Barnaba (1958)
This paper describes the Mesozoic structure of the Gubbio ridge through  basic 
field mapping. The ridge corresponds to a NW-SE trending anticline  having a 
length of 13 km and a width of 4 km. The western limb of this NE-verging 
fold is cut by a major normal fault and dropped under the Quaternary deposits 
of the Gubbio basin, whereas the bedding of the eastern gradually turns to 
vertical. The N60W striking Gubbio normal fault is 14 km-long, dips 60 to 
70 toward the SW and truncates the older fold along its main axis. A 
secondary NE-SW striking normal fault system with maximum single offset 
of 100 m is widely recognised in the area. In some cases these secondary faults 
coincide with the periclinal closure of the Mesozoic  anticline.

GE.MI.NA. (1962)
This paper reconstructs the geometry of the contact between the bedrock and 
the basin filling based on drillings and geophysical data. In the central-
southern  portion of the Gubbio basin the Quaternary sediments exhibit a 
sharp NW-dipping step and their thickness increases from 300 to 500 m. 
Fluvial-lacustrine sediments fill the NW-SE Gubbio basin and are 
stratigraphically in contact with the bedrock. Almost everywhere this facies 
change occurs by a 5 to 25 m-thick clay unit (Argille Verdi fm.). The fluvial-
lacustrine sequence exhibits a clayey-lignitic complex at the base, a clayey-
sandy complex and an alluvial complex at the top. The oldest complex dips 
toward the N-NE and increases both its thickness (from 50 to 170 m) and its 
dip angle as it gets closer to the main fault. 

Cattuto (1973)
This investigator provides a map of geomorphological elements linked to the 
evolution of the Chiascio river close to the Gubbio basin. Two orders of sub-
horizontal relict surfaces, whose height decreases from north to south, and 
two orders of fluvial terraces are identified only west of Col Palombo, together 
with. V-shaped valleys of the Chiascio river tributaries. Based on this 
geomorphic dataset Cattuto hypothesises a prevalent NW-SE trend of rivers 
following the main geological structures in the Upper Pliocene. The 
formation of the Gubbio lake took place in the Middle-Lower Pleistocene. 
During the Middle Pleistocene strong active erosion of the Chiascio river 
breached the local divide near Col Palombo, producing river captures 
mainly along the NE-SW direction and emptying the Gubbio lake.

I.S.C. (1984)
This bulletin provides the essential parameters of the 29 April 1984, Gubbio  
earthquake. Origin Time 5:02:59.3; epicentral latitude 43.25 N; epicentral  
longitude 12.52 E; depth 7 km; magnitude Mb 5.1, Ms 5.2.

Barchi et al. (1984)
This work uses the macroseismic intensity data of the April 1984 Gubbio 
earthquake (maximum intensity VII) to estimate the focal depth of the event 
(15+/-3 km) and to assess a macroseismic magnitude (M=5.0). The intensity 
VII and VI isoseismals are elongated NW-SE like the main tectonic structures 
of the Apennines, whereas those of lower intensity (V and IV) strike in the 
opposite direction. A similarity between the elongation of the damage pattern 
and the strike of major extensional faults is also observed. Local 
amplifications are identified corresponding with fluvial terraces.

Dziewonski et al. (1985)
These investigators provide the centroid-moment tensor solution for the 29 
April 1984 Gubbio earthquake. The earthquake had a normal faulting 
mechanism with plane A striking 143 and dipping 21, plane B striking 304 
and dipping 70, P-axis striking  203 and dipping 64, and T-axis trending 
039 and dipping 25. They also estimate a seismic moment of 3.4x10**24 
dyne-cm.

