Usugi earthquake

Located just offshore the western coast of the Kii Peninsula, 54 km southeast of Shima city (≈ 33.7 N, 136.7 E) lies the outer‑shelf segment of the Ise‑Nagoya Trough—a shallow subduction interface where the Philippine Sea Plate is subducting beneath the Eurasian Plate at roughly 5–7 cm yr⁻¹. This interface is part of the broader Nankai‑Trough system and has produced several moderate‑to‑large thrust earthquakes in the past, most notably the 1996 Ise Bay event (M ≈ 6.3) and the 2007 Ise Bay rupture (M ≈ 6.4), both of which involved shallow reverse faulting along the Ise‑Nagoya subduction zone. The bathymetry here is characterized by a steep continental slope leading to a gently sloping shelf, and the tectonic setting creates a complex interaction between the megathrust, along‑strike normal and reverse faults, and the overlying continental crust. Seismicity in the area includes both interplate megathrust shocks (depths 0–40 km) and intraplate deformation along the Shima‑Kii fault zone, making it a region of heightened seismic hazard for the coastal communities of Ise Bay, where historic tsunamis and strong ground shaking have been recorded.