A new high‐quality waveform inversion focal mechanism database of the Calabrian Arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions. The new database has then been used for computation of posterior density distributions of stress tensor components by a Bayesian method never applied in south Italy before the present study. The application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated. Our results well constrain the extensional domain of Calabrian Arc and the compressional one of the southernmost Tyrrhenian Sea. In addition, previously undetected transcurrent regimes have been identified in the Ionian offshore. The new information released here will furnish useful tools and constraints for future geodynamic investigations.
We analyze the seismicity of southern Calabria, the most active area of Italy from the seismic point of view, and compare it with geodetic data available from literature. Our analysis focuses both on the strongest earthquakes of the last centuries reported in the Italian historical seismic catalog and on seismicity recorded in the last decades by instrumental networks. The data highlight that strong shallow seismicity of southern Calabria, imputed to normal faulting by previous investigators, corresponds to low values of local, geodetic horizontal strain rate. This situation is quite different from that observed along the Apennines from central Italy to northern Calabria, where normalfaulting strong earthquake activity corresponds to relatively large values of extensional strain rate. On the other hand, the strong earthquake activity of southern Calabria corresponds to marked variation of vertical displacement rates detected from west to east in the same area. We frame these evidences into the regional geodynamic model assuming the coexistence of Africa-Europe NNW-trending plate convergence and SEward residual rollback of the Ionian lithospheric slab subducting underneath the Tyrrhenian-Calabria unit. Taking also benefit from the recently found relationship between the two strongest earthquakes of the 20th century in Italy (the southern Calabria earthquakes of 1905 and 1908 of magnitude 7.5 and 7.1, respectively), we propose that instabilities of the upper bending part of the subduction slab may perturb shallow normal faults in the overriding plate and concur to shallow seismicity of southern Calabria jointly with the dynamics of differential vertical motion marked by geodetic data. The opposite action of lithosphere convergence and rollback may justify low values of horizontal strain rate in the low coupling scenario of the Ionian and Tyrrhenian-Calabria units.
ius.mi.ingv.it/CPTI15-DBMI15/) indicates that major earthquake effects in Rometta were frequently greater compared to nearby locations thus leading us to investigate the presence of heterogeneous geological settings potentially able to produce significantly differentiated seismic responses.A quick estimate of the surface geology effects on seismic motion is provided by the Horizontal to Verti-
On December 28 th 1908 the city of Messina was destroyed by one of the most catastrophic Italian earthquakes of the last centuries (M w =7.1, I = XI) which caused more than 60000 deaths and destruction in many localities of Sicily and Calabria. In this study we present the results of more than 100 seismic ambient noise measurements carried out in the framework of the first massive seismic site response survey performed in the city of Messina. Starting from geological information and historical reports reconstructing the damage scenario of the 1908 event, we have identified several sites particularly interesting for seismic response investigations. This extensive survey allowed us to evaluate the fundamental resonance frequency for each investigated site and to identify the areas prone to site amplification. Measurements have been performed by using 3-component velocimeter, Micromed Tromino, and the collected dataset has been processed by applying the Horizontal-to-Vertical Spectral Ratio technique. For each investigated site we provide the fundamental resonance frequency and a preliminary information on the metamorphic bedrock depth. The massive dataset collected and the results obtained will be useful for the seismic microzonation of the urban territory of Messina.
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