Presentation Information
[S04-04]Rheological modeling for assessing the effect of seamount subduction
*Erika Jessenia Moreno1, Vlad Constantin Manea2, Shoichi Yoshioka3, Marina Manea2, Nobuaki Suenaga3, Masataka Kinoshita1 (1. Earthquake Research Institute, 2. Computational Geodynamics Laboratory, Instituto de Geociencias, Universidad Nacional Autónoma de México, 3. Research Center for Urban Safety and Security, Kobe University)
The Kyushu-Palau Ridge (KPR) marks a sharp boundary between the Ryukyu Trench, where the subducting Philippine Sea (PHS) plate is older than 50 Ma, and the Nankai Trough, where the PHS plate subducts at ages ranging from 26 to 15 Ma. Heat flow measurements reveal elevated values near the youngest position along the Nankai Trough and significantly lower values toward the Ryukyu Trench. The region of lower heat flow corresponds to the location where tectonic tremors occur in KPR. Several hypotheses suggest that the low heat flow anomaly, along with the associated seismic activity (low-frequency events and tremors), is linked to the presence of a subducting seamount. To investigate the dynamic effects of seamount subduction on subduction zone processes, we employ time-dependent high-resolution two-dimensional thermomechanical models with visco-elasto-plastic rheology to evaluate how seamount subduction influences the slab thermal structure, plate geometry, stress distribution, and strain rate along the interface between the slab surface and the forearc. Key parameters analyzed include the age of the subducting plate, the internal friction angle of the seamount and sediments, and sediment density. Two types of numerical models are developed to compare, and investigate the sensitivity of the subducting PHS plate to seamount subduction. The total time of evolution ir 3 Myr. Model 1 uses a plate age of 25 Ma without incorporation of a seamount, while Model 2 also features a 25 Ma plate but includes a seamount. The density of sediments in the forearc varies with depth and have a low internal friction angle of 5°. The internal friction angle for both the seamount and the oceanic and continental plates is set at 30°. Modelling results indicated that incorporation of a seamount leads to greater deformation of the forearc and increased sediment accumulation compared to Model 1. In terms of deformation, we observe the formation of a series of shear bands in the upper crust in the proximity to forearc that differs between the two models. Regarding stress accumulation along the plate interface, Model 1 shows a continuous increase in stress along the entire plate interface, with lower stress concentrations observed in regions where the slab interacts with the sediments. The evolution of Model 2 is more complex and can be divided into two distinct phases. In the first phase, at the beginning of seamount subduction, the interaction between the sediments and the seamount induces significant deformation, and is marked by elevated strain rates and low stress along the boundary between the seamount and the sediments. In the second phase, the seamount interacts with the continental crust, and strain rates along the slab boundary decrease, while stress accumulation reaches its peak. Numerical modelling results indicate that seamount subduction exerts a localized influence on the stress regime within both the forearc and the continental crust. Furthermore, the type of mechanical coupling of the slab and forearc-continental crust appears to depend on whether the specific rheology of the seamount encounters during subduction.
