Figure 2

Subduction plate boundary model. (a) A 3-D view of a subduction plate boundary model with frictional parameter γ = a − b. (b) Frictional parameters (a, γ, d _c ) and the superhydrostatic pore pressure factor κ as functions of distance along the dip direction from the surface, where (a₁, a₂) = (2, 5) [×10⁻³], (γ₁, γ₂, γ₃^strong, γ₃^weak, γ₄) = (0.7, 0.01, −0.98^strong, −0.3^weak, 4.9) [×10⁻³], (d_{c 1}, d_{c 2}, d_{c 3}, d_{c 4}) = (10, 0.3, 0.4, 400) [mm], and (κ₁, κ₂, κ₃) = (1.0, 0.07, 0.13). Half the length of the minor axis (along the dip) of the elliptical asperity takes the following values: for the large asperity (LA), (R₁, R₂, R₃) = (30, 33, 35) [km], and for the shallow small asperities (SA), (r₁, r₂, r₃) = (2, 2.25, 2.5) [km], where the aspect ratios for the LA and SA are 1.25 and 1.5, respectively. The distances between the central points of the SA along the strike and dip direction are 2 and 2.5 km, respectively. The values of the frictional parameters and κ are based on rock laboratory results (e.g., Blanpied et al. 1998) and observational results (Ariyoshi et al. 2007), respectively. (c) Depth of plate interface drawn by B-spline curve with 16 fixed points: (ξ, φ) = (0, 4), (10, 4), (30, 5), (50, 5), (53, 8), (67, 8), (70, 8), (90, 8), (120, 10), (140, 12), (160, 17), (168, 22), (182, 22), (190, 22), (200, 22), (215, 27), where ξ and φ are distances along the dip direction from the surface and dip angle (in degrees), respectively.