Shallow Creep in the Leaky Stress Shadow of Locked Zones of Subduction Megathrust

Abstract In some subduction zones such as Nankai, creeping of the shallow part of the megathrust in the stress shadow of deeper locked zones is detected by seafloor geodetic measurements and/or reflected by slow earthquakes (SEQs). Here we explain that shallow creep occurs in the stress shadow for two reasons: (a) prolonged afterslip and (b) a leaky stress shadow due to off‐fault elastic interseismic deformation around locked patches. Relative to the size of the locked patches, a larger shadow zone endures longer duration of afterslip and greater stress leakage. With rate‐state friction modeling, we show that the shallow creep and accompanying SEQs at Nankai likely indicate a combination of the two mechanisms. The paucity of evidence for shallow creep at Cascadia likely indicates that the shadow zones are very small or, in some areas, absent.