Microseismic activity and fluid fault interactions: some results from the Corinth Rift Laboratory (CRL), Greece
Résumé
The Gulf of Corinth, in western-central Greece, is one of the fastest continental rifts in the
world. In its western section near the city of Aigion, the previous work has outlined the
existence of a shallow dipping seismogenic zone between 5 and 12 km. This seismic activity
has 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 complex
structural fault system that associates both shallow dipping elements and subvertical structures
with very different azimuths, some of which extend to depths greater than that of the shallow
dipping zone. The swarm activity associates intensely active, short crises (a few days) with
more quiescent periods. The long-term growth velocity of the seismically activated domains
is compatible with a fluid diffusion process. Its characteristics are discussed in the context of
the results from the 1000 m deep AIG10 well that intersects the Aigion Fault at 760 m. The
vertical growth directions of the seismically activated volumes outline two different sources for
the fluid and imply non-steady pressure conditions within the seismic domain. The diffusivity
along the cataclastic zone of the faults is in the order of 1 m2s−1, while faults act as hydraulic
barrier in the direction perpendicular to their strike. If the vertical direction is a principal
stress component, the high pore pressure values that must be reached to induce slip on the
shallowly dipping planes can result only from transitory dynamic conditions. It is argued that
the shallow dipping active seismic zone is only local and does not correspond to a 100 km
scale decollement zone. We propose to associate the localization process with deep fluid fluxes
that have progressively modified the local stress field and may be the cause for the quiescence
of the West Heliki Fault presently observed.
Origine : Fichiers éditeurs autorisés sur une archive ouverte
Loading...