NW-dipping versus SE-dipping causative faults of the 1783 M7.1 Southern Calabria (Italy) earthquake: The contribution from the analysis of the coseismic hydrological changes

The 1783 Mw7.1 Southern Calabria (Italy) earthquake originated a remarkable
number of observations of hydrological changes (variations of flow in springs
and streams, liquefaction, changes in water temperature) that occurred in
different localities. To provide further constraints on the mechanism and the
geometry of the causative fault of the event, I compared the distribution of the
hydrological changes with the coseismic strain produced by eight seismogenic
sources proposed for the earthquake. The most important outcomes of the
study can be summarized as follows: a) the group of potential sources that
display the best agreement between expected deformation and hydrological
signature consists of NW-dipping systems of three to four surface-rupturing
almost pure normal fault segments (Cittanova fault system), capable of
generating earthquakes of magnitude Mw6.9–7.1; b) the distribution of the
observed coseismic hydrological anomalies does not support the role of the SEdipping
faults as potential sources of the 1783 earthquake; c) the pattern of
deformation associated with the best fit source strengthens the hypothesis that
the 20 km-long surface ruptures testified soon after the 1783 event reflect
primary faulting; d) a minimum magnitude Mw6.9–7.0 is required to obtain the
pattern and the extent of distribution of the coseismic hydrological changes
observed in the field; e) the location of the hydrological variations that were
observed only along the western side of southern Calabria suggests that the
Cittanova fault system acts as a hydrological barrier that hampers the
groundwater circulation toward the East