Possible Tectonic Styles of Future Earthquakes from Seismic Moment Tensors of Previous Events: An Example in Italy

During the new elaboration of the hazard model for Italy, a study on the indications we may collect concerning the tectonic style of future earthquakes and seismic ruptures has been done. All available seismic moment tensors for relevant seismic events (Mw starting from 4.5) of the last 100 yrs, first arrival focal mechanisms for less recent earthquakes and geological data on activated faults have been collected in a unique database, that includes thousands of data all over the Italian peninsula. After several summation trials, changing parameters, seismogenic thicknesses and taking into account the characteristics of seismicity distribution, a unique computation procedure has been applied to each of the 50 seismic zones of the new seismogenic zoning for Italy. The results for several seismic zones are very stable, for instance, in the southern Apennines we expect mostly extensional earthquakes, although in the outer part of the chain strike-slip events are possible. In the northern part of the Apennines, we also expect different, opposite tectonic styles for different hypocentral depths. In several zones characterised by a low seismic moment release, the next possible tectonic style of future earthquakes is less clear and it has been represented using different combination (total or partial) of random sources. A comparison of our results with recent earthquake moment tensors show a good agreement with the computed possible tectonic style.