A Multiscale Application of the Unified Scaling Law for Earthquakes in the Central Mediterranean Area and Alpine Region
Résumé
We study the parameters A, B, and C of the Unified Scaling Law for Earthquakes (USLE) in the Central Mediterranean area and Alpine region on the basis of a variable space and time scale approach. We make use of regional and local earthquake catalogues. Accordingly, we investigate three different scales: the scale of the Central Mediterranean and Alpine region spanning different geological domains, the scale of the Alps focusing on a single geological entity, and the scale of an active fault system at the junction between the southeastern Alps and the external Dinarides in Northeastern Italy and Western Slovenia. Maps based on the varied time and location scales are compared with each other. The observed temporal variability of the A, B, C coefficients indicates significant changes of seismic activity at the time scales of a few decades. Therefore, it is highly recommended to use all the data available for long-term seismic hazard assessment in conjunction with a real-time monitoring of these characteristics for possible evaluation of time-dependent risk at the intermediate-term scales of a few years. The confirmed fractal nature of earthquakes and their distribution in space implies that the traditional estimations of seismic hazard for cities and urban agglomerations are usually underestimated. The degree of underestimation by traditional methods of seismic risk at a city is illustrated by providing estimates of hazard and related personal hazard, which are oversimplified examples of seismic risk assessment accounting for fractal properties of earthquakes in the major cities of the Central Mediterranean and Alpine region.