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Titel |
Dynamics of the 2007 Eruptions of Piton de la Fournaise and the Related Caldera Collapse from a Single Very Broad-band Seismic Station |
VerfasserIn |
Fabrice R. Fontaine, Genevieve Roult, Laurent Michon, Guilhem Barruol, Valerie Ferrazzini, Andrea Di Muro, Dominique Reymond, Aline Peltier, Thomas Staudacher |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250093320
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Publikation (Nr.) |
EGU/EGU2014-7939.pdf |
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Zusammenfassung |
Seismic records from the RER very broad-band seismic station (La Réunion Island)
belonging to the GEOSCOPE network are investigated to understand the eruptive succession
(February to May) of Piton de la Fournaise and the caldera collapse episode of April 2007.
Data first indicate that the short-lived, small volume, summit eruption of February 18
occurred during a phase of continuous inflation initiated in January 2007. Inflation
decelerated around 2 weeks before a second short-lived small volume eruption on March
30-31 on the SE flank, almost simultaneous with a sudden, large deflation of the
edifice. Deflation rate, which had stabilized at a relatively low level, increased anew
on April 1 while no magma was emitted, followed on April 2 by a more distant
and one of the most voluminous eruptions of the last two centuries at La Réunion
Island. The RER station shows that very long period (VLP) and ultra long period
(ULP) events developed during this period. Seven ULP events preceded the caldera
collapse and 48 ones occurred during the caldera collapse over 9 days, most of
which during the first 30 hours. A thorough examination of the seismic signals
corrected for tide effects shows that each collapse event was coeval with VLP and ULP
signals. Each individual collapse showed similar ULP and VLP signals characterized
by periods of ~ 500 s and ~ 7 s, respectively. The back-azimuth of most ULP
signals related to the caldera collapse points clearly toward the Dolomieu caldera.
The strikingly constant duration of the VLP signals (around 20 s) related to the
collapse events and their occurrence before the collapse initiation suggest a physical
control of the volcanic edifice. Waveforms and spectrograms of the various caldera
collapse events show very homogeneous patterns, suggesting a similar and repeating
volcano-tectonic process for the formation of the VLP signals events. Although tilt may be
responsible of part of the ULP signals observed during the collapse events, we
show that it cannot explain most of the records. The ULP signals occurring during
the collapse and also recorded by the OVPF GNSS (Global Navigation Satellite
System) permanent network likely correspond to relaxation of the volcanic edifice.
This analysis allows us to propose a scenario that may explain each successive
collapse event as starting with a short-period event induced by the rock failure,
followed by a VLP signal induced by dip-slip motion on the caldera ring fault,
and ending with a ULP signal likely related to a relaxation process of the edifice. |
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