Crustal deformation dynamics and stress evolution during seamount subduction: High-resolution 3-D numerical modeling

摘要

Seamounts or submarine volcanoes frequently collide with the overriding crust along presently active subduction zones locally modifying stress and permanent deformation patterns. Dynamics of this process is not fully understood, and several end-member scenarios of seamount-crust interaction are proposed. Here we use high-resolution 3-D numerical models to investigate evolution of crustal deformation and stress distribution within the upper plate induced by the underthrusting of subducting seamounts. The dynamical effects of the upper plate strength, subduction interface strength, and strain weakening of the crust are investigated. Experiment results demonstrate that characteristic crustal fracturing patterns formed in response to different seamount-crust interaction scenarios. Indenting seamounts strongly deform the overriding plate along a corridor as wide as the underthrusting seamount by constantly shifting subvertical shear zones rooted at the seamount extensions. A reentrant develops during initial seamount collision. A topographic bulge atop the seamount and lateral ridges emerge from further seamount subduction. Obtained stress pattern shows areas of large overpressure above the rearward and large underpressure above the trenchward flank of the seamount. Results of numerical experiments are consistent with seismic reflection images and seismic velocity models of the upper plate in areas of seamount subduction along the Middle America Trench and give important insights into the long-lasting question, whether subducting seamounts and rough seafloor act as barriers or asperities for megathrust earthquakes.