The 2008 Deep Earthquake Near Mil’kovo, Russia

On 24 November 2008 at 09:02 local time, a magnitude 7.3 earthquake struck 284 km west-southwest of Mil’kovo in Russia’s Kamchatka Peninsula. The event originated at a focal depth of 492.3 km, placing it well within the mantle portion of the subducting slab. No surface damage or casualties were reported, consistent with the extreme depth that dissipates most seismic energy before it reaches the surface. Kamchatka occupies the northern segment of the Kuril-Kamchatka subduction zone, where the Pacific Plate descends beneath the Okhotsk Plate at roughly 7–8 cm per year. This convergence produces both shallow megathrust earthquakes and a pronounced Wadati-Benioff zone of intermediate- and deep-focus seismicity. Earthquakes exceeding 300 km depth occur regularly along the arc, generated by dehydration embrittlement and phase transitions within the cold slab core. The 2008 event belongs to this deep population. Its epicentral location aligns with the projected continuation of the subducting Pacific slab beneath central Kamchatka. Focal mechanisms for comparable events typically show down-dip tension or compression, reflecting stresses accumulated as the slab encounters resistance at the 660 km discontinuity. Kamchatka’s seismic history is dominated by great subduction-zone earthquakes. Notable examples include the 1952 M 9.0 event off the peninsula’s east coast and the 1737 M ~9.0 earthquake that generated a trans-Pacific tsunami. Deep-focus activity has also been documented, with several M 7+ events recorded since instrumental monitoring began in the early twentieth century. Since 2000, the M 7.3 of 24 November 2008 remains the only earthquake of that magnitude or larger within the immediate region. Modern seismic networks operated by the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences and global agencies continue to track slab seismicity. These observations refine models of slab geometry and thermal structure, improving long-term hazard assessments for the sparsely populated but volcanically active peninsula.

References

USGS Earthquake Catalog (event page for 2008-11-24 M 7.3 Kamchatka) Global CMT Catalog Russian Academy of Sciences Geophysical Survey, Kamchatka Branch annual reports