To gain new insights into patterns of earthquake activity in the Northwest Pacific, we study regional variability of the unified scaling law for Earthquakes (USLE) coefficients in separate seismic focal zones within the Kuril–Kamchatka Slab and the western segment of the Aleutian Arc. USLE states that the expected annual number of magnitude M or larger earthquakes in an area of linear dimension L, N(M, L) follows the relationship log10N(M, L) = A + B(6.5 − M) + C × log10L, within the magnitude range [M−, M+] where A, B, and C are empirical constants. USLE complements the a- and b-values of the Gutenberg-Richter relationship with C, an estimate of the fractal dimension of epicenters at a given site. USLE allows for realistic rescaling of seismic hazard to the size of exposure at risk, and its control parameter η = 10B×(6.5−M) × LC tunes regional distribution of inter-event times τ. We have analyzed over 25,000 shallow and 4,200 intermediate-depth earthquakes in the five distinct three-dimensional structures of the Northwest Pacific—four within the Kuril–Kamchatka Slab and one in the western segment of the Aleutian Arc—using data from the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences for the period 1996–2022. We found that (i) the Kuril–South Kamchatka Slab and North Kamchatka Slab zones, at shallow depths, show the highest earthquake rates and relatively high values of the fractal dimension C=1.45 and 1.49, respectively; (ii) the fractal dimension C=1.34 in the Commander Islands zone; (iii) the Kuril–South Kamchatka Slab and North Kamchatka Slab, at intermediate-depths, are characterized with C=1.46 and 1.43, respectively. The zone-specific USLE coefficients compared to those derived for the entire catalogs of shallow and intermediate-depth earthquakes underscore the importance of localized seismic hazard assessments. The regional combinations of the USLE coefficients display complex correlation patterns of different types in preselected volumes of seismic genesis in the hierarchically self-organized lithosphere of the Earth. The stable levels of the moving average trends of the USLE control parameter η for all three shallow and two intermediate-depth sub-regions suggest consistent seismic behavior over the time considered.

The seismicity of the Northwest Pacific from the viewpoint of unified scaling law for earthquakes

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2026年6月22日

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Anastasia Nekrasova,
Vladimir Kossobokov

摘要

To gain new insights into patterns of earthquake activity in the Northwest Pacific, we study regional variability of the unified scaling law for Earthquakes (USLE) coefficients in separate seismic focal zones within the Kuril–Kamchatka Slab and the western segment of the Aleutian Arc. USLE states that the expected annual number of magnitude M or larger earthquakes in an area of linear dimension L, N(M, L) follows the relationship log₁₀N(M, L) = A + B(6.5 − M) + C × log₁₀L, within the magnitude range [M−, M+] where A, B, and C are empirical constants. USLE complements the a- and b-values of the Gutenberg-Richter relationship with C, an estimate of the fractal dimension of epicenters at a given site. USLE allows for realistic rescaling of seismic hazard to the size of exposure at risk, and its control parameter η = 10^B×(6.5−M) × L^C tunes regional distribution of inter-event times τ. We have analyzed over 25,000 shallow and 4,200 intermediate-depth earthquakes in the five distinct three-dimensional structures of the Northwest Pacific—four within the Kuril–Kamchatka Slab and one in the western segment of the Aleutian Arc—using data from the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences for the period 1996–2022. We found that (i) the Kuril–South Kamchatka Slab and North Kamchatka Slab zones, at shallow depths, show the highest earthquake rates and relatively high values of the fractal dimension C=1.45 and 1.49, respectively; (ii) the fractal dimension C=1.34 in the Commander Islands zone; (iii) the Kuril–South Kamchatka Slab and North Kamchatka Slab, at intermediate-depths, are characterized with C=1.46 and 1.43, respectively. The zone-specific USLE coefficients compared to those derived for the entire catalogs of shallow and intermediate-depth earthquakes underscore the importance of localized seismic hazard assessments. The regional combinations of the USLE coefficients display complex correlation patterns of different types in preselected volumes of seismic genesis in the hierarchically self-organized lithosphere of the Earth. The stable levels of the moving average trends of the USLE control parameter η for all three shallow and two intermediate-depth sub-regions suggest consistent seismic behavior over the time considered.