HR: 1340h
AN: V53C-1417    [Abstracts]
TI: How much is the volcano seismicity directly driven by volcano processes?
AU: * Traversa, P
EM: paola.traversa@obs.ujf-grenoble.fr
AF: Laboratoire de Géophysique Interne et Tectonophysique, Observatoire de Grenoble, Université Joseph Fourier, France, LGIT BP 53-1381 rue de la Piscine Cedex 9, Grenoble, 38041, France, Metropolitan
AU: Grasso, J
EM: grasso@obs.ujf-grenoble.fr
AF: Laboratoire de Géophysique Interne et Tectonophysique, Observatoire de Grenoble, Université Joseph Fourier, France, LGIT BP 53-1381 rue de la Piscine Cedex 9, Grenoble, 38041, France, Metropolitan
AU: Helmstetter, A
EM: ahelmste_at_obs.ujf-grenoble.fr
AF: Laboratoire de Géophysique Interne et Tectonophysique, Observatoire de Grenoble, Université Joseph Fourier, France, LGIT BP 53-1381 rue de la Piscine Cedex 9, Grenoble, 38041, France, Metropolitan
AU: Saccorotti, G
EM: saccorotti@pi.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, sezione di Pisa, Via della Faggiola, 32, Pisa, 56126, Italy
AU: Ferrazzini, V
EM: ferraz@ipgp.jussieu.fr
AF: Observatoire Volcanologique du Piton de la Fournaise, Reunion Island, IPG Paris, France, 14 RN3 - Km 27 La Plaine des Cafres, Réunion, 97418, France
AB: To investigate how much of volcano seismicity is related to fluid movement within a volcanic edifice, we analysed seismicity patterns associated to different volcano activities: Vesuvius (1972-2006, dormant), Piton de la Fournaise (2005-2006, 3 eruptions), Etna (1988-2001, 9 eruptions and the 2002-2003 long lasting eruption), 7 dyke intrusions at Piton de la Fournaise (1988-1992). First, we homogenize the different datasets and purify them from local network bias by normalizing the seismicity rate and energy by the catalogue magnitude spreads and the local seismogenic volume. Second, using different techniques, we quantify seismic energy release and foreshock and aftershock rates from volcano seismicity catalogues. Analysis of foreshocks and aftershocks rates allows to distinguish and to quantify the amount of seismicity generated by earthquake interactions from the one directly driven by volcanic processes. Preliminary results show that (i) there is no significant change between the seismicity of a dormant volcano, the inter-eruption seismicity on active volcanoes and the tectonic seismicity: the earthquake interaction levels, as measured by aftershock rates, are comparable in the different cases; (ii) during the last phase of magma propagation within the volcanic edifice, i.e. few hours from the surface lava flow, there is a huge increase in seismicity rate which is dominated by uncorrelated seismicity, i.e. there is a lack of aftershocks â€"foreshocks patterns during the dyke propagation phase. This results suggests that for volcano seismicity, as well as for tectonic seismicity, an increase in the external forcing (i.e. magma injection in the volcanic edifice in the first case and the occurrence of a tectonic earthquake in the other one) is followed by an increase in the seismicity rate. Whereas in the tectonic case the observed increase in seismicity rate is driven by events that are correlated in time, i.e. aftershocks, for the volcano driven seismicity the increase in rate is solely due to the uncorrelated component of seismicity. These are positive evidences for the loading rate or/and the fluid-temperature to drive the peculiarity of volcano seismicity rate.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting