Geodynamics of Bending-related Normal Faults in Subducting Plates

We investigated bending-related normal faults in subducting plates along several subduction zones through analyzing high-resolution multibeam bathymetry data and geodynamic modeling. The investigated systems include the Tonga, Izu-Bonin-Mariana, Japan, Middle America, Chile, and Puerto Rico trenches. Investigation was focused on spatial variations in normal faulting patterns from trench axes to the outer rise regions. Results of analyses revealed several key observations: (1) Most bending-related normal faults are sub-parallel to the local and regional strikes of the trench axis, including regions of significant trench-axis curvatures. (2) For trenches of significant oblique subduction components, e.g., Tonga and Puerto Rico trenches, the strikes of normal faults still remain sub-parallel to the trench axes. (3) Normal faults could be identified near outer-rise region, but normal faults with relatively large throws are generally located much closer to the trench axis, in regions of relatively large topographic slope. (4) Normal faults can cut through most of the seamounts near trench axes. We speculate that near-trench normal faults are generated by extensional stress due to plate bending and gravity sliding. Geodynamic models are being developed to investigate how near-trench normal faults evolve subjected to various tectonic forces at subduction zones, including subduction-induced plate bending, slab pulling, gravity sliding, and seamount loading, etc.