COMMENTS

The northern Marche coastal zone is presently affected only by low seismic activity, but 
damaging earthquakes struck this area in the recent past (e.g. in 1930, Senigallia). A 
NW-SE trending minimum stress axis and a NE-SW trending maximum 
compressional stress axis were shown respectively by bore-hole breakouts and 
earthquake focal mechanisms (Mariucci et al., 1999; Frepoli and Amato, 1997). The 
available field geological observations are still inadequate to devise a fully convincing 
correlation between the occurrence of earthquakes and realistic seismogenic sources. 
However, the most realistic hypothesis that can be envisaged to-date on the basis of the 
local geologic setting considers the blind thrust-faults located at the leading-edge of
the Apennines accretionary prism as the main active and probably seismogenic faults 
in the area. In addition, it seems likely that two parallel fault-alignments of this sort 
exist along the northern Marche offshore.

This source is correlated with the 17 March 1875 Romagna Sud-Orientale earthquake. 
The seismogenic fault may correspond to a blind thrust-plane driving the growth of a 
coastal anticline. The location and geometry of the fault plane are based on local 
geologic and geomorphic observations and are partly extrapolated from the similarity 
between this area and the adjacent ones. In addition, the reports of a tsunami (Boschi et 
al., 1995) help locating the fault near the shoreline. The size of the fault size conforms 
to what is predicted by empirical relationships between length/width and magnitude 
relative to the 17 March 1875 Romagna Sud-Orientale earthquake.


OPEN QUESTIONS

1) The intensity data points for the 1875 earthquake are rather sparse where the fault 
plane is presumed to project to the surface. May this imply that the causative fault is 
elsewhere?

2) Could this fault be located offshore?
