New 1D velocity model and absolute locations image Mayotte seismo-volcanic region

Abstract:

Since May 2018, a major volcano-seismic crisis has been happening offshore Mayotte Island, in the Comoros archipelago. With 5.8 km³ of magma emitted from a deep reservoir, intense seismic activity and deformation that hasn’t stopped after more than 2 years, this crisis is unprecedented and represent the largest basaltic eruption in erupted volume and duration since the Laki eruption (Iceland) in the 18th century. Since May 2019, several oceanographic campaigns deployed a dense network of Ocean Bottom Seismometers (OBS), associated with previous and new land stations, around the newly active region (https://doi.org/10.18142/291). The OBS were installed in 4 months periods, with in total 71 OBS and land stations between February and November 2019 and up to 25 for each period. This network was able to detect two clusters of earthquakes: a main group located 5 to 15 km offshore Petite-Terre, at depths between 20 and 55 km, and a secondary cluster between 25 and 50 km offshore, at depths ranging from 40 km to 15 km, the shallowest events closer to the new volcanic edifice (NVE). The main cluster is focused in a circular « donut » shape, potentially related to the roof collapse of a deep reservoir caused by the withdrawal of magma, while the secondary cluster is focused in a N130-elongated seismic structure, probably related to movements of fluids from the deep reservoir to the NVE and other active vents. These results show that Mayotte on-going eruption provides exceptional observations on the development and evolution of a volcanic seamount and its associated seismicity. To place even better constraints on the magmatic, hydrothermal and tectonic processes occurring around the seismically active area, we use the best located events from a dataset of almost 4000 manually-picked earthquakes to develop a new 1D velocity model for the area and to relocate all events. The new velocity model greatly improve earthquakes’ locations, with better RMS and ellipsoidal errors, particularly for the secondary cluster. The relocation of both clusters with this new model show more detailed seismic structures. The new model also provides better locations of the events without the OBS data, as used for the continuous daily monitoring, greatly improving the day-to-day hazard assessment for Mayotte exposed population.