FAULT GEOMETRY

Bollettinari and Panizza (1981) 
Immediately following the November 23, 1980 earthquake they surveyed the  
epicentral area looking for coseismic effects on the local geology and 
geomorphology. They describe a 2 km-long, WNW-trending surface fault, producing 
about 50 cm of subsidence of the northern part of the Pantano di San Gregorio 
Magno plain and of the northern slope of Difesa di Ripa Rossa.

Carmignani et al. (1981)
These investigators study the main direction of the surface fractures related 
to the 1980 earthquake. They also describe NW- to WNW-trending fractures cutting 
the north-eastern side of Mt. Marzano - Mt. Sette Cuponi massif and Piano di 
Pecore plain for a total length of about 500 m and producing a maximum vertical 
offset of 1m. They interpret them as an effect of differential compaction which 
is not directly related to the slip of the seismogenic fault at depth.

Del Pezzo et al. (1983)
On the basis of the analysis of seismograms and strong motion data of the 1980 
earthquake, they suggest a multiple rupture process composed at least of three 
sub-events.

Deschamps and King (1983, 1984)
These investigators calculate the fault plane solution for the 1980 
Earthquake. They obtained a normal faulting mechanism with a component of 
left lateral movement on a high-angle NW-trending NE-dipping plane.  They also 
identify three regions of high concentration of aftershocks separated by areas 
of reduced seismicity, the northern of which corresponds to the Sele river gap. 
They also speculate on the lack of clear surface faulting and presence of 
different fault mechanism of the aftershocks.

Westaway and Jackson (1984)
They identify and describe in detail two distinct sections of surface rupture: 
the northern is 10 km-long and bounds the north-eastern side of Mt. Marzano; the 
southern is 3 km-long, is located in the Pantano di San Gregorio Magno plain, 
and includes some of the fractures described by Carmignani. 
On the basis of the consistence between these observations and seismological 
evidence they suggest that these surface faults are of primary tectonic origin. 
Because of the location of the coseismic ruptures with respect to the 
Mainshock, they suggest that the rupture nucleated at a depth of 10 km on a 
high-angle NE-dipping NW-striking planar fault.

Crosson et al. (1986)
On the basis of the aftershocks distribution, the pattern of strong ground 
motion, focal mechanism of the mainshock and of quantitative modelling of the 
pattern of coseismic elevation changes of two levelling profiles, they 
reconstruct the complex rupture history of the 1980 earthquake. Their model 
predict two high-angle, NW and NE-trending perpendicular normal faults. In their 
hypothesis the 40 sec sub-event occurred on the NE-trending fault.

Westaway and Jackson (1987)
By means of different studies they show that the 1980 earthquake involved a 
complex sequence of fault ruptures with at least six sub-events. The first four 
events occurred within 10 sec of the origin time on three distinct NW-striking, 
NE-dipping, high angle fault sections, whereas the two later events occurred on 
two low-angle, NE-dipping normal faults located at the base of the seismogenic 
zone.

Funiciello et al. (1988a, b) and Pantosti and Valensise (1990)
These papers describe in detail the geometry of the 1980 surface fault. They 
extend the rupture recognised by Westaway and Jackson to as much as 38 km, from 
Monte Caravella to San Gregorio Magno. Scarp heights ranges between 0.4-1 m. The 
authors associate the main sub-event to a N315 steeply NE-dipping located 
between M. Caravella and M. Carpineta, the 20 sec sub-event to a N300 steeply 
NE-dipping plane located in San Gregorio Magno plain, and the 40 sec sub-event 
to an antithetic high-angle SW-dipping fault located about 10 km away the main 
rupture. They interpret the surface faulting discontinuities between the 
different segments of the main fault as mixed relaxation-geometric barrier.

Bernard and Zollo (1989)
They re-analyse all the data available on the 1980 earthquake and describe the 
kinematics of the process of rupture as consisting of three main episodes. They 
suggest that the rupture started near the north-eastern edge of the Mt. 
Marzano segment, propagated to the north on a high-angle NE-dipping fault, 
then the 20 sec sub-event occurred on a low-angle NE-dipping normal fault 
located between 8 and 12 km of depth and associated with secondary faulting on a 
steeper plane reaching the surface in the San Gregorio Magno plain. Following 
their interpretation the 40 sec sub-event nucleated on an high-angle SW-dipping 
antithetic fault.

