Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes

Studies of slow earthquakes during the last decade have suggested a relationship between various types of earthquakes occurring at the interface between subducting oceanic plates and overlying continental plates. Such a relationship has been postulated for slow earthquakes, which are distributed between the stable sliding zone and the locked zone, and megathrust earthquakes, which are located in the locked zone. The adjacency of the respective sources of slow and megathrust earthquakes suggests expected interactions between these two types of earthquakes. Observed interactions between different types of slow earthquakes located at neighbor area suggest a common triggering mechanism in the seismogenic zone. Also, it is expected that stress accumulations in the locked zone should influence stress regimes in surrounding regions; thus, slow earthquake activity in the stable sliding zone may change in response to stress build-up in the locked zone. Numerical simulations reproducing both megathrust and slow earthquakes show a shortening of the recurrence interval between slow earthquake episodes leading up to the occurrence of a megathrust earthquake. Similarities between the activities of slow and megathrust earthquakes, such as those related to periodicity and patterns of multisegment ruptures, are useful for understanding megathrust earthquakes, particularly given the higher frequency of occurrence of slow earthquakes. From this perspective, the continuous and accurate monitoring of slow earthquake activity is important for evaluating the occurrence potential of megathrust earthquakes.