The French seismic CATalogue (FCAT-17)

Abstract

In regions that undergo low deformation rates, as is the case for metropolitan France (i.e. the part of France in Europe), the use of historical seismicity, in addition to instrumental data, is necessary when dealing with seismic hazard assessment. This paper presents the strategy adopted to develop a parametric earthquake catalogue using moment magnitude M w , as the reference magnitude scale to cover both instrumental and historical periods for metropolitan France. Work performed within the framework of the SiHex (SIsmicité de l'HEXagone) (Cara et al. Bull Soc Géol Fr 186:3-19, 2015. doi:10.2113 and SIGMA (SeIsmic Ground Motion Assessment; EDF-CEA-AREVA-ENEL) projects, respectively on instrumental and historical earthquakes, have been combined to produce the French seismic CATalogue, version 2017 (FCAT-17). The SiHex catalogue is composed of *40,000 natural earthquakes, for which the hypocentral location and M w magnitude are given. In the frame of the SIGMA research program, an integrated study has been realized on historical seismicity from intensity prediction equations (IPE) calibration in M w detailed in Baumont et al. (submitted) companion paper to their application to earthquakes of the SISFRANCE macroseismic database (BRGM, EDF, IRSN), through a dedicated strategy developed by Traversa et al. (Bull Earthq Eng, 2017. doi:10. 1007/s10518-017-0178-7) companion paper, to compute their M w magnitude and depth. Macroseismic data and epicentral location and intensity used both in IPE calibration and inversion process, are those of SISFRANCE without any revision. The inversion process allows the main macroseismic field specificities reported by SISFRANCE to be taken into 123Bull Earthquake Eng DOI 10.1007/s10518-017-0236-1 account with an exploration tree approach. It also allows capturing the epistemic uncertainties associated with macroseismic data and to IPEs selection. For events that exhibit a poorly constrained macroseismic field (mainly old, cross border or off-shore earthquakes), joint inversion of M w and depth is not possible, and depth needs to be fixed to calculate M w . Regional a priori depths have been defined for this purpose based on analysis of earthquakes with a well constrained macroseismic field where joint inversion of M w and depth is possible. As a result, 27% of SISFRANCE earthquake seismological parameters have been jointly inverted and for the other 73% M w has been calculated assuming a priori depths. The FCAT-17 catalogue is composed of the SIGMA historical parametric catalogue (magnitude range between 3.5 up to 7.0), covering from AD463 to 1965, and of the SiHex instrumental one, extending from 1965 to 2009. Historical part of the catalogue results from an automatic inversion of SISFRANCE data. A quality index is estimated for each historical earthquake according to the way the events are processed. All magnitudes are given in M w which makes this catalogue directly usable as an input for probabilistic or deterministic seismic hazard studies. Uncertainties on magnitude...

Exploration tree approach to estimate historical earthquakes Mw and depth, test cases from the French past seismicity

“…the cases of single/ sporadic (if any) quantified IDP available, the depth must be determined a priori using complementary information. Manchuel et al (2017), divide the French metropolitan territory and surrounding areas into the following nine regions: the French Alps, the Pyrenees, the Armorican Massif, the European Cenozioc Rift System (ECRIS), the Provence, the Tricastin region, the Hainaut, the Atlantic Ocean zone and the rest of France (see Fig. 3 in Manchuel et al 2017).…”

“…Each region is considered homogeneous in terms of seismogenic depth properties. In each of them, Manchuel et al (2017) build a regional depth distribution using the earthquake depths computed using the WLSQ inversion proposed in the present paper (i.e. the depth of the earthquakes falling in the cases described in Sect.…”

“…4). Following the regionalization scheme proposed by Manchuel et al (2017) the 1509 Manosque earthquake is located within the Provence region. The earthquake depth is then fixed a priori to the value of 6 km, with an associated uncertainty r log10(h) = 0.20 (see Table 1 Fig.…”

“…Following the seismogenic depth regionalization scheme proposed by Manchuel et al the 1852 Albertville earthquake is located within the Alps region. The earthquake depth is then fixed a priori to the value of 7 km, with an associated uncertainty r log10(h) = 0.24 (see Table 1 in Manchuel et al 2017). For each IPE, the magnitude is then computed inverting Eq.…”

“…When applied in a systematic manner, it allows to obtain consistent (homogeneous) magnitude and depth estimates over the whole historical period (e.g. in France, see the companion paper by Manchuel et al 2017). Depending on the case, the adopted strategy implies: (1) a ''Complete ET'' magnitude and depth simultaneous inversion scheme, when dealing with well documented events that exhibit a decay of macroseismic intensity with distance; (2) a ''Simplified ET'' magnitude and depth simultaneous inversion scheme when dealing with either, offshore or cross border events, which lack information at short epicentral distances but dispose of reliable data at large ones; (3) a priori-depth-based magnitude computation when dealing with poorly described (mainly ancient) events, only known by single/sporadic intensity data or worse, only few ''felt'' testimonies.…”