The Importance of Elastic Property Contrast at Continent-Ocean Margins on Subduction Initiation

For many decades, visco-plastic rheological contrast between oceanic and continental lithosphere has been thought to be a dominant factor in causing the nucleation of weak zones during the initiation of subduction zones. However, in this study, we suggest that a simple contrast in elastic property (e.g., Young’s modulus and shear modulus) may hold the key in explaining a bimaterial instability behavior. Thermo-mechanical numerical simulations based on FEM, using 1 million elements, were performed to understand the effects of elastic deformation and initiation of asymmetric rupture for 1E6 years. In our model, two lithospheres, oceanic and continental, which are simply in contact with one another without predefined weak zone were compressed at a constant rate of 2-10 cm/yr. To explore the effects of elastic property contrast, the Young’s modulus of continental lithosphere was fixed at 1E11 Pas while that of oceanic lithosphere is varied by a factor of 10 (from 1E11 to 1E12). We also examined the role of activation energy differences between two lithospheres by varying their ratios. From our preliminary results, the elastic property contrast appears to be a far more important controlling factor in causing asymmetric instability at the interface between two lithospheres than activation energy contrast. In particular, asymmetric rupture developed more rapidly, at timescales between 10**5 and 10**6 years and the temperature in the shear zone was higher when higher elastic property ratio was prescribed than that of low elastic property ratio. We investigate whether the difference in the elastic property ratio may be an important factor in explaining the morphological difference in the subduction geometry at Mariana and Chilean trenches.