9:45 AM - 10:00 AM
[STT38-04] Three-dimensional thermal structure modeling in the Alaska subduction zone
Keywords:temperature, three-dimensional modeling, numerical simulation, Alaska, subduction zone
In the Alaska subduction zone, megathrust earthquakes such as the 1964 Alaska earthquake (Mw 9.2), and slow earthquakes such as slow slip events and tectonic tremors have occurred near the plate boundary.
In this region, the Pacific plate is subducting beneath the North American plate, and recent studies have revealed that the Yakutat terrane is subducting at the eastern edge of the Pacific plate. The Yakutat terrane has a significantly different tectonic setting from that of the Pacific plate, and is characterized by the occurrence of tectonic tremors, the absence of volcanoes, and the remarkable thicknesses of the marine sedimentary layer and the oceanic crust.
In this study, we constructed a three-dimensional thermomechanical model associated with the simultaneous subduction of the Yakutat terrane and the Pacific plate to identify the thermal conditions of the region where such interplate seismic events take place in the Alaska subduction zone.
In this numerical simulation, the subduction history of the plate was considered, referring to the plate rotation model, and the subduction velocities were given independently for the Yakutat terrane and the Pacific plate. We also assigned the thicknesses of the marine sedimentary layer and the oceanic crust separately for both regions. In addition, we introduced a low-viscosity layer at the plate boundary below the mantle wedge, which allows for lower temperatures in the forearc region.
Under these conditions, we solved the time-dependent problem of the temperature and mantle flow velocity fields from millions of years ago to the present, using the finite-difference method.
The present temperature field obtained from the numerical simulation was compared with the Curie-point depth distribution and heat flow observations, and we attempted to construct a model in which the residuals between the observed and calculated values can be minimized.
In the future, based on the thermal structure obtained from the numerical simulations, we plan to investigate the relationship between interplate seismic events and dehydration, using phase diagrams of hydrous minerals in the marine sedimentary layer and the oceanic crust.
In this region, the Pacific plate is subducting beneath the North American plate, and recent studies have revealed that the Yakutat terrane is subducting at the eastern edge of the Pacific plate. The Yakutat terrane has a significantly different tectonic setting from that of the Pacific plate, and is characterized by the occurrence of tectonic tremors, the absence of volcanoes, and the remarkable thicknesses of the marine sedimentary layer and the oceanic crust.
In this study, we constructed a three-dimensional thermomechanical model associated with the simultaneous subduction of the Yakutat terrane and the Pacific plate to identify the thermal conditions of the region where such interplate seismic events take place in the Alaska subduction zone.
In this numerical simulation, the subduction history of the plate was considered, referring to the plate rotation model, and the subduction velocities were given independently for the Yakutat terrane and the Pacific plate. We also assigned the thicknesses of the marine sedimentary layer and the oceanic crust separately for both regions. In addition, we introduced a low-viscosity layer at the plate boundary below the mantle wedge, which allows for lower temperatures in the forearc region.
Under these conditions, we solved the time-dependent problem of the temperature and mantle flow velocity fields from millions of years ago to the present, using the finite-difference method.
The present temperature field obtained from the numerical simulation was compared with the Curie-point depth distribution and heat flow observations, and we attempted to construct a model in which the residuals between the observed and calculated values can be minimized.
In the future, based on the thermal structure obtained from the numerical simulations, we plan to investigate the relationship between interplate seismic events and dehydration, using phase diagrams of hydrous minerals in the marine sedimentary layer and the oceanic crust.