Scientific files
 
EARTHQUAKE at Bagnères-de-Bigorre (Hautes-Pyrénées) on 1 April 2010

Description of the event

 = 4.3, located 16 km to the South-east of Bagnères-de-Bigorre in the Hautes-Pyrénées, at latitude 43.02° N and longitude 0.32° E (Fig. 1). Taking into account its magnitude, this event was recorded on all the stations belonging to the seismic network of the CEA-DASE (Fig. 2). The earthquake was felt by the population up to a distance of 40 km around the epicentre.
For the time being, this event has not been followed by aftershocks in the zone of the epicentre.

Localisation de l'événement du 01/04/2010 à 03h36 T.U. (étoile blanche) et de la sismicité instrumentale (points rouges) et historique (points jaunes).
 Figure 1: Location of the event on 01/04/2010 at 03h36 UTC (white star), as well as instrumental seismicity (red circles) and historical earthquakes (yellow circles) contained in the LDG database.


Signaux sismiques enregistrés lors du séisme du 01/04/2010 (partie 1).


Signaux sismiques enregistrés lors du séisme du 01/04/2010 (partie 2).
 Figure 2: Seismic signals recorded during the seismic event on 01/04/2010.

Tectonics and seismicity

The earthquake of 1 April 2010 in the Hautes-Pyrénées (Bagnères-de-Bigorre) is located on the North Pyrenean Fault (NPF), which is weakly expressed in this area (Fig. 3). The FNP is a major East-West trending fault on the northern boundary of the Pyrenees, extending over the entire length of the chain. It represents the suture of the Iberian and Eurasian plates, which have been undergoing more or less North-South convergence from approximately 65 Ma ago. The North-Pyrenean zone is located to the north of the FNP and south of the North Pyrenean Thrust Front (NPTF), corresponding to an area of thinned crust formed during an extensional phase related to the opening of the Bay of Biscay, prior to the phase of compression. The Palaeozoic axial zone, to the south of the NPF, is characterized by the presence of the highest summits of the chain. The general tectonic stress regime accounting for the current seismicity of the Pyrenees is a roughly North-South compression (Delouis et al., 1993), with the Iberian domain being thrust under Eurasia towards the north, at least in the central and eastern parts of the chain (Souriau and Granet, 1995).
The earthquake took place in the Hautes-Pyrénées (Fig. 1), which represents the most seismically active area of metropolitan France in terms of rate of seismicity. On average, one or two shocks of magnitude (ML LDG) greater than 5 are observed in this region per decade. The main earthquakes of the Western and Central Pyrenees are listed in Table 1.

Name of earthquake Date Maximum intensity (MSK) Magnitude*
Central Pyrenees,
Bigorre
21/06/1660 VIII-IX 6,1
Central Pyrenees,
Juncalas
24/05/1750 VIII 5,5
Western Pyrenees,
Ossau Valley
22/05/1814 VII 5,1
Central Pyrenees,
Argelès Gazost
20/07/1854 VII-VIII 5,3
Western Pyrenees,
Ossau Valley
22/02/1924 VII 4,9
Western Pyrenees,
Arette
13/08/1967 VIII 5,3
Western Pyrenees,
Ossau-Arudy Valley
29/02/1980 VII-VIII 5,7
Western Pyrenees,
Basque Country
06/01/1982 VI-VII 5,0
Central Pyrenees,
Bigorre
04/10/1999 VI 5,1
Central Pyrenees,
Bigorre
17/11/2006 VI 5,4
 Tableau 1: Main earthquakes of the Western and Central Pyrenees. (*) = local Magnitude ML given by LDG for events after 1962, and magnitude estimated from macroseismic intensities for the earlier events.



Carte structurale de l’orogène pyrénéen en France. (Mattauer et Henry, 1974). Etoile rouge : localisation de l’épicentre du séisme du 1 avril 2010 dans les Hautes-Pyrénées (Bagnères-de-Bigorre).
 Figure 3: Structural sketch map of the Pyrenean orogenic belt in France. (Mattauer and Henry, 1974). Red star: location of the epicentre of the earthquake of 1 April 2010 in the Hautes-Pyrénées (Bagnères-de-Bigorre).

Figure 4 below shows the statistics year by year since 1970 within a radius of 100 km around the epicentre of the earthquake of 1 April 2010.

Histogramme de la sismicité au voisinage de  Bagnères-de-Bigorre depuis 1970 (base de données LDG).
 Figure 4: histogram of seismicity in the vicinity of Bagnères-de-Bigorre since 1970 (LDG database).