Seismic Activity in the Kuril Islands Region: The April 2013 M7.2 Event

The Kuril Islands form a volcanic archipelago extending from Hokkaido, Japan, to the Kamchatka Peninsula of Russia. This chain occupies a tectonically active segment of the Pacific Ring of Fire, where the Pacific Plate converges with and subducts beneath the Okhotsk Plate at rates of approximately 8–9 cm per year. The resulting megathrust interface and associated intraslab stresses generate frequent earthquakes at varying depths, accompanied by andesitic volcanism.

On 19 April 2013 at 03:05 UTC, a magnitude 7.2 earthquake occurred 252 km east-northeast of Kuril’sk on Iturup Island. The event registered at a focal depth of 110 km, placing it within the intermediate-depth portion of the subducting slab. No other earthquake of M7.0 or greater has been recorded in the immediate vicinity since 1 January 2000.

Intermediate-depth seismicity in this arc commonly arises from dehydration embrittlement and phase transitions within the descending oceanic lithosphere. The 2013 event is consistent with this mechanism, occurring well below the seismogenic megathrust and therefore posing a lower tsunami threat than comparable shallow events. Regional seismic networks recorded aftershocks distributed along the slab, confirming the intraslab character of the rupture.

The broader geological history of the Kuril–Kamchatka arc reflects continuous subduction since at least the Late Cretaceous, producing a well-developed volcanic front and back-arc basin. Historical records document recurrent large earthquakes, including great events in 1952 and 1963, underscoring the persistent seismic hazard along the entire margin.

References

USGS Earthquake Catalog (event parameters)
Geological Survey of Japan (arc tectonics summary)