The detection and localization of the numerous low-magnitude earthquakes occurring along active oceanic ridges provide important insights into the various magmatic, tectonic or hydrothermal processes which generate theses earthquakes. However, these processes mainly generate low-magnitude seismic events that are not detected - or in any case, poorly located- by land-based seismological global networks. The deployment of autonomous hydrophone arrays, moored within the SOFAR channel, overcomes this difficulty: hydrophone arrays have shown their capability to detect and precisely locate (< 2 km) typically 30 to 40 times more events than those listed in global catalogs.

The first objective of the HYDROMOMAR project was to deploy five hydrophones and to increase the length of the hydroacoustic data series of observation at a regional scale. These hydroacoustic data series are proposed within the general framework of the deployment of permanent observatories dedicated to the study of active processes in the ocean area as part of EMSO-Azores project and of the « Ocean-Earth Interactions » theme of the EUR ISblue, Brest. Recently, a second objective of the HYDROMOMAR data series was developed with the characterization of sounds emitted by baleen whales. Acoustic monitoring of baleen whales is necessary in order to establish a database of whale songs present in the Atlantic Ocean, south of the Azores, and afterwards to study their migratory routes.