The scientific goal of the HYDROMOMAR18 survey is the study of the accretionnary processes at the axis of a slow ridge, in a context where this ridge interacts with a hot spot, that of the Azores. The observation and location of the small-magnitude earthquakes occurring along accreting ocean boundaries provides insight into the various geodynamic, magmatic, tectonic, hydrothermal, ... processes that occur along these boundaries. However, these processes, generating earthquakes of magnitude mostly less than 5, represent barely 1% of earthquakes detected by global terrestrial seismic networks in the MOMAR zone. In addition, the seismicity observed at  a ridge has a low occurrence rate of more than 5 years. Therefore, the deployment of autonomous hydrophone networks in the SOFAR channel is necessary to study the active processes along the oceanic ridges, that is to say, record for several hundreds of kilometers of  earthquakes  with small magnitudes (M <4) and with a seismic cycle high (1 occurrence every 5 years). Five hydrophones have been deployed in the area south of the Azores from 25 June to 7 July 2018 and will be recovered in June 2020.