In tectonically active areas, such as the Italian peninsula, identifying the faults responsible for the strong earthquakes is often challenging, especially when they occurred in historical times. In such cases, geoscientists need to integrate all the available information from historical reports (Guidoboni et al., 2019), surface geology and geophysics to constrain the seismogenic faults. This is the case of the southern Calabrian arc, in the area between the Catanzaro and the Messina Straits, that after a paroxysmal activity with six Mw 6.5-7 events in 125 years from 1783 to 1908 and other two Mw 6 events in 1791 and 1894, has only released small shocks with a few minor isolated sequences (Mw<4.5). Despite the strongest Calabria earthquakes have been largely studied, robust and commonly accepted seismic sources are still missing. To contribute to the debate, we reviewed and updated, according to EMS scale (Grüntal, 1998), the macroseismic fields of the five main events of the 1783 Calabria sequence (5, 6 and 7 February, 1 and 28 March, Mw 5.9 to 7.1), two other destructive events located in the same epicentral area of the 1783 sequence (1791, Mw 6.1 and 1894, Mw 6.1), along with the Messina Strait 1908 earthquake (Mw 7.1). The new macroseismic fields were analyzed using a series of MATLAB algorithms to identify 1) the unitarity of the field or its partitioning in sub-sources and 2) the field and subfields main elongation. By using a collection of earthquake scale laws (e.g., Wells & Coppersmith, 1994) from literature and calculating the equivalent magnitude of seismic events (Gasperini et al., 2010), average source parameters (Length, Width, Area), with their range of variability, were evaluated. From these data, the MATLAB algorithm processes and produces an elliptical map-view representation of the source geometry for each earthquake analyzed. We also elaborated an updated map of the major late Quaternary-Pliocene extensional fault systems of the Calabrian Arc and a new catalogue of coseismic effects of the main events. We compared the computed source parameters with the geometry and dimensions of the mapped faults and advanced new alternative hypotheses on the earthquake/fault associations with respect to the models available in the literature, and in the case of multiple proposed solutions, we helped identify a better-constrained source. In particular, we have suggested new seismotectonic hypotheses for the 1908 earthquake and the 28 March shock of the 1783 sequence, based on the new shape of their macroseismic fields and comparing our results with the clues obtained studying the seismogenic behaviour of faults from recent instrumental sequences in central Italy. Finally, we reconstruct the time-space evolution of the seismicity along an ideal transect across the axis of southern Calabria during the last fifth centuries.
Revision and analysis of macroseismic data of some strong Calabria earthquakes (Italy) for seismotectonic purposes
Andrenacci C.;Bello S.;de Nardis R.;Pietrolungo F.;Lavecchia G.
2023-01-01
Abstract
In tectonically active areas, such as the Italian peninsula, identifying the faults responsible for the strong earthquakes is often challenging, especially when they occurred in historical times. In such cases, geoscientists need to integrate all the available information from historical reports (Guidoboni et al., 2019), surface geology and geophysics to constrain the seismogenic faults. This is the case of the southern Calabrian arc, in the area between the Catanzaro and the Messina Straits, that after a paroxysmal activity with six Mw 6.5-7 events in 125 years from 1783 to 1908 and other two Mw 6 events in 1791 and 1894, has only released small shocks with a few minor isolated sequences (Mw<4.5). Despite the strongest Calabria earthquakes have been largely studied, robust and commonly accepted seismic sources are still missing. To contribute to the debate, we reviewed and updated, according to EMS scale (Grüntal, 1998), the macroseismic fields of the five main events of the 1783 Calabria sequence (5, 6 and 7 February, 1 and 28 March, Mw 5.9 to 7.1), two other destructive events located in the same epicentral area of the 1783 sequence (1791, Mw 6.1 and 1894, Mw 6.1), along with the Messina Strait 1908 earthquake (Mw 7.1). The new macroseismic fields were analyzed using a series of MATLAB algorithms to identify 1) the unitarity of the field or its partitioning in sub-sources and 2) the field and subfields main elongation. By using a collection of earthquake scale laws (e.g., Wells & Coppersmith, 1994) from literature and calculating the equivalent magnitude of seismic events (Gasperini et al., 2010), average source parameters (Length, Width, Area), with their range of variability, were evaluated. From these data, the MATLAB algorithm processes and produces an elliptical map-view representation of the source geometry for each earthquake analyzed. We also elaborated an updated map of the major late Quaternary-Pliocene extensional fault systems of the Calabrian Arc and a new catalogue of coseismic effects of the main events. We compared the computed source parameters with the geometry and dimensions of the mapped faults and advanced new alternative hypotheses on the earthquake/fault associations with respect to the models available in the literature, and in the case of multiple proposed solutions, we helped identify a better-constrained source. In particular, we have suggested new seismotectonic hypotheses for the 1908 earthquake and the 28 March shock of the 1783 sequence, based on the new shape of their macroseismic fields and comparing our results with the clues obtained studying the seismogenic behaviour of faults from recent instrumental sequences in central Italy. Finally, we reconstruct the time-space evolution of the seismicity along an ideal transect across the axis of southern Calabria during the last fifth centuries.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