Valensise et al. (1989)
On the basis of geodetic observations, depth distribution of aftershocks and 
localisation of nucleation points, they analyse the complex time-history for the 
1980 events. According to them the main-shock was composed of three sub-events 
(0 sec, 20 sec and 40 sec), the first two of them nucleated on NW-trending, NE-
dipping high-angle normal faults and produced surface faulting. Conversely the 
40 sec sub-event occurred on an antithetic SW-dipping structure striking 
parallel to the main fault which did not produce surface faulting.

Amato and Selvaggi (1993)
By means of a computed three-dimensional velocity model of the volume affected 
by the main-shock and by the aftershocks of the 1980 earthquake they suggest 
that the rupture started at a depth of about 10 km on a 60 NE-dipping plane 
that steepens to vertical in the upper 6-7 km. They also interpret the 
antithetic fault, responsible for the 40 sec sub-event, as a reactivated NE 
verging thrust inherited by the pre-Pliocene compressional tectonics.

Pingue et al. (1993)
They model the 1980 source from levelling data. They obtained a source that 
consists of three fault sections each correlated to a sub-event. Because the 0 
sec sub-event was composed of three rupture pulses they propose for it a 25 km-
long, N317 striking, high-angle fault plane, that would be the summation of the 
contribution of all these pulses. They also suggest that the 20 sec sub-event 
involved a low-angle NE-dipping fault and that the 40 sec event occurred on an 
high-angle SW-dipping antithetic fault, similar to that proposed by Pantosti and 
Valensise (1990).

Westaway (1993)
On the basis of a re-examination of P-wave arrival time data he relocates the 
nucleation point of the initial fault rupture of the 1980 earthquake and 
describes the kinematics of the faulting process. By means of analysis of 
aftershock location and of ground acceleration evidence he suggests a fourth NW-
trending fault rupture near Castelfranci north-west of the northern end of 
the Picentini fault; he also hypothesizes that the 20 sec sub-event involved a 
low-angle NE-dipping fault at the base of the brittle upper crust.


PALEOSEISMOLOGY

Pantosti et al. (1989)
They provide the preliminary results of trench studies conducted at Piano di 
Pecore site. They recognise four paleo-earthquakes occurred in the 
last 6700 years and provide a preliminary slip rate of 0.4 mm/yr and average 
recurrence time of 1700 years for the Irpinia fault. On the basis of the close 
similarity between the deformation pattern of these paleo-events with that of 
the 1980 earthquake, they suggest that this earthquake is characteristic for 
this fault. They did not found evidence in the trenches for the 1694 earthquake, 
commonly considered the twin of the 1980 earthquake. On this basis they suyggest 
that the 1694 event occurred on the antithetic structure responsible for the 40 
sec sub-event. 

DAddezio et al. (1990, 1991)
On the basis of detailed analyses and logging of two trenches excavated at 
Pantano di San Gregorio Magno they recognise the geologic records of four 
paleoevents, preceding the 1980 earthquake; radiometric dating of organic 
samples taken from the sedimentary sequence was used to constrain the age of 
occurrence of paleoearthquakes. A slip rate of 0.3 mm/yr and average 
recurrence time of about 2000 years, in agreement with the results obtained at 
Piano di Pecore site are estimated for the San Gregorio fault section. The 
authors point out that the occurrence of surface faulting events in these two 
sites with similar dislocation magnitude and geometry, strengthen the idea that 
the 1980 earthquake can be considered characteristic for the Irpinia Fault.

Pantosti et al. (1993a, b) 
By using all the ages ranges of occurrence for the paleo-earthquakes recognised 
in the Irpinia trenches along with the reviewed amount of displacement observed 
in the trenches, they suggest that the 1980 earthquake is characteristic for 
this source and that the three sections of the fault that produced surface 
faulting rupture always synchronously. They also re-evaluate the slip rate and 
the average recurrence time for the Irpinia Fault, giving respectively 0.17-0.60 
mm/yr and 2150-3140 yr with about 2000 years as preferred estimate for the 
average recurrence time. They confirm the lack of evidence for the 1694 
earthquake surface faulting in the trenches. Assuming an average fault dip of 
60 they evaluate an extension rate contribution of the Irpinia Fault close to 
0.2 mm/yr; on the basis of stratigraphic consideration and assuming that the 
slip rate has been constant during Holocene, they calculate that the inception 
of the activity of this fault 
should postdate 0.7-1.0 Myr.
