Fluid flow and seismicity pattern: Evidence from the 1997 Umbria-Marche (central Italy) seismic sequence

We model the spatial and temporal evolution of seismicity during the 1997 Umbria-Marche seismic sequence in terms of subsequent failures promoted by fluid flow. The diffusion process of pore-pressure relaxation is represented as a pressure perturbation generated by coseismic stress changes and propagating through a fluid saturated medium. The values of isotropic diffusivity range between 22 and 90 m(2)/s. The calculated value of anisotropic diffusivity (Daniso = 250 m(2)/s) is largest along the average strike (N140 degrees) direction of activated faults. Our results suggest that the observed spatio-temporal migration of seismicity is consistent with fluid flow.