A comparison of free-surface tracking methods for numerical modeling of rifting based on ASPECT

초록

The rifting is a unique geodynamical process of the Earth, which involves crustal thinning, continental breakup, and seafloor spreading due to the extensional stress driven by plate relative motions and plume. In this study, we compare the morphological structures and calculation time based on two free-surface deformation simulation approaches, Sticky-Air (SA) and Arbitrary Lagrangian-Eulerian (ALE) methods. We adopt the finite element geodynamic software, ASPECT, recently widely used in modeling rifling. In the rifting evolution in the SA method, continental breakup and subsequent similar to 100 km seafloor spreading proceed for 5.3 Myrs. On the other hand, the ALE method shows just crustal thinning and mantle upwelling, which reaches no continental breakup. The ALE method spends 2 calculation time compared to the SA method because the mesh grids directly deform following the velocity field in the ALE method. We perform a series of modeling using various values of SA layer thickness (5, 10, 15, 20 km) to evaluate the effects of the SA layer on rifling evolution and calculation time. The smaller SA thickness, which refers to the smaller model size, tends to decrease calculation time. The process of rifting evolution becomes slower in the small SA thickness model because the top boundary condition strongly influences the deformation of the upper crust. We suggest that the ALE method, which excludes the effect of the top boundary condition, is more effective when the computational resources are sufficient. When the SA method is adopted, the SA thickness should be larger than similar to 15 km for decoupling the upper crust and SA layer. We expect that the efficient selection of free-surface simulation methods, aided by our comparison study, contributes to understanding the rifted basin (e.g., East Sea) and crustal structure.

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