COMMENTS

The identification of the Melandro-Pergola source has been based on the 
observation of geomorphological and topographic anomalies constrained by 
extrapolations from neighbouring faults (Irpinia South source to the north and 
Agri Valley source to the south).

The Melandro-Pergola basin is one of many intermountain depressions filled 
with lower-middle Pleistocene continental deposits. These were subsequently 
incised as a result of regional uplift and mildly deformed by a local tectonic 
source. The pattern of incision suggest the existence of a slight asymmetry of 
the basin, which exhibits a SW flank steeper than the NE-flank with a depocenter 
located half-way near the intersection of the Pergola and Melandro rivers (Ponte 
d'Isca). A characteristic aggrading behaviour is observed along a ~5 km stretch 
of the river. This configuration is compatible with the action of a NW-trending, 
NE-dipping major fault.

The surface trace of the source has been located coincident with a series of 
small perched basins and valleys located on top of the mountain ridge that 
separates the Melandro river valley from the Vallo di Diano to the SW. This 
topographic feature is continuos for the entire length of the source (i.e. about 
18 km) and is well aligned with a similar feature characterising the Maddalena 
Mts. ridge (i.e. where the Agri Valley source cuts the surface).

The surface expression and long-term deformation of the Irpinia South source to 
the NW and of the Agri Valley source to the SW are very similar to those 
proposed for the Melandro-Pergola source. In all cases we observed rejuvenation 
of inherited topography and recent deformation confined along topographic 
crests.

The width of the source is slightly smaller than that of the two adjacent 
sources and has been selected using an aspect-ratio criterion based on the 
assumed source length. Benedetti et al. (1998) hypothesised the presence of Late 
Quaternary SW-dipping normal faults on the eastern flank of the Vallo di Diano. 
These would be part of a larger normal fault system that would include also some 
SW-dipping normal faults located on the eastern side of the high Agri river 
valley. According to them this fault system would be the source of the 16 
December 1857 earthquake, and the Vallo di Diano segments slipped during a 
strong foreshock.

The mere existence and the Late Quaternary activity of the SW-dipping Vallo di 
Diano fault system, that would be formed by two right-stepped segments located 
right behind the Melandro-Pergola source, is not accepted by all workers. In 
addition, activity of one of the two would exclude activity of the other.

This source is not associated with any historical or instrumental earthquake; as 
such, it may well represent a potential seismic gap. This observation is much 
more important in light of a stress transfer hypothesis, since both neighbouring 
sources have generated large historical earthquakes in relatively recent times 
(23 November 1980 - Irpinia South, and 16 December 1857 - Agri Valley). Stress 
transfer considerations along with the source geometry and kinematics suggest 
that this is a probable candidate for an impending large earthquake (M up to 
6.3).

The epicentral area of the August 19, 1561 earthquake (Me=6.4) falls close to 
the northern tip of this source. The event heavily struck the northern end of 
the Vallo di Diano. However, the epicentral location of this event is still 
debated and has been attributed either to a seismogenic source located on the 
eastern flank of the Vallo di Diano or to a source in the Melandro river valley 
(Mucciarelli et al., 1999). The distribution of damage associated with this 
event does not seem to bear any relationships with the location and geometry of 
the Melandro-Pergola source, since the stronger intensities were recorded along 
a NE-SW trend. Mucciarelli et al. (1999) also demonstrated that high and very 
high site amplifications can explain the strong damage observed at sites located 
in the northern Vallo di Diano. Following this observation, the calculation of 
the source geometry from corrected intensities using the Boxer code (Gasperini 
et al., 1999) yielded a NE-SW oriented source, which suggests the activation of 
a transverse lineament (notice that the 1990 Potenza seismic sequence is also 
somehow related with activity of a more northerly portion of the same 
lineament).


OPEN QUESTIONS

1) Is the northern Vallo di Diano normal fault system active? Is it the source 
of the strong fore-shock of the 1857 earthquake located to the NW of Val d'Agri 
as proposed by Benedetti et al. (1998)?

2) Where is the source of the 1561 earthquake located? What is its orientation?

3) Does the Melandro-Pergola source represent a seismic gap?
