Modelling Three-Dimensional Stress Distribution in Subducting Slabs: Implications for Large Magnitude Seismicity at Active Margins

Megathrusts host the majority of large (Mw > 7) earthquakes occurring at convergent margins. Several parameters (e.g., sediment thickness and curvature, among others) have been put forth as the main control of giant earthquake occurrence, although investigations are still underway. Here, we explore the link between large-scale subduction and the seismicity magnitude at plate margins where the largest earthquakes occurred. We develop 3-dimensional models of deforming plates from surface to mantle depth solving for the elastic stresses inside the lithosphere under the load of the slab. Realistic load distributions are derived from the USGS Slab 2.0 dataset, which provides slab depth and thickness of all active subduction zones, while magnitudes are constrained by estimated values from flexural analyses at oceanic trenches. We show that where the depth of the attached slab varies largely along the trench, lateral stresses in the direction of the trench are maximized. An estimate of synthetic moments, Msyn, along the trench is achieved by integrating the stresses and considering characteristic lengths constrained from the interface geometry. A comparison of synthetic and observed seismic moments released along major subduction zones, Mo, indicate that Mo Msynk where k 1. The synthetic moments match most of the moments released by large earthquakes across more than 2 orders of magnitude, while systematically overestimating the moments in the Alaska-Aleutian and Ryukyu-Nankai subduction zones. We explain this as the portion, significant to the total, of the potential recoverable stress accommodated during actual events.