Regional seismicity of the Mid-Atlantic Ridge: observations from autonomous hydrophone arrays

Autonomous hydrophones arrays are an excellent tool for monitoring mid-ocean ridge seismic activity. The major advantage of using arrays of autonomous hydrophones for recording deep-ocean ridge earthquakes is its low magnitude detection thresholds achievable using hydroacoustic techniques. Regional analysis of the detection thresholds of the different autonomous hydrophones arrays deployed along the Mid-Atlantic Ridge reveals the strong influence of the detection threshold in the number of recorded events and it must be taken into account in any further analysis. In this study, the analysis of both autonomous hydrophones and teleseismically detected Mid-Atlantic Ridge seismicity reveals that the background seismicity from the relatively short recording periods of the autonomous hydrophones mimic the results of the much longer teleseismic recording. It also reveals that seismicity generally cluster at both the segment scale and on Mantle Bouguer Anomaly maxima. The big majority of these clusters seem to be related to dyke intrusions and propagation along the Mid-Atlantic Ridge. These dyke intrusions interact with the mainshock-aftershock sequences. The seismic sequences mainshock-aftershock analysis reveals that the strength of the faults is highly influenced by the mode, or style, of faulting. Detachment faults, which are ubiquitous along the Mid-Atlantic Ridge, can produce more prolific shorter duration seismic sequences revealing faster and reduced strain releases in comparison to higher angle normal faults. This reduced strain release is most likely to occur due to the presence of higher levels of serpentinization on detachment faults. Higher levels of serpentenisation can also promote an aseismic transient slip on the mainshock-aftershock sequences.