Toward Forecasting Volcanic Eruptions using Seismic Noise

During inter-eruption periods, magma pressurization yields subtle changes of the elastic properties of volcanic edifices. We use the reproducibility properties of the ambient seismic noise recorded on the Piton de la Fournaise volcano to measure relative seismic velocity variations of less than 0.1 % with a temporal resolution of one day. Our results show that five studied volcanic eruptions were preceded by clearly detectable seismic velocity decreases within the zone of magma injection. These precursors reflect the edifice dilatation induced by magma pressurization and can be useful indicators to improve the forecasting of volcanic eruptions.Comment: Supplementary information: http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguier_SI.pdf Supplementary video: http://www-lgit.obs.ujf-grenoble.fr/~fbrengui/brenguierMovieVolcano.av

Sounding the plume of the 18 August 2000 eruption of Miyakejima volcano (Japan) using GPS

We processed 79 days of GPS data collected at four stations on Miyakejima volcano (Japan) before and during its eruption in 2000. This period includes a strong seismic swarm (27 June to 8 July) followed by five eruptions (8 and 14-15 July, 10, 18, and 29 August). Surface motion is strong during the seismic swarm, then remains almost steady during eruptions. However, during each eruption, we found anomalous values of the LC (ionosphere free) double differences, especially on 18 August, with a peak of 0.6 cycles (i.e., an apparent 290 mm increase of the satellitestation range). We cannot explain these anomalies by temporary ground displacements during the events. Instead, we propose that they are due to path delay effects in the hot volcanic plume. By adapting a seismic tomography algorithm, the refractivity anomaly and the inferred temperature in the plume is mapped in time and space

Sismomètre optique sous-marin : avancement et perspectives

International audienceCes dernières années ont vu le développement de sismomètres optiques innovants, haute résolution et faible coût permettant la mise en place d’une solution de surveillance en temps réel de sites d’intérêt. Les champs d’application de ces avancées significatives sont multiples : exploration industrielle du sous-sol ou stockage souterrain, surveillance d’ouvrage d’art, de sites industriels, ou sites naturels présentant un risque tellurique élevé.L’IPGP, le Groupe ESEO et leurs partenaires Géosciences Montpellier et le Laboratoire d'Analyse et d'Architecture des Systèmes (LAAS) de Toulouse ont mené un certain nombre de campagnes de qualification de leurs premiers prototypes de sismomètres optiques 2 Hz, au Laboratoire Souterrain Bas Bruit (LSBB) de Rustrel notamment. Cela a permis une première validation de l’ensemble des fonctions opto-mecaniques et traitement du signal de ces capteurs. Ainsi, le niveau de bruit atteint par le dispositif est inférieur à 1ng.Hz-1/2 dans la bande 0,5-5Hz et reste inférieur à 10ng.Hz-1/2 dans la bande 0,15-20Hz.L’un des axes de développement actuels, cofinancé par la Société d’Accélération du Transfert de Technologies (SATT) Ouest Valorisation, consiste en l’adaptation de ces technologies au milieu marin. Dans cette deuxième campagne, l’intégration du système de conditionnement et traitement des signaux optiques a fortement évolué, permettant notamment une baisse significative de sa consommation électrique (d’un facteur dix). Ce dispositif autonome est à présent déployé sur une plateforme en rade de Brest. Nos géophones optiques ont été conditionnés dans une enceinte hyperbare, elle-même installée en fond de mer à 500 mètres environ de la plateforme.Cette présentation a pour objectif de faire partager les tenants et aboutissants d’un tel développement et l’avancée de nos observations. Ces dernières pourront être par la suite corroborées par celles de l’IFREMER qui dispose d’un capteur en expérimentation à côté du nôtre

3-D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations

International audience[1] We invert Rayleigh waves reconstructed from cross-correlations of 18 months of ambient seismic noise recorded by permanent seismological stations run by the Piton de la Fournaise Volcanological Observatory. By correlating noise records between 21 receivers, we reconstruct Rayleigh waves with sufficient signal-to-noise ratio for 210 inter-station paths. We use the reconstructed waveforms to measure group velocity dispersion curves at periods between 1.5 and 4.5 s. The obtained measurements are inverted for two-dimensional group velocity maps and finally for a 3-D S-wave velocity model of the edifice from +2 to À1 km above sea level. Our results clearly show a high velocity body spatially delimited by the borders of the active 10 km wide caldera. The preferential N30°-N130° orientations of this anomaly at À0.5 km below sea-level is an evidence of the preferential paths of magma injections associated to the NE-SE Rift Zones. This structure is surrounded by a low-velocity ring interpreted as effusive products associated to the construction of the Piton de la Fournaise volcano on the flank of the older Piton des Neiges volcano. Citation: Brenguier, F., N. M. Shapiro, M. Campillo, A. Nercessian, and V. Ferrazzini (2007), 3-D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations, Geophys

Real time monitoring of relative velocity changes using ambient seismic noise at the Piton de la Fournaise volcano (La Réunion) from January 2006 to June 2007

International audienceWe present the results of a real time method based on coda-wave interferometry from seismic noise cross-correlation functions for relative seismic velocity variations monitoring on a volcanic edifice. The ambient seismic noise at the Piton de la Fournaise volcano on La Réunion island is analyzed from January 2006 to June 2007. During this period, five eruptions occurred showing a great diversity in eruption duration, intensity and eruptive fissure location. Two different methods are used to compute the velocity variations in order to compare their stability in quasi real-time routine. We compare the obtained velocity variations with the surface deformation observed by GPS and extensometers networks. This allows us to identify and quantify three major processes at the origin of seismic wave velocity variations in the edifice. Firstly, the observed pre-eruptive summit inflation is accompanied by a decrease in seismic velocity. Secondly, the edifice deflation following the opening of an eruptive fissure is characterized by an increase of the velocity. Finally, the summit caldera collapse generates a strong velocity drop. Coda-wave interferometry from seismic noise cross-correlation functions in quasi-real time may allow us to forecast eruption and constrain the processes taking place in the volcanic plumbing system

High resolution optical seismometer for real-time monitoring of ocean-bottom seismicity

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High resolution optical seismometer for real-time monitoring of ocean-bottom seismicity

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The volcano–seismic crisis in Afar, Ethiopia, starting September 2005

International audienceWe describe the seismo–volcanic crisis that occurred in northern Afar in late 2005, which involved 15 earthquakes greater than M5 and a small explosive silicic eruption from a vent called Da'Ure (at 12.651°N., 40.519°N) close to Dabbahu volcano. The purpose is to pull together the different sources of information into a coherent preliminary interpretation of what happened. The main geophysical data are the locations of the largest earthquakes, and a radar interferogram of unusually high quality that reveals injection of a 60 km long dyke with surface deformation expressed as normal faulting. Subsidence occurred around the Dabbahu volcanic edifice. Most of the dyke is likely to have been basaltic rather than silicic although the eruption was silicic. The volume of the subsidence represents at most 25% of the magma injected into the dyke. The silicic eruption was possibly triggered by interaction of basaltic magma with a shallow silicic reservoir. At about the same time as the eruption and dyking episode, some activity appears also to have taken place at the lava lake at Erta Ale volcano, some 150 km to the north of the eruption site. We evaluate the possibility that there may be some link by calculating stresses associated with opening of the fissure and looking at the activity of the lava lake as revealed by the thermal anomaly seen by weather satellites

High resolution optical displacement sensor: Development and qualification for remote applications in seismology and volcanology

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