Magnitude and focal mechanism computations for the Saint-Berat earthquake of 4 October 1999.

This paper exposes the various magnitude and focal mechanism computations d one for the Saint-Beat (Pyrenees) earthquake of 4 October 1999 at 18:14 UT. The focal mechanisms have been obtained either by regional moment tensor i nversion, for which the procedure is briefly described, or from first motio n polarities. Although there is a disagreement about the direction of dip o f the preferred fault plane, this one is almost sub-vertical and seems to e xhibit a global east-west orientation, with a T axis oriented north to NNE and a P axis oriented SSE to south-east. Fire also deduced from the inversi on a seismic moment of 4.3.10(15) N.m, corresponding to a Mu' magnitude of 4.4. This one equals the m(b) magnitude reported by the US Geological Surve y and is between the extreme magnitudes Msz 3.7 and M-L 4.8 reported by the ReNaSS. (C) 2000 Academie des sciences / Editions scientifiques et medical es Elsevier SAS.