Menichetti et al. (1986)
These investigators present a geologic-structural study of the Gubbio area. 
Four tectonic syn-orogenic units, each one thrust over the adjacent one, are 
recognised in the area between the Upper Tiber Valley and the Umbria-
Marche Apennines. The compressional phase in the area is witnessed by deep 
thrusts that gave rise to the Mesozoic structures of Gubbio and the Umbria-
Marche Apennines, and by shallow thrusts that allowed each unit to override 
the adjacent one. The studied area was first affected by shallow thrusting and 
only later by deeper ones, in a two-stage deformational history that gave 
origin to a complex set of structures. The old thrust front of Padule, on the 
eastern side of the Gubbio basin, is cut by the younger Gubbio anticline. This 
latter structure and its associated frontal syncline overrode together. The 
easternmost backthrust syncline forms a triangular zone between Gubbio and 
the Apennines ridge. Most of the compressional structures of the syn-orogenic 
units seem to terminate against a NE-SW lineament that also coincides with 
the southern periclinal closure of the Gubbio Anticline.

Haessler et al. (1988)
This work analyses an instrumental dataset recorded by a local network set up 
two days after the 29 April 1984 Gubbio main shock. The dataset is composed 
of 300 microearthquakes (Ml<3.5). The aftershocks follow a N140 trend and 
lie within a 20 km-long, 6 km-wide domain. The spatial distribution of the 
aftershocks describes two parallel linear  NW-SE oriented clusters set apart 
about 2 km, suggesting that an equivalent en-echelon fault arrangement is 
involved at depth. Most of the aftershocks lie between 2 and  8 km depth. The 
paper also presents a focal mechanism obtained from first motion polarities 
for the 29 April main shock, showing a WNW strike with a small left lateral 
component: plane A strikes 292 and dips 74, plane B strikes 074 and dips 
19. The paper supplies also the focal mechanism of 65 aftershocks and the 
resulting stress tensor orientation (N-S sigma 3 axis). The relocated 
mainshock lies near the SE edge of the larger cluster of aftershocks and its 
position suggests a rupture directivity towards NW. No surface rupture was 
observed.

Deschamps et al. (1989)
The authors provide a dataset of about 400 events with magnitude ranging 
between 0.8 and 3.1, recorded by a microearthquake network that was installed 
around the Gubbio basin during May-
June 1987. The shallower seismicity seems to be organised in clusters near 
Gubbio and Valfabbrica. Its main trend strikes NW-SE and deepens gradually 
toward the SE. 58% of the recorded events are confined between 3 and 7 km 
depth. The good station coverage allows these investigators to calculate 37 
focal mechanisms, which exhibit dominant normal faulting.

Selvaggi et al. (1989)
This work presents a geomorphologic and stratigraphic analysis that allows a 
characterisation of the Quaternary evolution of the Gubbio basin. This area is 
bordered to the east by a large normal fault and to the west by an antithetic 
extensional structure. The maximum depth to the bedrock beneath the basin 
is estimated to be about 600 m. The authors suggest that the maximum 
activity of the main fault occurred in the Lower Pleistocene. The basin filling 
complex includes a lignitic horizon that thickens toward the main fault and is 
interpreted as evidence for syn-sedimentary tectonic activity. During the 
Middle Pleistocene the tectonic activity diminished favouring the infilling of 
the basin. A few lines of geomorphic evidence of post-Lower Pleistocene 
activity of the Gubbio normal fault are also listed: tilting of fluvial erosional 
surfaces; subsidence of the central sector of the basin and subsequent burial by 
post-Wurm alluvial fans; the formation of a 2 km-long fault scarp on the 
recent Gubbio alluvial fan.

Westaway et al. (1989)
This paper presents a first-motion focal mechanism for the 29 April 1984 
Gubbio earthquake: Plane A strikes 135 and dips  55, Plane B strikes 315 
and dips 35.

