Abstract
This study deals with the earthquakes which occurred in southeastern Sicily in 1693 (January 9 and 11, Mw ≈ 6.1 and 7.3, respectively). Although they have been largely studied, robust and commonly accepted seismic sources are still missing. We performed a revision of the 1693 macroseismic data and, for the fore and main-shocks, modeled new NNE-SSW trending seismic sources. In the Hyblean Plateau area, we carried out an analysis of DEM and aerial photos to map tectonic features. Then, we performed field surveys on the main faults, and a morphotectonic study with the aim of characterizing the activity of mapped faults. The study revealed the presence of three main fault systems. The first is the Palazzolo-Villasmundo Fault System, composed of NNE-SSW and NE-SW trending north-west-dipping normal faults. Some of these faults could be reactivated as reverse faults. The second is the Augusta-Floridia Fault System, made of NNW-SSE and NW-SE normal faults. The third is composed of faults which have never been mapped before: the Canicattini-Villasmundo Fault System that shows both a segmented and stepping pattern, almost N-S trending and west-dipping normal faults; some of these faults show a left-lateral movement. The morphotectonic study demonstrated that the fault systems are active. Furthermore, both strike and kinematics of the studied faults well match with the regional stress field characterized by a NW-SE σ1, which in the study area is probably both affecting some pre-existing faults, the Palazzolo-Villasmundo and the Augusta-Floridia Fault Systems, and causing the formation of new faults, the Canicattini-Villasmundo Fault System. The latter system lies across the Hyblean Plateau with a total length of 35 km and, due to its aligned segmented pattern, it can be the surface expression of a master fault that seems dividing the Hyblean Plateau in two blocks. Moreover, the Canicattini-Villasmundo Fault System well fits the southern part of the 1693 revaluated seismic sources and matches with a current alignment of shocks mainly characterized by left-lateral focal mechanisms on almost N-S fault planes. Considering the possible rupture length in depth, it could manage to release Mw ≈ 7.1 earthquakes, representing a valuable candidate source for the 1693 earthquakes.
Highlights
South-eastern Sicily was affected by some of the strongest earthquakes of the Italian history such as the 1169, 1542 and 1693, 1818 events, with epicentral intensity (Io) up to 11 (MCS)and equivalent moment magnitude up to Mw 7.3 (Rovida et al, 2019).This study deals with the foreshock-mainshock pair of the 1693 seismic sequence, which began on January 9 with a strong foreshock (Mw ≈ 6.1), culminated with the catastrophic January 11, 1693 event (Mw ≈ 7.3) and continued for more than 2 years (e.g. Boccone, 1697)
Since the number of localities affected by the foreshock is probably higher, it is reasonable to hypothesize that the macroseismic field could be incomplete (Figure 4A)
The second system, already known in literature, is the Augusta-Floridia Fault System (AFFS in Figures 6A,B and Table 2). It consists of NNW-SSE and NW-SE trending normal faults, giving rise to horst and graben structures, such as the Augusta Graben to the north-east and the Floridia Graben to the south-east (Lentini et al, 1994; Catalano et al, 2010), separated by the Augusta Horst (Figures 6A,B). The former is bordered by the Monte Tauro Fault (MTF) and the Augusta Fault (AF), while the Floridia Graben is bordered by the North Canicattini Fault (NCF) and the Floridia Fault (FF)
Summary
South-eastern Sicily was affected by some of the strongest earthquakes of the Italian history such as the 1169, 1542 and 1693, 1818 events, with epicentral intensity (Io) up to 11 (MCS)and equivalent moment magnitude up to Mw 7.3 (Rovida et al, 2019).This study deals with the foreshock-mainshock pair of the 1693 seismic sequence, which began on January 9 with a strong foreshock (Mw ≈ 6.1), culminated with the catastrophic January 11, 1693 event (Mw ≈ 7.3) and continued for more than 2 years (e.g. Boccone, 1697). The extent of the damaged area, the great number of victims (more than 60,000), and the numerous coseismic effects make the 1693 mainshock one of the most destructive seismic events in the Italian seismic history. It was felt as far as northern Calabria and along the Africa coast (Guidoboni et al, 2018). Despite the catastrophic consequence and the extensive environmental effects, the causative source/s of these earthquakes is/are still matter of debate for several aspects, such as: 1) the occurrence of multiple shocks, which complicated the macroseismic field; 2) the proximity of the maximum damaged area to the coast; 3) the tsunami following the mainshock, suggesting that the earthquake source was located
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