COMMENTS

The Mt. Gorzano range shows an outstanding relief at the base of which there is a 30 
km-long normal fault system that accounts for a maximum stratigraphic separation 
of ca. 1500 m, determined from displaced Messinian (5.2-6.7 Ma) bedded terrigenous 
units (see also Calamita et al., 1995). Using these figures a long-term slip-rate of 0.22-
0.29 mm/y is obtained. However, assuming that the displacement may have taken 
place only after the onset of the extensional regime in this region (Middle-Late 
Pliocene-Pleistocene? See for example Ghisetti and Vezzani, 2000), an even faster slip 
rate could be found. A slip-rate of less then 0.1 mm/y could be inferred on the basis of 
the displacement of a Villafranchian surface described by Bachetti et al. (1990) and 
Blumetti et al. (1993), assuming the Villafranchian age to be about 2 Ma. However, 
correlating erosive geomorphic features is usually quite problematic. Bachetti et al. 
(1990) point out that the fault may be still active, having caused tilting of a 39.7 ka old 
palustrine deposits, from which a slip rate of 0.22-0.40 mm/y could be inferred. 
Bachetti et al. (1990) also conjectured that such tilting must have occurred during a 
surface faulting event, suggesting that the fault may have a seismogenic nature, but 
did not provide evidence of the associated fault scarp.

The Mt. Gorzano fault-system has been split into two fault segments, each one 
representing an individual seismogenic source. The Amatrice Source, which is 
discussed here, is the northernmost segment in the system. This source might be 
correlated with the 7 October 1639 earthquake. However, although the earthquake 
location is in good accordance with the location and geometry of the Mt. Gorzano 
fault-system, the geometrical properties of the historical source are not (compare the 
orientation of the geological source discussed here with that of the source obtained 
from intensity data alone). The two sources differ by about 80 in strike and a few km 
in length.


OPEN QUESTIONS

1) Is the 7 October 1639 earthquake associated with the Amatrice Source?

2) If so, does this historical earthquake testify to the typical behaviour of this source?

3) If not, does the Mt. Gorzano fault-system contain potential sources for moderate to 
large earthquakes?
