Abstract : Autonomous Hydrophones (AuH) arrays are excellent to seismically monitor mid oceanic ridges. One of their advantages is the ability of estimating, both for speciﬁc array geometries and speciﬁc oceanic regions around the globe, the error of the seismic locations. This has been implemented for all the AuH arrays deployed on the Mid-Atlantic Ridge (MAR). Another advantage of the AuH is its low detection threshold. An analysis of the detection thresholds of the AuH that were deployed in the MAR revealed that this feature can greatly impact the number of recorded events, and that this must be considered for further analyses. Transmission Loss analysis shows that the AuH Source Level of an earthquake is mainly due to the conversion from seismic to acoustic energy while the propagation paths play a smaller contribution. An analysis of MAR seismicity reveals that the AuH recorded seismicity mimics the longer time span of teleseismically recorded seismicity and that both are inﬂuenced by crustal thermal structure variations along the ridge. AuH recorded seismic clusters are directly linked with teleseismically recorded events and the sections where they occurred are the most active sections of the MAR. Seismicity generally clusters at segment extremities and at the segment scale, on MBA maxima. Size-frequency and mainshock-aftershock analyses of the clusters reveal that aftershock decay rate is inﬂuenced by the mode of faulting. Detachment faults produce seismic sequences with faster decay rate associated with a reduced strain release in comparison to normal faults. This implies the presence of higher levels of serpentinisation on detachment faults.