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Very long-period and ultra-long-period seismic signals detected before and during the formation of the Dolomieu caldera on Reunion Island in 2007

Caldera collapses (giant circular or elliptical volcanic craters formed by the emptying of the magma chamber) are rare phenomena. Only seven have occurred in the last hundred years. These events can bring about major, even catastrophic, changes to the landscape, the environment and the activity of volcanic edifices.

Very long-period and ultra-long-period seismic signals detected before and during the formation of the Dolomieu caldera on Reunion Island in 2007

Publication date: 07/06/2019

Observatories, Press, Research

Related teams :
Volcanic Systems

Related themes : Natural Hazards

On April 5th  2007 at 20:48 (GMT), the Dolomieu caldera of Piton de la Fournaise collapsed in an abnormally slow earthquake of magnitude MS ≈ 4.8, three days after the start of the historic eruption (in terms of the volume of lava emitted).

Spectrogram of the North-South component of the RER permanent seismometer of the GEOSCOPE/IPGP network, showing VLP and ULP signals during the Dolomieu collapse.

Data from the RER permanent seismological station in the GEOSCOPE/IPGP network near the Dolomieu crater show that the formation of the caldera in April 2007 was the result of a sequence of 48 successive summit collapses over 9 days. 4 days after the first summit collapse, a caldera 340 m deep formed.

Recordings from the very wide bandwidth RER seismic station enabled us to identify ultra long period (ULP) signals accompanied by very long period (VLP) signals, of an equivalent duration of 20 seconds, before the collapse at the surface and during the formation of the Dolomieu caldera. The similarity of the characteristics of these signals suggests that the first collapse at depth took place approximately 20 hours before the surface rupture and the start of caldera formation.

The identification of these two types of signal shows that it is possible to use a broadband seismometer to detect collapses at depth and therefore to anticipate the formation of a caldera at the surface when the aspect ratio between the depth of the magma chamber and its diameter is high. The results of this study also provide a better understanding of the dynamics and processes at the origin of a magmatic caldera.

 

 

Ref: F. R. Fontaine, G. Roult, B. Hejrani, L. Michon, V. Ferrazzini, G. Barruol, H. Tkalčić, A. Di Muro, A. Peltier, D. Reymond, T. Staudacher & F. Massin, Very- and ultra-long-period seismic signals prior to and during caldera formation on La Réunion Island, Scientific Reports 9, Article number: 8068 (2019), doi: 10.1038/s41598-019-44439-1

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