Hydroacoustic Study of a Seismic Swarm in 2016–2017 near the Melville Transform Fault on the Southwest Indian Ridge

Abstract

Hydroacoustic monitoring has become particularly efficient for studying the low-magnitude seismicity occurring at mid-ocean ridges. In 2016–2017, a seismic swarm occurred near the Melville transform fault of the ultraslow-spreading Southwest Indian Ridge in the Indian Ocean. It comprised 258 events in the land-based International Seismological Centre catalog, extending from June 2016 to March 2017. We examined this seismicity using hydroacoustic records from three to nine hydrophones moored in the southern Indian Ocean from the Hydroacoustic Observatory of Seismicity and Biodiversity in the Indian Ocean (OHASISBIO) temporary network and the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization. We detected 27,624 hydroacoustic events spanning 298 days (1 June 2016–25 March 2017) with lower localization and origin time errors. These include several energetic, short-duration impulsive events, which we interpret as due to lava–water interactions on the seafloor. The spatio-temporal distribution of all the detected events does not show clear tectonic mainshock–aftershock sequences and suggests a magmatic origin of the swarm with bursts of seismicity likely caused by dike emplacements.

Hydroacoustic Monitoring of Mayotte Submarine Volcano during Its Eruptive Phase

“…We mainly focused on impulsive events, using the same method as Bazin et al [36], but we also picked two other types of signals of interest: a few earthquakes and one landslide. We estimated the origin of earthquakes by picking the T-phase arrival times at their maximum amplitude in the spectrograms [25]. In the case of an earthquake, the located source is not the hypocenter but the acoustic radiator on the seafloor (proxy of the epicenter for a shallow earthquake).…”

“…For one of those signals, we picked the first arrival and the maximum of the energy envelope and derived two locations. The picking of the impulsive events was improved in a second iteration by zooming-in on a 120 s time window centered on the event [25].…”

“…Finally, some instrument arrays have been able to detect effusive submarine activity. As they release less acoustic energy, those are much harder to detected [19,[23][24][25]. However, when they are detected, these signals provide information to monitor the timing and location of lava flows and its emplacement rate [24,26].…”