AMQ 24 Giraudi impaginato 04082014


 

   

 Available online http://amq.aiqua.it ISSN (print): 2279-7327, ISSN (online): 2279-7335 
 
 
 

Alpine and Mediterranean Quaternary, 27 (1), 2014, 5 - 28 

QUATERNARY STUDIES AS A TOOL TO VALIDATE SEISMIC HAZARD POTENTIAL OF 
TECTONIC STRUCTURES: THE CASE OF THE MONFERRATO THRUST FRONT 

(VERCELLI PLAIN, NW ITALY) 
 

Carlo Giraudi 
 

ENEA C.R. Saluggia, Vercelli, Italy 
Corresponding author: C. Giraudi <carlo.giraudi@enea.it> 

 
 

ABSTRACT: This paper proposes the study of the Quaternary geological evolution of the Vercelli Plain (Piedmont, NW Italy) with the aim 
of validating the reliability of assumptions about seismic hazard of tectonic structures based on seismotectonic data obtained from stud-
ies at regional scale. In particular, the Quaternary evolution is interpreted in order to verify and date the tectonic activity of the Monferrato 
thrust front, i.e., the westernmost arch of the buried northern Apennines front. 

In reference to the main purpose of the work, it is observed that only some stretches of the buried front (Lucedio and Cavourrina 
fault and, very likely, the flexures of Crescentino and Morano Po) were active between 870 and 400 ka BP.  

After 400 ka BP, near Crescentino and Trino, some structures transversal to the Monferrato front were probably activated, inducing 
the uplift of N-S elongated areas. The uplift affected both the northern Monferrato slope and the areas of the plain located south and 
north of the thrust front. The uplifted Trino area was limited to the east by the Salera Line. There are no indications of structures (fault or 
flexure) to the west of the Trino area or which form the limits of the uplifted Crescentino area, although their presence could be hypothe-
sized. 

The Salera Line is the most important identified structure; it is very likely a complex-kinematics fault that was active from the Plio-
cene to the Upper Pleistocene and the Holocene. It continues to the south inside the hill areas, for a length of about 20 km. 

Therefore, the recent tectonic movements are not associated with the Monferrato thrust front, as claimed by other authors, but rather 
with N-S structures which are transversal to the front. Although elements to evaluate the seismic hazard possibly associated with these 
structures are not available, it is unlikely that the seismicity alone of the easternmost Apennine fronts (Emilia and Ferrara Folds) can 
provide useful information to assess the seismic hazard of the Vercelli Plain and of Northern Monferrato.  

 
KEYWORDS: quaternary evolution, buried tectonic structures, climatic impact, climate and tectonic interaction, river diversions, Vercelli 
Plain, Monferrato hills. 

1. INTRODUCTION 
 
A detailed study of the Quaternary evolution of the 

Vercelli Plain (Northwestern Italy) is used here as a tool 
to assess the reliability of previous assumptions based 
on seismic hazard which were generally based on the 
analysis of historical seismicity, on the evolution of the 
drainage network, on the presence of Quaternary sedi-
ments displaced by faults, and on GPS measurements. 

Data collected and presented in this paper are inter-
preted in order to verify and date the tectonic activity of 
the buried thrust front of this sector of the Apennines. As 
Quaternary sediments of the Vercelli Plain bury the 
Monferrato thrust front (i.e., the westernmost of the 
three major buried arches of the Northern Apennines; 
Fig. 1A) the detailed geological and geomorphological 
study of the plain provides a reliable tool for understand-
ing the possible activity of the front.  

In fact, according to several Authors (e.g. Costa, 
2003; Dela Pierre et al. 2003b; Galadini et al., 2012) the 
activity of the frontal thrust of Monferrato ended in the 
early Pleistocene while, further to the East, the Emilian 
and Ferrara fronts are still active. This is testified also by 
historical and instrumental seismicity, which is totally 
absent in the Monferrato front, and increases toward the 
Emilian folds (Galli, 2005), reaching a maximum in the 
Ferrara Folds (Galli et al., 2012; Burrato et al., 2012a). 

