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

Hydroacoustic monitoring has become particularly efficient for studying the low-magni-tude 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 impul-sive events, which we interpret as due to lava-water interactions on the seafloor. The spa-tio-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.