10:45 AM - 12:15 PM
[SCG45-P08] Diversity and transition of slip behaviors for two-phase mélange in subduction shear zones
Keywords:subduction zones, two-phase mélange, slip behaviors
A variety of slip behaviors, ranging from aseismic creep (mm/yr), slow slip (mm/week) to unstable seismic slip (m/s), have been observed in subduction zones. Understanding the mechanisms that determine the slow versus fast slip mode is critical for assessing seismic hazard along subduction zones. Geological observations of exhumed subduction zones reveal a mélange shear zone structure, with competent blocks embedded in an incompetent matrix. This suggests that deformation is accommodated by a combination of frictional sliding and viscous creep. Here we use a 2D finite difference visco-elasto-plastic numerical code to quantitatively study how mélange properties can influence the resultant slip behaviors. We generate synthetic models with various ratios of strong blocks in a weak matrix and vary the rheological parameters of such a two-phase mélange. Our results show that matrix viscosity and block percentage are the key parameters that control the slip behaviors. At extremely low values of matrix viscosity and block percentage, the resultant slip mode is aseismic slip. In contrast, frictional behavior can become predominant when matrix viscosity is extremely high. As the block percentage increases, the slip behavior varies from slow aseismic slip to fast seismic slip. Intermediate between the above extreme situations, a hybrid mode of slow and fast slip can emerge, whose exact behavior depends on the detailed values of matrix viscosity and block percentage. These results demonstrate that the variation of mélange properties can account for the diversity and transition of slip behaviors in subduction shear zones. Moreover, these results can provide a guidance for constraining the compositional and rheological properties of subduction shear zones from observed slip behaviors.