COMMENTS

On 23 July 1930 the Irpinia region was struck by a large earthquake and several 
villages were almost completely destroyed. The exact location and sense of dip of 
the earthquake causative fault are still being debated, also because of the 
characteristics of the lithological units of the area, mainly clay rich-sediments, 
which allow an easy development of fractures and landslides. We chose the ESE-
WNW oriented source proposed by Gasperini et al. (1999) as the most reliable, 
taking into account the agreement with the few available focal mechanisms and 
the good quality of the 1930 macroseismic intensity dataset. The available fault 
plane solutions (Martini and Scarpa, 1983; Jimenez, 1991; Selvaggi et al., 1997) all 
suggest normal faulting along roughly E-W striking planes with a secondary 
component of strike-slip.

There are also several contemporary reports of fractures and landslides activated 
in the epicentral area, but none of them, because of their small extent and 
probably predominant gravitational component, could be easily identified as an 
expression of the fault at the surface.

There are some indications for a double shock both because of the damage 
distribution pattern and of a strong foreshock, that was felt 2 hours before the 
main event, which may have already partially damaged the area.
A possible Apennines-parallel source is shown in the Neotectonic map of 
southern Italy (Ciaranfi et al., 1983), where a 30-40 km-long, NW-SE striking, west 
dipping normal fault is mapped between Monteverde and Savignano Irpino. 
Note that on the geological sheet No. 174 (scale 1: 100.000) this and other similar 
normal faults probably correspond to tectonic lineaments of undefined type 
separating Pliocene and Miocene deposits. The location and geometry of Ciaranfi 
et al.'s (1983) fault put it very close to the 32 km-long, ~130- striking, 50-60 W-
dipping normal fault proposed by De Martini (unpublished paper) as responsible 
for the 1930 earthquake; the work is mainly based on geodetic levelling data 
(I.G.M.I.) surveyed in the northern sector of the epicentral area at the end of the 
XIX century and about 20 years after the earthquake. This source hypothesis could 
also explain the westward extent of damage (Alfano, 1931) and the subsidence of 
the S. Angelo hill near Savignano (Vari, 1930), but is still preliminary and 
for this reason was not considered for the purpose of this Database. 


OPEN QUESTIONS

1) What is the true geometry of the fault(s) responsible for the 23 July 1930 
earthquake?

2) Did the 23 July 1930 earthquake rupture at the surface?

3) Was the event a single or a double shock (i.e., a large shock composed of two or 
more subevents)?
