Transcript F. Brenguier - Institut de Physique du Globe de Paris

Seismic velocity imaging and
monitoring of volcanic areas
using ambient seismic noise
F. Brenguier (OVPF/IPGP), D. Clarke (IPGP), N. M. Shapiro (IPGP), M. Campillo
(LGIT), E. Larose (LGIT)
Institut de Physique du
Globe de Paris/
Observatoire
Volcanologique du
Piton de la Fournaise
Laboratoire de
Géophysique Interne et
Tectonophysique
(Grenoble)
Virtual seismic source reconstruction
sensor
Noise sources
Shapiro et al. (2005)
A case study: Piton de la Fournaise
volcano, La Réunion island
S 21°
E 55°30
3D velocity imaging – Virtual sources
Perturbations to a
horizontally averaged model
3D velocity imaging – Results
solidified intrusive
magma bodies
effusive material
Perturbations to a
vertically averaged model
Brenguier et al., GRL, 2007
Vp compared to Vs tomography
W
Prôno et al., JVGR, 2009
E
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
Temporal changes of seismic velocities
using cross-correlations of seismic noise
Synthetic velocity decrease
Velocity changes on Piton de la Fournaise
Velocity drops preceding eruptions
Brenguier et al., Nature Geoscience, 2008
Velocity change
regionalization
Seismic velocity changes as a proxy for
magma forcing (1)
Magma forcing involves
dilatancy of volcanic
edifices
We use the term « magma forcing » do describe
the mechanisms of stress induced magma
pressurization and injection.
= magma
forcing
Shih-Che Yuan, J. P. Harrison (2004), An empirical dilatancy index for the dilatant deformation of rock
International Journal of Rock Mechanics and Mining Sciences, Volume 41, Issue 4
Seismic velocity changes as a proxy for
magma forcing (2)
Seismic velocities are
strongly sensitive to
crack density.
O'Connell, R. J., and B. Budiansky (1974), Seismic Velocities in Dry and Saturated Cracked
Solids, J. Geophys. Res., 79(35), 5412–5426
Link between temporal
changes and structure
Magmatic intrusive complex
Localization of the dyke’s
injection zone ?
coherence
Relative travel time change
coherence
Relative travel time change
VELOCITY DECREASES
Long-term velocity changes
ALL STATIONS
SUMMIT STATIONS
year
Clarke et al., In preparation
Eruptive cycles
coherence
Relative travel time change
Peltier et al., JVGR, 2009
year
Conclusions and prospects
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,
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
Toward real-time monitoring
The last eruption of April 2007
http://www.fournaise.info/eruption2avril07.php