プレート境界地震の規模と発生間隔変化のメカニズム

抄録

There are some systematic variations in size and recurrence interval of earthquakes in subduction zones. Such variations, especially variation in recurrence time depending on earthquake size, are incorporated in hazard predictions for earthquakes in many countries including Japan, although the physical mechanism has not been revealed yet. We model an interplate earthquake as release of slip deficit with high slip rate. The slip deficit accumulation occurs on an area where slip velocity is significantly lower than the surrounding area mainly due to mechanical coupling of plate boundary. Spatial and temporal variation in slip on a plate boundary can be described mathematically with equations for stress change due to slip, a relation between stress, strength and slip velocity, and an evolution law of strength. Numerical simulations based on such model with heterogeneous frictional property qualitatively reproduce the variation pattern of size and time interval of great interplate earthquakes in some subduction zones. The recurrence time variation depending on size for the Nankai subduction zone arises from the specific layout of inhomogeneities of the region. Since such variations are seen in other subduction zones, there may exist other mechanisms related to specific or general patterns of heterogeneity in frictional properties.