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

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 degrees 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 similar to 10(-13) to 10(-12) m(2) within layer 2B over a calculated diffusive lengthscale of 2.0 km. Citation: Stroup, D. F., M. Tolstoy, T. J. Crone, A. Malinverno, D. R. Bohnenstiehl, and F. Waldhauser (2009), Systematic along-axis tidal triggering of microearthquakes observed at 9 degrees 50'N East Pacific Rise, Geophys. Res. Lett., 36, L18302, doi:10.1029/2009GL039493.