On the other hand, the results of other seismotec-
tonic research, conducted at the scale of the whole Po 

Valley, led to the hypothesis that the Monferrato front 
may be seismically active, even if characterized by 
earthquakes with long return periods. Both Bonadeo et 
al. (2010) and Michetti et al. (2012), suggest that the 
level of seismic activity of the Monferrato front could be 
similar to the two other Northern Apennine fronts. In-
deed, according to Michetti et al. (2012), the Monferrato 
front might be able to generate earthquakes of Mw 6. 

In the past, the presence of the Trino isolated ridge 
(known as RIT in the literature), lying above the buried 
Monferrato front, had already stimulated research by the 
Working Group on the Po Valley Quaternary (Gruppo di 
Studio del Quaternario Padano: GSQP, 1976) which 
established that the area could have been affected by 
Middle Pleistocene tectonic activity. Moreover, geodetic 
data reported in Arca & Beretta (1985) provide informa-
tion on some aseismic deformations that occurred along 
a section which crosses the SE portion of the area of 
this study during the period between 1897 and 1957. 

Thus, the conflicting interpretation of tectonic activity 
and seismic hazard, and the presence of aseismic defor-
mations, require detailed study of the Quaternary geo-
logical evolution to determine which deformations were 
recorded by sediments and landforms, and thus which 
structures are likely to be active.  

In this paper, the evaluation of the deformation of 
Quaternary sediments, including those dated as the last 
2-3 ka, suggests the activity of tectonic structures which 
only partially match those hypothesized in the literature. 



 

   

 

To assess adequately the tectonic evolution 
of this area, this study takes into account the 
interaction between sedimentary and erosive 
phases driven by climate and those probably 
influenced by tectonics, starting from the up-
per Lower Pleistocene. 

 
2. STUDY AREA 
 

The Vercelli plain lies between the river 
Dora Baltea and the Ivrea morainic amphi-
theatre to the west, the river Po and the Mon-
ferrato hills to the south, the river Sesia to the 
east and the rivers Elvo and Cervo to the 
north (Fig. 2A). The plain is mainly formed by 
Plio-Pleistocene sediments, but in its south-
ern part a thin Quaternary sedimentary cover 
lies on marine sediments. The Tertiary ma-
rine sediments, outcropping in the Po river-
bed, are folded and heavily deformed by the 
activity of the northernmost Monferrato thrust 
front (SGd’I, 1969a; Dela Pierre et al., 
2003a).  

A large part of the Vercelli plain is in the 
Sesia River catchment whereas only the 
western and southern portions of the plain 
are in the catchments of the rivers Dora Bal-
tea and Po (Fig. 2B).  

It should be noted than the Po catchment, 
which includes a large area of the western 
Alps and the northern slope of the Torino and 
Monferrato hills, before receiving the Stura di 
Monferrato stream, narrows to 1.5-2.5 km 
(Fig. 2B). In the Monferrato hills the divide of 
the small catchments that drain toward the Po 
migrates abruptly towards the north and re-
mains very close to the plain down to the 
confluence with the Stura stream. Starting 
from the area of Gabiano, the bed of the Po is 
always very close to the hill slope and erodes 
it. The narrowing of the Po catchment in the 
southern Vercelli plain and in the northern 
Monferrato slope is an apparent anomaly 
compared to the westernmost areas.  

The Po, which is the main watercourse in 
the study area, during the Quaternary was 
mostly flowing south of the Monferrato hills. It 
migrated north of the hills only after a diver-
sion that took place during the Late Pleisto-
cene (Carraro, 1976; Carraro et al.,1980; 
1995). 

Before the diversion, the rivers Sesia and 
Dora Baltea flowed into a river, which from 
now on will be referred to as the DROS, 
formed by the confluence of the rivers Dora 
Riparia, Orco, Stura and other smaller 
streams, whose basin was in the north-western part of 
the Alps. 
 
3. METHODS 
 

In this paper a detailed discussion of the topog-
raphical, geomorphological and geological elements is 

presented in order to assess the chronology of the tec-
tonic phases and to verify whether the most recent tec-
tonic activity is actually connected with the Monferrato 
thrust front or with other structures. Topographic obser-
vations are based on the trend of the contour lines re-
ported (Ajassa et al., 1990) on the Elevation Map of the 
Piedmont Plain (Carta altimetrica dell'alta pianura 

 
 

Giraudi C. 

