Seismic Dynamics in Advance of and After the Largest Earthquakes, 1985-2020
Résumé
For each of all 156 largest earthquakes (M ≥ 7.5, depth < 300 km) worldwide in 1985-2020, we characterize the dynamics of the foreshock and aftershock sequences nearby their epicentres in terms of (1) seismic rate, N; (2) the Benioff strain release, Σ; (3) inter-event time, τ; (4) the Utsu estimate of the Gutenberg-Richter constant, b; and (5) the control parameter, η, of the Unified scaling law for earthquakes (USLE), i.e. a generalization of the Gutenberg-Richter relationship accounting for naturally fractal distribution of earthquake loci. Such a multi-parametric description of earthquake activity provides the quantitative evidence for better understanding seismic process in advance and after catastrophic phase transitions in dynamics of the hierarchically organized system of lithospheric blocks-and-faults. The study confirms the existence of the spatiotemporal patterns and different regimes of regional seismic energy release; in particular, the stability of the USLE control parameter levels that are interrupted by mid- or even short-term bursts of activity associated with major catastrophic events, as well as variability of seismic activity in advance and after the main shocks. Statistically, the results of the uniform analysis of series of the moderate earthquakes at locations of 97 thrust, 21 normal, and 38 strike-slip earthquakes do not support the presence of universality in seismic energy release, provide fundamental constraints on modelling realistic earthquake sequences by geophysicists, and, therefore, can be used to improve local time-Dependent Assessment of Seismic Hazard.