10:45 〜 11:00
[S26-2-02] Modelling three-dimensional hydrothermal heat transport around the Nankai Trough
To understand the behaviour of mega-thrust earthquakes, estimating temperature structure of the subduction zone is a key issue. The Nankai Trough, with a lot of heat flow data, is one of the best regions for this purpose. The major features of the available data are high heat flow (more than twice that expected from thermal models with the corresponding plate age) at the Muroto area, moderately high heat flow (at most 1.5 times that expected from thermal models) at the Kumano area (150 km east of the Muroto area), and a gradual heat flow variation between these areas with the spatial scale of ca. 50 km.
Spinelli and Wang (2008) proposed a thermal model including hydrothermal circulation to explain the high heat flow at the Muroto area. They assumed that the uppermost 500 m of the oceanic plate (usually called aquifer) is permeable both before and after subduction. This model explains the heat flow data and gives an important aspect that temperature at depth along the aquifer is decreased by 50 degrees Celsius.
Here we extend Spinelli and Wang's (2008) model so that the heat flow variation between the Muroto and Kumano areas can be targeted. We pay attention to hydrological structure of the crust and irregular slab geometry between these areas, which reflects paleo-spreading direction. We construct a three-dimensional model including anisotropic aquifer permeability to include these features.
Results are summarised as follows. 1) Taking a high permeability entire of the areas results in pervasive high heat flow. 2) High permeability at the Murtoto area and low permeability at the Kumano area with a sharp contrast between these areas, results in a sharp heat-flow contrast between these areas. These are not the case. 3) We consider anisotropy in permeability, in which the Muroto area has high permeability and the Kumano area has high permeability only in the direction parallel to the trench axis. This model can explain the heat flow variation between these areas.
Spinelli and Wang (2008) proposed a thermal model including hydrothermal circulation to explain the high heat flow at the Muroto area. They assumed that the uppermost 500 m of the oceanic plate (usually called aquifer) is permeable both before and after subduction. This model explains the heat flow data and gives an important aspect that temperature at depth along the aquifer is decreased by 50 degrees Celsius.
Here we extend Spinelli and Wang's (2008) model so that the heat flow variation between the Muroto and Kumano areas can be targeted. We pay attention to hydrological structure of the crust and irregular slab geometry between these areas, which reflects paleo-spreading direction. We construct a three-dimensional model including anisotropic aquifer permeability to include these features.
Results are summarised as follows. 1) Taking a high permeability entire of the areas results in pervasive high heat flow. 2) High permeability at the Murtoto area and low permeability at the Kumano area with a sharp contrast between these areas, results in a sharp heat-flow contrast between these areas. These are not the case. 3) We consider anisotropy in permeability, in which the Muroto area has high permeability and the Kumano area has high permeability only in the direction parallel to the trench axis. This model can explain the heat flow variation between these areas.