The 2010 M7.0 Earthquake Southeast of Katsuren-haebaru

On 26 February 2010 at 20:31 local time, a magnitude 7.0 earthquake occurred 70 km southeast of Katsuren-haebaru, Okinawa Prefecture, Japan, at a focal depth of 25 km. This event is recorded as the sole strong earthquake (M7.0 or greater) in the immediate region since 1 January 2000. Katsuren-haebaru lies on the main island of Okinawa within the central Ryukyu arc. The arc forms part of the convergent boundary where the Philippine Sea Plate subducts northwestward beneath the Eurasian Plate at the Ryukyu Trench. Subduction rates average 6–8 cm per year, generating megathrust earthquakes, intraslab events, and associated normal faulting in the overriding plate. The 25 km depth of the 2010 event places it within the upper portion of the subducting slab, consistent with typical intermediate-depth seismicity along this margin. The Ryukyu subduction zone has produced recurrent large earthquakes throughout the Holocene. Paleoseismic and historical records document events in 1771 (estimated M7.4–8.0) and 1911 (M8.0), both of which generated significant tsunamis affecting the island chain. Modern instrumental monitoring since the late twentieth century confirms persistent background seismicity, with the majority of events occurring at depths between 10 km and 40 km along the plate interface and within the downgoing slab. Crustal structure beneath Okinawa includes a thinned continental margin overlying the subducting slab, with active normal faulting in the back-arc region linked to extension in the Okinawa Trough. These tectonic elements contribute to the elevated seismic hazard recognized for the prefecture by Japanese government assessments.

References

United States Geological Survey Earthquake Catalog
Japan Meteorological Agency Seismological Data
Geological Survey of Japan, AIST – Tectonic Map of the Ryukyu Arc