Systematic along‐axis tidal triggering of microearthquakes observed at 9°50′N East Pacific Rise

Abstract

Hydrothermal fluid circulation at mid‐ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid Earth, and supports chemosynthetic microbial and macro‐faunal communities. The structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems; however, direct measurements of subsurface processes remain technologically challenging to obtain. Previous studies have shown that tidally‐induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times. In this study, we observe systematic along‐axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9°50′N East Pacific Rise. We interpret this systematic triggering to result from pore‐pressure perturbations propagating laterally through the hydrothermal system. Based on our observations and a one‐dimensional pore pressure perturbation model, we estimate bulk permeability at ∼10 −13 to 10 −12 m 2 within layer 2B over a calculated diffusive lengthscale of 2.0 km.