COMMENTS

The geometry of the Montello source was chosen following the paper of Benedetti et 
al. (2000), along with other geological, geophysical and geodetic observations. The dip 
of the source (30) was obtained by averaging the dip of the flat (12) and of the ramp 
(45) of the thrust modelled by Benedetti et al. (2000). The depth of the upper and 
lower tip (2 and 6 km, respectively: 1 and 6 according to Benedetti et al. (2000)) were 
obtained following geophysical and seismological observations that limit the regional 
seismogenic layer to a depth of about 6-7 km. The strike was taken to be same as that 
of the morphological anticline, while the length of the source was constrained to the 
southwest by the presence of the transverse Montebelluna Fault (Zanferrari et al., 1980), 
and to the northeast by the morphological termination of the anticline. The observation 
that the culmination of the morphological anticline is not symmetrical with respect to the 
geological structure (i.e. the maximum elevation is observed close to the southwestern 
termination) may suggest a left-lateral component of slip on the fault plane. The 
NNW-oriented vector of the Africa-Europe convergence predicts the same component 
of motion on NE-SW-striking faults.

Benedetti et al. (2000) hypothesise that the Montello thrust may have slipped three 
times in the past 2,000 years (778 A.D., 1268 A.D. and 1859 A.D. earthquakes), yielding 
a mean recurrence time of about 500 years. This assumption is very uncertain because 
of the poor quality of the information regarding these events; moreover the 
magnitude of these earthquakes calculated from historical reports is too low with 
respect to that expected from a fault with the geometric characteristic of the Montello 
Source. It is plausible to hypothesise that these earthquakes may be related to another 
nearby structure (e.g.: Montebelluna Fault for the 778 and 1268 earthquakes?), and 
that the Montello thrust fault may represent a main "silent" source. The presence of 
uplifted and deformed river terraces testifies that the Montello is a growing anticline, 
and hence the problem is to verify if it is growing by discrete events (=earthquakes), 
perhaps at very long intervals, or if the thrust fault is slipping aseismically. 
Because of these ambiguities, we included in the Database a recurrence interval 
longer than 700 y. This is based on the observation that none of the historical 
earthquakes reported in the Italian Catalogues of seismicity for the past seven
centuries can be convincingly referred to the Montello surce.

The area located between the Montello and Cansiglio sources is characterised by the 
absence of historical and instrumental seismicity. From the geological standpoint it 
represents the northeastern prolongation of the Montello anticline, separated from it 
by a NW-striking transverse lineament going through the Nervesa gap (Zanferrari et 
al., 1982; Bigi et al., 1983; Ambrosetti et al., 1983; Slejko et al., 1987). On the basis of 
these geological observations we may hypothesise that there exists another blind 
thrust geometrically similar to the Montello Source. The geodetic line analysed by De 
Martini et al. (1997, 1998) shows relative uplift when crossing the axis of the eastern 
anticline close to the town of Susegana; these workers interpreted this evidence as 
due to motion on a single N248-striking, 60-dipping, 18 km-long blind thrust. The 
orientation of this fault is more easterly than that obtained from geological evidence 
alone, however, it must be considered that geodetic modelling has poor control on 
fault strike and can not distinguish between a single-fault and a two-faults model.

The 25 February 1695 earthquake is not associated with confidence with any source. 
Benedetti et al. (2000), hypothesise that it may have been generated by a NE-SW 
striking thrust fault located beneath the Asolo hills, west of the Montello anticline; 
on the contrary the intensity-based solution exhibits a NNW-striking source for this 
large earthquake (see section of Database on Historical Sources). The official 
geological map of the area and other published sections do not report any thrust fault 
and associated folds south of the Bassano Line (that represents the most external 
thrust front of the Venetian Alps ), except for the Montello thrust (Doglioni, 1990). 
On the contrary the Asolo hills have a monoclinal geometry characterised by bedding 
steeply dipping toward the SSE and deeply involved by the thrusting of the Venetian 
Alps (triangle zone). These considerations lead to hypothesise that the causative fault 
of the 1695 earthquake may be a structure transversal to the mountain front and 
limiting to the south-west the Montello thrust fault (Montebelluna Fault).


OPEN QUESTIONS

1) Is the Montello Source associated with any historical earthquakes, or does it 
represent a seismic gap?

2) If the three earthquakes (778 A.D., 1268 A.D. and 1859 A.D.) are really associated 
with the Montello source, as hypothesised by Benedetti et al. (2000), does this mean 
that its seismic behaviour is characterised by a smaller and more frequent 
earthquakes than expected, each one rupturing a small fraction of the entire 
structure?

3) Is the 25 February 1695 earthquake associated with the Montello source or, as 
hypothesised by Benedetti et al. (2000), with a seismogenic source located west of the 
Montello under the Asolo Hills? Or was it generated by the Montebelluna Fault 
(Zanferrari et al., 1982; Castaldini and Panizza, 1991; among others) as proposed by the 
compilers of this Database (see Asolo Source)?

4) Is the area located between the Montello and Cansiglio sources a seismic gap?
