Description: Pino et al. (2021, hereinafter PIN2021) commented on the paper by Barreca et al. (2021, hereinafter B2021) titled: “The Strait of Messina: Seismotectonics and the source of the 1908 earthquake”, which was published in the journal Earth-Sciences Reviews in May 2021. PIN2021 argued both on the “source model of the 1908 EQ”, as proposed by B2021, and on the existence of the newly discovered causative fault (i.e. the B2021W-Fault). Based on “objective reading of achieved results along with other existing geophysical information…“, PIN2021 conclude: “the source mechanism for the 1908 EQ is based on incorrect assumptions, while their results are internally inconsistent and with other independent observations”. According to PIN2021, the inconsistency of the proposed “source mechanism”, which foresaw the possibility of an aseismic slip on a low-angle discontinuity preceding the 1908 mainshock (see B2021), would be mainly demonstrated by “the lack of significant variations of the relative sea level in the Messina harbor area, in the time period relevant for the levelling data (1907-1908) ……. and at least for the decade preceding the event”. Moreover, to demonstrate that the deformation is mostly coseismic, PIN2021 proposes a sea level diagram based on unreliable data from the Messina tide gauge. In this paper, we demonstrate that the comments by PIN2021 are unfounded. We strongly confirm the scientific validity of the model proposed in B2021.

Description: Published

Description: 103866

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: More than 100 years after the devasting Messina-Reggio Calabria earthquake (M = 7.1), the largest seismic event ever recorded in southern Europe in the instrumental epoch, its causative seismic source is still unknown, and the several rupture models proposed in the last decades are far from any shared solution. Data interpretation on a new dataset of sub-seafloor geophysical soundings with unprecedented resolution, relocated seismicity, and Vp model, together with morphotectonic investigations and inverse modelling of available levelling data, provide additional constraints on the deformation mechanisms and seismotectonics of the Strait of Messina area. Highresolution seismic lines in the offshore, along with displaced Quaternary marine terraces on land, point to active deformation along a previously unmapped ~34.5 km-long extensional fault. Spatial distribution of relocated earthquakes highlighted that a cut-off of the seismicity occurs within the crustal depth. The seismic discontinuity roughly delineates a foreland-dipping and low-angle discontinuity apparently confirming previous studies predicting low-angle seismogenic sources for the 1908 seismic event. However, according to the overburden stress and the attitude of the discontinuity, stress analysis suggests that a seismic slip is unlikely along it. This therefore weakens the hypothesis that a large earthquake may have nucleated along a low-angle discontinuity. Rather, aseismic creeping is instead expected since movement is allowed only by assuming a mechanical weakness of the plane. This mechanical behaviour is currently also supported by the large interseismic strain-rate recorded in the area. Both seismic tomography and crustal-to-subcrustal scale 3D-modelling strongly suggest a cause-and-effect relationship between slab retreat, mantle wedging, uplift in the upper plate block, and active extension in the Strait of Messina area. Lithospheric doming of the upper plate is here interpreted to be the main process controlling uplift in the Peloritani Mts. of Sicily and subsidence in the Strait of Messina region where deformation is mainly accommodated by the weak low-angle discontinuity. In this frame, an almost aseismical slip towards the foreland of the low-angle discontinuity is here accounted to produce stress perturbation in the area. Coulomb stress change modelling revealed that simulated normal slip on the foreland-dipping discontinuity can induce additional stress and promote failure in the overlying brittle faults. An excellent fit between calculated and observed subsidence is achieved by geodetic data inversion that resolved a normal slip on the low-angle discontinuity and a transtensional (slightly left-lateral) motion on the 34.5 km-long and previously unknown extensional fault. The fault-length along with the observed seafloor displacement make this tectonic structure as the most likely to have produced large earthquakes in the Strait of Messina area.

Description: Published

Description: 103685

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: Argnani (2021, hereinafter ARG2021) commented on the paper by Barreca et al. (2021, hereinafter BRC2021) titled: “The Strait of Messina: Seismotectonics and the source of the 1908 earthquake”, in which a new seismotectonic model and constraints on the possible source fault (the so-called W-Fault) for the 1908 disastrous seismic event were provided. Results from BRC2021 led to a revision of most of the previously published papers on the issue. ARG2021 commented both on the recent activity of the W-Fault and even about its existence in the offshore. In fact, according to the author's inferences: “it may belong to a fault system that is no longer active” and, contradictorily, “the offshore occurrence of the W-Fault is not supported by the data”. The comment is mostly based on a new tectonic interpretation that the author performed directly on the BRC2021 figures, where the offshore portion of the W-fault is illustrated. In this reply, we demonstrate that the interpretation provided by ARG2021 is affected by several oversights that led the author to erroneous conclusions about the issue. Accordingly, we strongly confirm both the occurrence of the W-Fault in the offshore and the present-day activity of this structure, the only active fault capable of producing large earthquakes in the Strait of Messina area.

Description: Published

Description: 103962

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal