Global Detection Capabilities of <i>T</i> Phases Using the IMS Hydrophone Network

Abstract In addition to monitoring the oceans for signs of nuclear explosions, data from the hydroacoustic component of the International Monitoring System (IMS) have been used for a broad range of civil and scientific applications. This includes studying T phases: seismic waves that convert to underwater acoustic energy at the bottom of the ocean and can travel with low attenuation in the ocean’s Sound Fixing and Ranging channel. This study analyzes T phases recorded from 2001 to 2024 at the six IMS hydrophone stations. Analysis reveals global ocean coverage and demonstrates the network’s ability to detect T phases primarily linked to submarine earthquakes concentrated along tectonic plate boundaries, particularly midocean ridges and transform faults. Notably, some T phases were recorded after propagating more than 20,000 km, exceeding the antipodal range. Results highlight the network’s significant contribution to our understanding of global ocean seismicity. A discussion is provided on earthquake events that led to major detection peaks of T phases in analyst-reviewed bulletins. Finally, it is shown that while T phase detection itself is not network dependent, associating them with events relies on IMS seismic network sensitivity for building the events.