COMMENTS

The Irpinia fault is certainly the best studied and best known source of the 
Database. Its location and geometry are well defined and a general consensus 
exists about a NE-dipping fault about 40 km-long. However, the source included 
in the Database includes only the faults responsible for the 0 and 20 sec 
mainshock subevents; the still unidentified tectonic structure responsible for 
the 40s subevent is not presently included in the Database. 

The main unresolved problem about this source is the lack  of a geological 
record of the 1694 earthquake in the trenches excavated at Piano di Pecore and 
Piano di San Gregorio Magno. The 1694 event was previously considered the direct 
ancestor of the 1980 event. Several hypotheses can be 
put forward to explain this circumstance: 
a) the 1694 earthquake occurred on the Irpinia Fault but its intensity was 
overestimated, which means that  it was not large enough to produce surface 
faulting. If this is the case, there is a chance that also other earthquakes 
that occurred in the same period and were studied with the same approach suffer 
from a similar problem. They would therefore need some reconsideration;
b) the 1694 earthquake did not occur on the Irpinia Fault but on a different 
structure with a geometry capable of producing a damage pattern very similar to 
that of the 1980 earthquake (e.g. the blind or hidden antithetic fault that is 
presumed to have ruptured in the 40 sec subevent could be a section of a longer 
structure that ruptured in 1694).

Extension rates across the Irpinia fault calculated by means of 
paleoseismological analyses are somewhat smaller than those expected based on 
calculations of historical moment rate and on geodynamic considerations. This 
suggests that there could be at least another active structure that accommodates 
the extension across the Apennines at this latitude, possibily antithetic (i.e., 
SW-dipping) to the structure revealed by the 1980 earthquake. 

The 2000 yr average recurrence time obtained by trenching analyses is much 
longer than that commonly expected on the basis of the Italian historical record 
of seismicity. This discrepancy should be seen as mainly due to the fact that 
by definition paleoseismology yields the true recurrence interval for an the 
individual source. A set of individual sources could concur (possibly even in a 
clustured fashion) in producing damage in the same general area, producing 
an apparently shorter recurrence interval.


OPEN QUESTIONS

1) Did the 1694 earthquake rupture the Irpinia fault? If this is the case, did 
it produce surface faulting? Does the geological evidence for this earthquake 
exist? 

2) Do the three sections that form the Irpinia source (associated with the 0 and 
20 sec subevents) always rupture synchronously, as seen in 1980 and as suggested 
by paleoseismology?

3) Does the source have a listric geometry in its southern part?

4) What is the age of inception of the activity of the Irpinia source? Is the 
poor geomorphic expression of this source due mainly to its youthfulness?
