Seismic velocity imaging and monitoring of volcanic areas using ambient seismic noiseF. Brenguier (OVPF/IPGP), D. Clarke (IPGP), N. M. Shapiro (IPGP), M. Campillo (LGIT), E. Larose (LGIT)

Laboratoire de Géophysique Interne et Tectonophysique (Grenoble)

Institut de Physique du Globe de Paris/ Observatoire Volcanologique du Piton de la Fournaise

Noise sources

Shapiro et al. (2005)

sensor

Virtual seismic source reconstruction

A case study: Piton de la Fournaise volcano, La Réunion island

S 21°

E 55°30

3D velocity imaging – Virtual sources

Brenguier et al., GRL, 2007

effusive material

3D velocity imaging – Results

solidified intrusivemagma bodies

Perturbations to a horizontally averaged model

Perturbations to a vertically averaged model

W E

Vp compared to Vs tomography

Prôno et al., JVGR, 2009

Prospects

Need to invert for a joint Vp/Vs tomographic model

Study of the link between seismicity and solidified intrusive magma bodies or magma reservoir using double difference relocalisation

Improve the Vs tomographic model by using broad-band seismic noise records

Synthetic velocity decrease

Temporal changes of seismic velocities using cross-correlations of seismic noise

Velocity changes on Piton de la Fournaise

Brenguier et al., Nature Geoscience, 2008

Velocity drops preceding eruptions

Velocity change regionalization

Seismic velocity changes as a proxy for magma forcing (1)

Magma forcing involves dilatancy of volcanic edifices

Shih-Che Yuan, J. P. Harrison (2004), An empirical dilatancy index for the dilatant deformation of rockInternational Journal of Rock Mechanics and Mining Sciences, Volume 41, Issue 4

= magma forcing

We use the term « magma forcing » do describe the mechanisms of stress induced magma pressurization and injection.

Seismic velocity changes as a proxy for magma forcing (2)

O'Connell, R. J., and B. Budiansky (1974), Seismic Velocities in Dry and Saturated Cracked Solids, J. Geophys. Res., 79(35), 5412–5426

Seismic velocities are strongly sensitive to crack density.

Localization of the dyke’s

injection zone ?

Magmatic intrusive complex

Link between temporal changes and structure

Long-term velocity changes

Clarke et al., In preparation

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Conclusions

We measure relative velocity changes with a precision of 0.02 %,

These changes are linked to dilatation induced by stress changes,

We identified precursors to the volcanic eruptions.

Prospects

We are looking to localize the velocity changes at depth (4D tomography),

Develop real-time passive monitoring procedures in Observatories,

Conclusions and prospects

UnderVolc project

20 broad-band seismometers + 16 gps + 1 infrasound sensor + photogrammetric system

Continuous recording and radio real-time data transfer and data distribution at day+1

Thank you for your attention !

Related presentations:

S23C-03. Temporal changes of seismic wavefield during the 2007 eruptions of Piton de la Fournaise, La Réunion island .  Y. Aoki; V. Ferrazzini S53A-1811

V23D-2107. A real time process for detection, clustering, and relocation of volcano-tectonic events at Piton de La Fournaise volcano..  F. Massin ; V. Ferrazzini; P. Bachelery; Z. Duputel

We are gratefull to the Piton de la Fournaise volcanological Observatory staff for providing high quality data !

Toward real-time monitoring

Eruption of July 2006

http://www.fournaise.info/eruption2avril07.php

The last eruption of April 2007

Toward real-time monitoring