LAUSR

Abstract Tidal triggering of earthquakes in diverse tectonic settings has been well documented, albeit the mechanisms and implications remain elusive. Here we present solid earth and ocean tide modulation of micro-seismicity, associated with caldera dynamics of the 2015 axial seamount eruption in the Juan de Fuca ridge, from well-monitored micro-seismicity catalog of mid-ocean ridge volcanoes to gain an insight into the complex interplay between volcano-tectonic and external influence of periodic tidal loading. We also report a significantly strong semi-diurnal tidal periodicity in pre-eruption and weak semi-diurnal tidal periodicity in the post-eruption phase, which converge with the statistical correlation with the tidal stress. We propose that during the pre-eruption stage, fault systems are critically stressed and more sensitive to stress perturbation by periodic tidal loading. However, during the eruption stage, volcano-tectonic processes dominated masking the tidal modulation in micro-seismicity. The unusual micro-seismicity modulation during pre-eruption magma chamber inflation and reactivation of normal faulting, explicitly during the lowest tide, can be explained by a complex interplay between magma chamber inflation and periodic tidal loading, with eventual feedback mechanism on the caldera ring fault system.