Synthesis of magnitude and focal mechanism computations for the M ≥ 4.5 earthquakes in France for the period 1995–2000

Abstract

This paper proposes a synthesis of thestudies made in terms of source parametersevaluation for the last earthquakes oflocal magnitude greater than 4.5 whichoccurred in or nearby France during thelast five years. Focal mechanisms andseismic moments have been computed for thethree most important events, largely feltby the population: St Paul de Fenouillet(February 18th 1996, ML 5.6),Annecy-Epagny (July 15th 1996, ML5.2) and St-Beat (October 4th1999, ML 4.8). These focal mechanismshave been obtained either by regionalmoment tensor inversion or from firstmotion polarities and are compared withcomplementary studies made on theseearthquakes. In addition, for the otherearthquakes of local magnitude greater than4.5 which occurred nearby French borderssince the beginning of the recording ofbroadband data by the ReNaSS(Reseau National de SurveillanceSismique, French Seismological Survey) inmid–1995, several magnitude calculationsconcerning the following earthquakes arepresented: Pamplona (25/2/1996, ML4.7), Aoste (31/03/1996, ML 4.6),Imperia (24/2/1997, ML 4.5),Barcelonette (31/10/1997, ML 4.8),Pamplona (27/10/1998, ML 4.9), andBonifacio (26/4/2000, ML 4.5). Localmagnitudes are usually higher thanthe Mb magnitudes reported by the PDE(Preliminary Determination of Epicenters),while the extension of the Msz scale toregional magnitudes and the Mw magnitudesderived from seismic moments give smallervalues. The relative importance of thevarious earthquakes in terms of surfacewave magnitude or seismic moment does notalways agree with that implied by localmagnitudes.