The 2003–2004 seismic swarm in the western Corinth rift: Evidence for a multiscale pore pressure diffusion process along a permeable fault system

Microseismic multiplets occurring in the western Corinth rift, Greece, during a large swarm are analyzed to retrieve their spatiotemporal characteristics. These multiplets activated small subfaults at depth (∼7 km), up to 1 km long, at the root of two parallel active normal faults. The swarm migrates westward nearly horizontally over 10 km at an average velocity of 50 m/d with a diffusivity of 0.5 m 2  s −1 . It successively activates the Aigion fault, a relay zone in its hanging wall, and the Fassouleika fault. Within each multiplet, hypocenters also migrate with diffusivities ranging from 0.001 to 0.4 m 2  s −1 . The largest internal diffusivities appear at the core of the layer defined by the clusters. These results are interpreted as a hydroshear process caused by pore pressure migration within permeable corridors resulting from the intersection of the major faults with a brittle geological layer inherited from the Hellenic nappe stack.