Imaging pre- and co-eruptive structural and mechanical changes on a volcano with ambient seismic noise

Anne Obermann, Thomas Planes, Eric Larose, Michel Campillo

Thursday 24 April 2014, by briandx // Publications

Imaging pre- and co-eruptive structural and mechanical changes on a volcano with ambient seismic noise.

Anne Obermann, Thomas Planes, Eric Larose, Michel Campillo


Abstract

Forecasting the location of an eruption is of primary importance for risk management in volcanic regions. Locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano. Based on recent results in wave physics, we develop an imaging procedure that is based on the sensitivity of scattered waves to weak changes in the multi-scattering media, and that allows localization of changes of scattering properties of the sampled medium. We study seismic data from the active volcano Piton de la Fournaise (PdF) on la Reunion Island, Indian Ocean, from June to December 2010. During this time two volcanic eruptions of Hawaiian style occurred at two different places. Nineteen broad-band stations record continuously ambient seismic noise at PdF. We calculate the cross-correlation functions between all the stations for the seven months
of interest. From the noise cross-correlations we obtain two types of measurements associated to two types of changes: apparent velocity variations related to changes in elastic properties of the medium and, waveform decoherence associated with variations in the scattering and thus geological structures. We observe that the temporal variations of both parameters are good precursors of potential volcanic eruptions at PdF. The location of pre- and co-eruptive changes from both parameters are in good agreement with the actual eruptive activities. These results demonstrate that the coda of ambient noise correlations contains deterministic information on the location of the eruptive processes in an active volcano. Our analysis offers an original and significant constraint on the location of forthcoming volcanic eruptions.

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