COMMENTS

Although several investigators mention the existence of scarps or fault breaks 
in young (post-Middle Pleistocene) deposits (e.g. Ascione et al., 1998, at 
an unspecified location at the edges of the Boiano Plain; Basili et al., 1999, 
along Mt. Patalecchia; Blumetti et al., 1999, across the Guardiaregia fan and at 
several other locations), no conclusive evidence exists to date for genuine 
surface faulting associated with the main active structures of this area. 
Trenching across one of these features (Blumetti et al., 2000) gave ambiguous 
results about the fault trace location and consequently about the recognition 
and dating of paleoearthquakes. The geometry of the main driving faults is 
therefore inferred from indirect geological observations. In particular, 
consensus on the assumed NE dip of the main fault has been gathered only in the 
past few years, and some investigators still contend that SW-dipping faults 
bounding the basin to the E also play a major role in the seismogenic process.
Given the expected size of the fault that controls the Boiano Basin and of the 
earthquakes generated by it (e.g., the 1805 event), the lack of unambiguous 
surface breaks could be interpreted as simply due to the youthfulness of the 
present tectonic regime, a condition observed elsewhere along the central and 
southern Apennines.

The extent of the Boiano Basin fault segment and of the 1805 coseismic rupture 
is discussed by Di Bucci et al. (2001), who point out that the Boiano 
extensional system is fully part of the much longer system that runs along this 
stretch of the Apennines. Normal faulting continues in the NW-SE direction well 
beyond the northwestern end of the Boiano Plain proper for at least 15 km (based 
on data from Corrado et al., 1998). Faults in this northern sector dip both 
toward the SW and the NE (although the master fault appears to be NE-dipping), 
favour the development of small Pleistocene basins such as the Carpino Basin, 
control the local drainage and generate a series of small horst and graben along 
this reach of the Matese-Frosolone structure. This section is separated from the 
Boiano Basin along an alignment that runs between Carpinone and Mt. Patalecchia, 
which corresponds to an important drainage divide and marks the boundary between 
areas with predominant E-W (to the SE of it) or N-S (to the NW of it) inherited 
strike-slip faults. Is this also an important segment boundary marking the 
northwestern end of the 1805 rupture? If the answer is yes, the section of fault 
to the north of this boundary would be unruptured in 1805 or in any other large 
earthquake of the past 4-5 centuries.

Di Bucci et al. (2001) also locate the southeastern boundary of the 
Boiano Basin extensional system between Guardiaregia and the Vinchiaturo Pass, 
just to the west of the Sepino Plain. They also suggest that the Morcone and 
Sepino Plains may be controlled by additional though secondary elements of 
the broader Matese extensional system, but contend that the 1805 was not large 
enough to have ruptured through these areas.

The total length of the Boiano segment proposed by Di Bucci et al. (2001) is 25 
km. This estimate compares well with the ca. 20 km geological model fault of 
Cucci et al. (1996) and with the ca. 25 km long source and 6.5 equivalent 
magnitude inferred for the 1805 earthquake by Gasperini et al. (1999). The three 
solutions also share a similar strike (within 5) and general fault location 
(within about 2 km).

In contrast with the previous interpretation and based on contemporary reports 
for surface breaks and geochemical phenomena, Blumetti et al. (1999) (based on 
evidence first put forward and discussed by Esposito et al., 1987) propose for 
the 1805 earthquake a coseismic rupture covering the entire distance from 
Isernia to Morcone (about 50 km). This interpretation effectively reduces the 
hazard associated with the Isernia-Carpino Plain and with the Sepino and Morcone 
Plains (respectively to the NW and SE of the Boiano Plain) because the relevant 
sections of the Apennines extensional system would have ruptured less than 200 
years ago in earthquakes that were large enough to produce sizeable surface 
effects (>6.0?).


OPEN QUESTIONS

1) Is the 25 km-long Boiano segment alone responsible for the 1805 earthquake, 
or did the rupture extend further towards the NW and SE? 

2) What is the potential of adjacent fault portions of same extensional trend? 

3) Does any of the reports of 1805 earthquake truly describe genuine surface 
breaks that could be used for characterising the activity of this segment? 

4) How much is the total slip accumulated along this fault? Is it another 
example of geologically youthful that would confirm the trend suggested by other 
large seismogenic sources of the southern Apennines?

5) Are the disturbances exposed in the only trench opened across a possible 1805 
earthquake scarp unambiguous enough to be used as actual evidence for 
paleoearthquakes?

