Seismicity of Piton des Neiges and Piton de la Fournaise
Start: 01 January 2022
Volcanological Observatory of Piton de la Fournaise (OVPF-IPGP)
Status: In progress
This thesis proposes to study the seismic phenomena in a volcanic environment by using the case of La Réunion Island. The island has two major volcanic edifices (Piton des Neiges and Piton de la Fournaise) where significant seismic activity is recorded. While the seismicity of the Piton de la Fournaise can be explained by its volcanic activity (more than three eruptions per year since 2014), the seismic activity of the Piton des Neiges (inactive for about 27,000 years) is still poorly known. Following several earthquakes detected and felt by the population below the northern flank of Piton des Neiges, several seismic stations have been deployed in the area. Our results obtained after hypocentral relocation indicate that the seismicity observed under the northern flank of the Piton des Neiges comes from a northeast dipping fault located in the oceanic crust, under the volcanic edifice. The orientation of this planar structure is consistent with the analysis of the focus mechanisms corresponding to a reverse fault. Our analyses are also based on the study of the variation in seismicity, which required, for the establishment of the completeness of the catalogue, the correction of the variations due to the densification of the seismic network since 2016. Our findings show that there is no significant variation in the b-value over time. The absence of intense seismic swarms suggests an origin that is not directly linked to transient magma transfer (contrary to what is observed at Piton de la Fournaise). These results are intended to contribute to the understanding of deep seismicity under inactive volcanoes. As far as La Réunion Island is concerned, they constitute a first step towards an explanation of the seismicity on the scale of the whole island.