Synthesis of 30 Years of Seismicity Induced by the Exploitation of the Lacq Gas Field

During the last 30 years, more than 1700 earthquakes have been recorded near the Lacq gas field. This large database has been recorded by a local network of 16 1-component seismometer from 1974 to 1997. Considering this seismicity as the brittle response of stress variations due to the depletion, we determine a synthetic model of deformation for the reservoir. This model is constrained by the spacial distribution of seismological events and by the geometry of the main faults obtained from 3D seismic data. This geometry appears strongly coherent with the analog model of deformation proposed by Odonne et al. (1999). Moreover, we observe a temporal evolution of the spacial distribution of the earthquakes: they are mainly located in the center of the structure during the first years and, later, we clearly observe a spacial migration of the events, showing a ring pattern distribution. Based on this various results, we propose a model of deformation of the Lacq gas field. New data, recently recorded with the new local network deployed in the vicinity of Lacq, are coherent with the proposed model.