either missing or of very poor quality. In this light, even if BDFA has been designed to integrate parameters required to implement a fault source model for PSHA, it is still necessary to make assumptions and account for alternatives when it comes to filling the model parameters.
In areas covered by the BDFA, the database represents the most complete source of information available in the literature to date. It is, however, clear that (1) the database needs to be extended to the entire country (metropolitan as well as neighbouring regions) for wider use than seismic hazards related to nuclear facilities, and (2) there is a need for future and periodic updating, especially in some areas such as the Alps and peripheral zones or the Rhine Graben.
However, for the time being, we are aware that the data contained in the
database are mostly of low resolution as expressed through the robustness
index. In metropolitan France, the main reasons for this situation are the
following:
Dating: because surficial deposits were strongly subjected to human
reworking and erosion (mostly linked to glaciations), few markers are
available to characterize the recent activity of faults (age, slip rates,
etc.). In parallel, few Quaternary formations have been the subject of
absolute dating campaigns and the age of deformations is often questionable.
In this light, projects aiming at developing methodologies (such as the
Proyecto Dataciòn performed in Spain, Santanach et al., 2001; Shyu et
al., 2016 in Taïwan) would help to reduce dating uncertainties. Palaeoseismic evidence and seismic activity occur due to the very long
recurrence periods of surface rupturing earthquakes. Because tectonic
deformation rates are of the order of or even lower than erosion rates, very
little palaeoseismic evidence has been identified so far in France. Then, the
best way we currently have to estimate the activity of faults is to be able
to associate them to earthquakes, either instrumental or historical ones.
Yet, apart from some temporary local seismic networks (Courboulex et
al., 2003; Cushing et al., 2008), we are rarely able to associate the
registered seismicity to a specific structure. It is then understandable that
such time-consuming/costly studies are not sufficiently profitable for
researchers in a context of scientific competition. In parallel, new ideas
regarding the seismic behavior of stable continental regions (Calais et
al., 2016) are sprouting, with the idea that the classical seismic cycle on a
fault may not be the most plausible hypothesis and that the seismic potential
could be more distributed in space and time. Then, questions arise related to
the definition of what a stable continental region is and how to
differentiate faults that could have the potential to produce major
earthquakes from faults that could not. These questions are of growing
importance. In any case, there is a crucial need to fund data gathering in
metropolitan France, but also in regions with comparable geodynamical
contexts in order to properly address and complement future seismic hazard
analysis based on faults. Hidden and blind faults: some faults and fault segments without
outcropping signatures have been recognized (such as the Belledone fault,
Thouvenot et al., 2003) and are integrated into the database. However,
studies conducted to highlight them are few in number. In this respect,
studies leading to the reprocessing of industrial seismic profiles are likely
to complete our knowledge, as well as studies devoted to relocate
instrumental seismicity (Thouvenot et al., 2003; Courboulex et al., 2003).
The BDFA project, although it represents the state of the art of published
studies, is inherently incomplete. It aims to be useful for identifying and
planning the scientific campaigns that will be necessary for site-specific
seismic hazard assessment studies. In this paper we propose a PSHA fault
source model based on the transposition of BDFA data in order to conduct an
exercise in the Upper Rhine Graben (developed in the parent paper – Part 2),
aiming to quantify the relative influence of fault parameters on the hazard
at a specific site. We underline here that industrial seismic data
reprocessed from the GEORG project (
We also point out that according to international safety guides (IAEA, 2010), the fault displacement hazard, related to a fault that has a significant potential for displacement at or near the ground surface, should be explored for facilities located in the vicinity of potentially active faults. This hazard analysis (FDHA), however, requires a detailed and local data set as well, that BDFA clearly does not fulfil, but which again represents a guide for future investigations in metropolitan France.
Finally, the ongoing post-2011 Tohoku earthquake discussions have led to extreme events being envisaged as scenarios against which nuclear power plants need to be prepared. One possible way to foresee these events for SHA purposes may be to evaluate the maximum magnitude derived from the sizes of potential earthquake sources (i.e. the active faults). In that sense, the presented database may be useful but additional discussions on criteria to define fault segmentation and consecutively the potential for multi-segment ruptures is needed, as recalled recently by the Kaikoura earthquake in New Zealand that ruptured a very high number of fault segments (Hamling et al., 2017).
In this paper, we present a first release of a database of potentially active faults (BDFA) that defines and characterizes faults in their current state of knowledge. Such a database may be used during the elaboration of fault-based models for future seismic hazard analysis (SHA), either deterministic or probabilistic. In this light, BDFA was designed to include appropriate seismotectonic parameters (geometry, segmentation, slip rate, etc.).
This first release of the BDFA results from a 4-year endeavour in defining and compiling the database. Besides problems related to the completeness of some fields and the complete translation of the database in English (in progress), homogenizing the database is our first objective for the next release. This last point is largely explained by strong regional heterogeneities in data availability. In parallel, a website is currently under construction and will help us to gather more users' feedback to improve the database.
As a matter of fact, BDFA must not be considered to be a complete database and therefore cannot be a substitute for the necessary in-depth studies required to evaluate the hazard at a specific site.
Data contained in BDFA are provided in the Supplement of this paper.
The authors declare that they have no conflict of interest.
This article is part of the special issue “Linking faults to seismic hazard assessment in Europe”. It is not associated with a conference.
The development of BDFA was funded by both the IRSN and the French ministry of environment. We first thank Hiromi Kobayashi and Vincent Courtray for their support to this project at the French Ministry for Environment. We would like to thank all persons that helped us to design and increment the database, and especially all the specialists who have agreed to review the forms associated to major faults of the database. We thank Oona Scotti for her fruitful comments, enthusiasm and help in writing and revising this paper. We finally sincerely thank Julian Garcia-Mayordomo and an anonymous referee for their careful review of our paper as well as Kuo Fong Ma for their constructive comments.
Despite all the care we have taken in the development of this database, it is possible that some errors remain here and there. We then would like to thank in advance all the persons that will contact us in order to share their experience and favour the development and quality of the database. Edited by: Francesco Visini Reviewed by: Julian Garcia-Mayordomo and one anonymous referee