Fault–fracture mesh development produces tectonic tremor in fluid-overpressured serpentinized mantle wedge

Abstract Deep tectonic tremor occurs repeatedly at the base of a forearc mantle wedge corner, where a highly fluid-pressurized serpentinite shear zone is thought to develop. However, the deformation mechanisms that accommodate these tremors within the shear zone remain unclear. Here, we present observations of deformation experiments on water-saturated serpentinite conducted at pressure–temperature conditions relevant to the tremor zone. We find that increasing pore fluid pressure gradually decreases sample strength and leads to a transition in the deformation mechanism from frictional sliding on several fault surfaces to distributed extensional and extensional–shear fracturing. Combined with field observations of a shallow mantle-wedge-derived serpentinite shear zone, our experimental results suggest that numerous brittle failures developing simultaneously throughout the shear zone generate bursts of tectonic tremor. Furthermore, the recurrence interval of the tremors is likely controlled by the time required for the fractures to be hydrothermally sealed through serpentine precipitation.