|EGS Beno Gutenberg Medallist - 2000|
for his fundamental contributions to the dynamics of the lithosphere-asthenosphere system, the construction of synthetic seismograms and statistical aspects of seismicity on a global scale
Prof. Panza, professor of seismology at the University of Trieste and head of the ICTP Structure and Non-Linear Dynamics of the Earth (SAND) programme in Trieste, was honoured for his scholarly achievements in earthquake modelling and for advancing international co-operation in earthquake analysis and prediction. The award, established in 1996, is named in honour of the great German-born seismologist who is credited with discovering the Earth's core in 1913 at the Geophysical Institute of Goettingen, and in helping to explain the physics of continental drift,
Prof. Panza has given an outstanding contribution to the study of the asthenospheric low-velocity channel, the accurate determination of surface waves magnitude and the multiscale use of the Gutenberg-Richter law.
Within the framework of a very large international co-operation Prof. Panza has formulated quite a revolutionary model for the lithosphere-asthenosphere system in the European area, which predicts the existence of almost aseismic lithospheric roots. These roots are located in correspondence with most of the orogenic belts and interrupt the asthenosphere low velocity channel, identified for the first time by Beno Gutenberg, in 1948. The model proposed by G.F. Panza for the first time in 1980 and subsequently refined, has stimulated a considerable amount of research at an international level, which has nicely confirmed the major 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, for the interpretation of the Quaternary magmatism, a new and unifying framework, generally accepted by petrologists and geochemists.
The construction of complete synthetic seismograms to be used for the realistic modeling of the Earth structure and of seismic sources has supplied the numerical tool which has permitted to give a theoretical basis for the Gutenberg's surface-wave magnitude (MS) calibration function, and to formulate, for the first time, the theoretical MS depth correction. The comparison of experimental data with the theoretical amplitude-focal depth relationships obtained using two different standard Earth models, clearly gives preference to the AK135F global model over PREM-C. The introduction of the depth correction for MS enables the computation of surface wave magnitude for all earthquakes, irregardless of their focal depth. This is especially important for the quantification of deep 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.
Particularly relevant is the application of complete synthetic seismograms to the study of seismic hazard by means of a physically rooted definition of local site effects, which takes into account the entire propagation process from the source to the target site. This is the main focus of an ongoing project on the Realistic Modelling of Seismic Input for Megacities and Large Urban Areas, supported by UNESCO-IUGS-IGCP and centered at the Abdus Salam International Centre for Theoretical Physics, in Trieste.
In connection with hazard estimation, by analysing the global seismicity G.F. Panza has shown that a single Gutenberg-Richter 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.