Menichetti et al. (1991)
These investigators map some important geological features in the area 
between the Tiber Valley and the Gubbio basin. A N130-trending system of 
normal faults dipping both towards the NE and the SW appears to dominate 
the local tectonics. This is suggested by several individual steep fault planes 
having a throw of tens to hundreds of meters. A main N140 and a 
subordinate N75 sub-vertical extensional joint systems related to a post 
compressional phase are also seen in the field, lending further support to a 
strain field with NE-SW oriented tensile vectors. The authors also describe a 
N-S transpressional fault system displacing several previously formed 
contractional structures with right-lateral kinematics. The Gubbio structure is 
a NE verging rootless anticline striking N130 and overthrusting a syncline of 
syn-orogenic formation. A SW-dipping main normal fault cuts the axial zone 
of the anticline, producing a vertical throw of more than 1000 m. This normal 
fault dips 50 to 70 to the SW and has an en-echelon pattern, WNW and 
NNW oriented in its NW and SE portions respectively, with a flex point 
located at Gubbio. At the surface the fault is 25 km long and exhibits its 
maximum offset close to Mt. Semonte. Although Quaternary piedmont 
deposits tend to hide the bedrock fault plane, some scarps on the slope debris 
and alluvial fans are observed and interpreted as surface fractures due to the 
activity of a fault splay of the main extensional structure. The basin is filled by 
300 m of lacustrine deposits, dipping toward the fault and showing a roll-over 
anticline geometry; its depocentre is located very close to the fault. 
Morphological surfaces lying on the hanging wall of the master fault are 
clearly tilted in the SE part of the Gubbio basin. Footwall uplift is seen on the 
NE side of the anticline, where fluvial paleosurfaces are uplifted by a few tens 
of meters and tilted towards the NE. The detachment of the fault is 
reconstructed using seismic profiles and field observations and assuming 2000 
m of total displacement, 1800 m of throw, 1300 m of heave, 55 of dip. The 
calculated depth of the detachment is 8 km using the Chevron method, 6 km 
using the Chevron modified method, 7.2 km with the area balance method.

Menichetti (1992)
In this article, based on well data and some morphological scarps, Menichetti 
suggests the existence of an antithetic fault on the west side of the Gubbio 
basin. The Gubbio fault has 1000 m of throw and the associated synthetic faults 
show an extra 500 m of vertical offset. Geophysical surveys show that the 
depocentre of the basin is located in the hanging-wall of the fault and very 
close to it. The bedrock-infilling contact is reconstructed using stratigraphic 
data from more than 50 deep wells. A clear step seen between Gubbio and 
Mocaiana is related to a synthetic fault. The maximum depth of the basin, 400 
m, occurs exactly where the main fault shows its maximum offset. The main 
alluvial fans, having a maximum thickness of 100 m, exhibit a deposition 
angle that agrees with the present slope of the relief. In a few cases, they are 
affected by fractures and drag folds, interpreted as due to slip on the main 
fault. 

Lavecchia et al. (1994)
This paper analyses regional tectonic, structural and earthquake data and 
describes the similarity between present and past geologic stress fields in the 
eastern sector of central Italy. The authors reconstruct a multistage history of 
deformation and discriminate three major seismotectonic domains: the 
Intramountain seismic zone (with strong extensional seismicity), the 
Foothills seismic zone (with deep compressional and shallow extensional 
seismicity), the Coastal seismic zone (characterized by compressional 
seismicity in the uppermost 5-10 km). The Gubbio-
Norcia-Sulmona fault pattern (named Breakaway fault zone) is identified as 
the youngest fault system and constitutes the easternmost limit of regional 
upper-crustal extension accommodated by a set of  en-echelon west-dipping 
master faults. The Breakaway fault zone does not coincide with the axis of 
crustal thinning, located 60-70 km to the West. The Apennines exhibit a 
basement-involved structural style, together with a multiple detachment 
system. At any time in the Apennines orogenic phase, contraction and 
extension were simultaneously active 75-100 km apart. During about 2 My 
extension and compression shifted towards the E by 40-50 km, at a rate of 2-2.5 
cm/y. Thus any area underwent folding and thrusting before the inception of 
extensional faulting, which occurred 2-3 My later. 

