New paleoseismological and morphotectonic investigations along the 2018 surface ruptures of the Fiandaca Fault, eastern flank of Etna volcano (Italy)

We present the first paleoseismological results
along the Fiandaca Fault, source of the 26 December 2018,
Mw 5.0 Fleri earthquake. This earthquake caused extensive
damage and 8 km of surface faulting. We excavated two exploratory
trenches close to the Fiandaca village, in the central
segment of the 2018 coseismic rupture. Analysis of trench
walls allows identifying, besides the 2018 event, two additional
historical surface faulting events. Based on amount of
displacement of dated stratigraphic units, including tephra
from the 122 BCE eruption, these historical events were similar
to the 2018 earthquake. The most recent one occurred in
the period 1281–1926 CE, most likely during the1894 earthquake.
The oldest one, previously unknown, occurred in the
Early Middle Ages (757–894 CE). When compared with the
available seismic catalogue for Mt. Etna volcano, this paleoseismic
evidence might suggest increased seismic activity
along the Fiandaca Fault in the last centuries. In order to
test this hypothesis, we conducted detailed morphotectonic
analyses and throw rate measurements across offset historical
lava flows. In addition, we developed a trishear kinematic
model that describes the fault zone and the morphological
features of the scarps. Throw rates mean values show
an increase from 3.3mmyr􀀀1 since the Greek-Roman period
reaching 7.8mmyr􀀀1 since the Late Middle Ages. These
findings highlight the needs of further investigations to evaluate
the slip rates variations of other faults accommodating
the flank instability. Our findings confirm that paleoseismological
and morphotectonic studies are of critical value for
defining surface faulting and seismic hazard in volcanic settings.