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IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety


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Apport des surveillances instrumentales de la Faille de la Moyenne Durance pour l'évaluation de l'aléa sismique


Congress title :AFPS'07 7ème Colloque National
Congress town :Chatenay Malabry
Congress date :04/07/2007

Summary

The IRSN has been monitoring the microseismicity around the Middle Durance Fault (MDF) since 1996 and has maintained 2 permanent GPS stations on each side of this structure since 1999. The location of microseismic events shows that the MDF mainly lies within the sedimentary cover between 0 and 4 km. However, crustal seismic activity is also observed. Focal mechanisms show dominant N-trending P-axes with a slight discrepancy in direction between the basement earthquakes and the sedimentary cover events. This could indicate a stress decoupling between thin-skinned tectonics and deep seated deformation. GPS data acquired since 1999 have confirmed the slow fault feature of the FMD. In spite of the uncertainties associated with this type of measurements, one has found the shortening rate could not exceed 0.1 mm/y. From these results a 3D segmentation model of the fault system has been obtained and a magnitude upper limit of the events the FMD can generate has been estimated between 6.3 and 6.5. Nonetheless the recording of a deep seismicity, especially under the Valensole plateau, does not allow preclude the presence of significant hidden sources.

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