Boncio et al. (1996)
These investigators report that, about 1 km SE of the town of Gubbio, the 
slope debris in contact with the bedrock fault plane shows deformations 
probably due to slip on the Gubbio fault. Extensional deformations on the 
Pleistocene fluvial-lacustrine sediments are observed along the fault South of 
Gubbio. Major normal and normal-oblique fault planes with striations were 
measured along the Gubbio normal fault. Most of the kinematic data are 
compatible with a NE-SW direction of extension. The inversion of slip data 
yields a triaxial-type stress tensor showing an almost horizontal N50- 
trending sigma 3. The present state of stress is determined using the focal 
mechanism of the earthquakes recorded during the May-June 1987 Gubbio 
campaign (with data from Deschamps et al. 1989). By applying the right 
dihedra method the authors stress the existence of three tensor groups. The 
main triaxial tensor has a N40-trending, nearly-horizontal sigma 3. A non-
triaxial (sigma 1>sigma 2=sigma 3) extensional tensor exhibits NW-SE and 
subordinate E-W directions. A non-triaxial (sigma 1=sigma 2>sigma 3) 
compressional tensor exhibits NW-SE and NNW-
SSE directions. The analysis of the nodal planes obtained for the 1984 Gubbio 
earthquake shows kinematic compatibility with the main tensor of the spread 
microseismicity. The NE-dipping nodal plane seems to be favoured by the 
value of the shape factor (R=0.52).

Boncio et al. (1998)
These workers describe the geometry of the NNW-SSE trending Altotiberina 
fault and of some antithetic splays. The work is based on field evidence and 
on interpretation of two commercial seismic lines, from the Tiber Valley to 
the Umbria-Marche Apennines, south of the CROP 03 line. The Altotiberina 
fault exhibits a staircase trajectory, starting as a steep, shallow fault below the 
Tiber Valley to the W and the becoming an almost flat surface to the E. Its dip 
angle is low-medium below the carbonate formations, at its eastern edge. The 
Gubbio fault is antithetic to the Altotiberina fault and reaches a maximum 
displacement of about 2000 m. To the South, shortening of the Gubbio 
anticline is transferred to the more internal Subasio anticline. The 
displacement of the Gubbio fault to the South is partitioned onto three minor 
structures, the easternmost of which is the Gualdo Tadino normal fault. 
Consequently a dextral transfer of both contractional and extensional 
structures is suggested. Detailed microseismic data supplied by the 1991-1994 
recordings of the local Umbria seismic network, by a temporary network set 
up soon after the 29 April 1984 M 5.2 Gubbio earthquake (Haessler et al., 1988) 
and during May-June 1987 (Deschamps et al., 1989), are also used for 
understanding the relationships between the Altotiberina fault and regional 
seismicity. The distribution of seismic activity appears to be controlled by the 
Altotiberina fault, which separates an active hanging wall block, slipping 
towards the NE, from an almost aseismic foot wall block. Frequent 
microearthquakes and moderate size earthquakes are related to the activity of 
antithetic fault splays, such as the Gubbio fault. The interpretation of two 
seismic profiles shows an active wedge-shaped rock volume, whose base 
deepens eastward. The seismicity of the Tiber Valley, of the Gubbio area and of 
the Umbria Valley is concentrated around 6 km depth and tends to deepen 
towards the ENE up to about 12 km East of Gubbio. The authors point out that 
seismicity tends to concentrate exactly where the Gubbio fault intersects the 
Altotiberina fault, at about 6 km depth. In summary, this seismotectonic study 
identifies an highly seismic crustal block located east of the Gubbio fault. This 
crustal block is characterised by small to moderate earthquakes and by frequent 
microseismicity mainly clustered in the foot wall of the Gubbio fault, 
especially near its branch point. A second crustal block, west of the Gubbio 
fault, has a relatively aseismic behaviour, the Gubbio fault playing a role of 
release-fault between both blocks. Here the shallow microseismicity is 
interpreted as the result of adjustment processes due to the collapse of the 
hanging wall.

Tavarnelli et al. (1999)
Based on a structural analysis these investigators suggest that the contact 
between pre-orogenic and syn-orogenic deposits in the forelimb of the Gubbio 
anticline corresponds to a bedding-parallel detachment that looks like a SW-
directed back-thrust. This contact appears to be truncated by a younger NE-
directed thrust that developed in the hanging wall of the Gubbio anticline. 
East of the Gubbio Mesozoic structure, the Mt. Pollo syncline is affected by 
normal faults that predate folding and syn-diagenetic faults caused by bulge 
uplift. This syncline is also cut by reverse faults, activated during flexural-slip 
folding and by a subsequent low-angle thrust, with a down-section trajectory 
producing extensional offset.

