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
coh
ere
nce
coh
ere
nce
ALL STATIONS
SUMMIT STATIONS
Re
lativ
e t
rave
l tim
e c
ha
ng
eR
ela
tive
tra
vel t
ime
ch
an
ge
VE
LO
CIT
Y D
EC
RE
AS
ES
year
Peltier et al., JVGR, 2009R
ela
tive
tra
vel t
ime
ch
an
ge
year
Eruptive cycles
coh
ere
nce
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