IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

0P1_2F-O1

Room B2

Date/Time: July 20 14:30-15:00

Recent results of noise-based seismic velocity monitoring at Piton de la Fournaise
Volcano, La Reunion
Florent Brenguier1 , Diane Rivet2 , Anne Obermann1 , Thomas Lecocq3 , Daniel Clarke2 , Nikolai Shapiro2 ,Michel Campillo1 , Eric Larose1 , Valerie Ferrazzini41

Institut des Sciences de la Terre, University of Grenoble, CNRS, France, 2 Institut de Physique duGlobe de Paris, France, 3 Royal Observatory of Belgium, Belgium, 4 Observatoire Volcanologique duPiton de la Fournaise, IPGP, France
E-mail: florent.brenguier@ujf-grenoble.fr

Piton de la Fournaise Volcano, a shield basaltic volcano located on La Reunion island, has been strongly active
these last 15 years with 2 eruptions per year on average. On April 2007, an unusually strong eruption occurredon the volcano’s south-eastern flank, ejecting a volume of over 240 million cubic meter of lava, that is, ten times
more than the typical value during the preceding decade. A few days later, the summit crater collapsed by 340
m. Since then, magmatic activity at PdF decayed until the last eruption of December 2010. Since 2000, Piton
de la Fournaise Volcano Observatory records seismic signals continuously from 20 short-period sensors locatedon PdF Volcano. This set of data together with recent fundamental advances in ambient noise seismology have
led to the development of a novel method to measure volcanic edifice seismic velocity changes continuously alongtime. Changes of seismic velocities of volcanic edifices are known to be sensitive to edifices deformation inducedby magmatic activity or gravitational flank instabilities. Edifice seismic velocities may also be induced by external
perturbations such as water content associated with rainfall, barometric pressure changes, temperature changes
or tides.
In order to measure highly precise seismic velocity changes we deployed 15 new broad-band seismic sensors on
PdF volcano between 2009 and 2011 in the framework of an international project called UnderVolc. During thattime period, 5 eruptions occurred and the last 10 months of records were characterized by an unusual low volcanicactivity. We focus on the location and characterization of edifice seismic velocity changes observed few weeks prior
to the October 2010 PdF eruption. We show that precursory seismic velocity changes depend upon the frequency
range of the filtered raw data. This observation seems to indicate a depth dependent process. We also present
results of lateral location of seismic velocity changes for this precursory episode. We also study the long-termchanges of seismic velocities during the low volcanic activity time period. Our results indicate a long lasting seismic
velocity increase that we interpret as being associated with the slow compaction of the edifice following the 2007
crater collapse. We also study the link between seismic velocity changes and external perturbations such as inparticular water content associated with rainfall. Finally, we have turned these fundamental developments into
an operational computer routine called MSNoise for the purpose of continuously monitoring in real-time seismic
velocity changes in volcanic domain.

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