Strong long-term seismic activity (LP) was recorded on a recently discovered submarine volcano near Mayotte, starting at 16:33 UTC on July 31, 2021. A total of 186 LP earthquakes were recorded in three separate swarms, each associated with a very long-term earthquake (VLP), according to the Mayotte Volcanological and Seismological Monitoring Network (REVOSIMA).
LP and VLP earthquakes are seismic signals commonly associated with resonances and movements of fluids (magmatic or hydrothermal) at depth.
"Work is currently underway to try to better understand these signals," REVOSIMA said in a statement.
"Some of these LP quakes were located about 1 km [0.62 mi] east of Petite Terre in the most active zone of the proximal seismic swarm, at a depth of about 1 km, in the same place where LP quakes are usually located ".
These earthquakes are of low magnitude and were not felt by the population.
The new swarm began at 13:00 UTC on 1 August.
The faintly felt M4.1 quake was recorded at 01:36 UTC on August 3 35 km (21.7 mi) east of Dzaoudzi at a depth of 39 km (24.2 mi).
During July, REVOSIMA recorded a total of 648 earthquakes - 374 volcano-tectonic earthquakes (VT), 265 LP earthquakes and 9 VLP earthquakes.
The main seismic activity was still concentrated 5-15 km (3, 1-9, 3 miles) east of Petite Terre, at a depth of 20-50 km (12-31 miles).
Surface displacements measured since July 1, 2018 by GPS stations in Mayotte indicate a total movement of GPS stations in Mayotte approximately 21-25 cm (8.2-9.8 inches) eastward; and subsidence of approximately 10 cm (3.9 in.) depending on their location on the island.
Since the end of 2020, the deformations have become insignificant, but now there has been an unexpected surge in activity, the reasons for which are not yet clear.