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Geometry and spatio-temporal evolution of the 2001 Agios Ioanis earthquake swarm (Corinth Rift, Greece)


Now at: Istituto Nazionale di Oceanografia e di Geofisica Sperimentale Borgo Grotta Gigante 42/C, 34010 Sgonico (TS), Italy.


The Agios Ioanis earthquake swarm occurred below the southern edge of the Corinth Rift (Greece). The swarm is of interest due to its location and especially because the activated structure is oriented at a high angle to the rift's major active normal faults. We present a detailed study of the swarm including a high-resolution relocation of multiplets, accompanied by an analysis of their geometry and of their spatio-temporal evolution. P- and S-wave traveltime delays, calculated in the spectral domain to within subsampling precision, are inverted considering all pairs of events. In a second step, the large-scale structure of the swarm is refined by inverting traveltime delays calculated from absolute wave arrival-times. The relocation image, in combination with the results of the multiplet geometrical analysis, reveals a complex structure suggesting seismic activity on parallel planes that strike southwest and dip to the northwest. We propose that this fault zone connects to the Kerinitis Valley, where geological observations suggest the presence of a transverse fault linking normal faults striking 100°N. The spatio-temporal evolution of the relocated seismicity provides evidence of a ∼20 m day−1 migration of seismic activity towards the surface. Assuming fluid-driven seismicity, we model the spatio-temporal evolution as the diffusion of a pore-pressure perturbation. The preferred model indicates a hydraulic diffusivity equal to 0.1  m2 s-1, suggesting that the spatio-temporal evolution of the seismicity is related to fluid flow at depth. Moreover, we estimate the hydraulic conductivity (1.15 × 10−5 m s−1) and the rock permeability (7 × 10−13 m2), which compare well to available local observations.

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