Temperature control on deep tectonic tremor belt in the Nankai subduction zone

Abstract

Deep tectonic tremors occur in the Nankai subduction zone, defining a belt-like zone with a width of a few ten km located at depths between 30 and 55 km along upper surface of the subducting Philippine sea slab. We interpret the geometry of the tremor belt based on temperature calculations. Time evolution of temperature is calculated using a 3-D heat conduction assuming constant geometry of the slab and the present-day plate convergence velocity. The results show that the tremors occur along the 450°C isotherm along the slab surface where the mantle wedge can be non-convective and already well-serpentinized. Two gaps of the tremor belts are explained by different mechanisms. The Ise gap is where the hanging wall is not mantle wedge but crust. The Kii Gap is not a gap orthogonal to the plate convergence direction, but only appears to be a gap because the isotherm of the plate surface steps in the plate convergence direction. The tremors can be caused by high pore-fluid pressure conditions due to aqueous fluids released by dehydration reactions in blueschist-facies oceanic crust to form eclogite facies. The depth of the tremor belt corresponds to that of decoupled, non-convective mantle wedge. Since the temperature and pressure are within the serpentinite stable condition, the released fluid would normally be absorbed by serpentinization of the mantle wedge peridotite. However, since the non-convective mantle wedge is already well serpentinized from exposure to previously released fluids, the newly released fluid is not absorbed and increases the pore pressure. Hosted file essoar.10512557.1.docx available at https://authorea.com/users/549855/articles/603763temperature-control-on-deep-tectonic-tremor-belt-in-the-nankai-subduction-zone Hosted file suppinfo.docx available at https://authorea.com/users/549855/articles/603763-temperaturecontrol-on-deep-tectonic-tremor-belt-in-the-nankai-subduction-zone Temperature control on deep tectonic tremor belt in the Nankai subduction zone