 
 
6 

Fig. 1 - Apennine thrust fronts buried below the Quaternary sediments of the Po 
Plain, and main structures of the Monferrato thrust front. 1A: general view of the 
Apennine buried fronts. 1B: the Monferrato-Torino Hills thrust front according to 
Costa (2003). 1C: the Monferrato thrust fronts below the Quaternary sediments of 
the Vercelli Plain, according to the Geological Map of Italy F. Vercelli (1969) and 
ENEL (1985). 1D: the Monferrato thrust fronts below the Quaternary sediments of 
the Vercelli Plain according to (MSdI = Bigi et al., 1990) and (CGT = Dela Pierre 
et al., 2003a). 

 



 

   

 

 
 

7 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 

piemontese in Italian) at the scale of 1:250,000. The 
data used to draw the topographical profiles are re-
ported on the Carta Tecnica della Regione Piemonte 
(the official regional topographic cartography) at a scale 
of 1:10,000. 

The profiles were designed using 5 m contour lines. 
The geological maps presented are the result of both 
field surveys carried out over a long period of time, and 
of the interpretation of aerial photographs. The flight 
done in the '50s (Istituto Geografico Militare, flight) was 
mainly used, as it is the most useful one for the recogni-
tion of low terrace scarps. As a matter of fact, agricul-
tural works carried out in the second half of the past 

century often erased morphological features that, in 
turn, could be relevant for the interpretation of the evolu-
tion of the area. 

The lithology of the sediment forming the surface of 
the terraces has been observed on terrace scarps, 
along the banks of streams and on ephemeral expo-
sures. Field data have been integrated with stratigraphic 
data from boreholes. In the area west of Ronsecco and 
NW of the RIT, the stratigraphy of the sediments was 
surveyed along several 2.5-m-deep, and 100-m-spaced 
trenches, all dug for the foundation of high voltage py-
lons, and arranged along two different alignments, for a 
total length of 7-8 km.  

Fig. 2 - Location of the studied area. 2A: contour map, slope of the plain, topographic anomalies and main geological structures buried 
below Quaternary sediments. 2B: the river Po catchment basin west of the confluence of the Stura stream. 



 

   

 

The chronological framework was mainly 
based on the morphological correlation be-
tween the terraces in the Vercelli Plain and 
the glacial and glaciofluvial features of the 
Ivrea moraine amphitheatre (Gianotti et al., 
2008). The age of some sediments has been 
constrained by previous geochemical char-
acterization of a tephra layer (ENEL, 1984), 
by the dating of a second tephra layer with 
the fission track method (ENEL, 1984), by 
some radiocarbon dating (Tropeano & Olive, 
1989; Giraudi, 1998) and by the presence of 
archaeological artefacts from the Lower Pa-
laeolithic to the Bronze Age (Fedele, 1976; 
GSQP, 1976; Giraudi, 1998). 

I have assessed the stratigraphy of the 
Quaternary deposits through both the strati-
graphy of water wells (Varalda et al., 2006; 
ARPA Piemonte, 2014), and direct observa-
tion of boreholes drilled in the framework of a 
study for the seismotectonic characterization 
of areas identified as possible locations of 
nuclear power plants, in the years between 
1976 and 1984 (ENEL, 1984). 

The ENEL data have already been used 
for the geological map of Italy at a scale of 
1:50,000 (Dela Pierre et al., 2003a) and the 
stratigraphies of the boreholes carried out by 
ENEL are listed and described in the Geo-
technical Data Bank of the ARPA Piemonte 
(2014). 

In order to infer the Quaternary tectonic 
deformations, thickness changes of alluvial 
and glaciofluvial sedimentary units and differ-
ent elevations of the base of sediments form-
ing the terraces have been evaluated. 

Indeed, the stratigraphic data show a 
great thickness variability of glaciofluvial and 
alluvial sediments forming the plain North 
and South of the Monferrato buried thrust 
front. 
 
4. GEOLOGY OF THE VERCELLI PLAIN 
 

The Vercelli plain is composed, almost 
completely, by glaciofluvial, fluvial and ae-
olian Quaternary sediments (SGd’I, 1969a). 
Marine tertiary sediments outcrop on the 
scarps of the highest terraces and in the bed 
of the river Po, i.e. where the river is eroding the north-
ern slope of the Monferrato Hills. 

