Abstract
We consider whether splay fault slip may be a factor influencing the behavior of megathrust earthquakes in the Nankai Trough. Consideration of tsunami inversion results from other studies indicates that slip on one or more splay faults may be particularly important for the segment of the Nankai Trough offshore western Shikoku. These results suggest that during at least twomegathrust earthquakes substantial slip may have occurred on one or more splay faults which cut the island arc crust over 100 km landward of the trench axis. In contrast to smaller subsidiary thrusts in the semi-consolidated and unconsolidated sediments very near the trough axis, the crustal faults considered here could accumulate and release considerable tectonic stress. Through a simple finite element calculation we demonstrate that slip on such faults can release some of the shear stress on the megathrust accumulated through plate subduction, and therefore may have some influence on the behavior of megathrust earthquakes.