Barchi et al. (1999)
This work focuses on the results of the analysis of the deep reflection seismic 
profile CROP 03 and of other commercial seismic lines, both orthogonal and 
parallel to the upper Tiber valley and to the adjacent Umbrian pre-Apennines. 
The subsurface geometry of the Altotiberina fault is presented in a geological 
section showing WSW-dipping antithetic faults, the most important of which 
affects the carbonatic anticlines of Gubbio and Assisi. The northernmost 
profile (Perugia massifs-Gubbio-Mt. Cucco) shows: 1) a flat and shallow 
trajectory of the western part of the Altotiberina fault, offsetting a marker 
reflector by 5 km; 2) the Gubbio fault, that is responsible for a total offset of 2 
km, merges in a thrust at 4 km depth and ends on the Altotiberina fault at a 
depth of 5.5 km. The next profile to the South (Perugia massifs-Fossato di 
Vico) exhibits steps of the Altotiberina fault trajectory and illustrates its flat 
portion, located near the Gubbio anticline. In this profile the Gubbio fault 
produces an offset of 1.3 km. The southernmost  profile (Assisi-Gualdo 
Tadino) shows that the Altotiberina fault has a more regular trajectory and 
that the Gubbio structure is distributed among three minor structures, the 
easternmost of which borders the east side of the Gualdo Tadino basin. A 
dextral N30-oriented transfer zone affecting both compressional and 
extensional structures is hypothesised. Finally, between Umbertide and 
Perugia the Altotiberina fault seems to deepen and shift westward.

Boncio et al. (2000)
This work presents a structural model for earthquake faulting in the Umbria-
Marche Apennines by integrated analysis of geological, geophysical and 
seismological data. The recent Norcia, Gubbio and Colfiorito earthquakes as 
well as a major group of microearthquakes are seen to be compatible with a 
tensional state of stress characterised by a NE-trending sub-horizontal sigma 3-
axis. This tensor, which is similar to the Plio-Quaternary stress field deduced 
from fault kinematics, may be considered representative of the mean regional 
present-day state of stress. The nucleation of the 29 April 1984 Gubbio 
earthquake is assumed to have occurred at the base of the aftershocks volume, 
close to the intersection between the SW-dipping antithetic normal fault and 
the main E-dipping Altotiberina fault. The observed low-angle dip (20-30) of 
the rupture might be explained by the inversion of a low-angle thrust, 
inherited from the Mio-Pliocene compressional phase, during the extensional 
regime. The progressive deepening of the hypocenters from the westernmost 
sectors (Gubbio) to the easternmost ones (Norcia) appears to be well related to 
the Altotiberina fault basal detachment, as shown by seismic profiles. An 
almost continuous microseismic activity (M < 3) is spread within the hanging 
wall volume of the Altotiberina fault. The seismic potential of the active faults 
is expected to be higher in the easternmost seismic zone, where the 
detachment is deeper.

Barchi et al. (2000)
In this work the geometry of the Gubbio fault is carefully analysed through 
the interpretation of six seismic profiles. The interpolation of the profile data 
allows the authors to reconstruct an isobath map of the fault. The 
reconstructed structure is N 120-striking, SW-
dipping and exhibits an offset of about 1500 m. The fault reactivated a thrust 
in its deepest part, thus acquiring a listric trajectory. The Gubbio fault is 
antithetic to the Altotiberina fault; the intersection between the two structures 
occurs at about 6 km depth in the southern part, rises to 4.5 km in the central 
part and deepens again to 5 km in the northern part. The sinistral bending of 
the surface trace of the fault seems to follow the deeper part of the structure. 
The Gubbio fault is hypothesised to be composed by two independently active 
segments; each segment is about 15 km-long and 11.5 km-wide. The thickness 
of the seismogenic layer is calculated to be about 5.5 km.
