Subduction Dynamics and Great Earthquakes

The majority of Earth's seismic energy has been released by a minority class of great earthquakes, with magnitudes (Mw) greater than 8.5, causing unprecedented damage in many portions of the world. Most of these events have occurred along the megathrust faults of subduction zones, with orogenic tectonics considered a prerequisite. The 2004 Sumatra earthquake (Mw =9.1) occurred in a region exhibiting an extensional back-arc basin, spurring a re-evaluation of global great earthquake risk. Here we define a new dataset of maximum earthquake magnitude for 256 global subduction zone segments, showing that the majority of great earthquakes occur in neutral tectonic regions, with lower normal stresses and fewer asperities than previously argued. In addition, all great subduction zone earthquake epicenters since 1900 have occurred within 25 percent of the total slab length closest to a terminal edge. We argue that pathways for mantle flow around a slab induce larger maximum earthquake magnitudes near the terminal edges of slabs by decreasing seismic coupling and increasing a trench's capacity to produce long rupture lengths.