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 Apennine 
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.

The Conero Offshore Source is correlated with the 23 December 1690 Anconetano 
earthquake. Its location relies on the distribution of intensity data points, which is in 
good agreement with geological observations at regional and local scales. The 
seismogenic fault may be correlated with a blind thrust-plane which drives the growth 
of an anticline in the near offshore. Such fault may form a splay in the middle of a 
longer thrust front, running all along the Marche offshore. The fault geometry at 
depth is based on a presumed similarity with neighbouring sources. Its size conforms 
to what is predicted by empirical relationships between length/width and magnitude 
relative to the 23 December 1690 'Anconetano' earthquake.


OPEN QUESTIONS

1) This source suggest the presence of an active thrust fault in the Adriatic offshore. 
Could this fault belong to a longer fault system?

2) How many parallel active thrust systems exist along the Adriatic coast?

3) Are these active fault systems entirely seismogenic?

