Accurate hypocentre locations in the Middle-Durance Fault Zone, South-Eastern France

A one-dimensional velocity model and station corrections for the Middle-Durance fault zone (south-eastern France) was computed by inverting P-wave arrival times recorded on a local seismic network of 8 stations. A total of 93 local events with a minimum number of 6 P-phases, RMS<0.4 s and a maximum gap of 220° were selected. Comparison with previous earthquake locations shows an improvement for the relocated earthquakes. Tests were carried out to verify the robustness of inversion results in order to corroborate the conclusions drawn from our findings. The obtained minimum 1-D velocity model can be used to improve routine earthquake locations and represents a further step toward more detailed seismotectonic studies in this area of south-eastern France

La sismicité instrumentale récente de la Provence dans son cadre sismo-tectonique

Seismicity in Provence from local seismic network. Seis-motectonic relationships. In the geodynamical setting of the Northwestern Mediterranean dominated by the convergence of the European and African plates with a rate of about 1 cm/year, Provence is a region of seismic risk as evidenced by the Lambesc earthquake in 1909 or epicenters all along the Durance valley. A local seismic network has been built up since 1983 and has grown to 8 stations equiped with short-period vertical seismographs and telemetered to a central recording station (Pic de Bertagne) where data are recorded on magnetic tape. A technique is being developed using a modern card-telephone line system to transmit data in near real-time to the processing center at Marseille-University. A data base is also produced for the period 1983-1993 and relevant seismicity is analysed in term of seismotectonic regions. Seismic activity is associated with two main types of tectonic features : NE-SW to NS strike-slip faults and EW trending thrust units. This pattern is consistent with the regional stress field associated with the SN convergence of African and European plates.La situation géodynamique particulière des structures géologiques de la Provence, au voisinage d'une frontière de plaques lithosphé-riques convergentes, fait de cette région une aire de risque sismique potentiel non négligeable, ce que corrobore l'examen de la sismicité historique et récente (séisme de Lambesc en 1909) ainsi que le canevas sismo-tectonique régional. Un réseau sismique local comportant 8 stations a été progressivement installé depuis 1983 sous l'égide de l'INSU. Pour des impératifs techniques, les signaux sont télémétrés vers un site central (Pic de Bertagne) où ils sont enregistrés sur bande magnétique avant d'être exploités en temps différé à l'Institut de Physique du Globe de Strasbourg. Une unité de transfert des données par voie téléphonique hertzienne vers le site de Saint-Jérôme -Université a été expérimenté, qui permet d'analyser la sismicité locale en temps quasi réel. Un fichier informatique a été constitué qui recense les épicentres pour la période 1983-1993. Leur analyse en termes sismo-tectoniques, confirme clairement qu'ils sont associés aux structures géologiques chevauchantes et décrochantes selon lesquelles s'accomode le raccourcissement lié à la compression subméridienne résultant de la convergence des plaques Europe et Afrique.Fourno J.-P., Roussel Jacques, Lécorché Jean-Paul. La sismicité instrumentale récente de la Provence dans son cadre sismo-tectonique. In: Géologie Méditerranéenne. Tome 20, numéro 1, 1993. pp. 7-23

Accurate hypocentre locations in the Middle-Durance Fault Zone, South-Eastern France

A one-dimensional velocity model and station corrections for the Middle-Durance fault zone (south-eastern France) was computed by inverting P-wave arrival times recorded on a local seismic network of 8 stations. A total of 93 local events with a minimum number of 6 P-phases, RMS<0.4 s and a maximum gap of 220° were selected. Comparison with previous earthquake locations shows an improvement for the relocated earthquakes. Tests were carried out to verify the robustness of inversion results in order to corroborate the conclusions drawn from our findings. The obtained minimum 1-D velocity model can be used to improve routine earthquake locations and represents a further step toward more detailed seismotectonic studies in this area of south-eastern France.Published3.2. Tettonica attivaN/A or not JCRope