Low-magnitude seismic activity between the Kamchatka July 20 and July 29, 2025, earthquakes. Spatio-temporal evolution recovered using waveform cross-correlation

TL;DR

This study uses waveform cross-correlation on IMS data to detect smaller seismic events, revealing detailed spatio-temporal seismic activity before the 2025 Kamchatka earthquake, enhancing understanding of earthquake preparation processes.

Contribution

It introduces a WCC-based detection method applied to IMS data to recover smaller seismic events, improving the analysis of seismicity evolution prior to major earthquakes.

Findings

Smaller seismic events were detected in zones with no prior located sources.

The method revealed detailed seismic activity leading up to the July 29, 2025 earthquake.

Enhanced detection capabilities can improve understanding of earthquake preparation processes.

Abstract

The M8.8 Kamchatka earthquake on July 29, 2025 was one of the largest in the first quarter of the 21st century. It deserves a thorough analysis including the preparation process. A smaller M7.4 earthquake occurred on July 20 with its epicenter within the confidence ellipse for the July 29 event. The aftershock sequence of the July 20 earthquake and the evolution of seismicity within the Kamchatka Peninsula region during 10 days period before the July 29 event may provide important information on the earthquake preparation and initiation processes. The CTBTO's International Monitoring System is one of the most sensitive global seismic networks comprising high-resolution array stations with enhanced sensitivity relative to three-component stations at the same locations. The International Data Centre of the CTBTO processes IMS data automatically and interactively to create a Reviewed Event Bulletin (REB), which serves as a source of information for the International Seismological Centre. Waveform cross-correlation (WCC) allows for additional detection capabilities to the IMS data and IDC processing when repeated seismicity is analyzed. The aftershock sequence of the July 20 earthquake is recovered using the WCC-based detection and phase association techniques as applied to the IMS data in order to accurately describe the spatio-temporal evolution of seismic process just before the July 29 event. With the reduced detection threshold, smaller events are found in the zones where the REB has no located sources. This finding opens up the possibility for a more detailed study of seismic and mechanical processes before the July 29 mainshock.