HR: 1340h
AN: T53C-1449    [Abstracts]
TI: Does Fluid Migration Explain The 1997 Umbria-Marche (Central Italy) Seismic Sequence?
AU: Chiaraluce, L
EM: chiaraluce@ingv.it
AF: Istituo Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Roma, RM 00143 Italy
AU: Piccinini, D
EM: piccinini@ingv.it
AF: Istituo Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Roma, RM 00143 Italy
AU: * Antonioli, A
EM: antonioli@ingv.it
AF: Istituo Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Roma, RM 00143 Italy
AU: Cocco, M
EM: cocco@ingv.it
AF: Istituo Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Roma, RM 00143 Italy
AB: We model the spatial and temporal evolution of seismicity during the 1997 Umbria-Marche (central Italy) seismic sequence in terms of subsequent failures promoted by fluid flow. This seismic sequence is characterized by six earthquakes with 5 < Mw < 6 and by an aftershocks sequence of thousand of events in a time span of few months. All the maishocks and most of the aftershocks show very similar focal mechanisms, characterized by normal faults on SW shallow dipping planes. The seismic sequence is characterized by an evident migration of seismicity along the strike of the main fault structure from NW toward SE The diffusion process of pore-pressure relaxation is modeled as a pressure pulse generated by coseismic stress perturbations and propagating through a fluid saturated medium. The time interval between subsequent instabilities can be written as t= X^t * D^-1 * X, where X is the inter-distance between the first (origin) event and following ones and D represents the diffusivity tensor, which depends on the permeability and porosity. The time interval t is measured from the origin time of the first event of the sequence, which is chosen as origin of the time-space coordinates This model allows the determination of diffusivity for both an isotropic and anisotropic poro-elastic medium. The estimated value of isotropic diffusivity for the whole sequence is D_{iso ≈ 50 m²/s. Diffusivity is largest along the average strike (N140°) direction of activated faults yielding an anisotropic value of D_aniso ≥q 250 m²/s. Our results suggest that the observed spatio-temporal migration of seismicity is driven by fluid flow.
DE: 0805 Elementary and secondary education
DE: 5102 Acoustic properties
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005