Observatoire des Sciences de l ’ Univers de Grenoble

This work focuses on the seismic response of a volcano to different magmatic processes with the aim of sheding light on their driving physics as tracked by seismicity. We study seismic time series recorded at basaltic volcanoes and identify generic seismicity patterns characteristic of (i) inter-eruptive, (ii) reservoir feeding, (iii) reservoir leak, and (iv) dyke injection phases of volcanic activity. Seismicity recorded during repose phases mimics the behavior of ”ordinary” tectonic seismicity. During the last phase immediately before an eruption, the stationary seismicity rate accompanying the dyke injection we observe on different volcanoes, reveals that the fluid-driven crack propagation is a scale independent stationary process. This is reminiscent of the brittle creep damage recorded in strain driven settings and it prevents any prediction of the eruption time. It argues for the stationary seismicity rate accompanying the intrusion to be a proxy for a constant magma supply rate from the magma reservoir. Through a numerical model of dyke propagation we validate the hypothesis of constant magma flow rate feeding the dyke in the volcano dynamics setting. The impact of such a model allows us to bound a minimum size for the magma reservoir and a maximum value for the magma overpressure at Piton de la Fournaise volcano. The exploration of the seismic sequence driven by the 2000 Izu Islands (Japan) dyke intrusion allows us to quantify the stress perturbations induced over space and time by this giant intrusive episode. We show that the dyke intrusion can be assimilated to a ”slow event” mainshock, which allows to follow the evolution of the brittle damage of the rock matrix during fracture propagation. On Ubinas andesitic volcano, we resolve an average acceleration of Long Period (LP) seismicity prior to both, explosions and LP events. It brings new evidence for LP events to be brittle damage events within a fluid-filled conduit. 2 te l-0 04 58 91 8, v er si on 1 22 F eb 2 01 0