Microseismic activity and fluid fault interactions: some results from the Corinth Rift Laboratory CRL, GreeceReport as inadecuate




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1 CRAAG - Centre de Recherche en Astronomie Astrophysique et Géophysique 2 IPGP - Institut de Physique du Globe de Paris

Abstract : The Gulf of Corinth, in western-central Greece, is one of the fastest continental rifts in theworld. In its western section near the city of Aigion, the previous work has outlined theexistence of a shallow dipping seismogenic zone between 5 and 12 km. This seismic activityhas been monitored with a network of 12 three-component stations for the period 2000–2007. Three, few months long, seismic swarms have been observed. They mobilize a complexstructural fault system that associates both shallow dipping elements and subvertical structureswith very different azimuths, some of which extend to depths greater than that of the shallowdipping zone. The swarm activity associates intensely active, short crises a few days withmore quiescent periods. The long-term growth velocity of the seismically activated domainsis compatible with a fluid diffusion process. Its characteristics are discussed in the context ofthe results from the 1000 m deep AIG10 well that intersects the Aigion Fault at 760 m. Thevertical growth directions of the seismically activated volumes outline two different sources forthe fluid and imply non-steady pressure conditions within the seismic domain. The diffusivityalong the cataclastic zone of the faults is in the order of 1 m2s−1, while faults act as hydraulicbarrier in the direction perpendicular to their strike. If the vertical direction is a principalstress component, the high pore pressure values that must be reached to induce slip on theshallowly dipping planes can result only from transitory dynamic conditions. It is argued thatthe shallow dipping active seismic zone is only local and does not correspond to a 100 kmscale decollement zone. We propose to associate the localization process with deep fluid fluxesthat have progressively modified the local stress field and may be the cause for the quiescenceof the West Heliki Fault presently observed.

Keywords : Dynamics and mechanics of faulting Seismicity and tectonics Back- arc basin processes Permeability and porosity Fault zone rheology





Author: S. Bourouis - F.H. Cornet -

Source: https://hal.archives-ouvertes.fr/



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