New Macroseismic and Morphotectonic Constraints to Infer a Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily)

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.

Pirrotta C., Barbano M.S. (2020). New Macroseismic and Morphotectonic Constraints to Infer a
Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily).
Front. Earth Sci. 8:550851. doi: 10.3389/feart.2020.550851