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 appreciab le part of research in modem 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 part icularly relevant the description of the asthenospheric low-velocity channe l, 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 t he European area predicts the existence of almost aseismic lithospheric roo ts. These roots are located in correspondence of most of the orogenic belts and interrupt the asthenosphere low velocity channel that has been identif ied by Beno Gutenberg in 1948. The model of the European upper mantle, prop osed for the first time in 1979 and subsequently refined, has stimulated a considerable amount of research, which has nicely confirmed the major innov ative features of the early model. At present, the subduction of the lithos phere at continent-continent collisions, supported not only by seismologica l data, is a widely accepted concept within the community of Earth scientis ts, even if it contradicts one of the basic dogmas of the original formulat ion of plate tectonics. The proposed model for the Alpine -Apennines area s upplies a new and unifying framework for the interpretation of the Quaterna ry magmatism, at present generally accepted by petrologists and geochemists . The theoretical basis for the Gutenberg's surface-wave magnitude calibratio n function has been supplied by the use of complete synthetic seismograms, and thus it has been possible to formulate the theoretical Ms depth correct ion. The introduction of the depth correction for Ms enables the computatio n of surface wave magnitude for all earthquakes, regardless of their focal depth. This is especially important for the quantification of subcrustal hi storical earthquakes, for which the seismic moment may be difficult to esti mate from recordings of early mechanical seismographs. The new Ms calibrati ng function yield both distance- and depth-independent magnitude estimates. The analysis of the global seismicity, using the seismotectonic regionaliza tion in subduction zones, mid oceanic ridge zones, island arcs, shows that a single Gutenberg- Richter (GR) relation is not universally applicable and that a multiscale seismicity model can reconcile two apparently conflictin g paradigms: the Self-Organized Criticality mechanism and the Characteristi c Earthquake concept. The multiscale representation has been applied to Ita ly, where the zones at the space scale of 400-500 kin quite well reproduce the shapes of the regions used to apply the, globally tested, CN intermedia te term earthquake prediction algorithm. (C) 2001 Elsevier Science B.V. All rights reserved.