Seismic Swarm PS20240817.1: Analysis of Recent Activity Near Petropavlovsk-Kamchatsky

A seismic swarm designated PS20240817.1 occurred 99 km east-southeast of Petropavlovsk-Kamchatsky, Russia, on 17 August 2024. The sequence began at 19:10 and concluded at 22:47, lasting 3 hours and 37 minutes. During this interval, five earthquakes were recorded with the following parameters:

• 19:10:26 UTC, magnitude 7.0, depth 29 km
• 19:21:39 UTC, magnitude 5.0, depth 35 km
• 19:40:01 UTC, magnitude 5.1, depth 57 km
• 22:27:08 UTC, magnitude 5.2, depth 35 km
• 22:47:37 UTC, magnitude 4.2, depth 43 km

The largest event reached magnitude 7.0 and was located only 5 km from the swarm center. Depths ranged from 29 km to 57 km, consistent with intermediate-depth seismicity in the region.

Regional Geological Setting

The Kamchatka Peninsula lies within the Pacific Ring of Fire at the convergent boundary between the Pacific Plate and the Okhotsk Plate. Subduction along the Kuril-Kamchatka Trench generates intense seismic and volcanic activity. The downgoing slab produces earthquakes at varying depths, with the Wadati-Benioff zone extending to several hundred kilometers. Crustal deformation and frequent moderate-to-large events characterize the area east of Petropavlovsk-Kamchatsky.

Historical Context and Prior Swarms

Since 1 January 2000, only three seismic swarms have been documented in the immediate vicinity. These occurred in 2001 (one event) and 2013 (two events). The 2024 swarm represents the fourth such episode in the catalog.

Strong earthquakes since 2000 have repeatedly affected the same sector. Notable events include an M 8.8 earthquake on 29 July 2025 centered 44 km from the swarm center, an M 7.4 on 20 July 2025 (39 km distant), an M 7.8 on 18 September 2025 (50 km distant), an M 7.4 on 13 September 2025 (35 km distant), and an M 7.0 on 17 August 2024 (5 km distant). These occurrences illustrate the persistent high seismic hazard along this segment of the subduction interface.

Swarm Characteristics and Implications

The tight temporal clustering of five events within less than four hours, combined with a magnitude range from 4.2 to 7.0, defines a typical swarm pattern for the region. Depths between 29 km and 57 km align with expected seismicity on or near the subducting slab. Such sequences often occur in the aftermath of larger mainshocks or as independent episodes driven by stress transfer within the slab.

Continued monitoring remains essential given the proximity to populated areas and infrastructure along the southeastern Kamchatka coast.

References

USGS Earthquake Catalog
Global CMT Project
Kamchatka Branch of Geophysical Survey RAS