Aftershock Features of 6.6 Vilyuchinsk Earthquake on April 03, 2023 (Kamchatka)

The article analyzes the aftershock activation observed in the south of Avacha Bay (Kamchatka) as a result of the Vilyuchinsk earthquake on April 03, 2023 M = 6.6 (φ = 52.58°N, λ = 158.78°E, h = 105 km). The total duration of this activation is estimated at 450 days. The linear dimensions of the studied area are limited horizontally by an ellipse with axes a = 34 km (azimuth α = 117°), b = 22 km, in the depth range h = 95–105 km. The orientation of the ellipse corresponds to one of the two nodal planes of the main event mechanism. Two stages in the attenuation of the aftershock flow were distinguished: 1) in accordance with the Omori law and with a duration of 8.4 days; 2) with exponential (τ = 140 days) attenuation until reaching the background seismicity level. In terms of the number of earthquakes, the two stages are comparable. The phase of regime change corresponds in time to the interval between the strongest aftershocks — April 11, 2023 5.5 and April 21, 2023 4.9. It is shown that these two earthquakes are a doublet based on the high correlation of waveforms and the proximity of their epicenters. A sharp postseismic decrease in the slope of the Gutenberg-Richter graph b by 1.5 times after the strongest aftershock on April 11, 2023 5.5 is shown, with subsequent recovery throughout the exponential aftershock regime. No variations were detected in the b parameter in the Omori regime.