Earth tides can reactivate shallow faults and trigger seabed methane emissions

The role of solid Earth tide in fault reactivation has significant implications for understanding earthquake triggering, carbon sequestration, and the global carbon budget. Despite extensive research on this topic over the years, the relationship between Earth tide and fault reactivation remains unclear. In this study, we investigate the potential influence of solid Earth tide on the reactivation of sub-seabed fractures and faults, which may lead to the release of methane from the seabed. For a period of two weeks, we monitored the sub-seabed temperature and pore-fluid pressure at two sites on an over-pressured fault system located in the Black Sea. Our observations revealed that, despite the ~790 m distance between the two sites, the response in terms of methane discharge was synchronous during the measurement period. Our analysis showed that the presence of over-pressured fluid promotes fault reactivation under solid Earth tide cycles, resulting in synchronized degassing events. We also showed that that these faults can be reactivated with relatively low stresses, no greater than 2 kPa, illustrating the fragile equilibrium of these greenhouse gas laden systems.