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

摘要

This paper proposes a synthesis of the studies made in terms of source parameters evaluation for the last earthquakes of local magnitude greater than 4.5 which occurred in or nearby France during the last five years. Focal mechanisms and seismic moments have been computed for the three most important events, largely felt by the population: St Paul de Fenouillet (February 18~(th) 1996, M_L 5.6), Annecy-Epagny (July 15~(th) 1996, M_L 5.2) and St-Beat (October 4~(th) 1999, M_L 4.8). These focal mechanisms have been obtained either by regional moment tensor inversion or from first motion polarities and are compared with complementary studies made on these earthquakes. In addition, for the other earthquakes of local magnitude greater than 4.5 which occurred nearby French borders since the beginning of the recording of broadband data by the ReNaSS (Reseau National de Surveillance Sismique, French Seismological Survey) in mid-1995, several magnitude calculations concerning the following earthquakes are presented: Pamplona (25/2/1996, M_L 4.7) Aoste (31/03/1996, M_L 4.6), Imperia (24/2/1997, M_L 4.5), Barcelonette (31/10/1997, M_L 4.8), Pamplona (27/10/1998, M_L 4.9), and Bonifacio (26/4/2000, M_L 4.5). Local magnitudes are usually higher than the M_b magnitudes reported by the PDE (Preliminary Determination of Epicenters), while the extension of the Msz scale to regional magnitudes and the Mw magnitudes derived from seismic moments give smaller values. The relative importance of the various earthquakes in terms of surface wave magnitude or seismic moment does not always agree with that implied by local magnitudes.