Events

Speaker: Maria Nikolinakou, Research Professor, UT Bureau of Economic Geology

Host: Kehua You

Title: Mechanisms for generating fluid overpressure at the trench of subduction zones and implications for megathrust weakening

Abstract: I discuss stress, pressure, and porosity in an evolving accretionary wedge using transient geomechanical models. The evolution of the stress state from that imposed by uniaxial burial seaward of the trench to Coulomb failure within the wedge generates overpressure and drives compaction above the décollement. Changes in both mean and shear stress generate overpressure and shear-induced pressures play a particularly important role in the trench area. In the transition zone between uniaxial burial and Coulomb failure, overpressures increase faster than overburden and are higher than footwall pressures. This rapid increase in overpressure reduces the effective normal stress and weakens the plate interface along a zone that onsets ahead of the trench and persists well into the subduction zone. It also drives dewatering at the trench, which enables compaction of the hanging-wall sediments and a porosity offset at the décollement. More broadly, our results may provide a hydromechanical explanation for a wide range of observed behaviors, including the development of protothrust zones, widespread occurrence of shallow slow earthquake phenomena, and the propagation of large shallow coseismic slip.