Pore fluid effects on elastic wave velocities of serpentinite and implications for estimates of serpentinization in oceanic lithosphere

Abstract Recent seismic refraction surveys at various outer-rise regions have identified low seismic velocities in the uppermost mantle, which is indicative of mantle hydration (serpentinization) related to water infiltration along bending-related faults prior to subduction. Serpentinization could lead to the development of pore spaces during hydration reaction, which influences seismic velocity. Here, we measured the elastic wave velocity of low-temperature serpentinites with various porosities and reevaluated the degree of serpentinization of the oceanic mantle in outer-rise regions, accounting for pore fluid effects. Experimental results show that the elastic wave velocity of serpentinite decreases with increasing porosity. This relationship indicates that the estimated degree of serpentinization decreases with increasing serpentinite porosity. We then applied these experimental data to the geophysical observations of the outer-rise regions to reevaluate the amount and the type of water carried into Earth's interior at subduction systems.