Are the source models of the M 7.1 1908 Messina Straits earthquake reliable? Insights from a novel inversion and a sensitivity analysis of levelling data

Abstract

For decades, many authors have attempted to define the location, geometry and kinematics of the causative fault for the 1908 December 28, M 7.1 earthquake that struck the Messina Straits between Sicily and Calabria (southern Italy). The coseismic displacement caused a predominant downwarping of the Straits and small land uplift away from it, which were documented by levelling surveys performed 1 yr before and immediately after the earthquake. Most of the source models based on inversion of levelling data suggested that the earthquake was caused by a low angle, east-dipping blind normal fault, whose upper projection intersects the Earth surface on the Sicilian (west) side of the Messina Straits. An alternative interpretation holds that the causative fault is one of the high-angle, west-dipping faults located in southern Calabria, on the eastern side of the Straits, and may in large part coincide with the mapped Armo Fault. Here, we critically review the levelling data with the aim of defining both their usefulness and limits in modelling the seismogenic fault. We demonstrate that the levelling data alone are not capable of discriminating between the two oppositely dipping fault models, and thus their role as a keystone for modellers is untenable. However, new morphotectonic and geodetic data indicate that the Armo Fault has very recent activity and is accumulating strain. The surface observations, together with appraisal of macroseismic intensity distribution, available seismic tomography and marine geophysical evidence, lends credit to the hypothesis that the Armo and possibly the S. Eufemia faults are part of a major crustal structure that slipped during the 1908 earthquake.

Tectonic expression of an active slab tear from high‐resolution seismic and bathymetric data offshore Sicily (Ionian Sea)

“…These faults pose a significant seismic and tsunami hazard in this region where nearly 200,000 deaths have occurred over the past five centuries [ Jenny et al ., ]. However, the sources of many of these earthquakes and tsunamis remain unknown or disputed to this day [ Piatanesi and Tinti , ; Gutscher et al ., ; Argnani et al ., ; Aloisi et al ., ], with some workers arguing for a contribution from submarine landslides in some cases [ Billi et al ., , ]. There is no consensus on the surface expression of the STEP fault and its trace through eastern and northern Sicily is uncertain (Figure ) [ Orecchio et al ., ].…”

Aeromagnetic investigation of southern Calabria and the Messina Straits (Italy): Tracking seismogenic sources of 1783 and 1908 earthquakes

“…A lively debate on causative fault characteristics also exists for the 1908 and 1783 Calabro‐Sicilian earthquakes, two of the most destructive Italian seismic events ever. The 28 December 1908 M 7.1 earthquake hit both NE Sicily and SW Calabria around the Messina Straits causing 80,000 casualties mostly in the Messina and Reggio Calabria towns [e.g., Aloisi et al , , Figure 1]. The 1783 seismic sequence gave five M ~ 6–7 main shocks between 5 February and 28 March, which devastated the whole south Calabria, and yielded several surface effects (landslides and lake damming) among which a remarkable 18 km long surface fracture, accurately described in 1784 by Déodat de Dolomieu in one of the first paleoseismological reports of history [e.g., Jacques et al , ].…”

“…Conversely, another set of models considers NW dipping, high‐angle normal faults on mainland Calabria as causative sources of the seism [ Schick , ; Mulargia and Boschi , ; Ghisetti , , ; Bottari et al , ; Westaway , ; Tortorici et al , ; Bottari , ]. Recently gathered field evidence along with a reevaluation of geodetic and seismic data have been used by Aloisi et al [, ] to identify the Armo fault (ARF), a NW dipping normal fault exposed in SW Calabria, as source of the 1908 event (Figure ).…”

“…Digital elevation model and main tectonic features of southern Calabria and northeastern Sicily. Main Pliocene‐Quaternary extensional faults (red) are from Catalano et al [] and Aloisi et al []; seismogenic source boxes (orange) are from Database of Individual Seismogenic Sources [ DISS Working Group , ]. The locations of the main shocks of the 1908 and 1783 earthquakes are from Schick [] and Jacques et al [], respectively.…”

A “Geodetic Gap” in the Calabrian Arc: Evidence for a Locked Subduction Megathrust?

“…The digital elevation model (DEM) is fromRyan et al (2009). (b) NW (fromAloisi et al, 2012;Galli & Bosi, 2002, 2003Galli & Peronace, 2015;Galli & Scionti, 2006;Minelli et al, 2016), SE (from DISS Working Group, 2015;Tiberti et al, 2017) dipping active fault data sets and subduction interface geometry. (c) Three-dimensional view of the broader study area is toward SSE.…”