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  Thèse d'Angèle Laurent

Detection, location and characterization of VLF events during the 2018-2019 seismovolcanic crisis in Mayotte
Encadrant (et co-encadrant) : 

The seismovolcanic crisis of Mayotte started in May 2018 with a sudden activation of seismicity to the east of the island. Along with thousands of volcano-tectonic earthquakes, an energetic very low frequency signal (VLF, 15 seconds of period) was recorded on November 11, 2018 at seismic stations worldwide. This exceptional monochromatic signal was not an isolated event: during this PhD we detected and analyzed several hundredths of such signals, all along the duration of the Mayotte crisis.
During this thesis, we will try:
Event location though spatial 3D back-projection of station-pair cross-correlation functions (Poiata et al., 2016), assuming surface-wave speed.
Comparison of the location of the VLFs in relation to the seismic swarms and the island of Mayotte.
To study the possible physical origin of such signals, we compare different types of source and we practise the direct modelling calculated with Instaseis (and/or Axitra) in order to understand the source, the path or site effects of these signals.
The aim of this thesis is to understand the phenomenon at the source of its low frequency and long duration monochromatic signals (VLF) and to integrate our results in the global context of the Mayotte seismic crisis. This thesis is done in collaboration with work carried out in parallel by other teams, laboratories and institutes (IPGP / CNRS / BRGM / IFREMER / IPGS ...).