Beno Gutenberg contribution to seismic hazard assessment and recent progress in the European-Mediterranean region

The fundamental work of Beno Gutenberg has inspired and guided an appreciable part of research in modern seismology, both from the experimental and the theoretical point of view. Among the several topics of seismology that have benefited from the fundamental contribution of Gutenberg, we consider particularly relevant the description of the asthenospheric low-velocity channel, the definition of the surface waves magnitude and the Gutenberg–Richter law, since they are pivotal tools for seismic hazard assessment. The quite revolutionary model for the lithosphere–asthenosphere system in the European area predicts the existence of almost aseismic lithospheric roots. These roots are located in correspondence of most of the orogenic belts and interrupt the asthenosphere low velocity channel that has been identified by Beno Gutenberg in 1948. The model of the European upper mantle, proposed for the first time in 1979 and subsequently refined, has stimulated a considerable amount of research, which has nicely confirmed the major innovative features of the early model. At present, the subduction of the lithosphere at continent–continent collisions, supported not only by seismological data, is a widely accepted concept within the community of Earth scientists, even if it contradicts one of the basic dogmas of the original formulation of plate tectonics. The proposed model for the Alpine–Apennines area supplies a new and unifying framework for the interpretation of the Quaternary magmatism, at present generally accepted by petrologists and geochemists. The theoretical basis for the Gutenberg’s surface-wave magnitude calibration function has been supplied by the use of complete synthetic seismograms, and thus it has been possible to formulate the theoretical MS depth correction. The introduction of the depth correction for MS enables the computation of surface wave magnitude for all earthquakes, regardless of their focal depth. This is especially important for the quantification of subcrustal historical earthquakes, for which the seismic moment may be difficult to estimate from recordings of early mechanical seismographs. The new MS calibrating function yield both distance- and depth-independent magnitude estimates. The analysis of the global seismicity, using the seismotectonic regionalization in subduction zones, mid oceanic ridge zones, island arcs, shows that a single Gutenberg–Richter ŽGR. relation is not universally applicable and that a multiscale seismicity model can reconcile two apparently conflicting paradigms: the Self-Organized Criticality mechanism and the Characteristic Earthquake concept. The multiscale representation has been applied to Italy, where the zones at the space scale of 400–500 km quite well reproduce the shapes of the regions used to apply the, globally tested, CN intermediate term earthquake prediction algorithm. q2001 Elsevier Science B.V. All rights reserved.