Seismic Swarm PS20061115.1: Kuril Islands Earthquake Sequence of November 2006

The Kuril Islands form a volcanic arc extending from Hokkaido to the Kamchatka Peninsula, marking the convergent boundary where the Pacific Plate subducts beneath the Okhotsk Plate at rates of approximately 8–9 cm per year. This tectonic setting produces frequent megathrust earthquakes and associated seismic swarms, reflecting episodic strain release along the subduction interface and within the overriding plate.

Seismic swarm PS20061115.1 began at 11:13 on 15 November 2006 and concluded at 05:00 on 18 November 2006, spanning 65 hours and 47 minutes. During this interval, 53 earthquakes were recorded, with the great majority nucleating at depths of 10 km. The sequence opened with a magnitude 8.3 mainshock at 11:14, followed by an energetic aftershock sequence that included multiple events of magnitude 6.0–6.7 within the first hours. Later activity tapered, featuring isolated magnitude 5.0–5.3 shocks through 18 November.

The swarm exhibited classic characteristics of a megathrust aftershock sequence: an initial high-magnitude trigger, rapid decay of event rate, and spatial clustering near the mainshock epicenter. Depths remained shallow (mostly ≤10 km) except for a few events reaching 30–40 km, consistent with rupture on or near the plate interface.

Since 1 January 2000, five comparable swarms have occurred in the Kuril region. Earlier episodes took place in 2003 (one swarm) and 2005 (one swarm), with three additional swarms recorded in 2006. This clustering underscores elevated seismic productivity along the central Kuril segment during the mid-2000s.

Two notable large earthquakes have occurred nearby since 2000. A magnitude 8.1 event struck on 13 January 2007, centered 91 km from the swarm locus, while a magnitude 7.4 shock occurred east of the islands on 15 January 2009, only 14 km from the swarm center. Both events further illustrate the persistent seismic hazard of the subduction zone.

The November 2006 swarm contributed to the regional strain budget following the great 2006 mainshock and preceded the 2007 event, highlighting the interconnected nature of rupture segments along the Kuril trench. Continued monitoring remains essential for assessing future megathrust potential in this highly active arc.

References
SeismoSight internal swarm catalogue (PS20061115.1 parameters and historical swarm statistics)
USGS Earthquake Catalog (regional magnitude ≥7.0 events since 2000)
Global CMT Project (focal mechanisms and depths for 2006–2009 Kuril events)