A new 1D velocity model and absolute locations image the Mayotte seismo-volcanic region

In May 2018, a seismically quiet region of the Indian Ocean awoke. More than 130 magnitude 4+ earthquakes were recorded in the first month, including a M-W 5.9 event on May 15th, 2018. This seismic activity was later identified as being related to an exceptional underwater volcanic eruption offshore Mayotte island, which had emitted more than 6.5 km(3) of lava by the time of writing. To better constrain the geodynamic processes responsible for the seismic and volcanic activity, a new network of ocean-bottom seismometers and land stations has been deployed around the seismically active region since February 2019. We present here an improved 1D velocity model for the active area and relocations of manually-picked earthquakes using this new model. The best-constrained events image detailed structures within two clusters of seismic activity east of Mayotte. The westernmost, proximal cluster, close to Mayotte's Petite-Terre island, has a donut shape horizontally and an hourglass shape in depth. The events distribution suggests the presence of a magma reservoir at around 27 km depth, with earthquakes focused along its sides, and a collapsing system underneath, related to the drainage of another, deeper magma storage zone. The distal cluster, focused 30-50 km offshore of Petite-Terre island, highlights the propagation of a dike between 45 and 25 km depth, aligned towards the new volcanic activity on the seafloor. We interpret this cluster as the fluid pathway towards the new volcano and nearby active seafloor lava fields. The improved velocity model also permits more robust daily monitoring of the seismicity using land stations, allowing local authorities to better assess seismic and volcanic hazards and to communicate them to the island's population. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

In May 2018, an exceptional underwater volcanic eruption offshore Mayotte island in the Indian Ocean led to frequent seismic activity in the region. To better understand and monitor the geological activities in the area, a new network of seismometers and land stations has been deployed since February 2019. Using an improved velocity model and relocation of earthquakes, researchers have identified detailed structures related to the seismic and volcanic activity, providing insights into the fluid pathways and magma reservoirs.