As already mentioned, the southernmost portion of 
the plain is formed by Quaternary sediments, less than 
15-20 m thick, lying on the Tertiary bedrock deformed 
by folds, fault and involved by the frontal thrust.  

The following description of Tertiary sediments and 
tectonic structures is based on data derived from geo-
physical researches and wells dug during oil exploration 
campaigns (Pieri & Groppi, 1981; Cassano et al., 1986) 
and the seismotectonic characterization of sites suitable 
for a nuclear power plant (ENEL, 1984). Lastly, data 
from the Po river bed derive from a survey of the out-
crops.  

4.1. Tertiary bedrock and main tectonic structures 
Previous works on the study area have stated the 

bedrock of the southern Vercelli plain is formed by Terti-
ary marine sediments involved in one or more thrust 
fronts. Tectonic interpretations (Fig. 1C; 1D) reported in 
SGd’I (1969a), ENEL (1984) and in Bigi et al. (1990) 
show that the northernmost thrust front (Balzola fault) 
affects at depth the Lower Pliocene marine sediments. 
South of the Balzola Fault, one or more thrust fronts are 
reported by the Authors. According to Costa (2003), the 
northernmost part of the Monferrato thrust front has 
been extruded northwards along two lateral structures 
(Fig. 1B) located east and west of the front. 

Borehole data (ENEL, 1984) aided in recognizing 

 
 
8 

 

Fig. 3 - Position of the boreholes and the wells, Tertiary and Early Pleistocene sedi-
ments lying below late Early Pleistocene to Holocene deposits. 3A: boreholes and 
wells used for their stratigraphic data. 3B: age of the sediments sampled in the 
boreholes covered by glaciofluvial and fluvial deposits, and outcropping in the Po 
river bed, main tectonic structures inferred from the borehole stratigraphy. 

 
 

Giraudi C. 



 

   

 

the presence of marine sediments below the Quaternary 
glaciofluvial and fluvial sediments, mainly dated from 
Eocene to Pliocene, but also to the onset of the Early 
Pleistocene, and of Early Pleistocene alluvial and lacus-
trine sediments (Fig. 3A, B). In this paper the Upper 
Pliocene marine sediments reported in ENEL (1984) are 
dated at the Early Pleistocene of the new international 
geochronological scale (Gibbard et al., 2010).  

Except for some areas (Oligocene, Pliocene and 
Early Pleistocene marine sediments outcropping or 
drilled in the RIT area and south of Crescentino) the 
boundaries between the different marine formations 
cannot be clearly traced. It follows that in Fig. 3 the sedi-
ments and their ages are shown with symbols in corre-
spondence to the places where they have been recog-
nized. 

Through borehole alignments (ENEL, 1984) it was 
possible to deduce the presence of at least two faults 
(Cavourrina and Lucedio Faults - Fig. 3A), the position 
of which lies within a 40-50-m-width strip matching the 
distance between the closest pair of boreholes.  

The Cavourrina Fault juxtaposes Oligocene and 
Pliocene marine sediments (Fig. 3B). The fault bounds 
the northern edge of the RIT and it was very likely re-
sponsible for its uplift. West of the RIT, the fault plane 
dips to the NW. North of the RIT, according to the drill-
ing stratigraphy, the fault plane is nearly vertical. South-
east of the RIT, the fault reaches at least the latitude of 
Trino (Fig. 3), where two closely spaced drillings show 
the presence of marls, probably Oligocene (in the west) 
and of Pliocene silty sands (in the east). There are no 
data that can be used to infer whether the fault contin-
ues to the south, outside of the area surveyed with bore-
holes.  

The Lucedio Fault trends WSW-ENE, being slightly 
convex northward. Here Pliocene and Lower Pleisto-
cene marine sediments are faulted against Lower Pleis-
tocene fluvial and lacustrine sediments, inducing the 
subsidence of the northern area at least after the Lower 
Pleistocene. In the alignment where the boreholes are 
closer, the northward dip of the fault plane cannot be 
less than 80°. 

Hydrogeological studies in the area (ENEL 1984) 
have shown that, just to the north of the Lucedio Fault, 
there are springs fed by water rising from deep aquifers 
(Fig. 3) having a chemical and isotopic composition very 
different from that of water of surrounding areas. 

The rise of deep water also occurs NW and SE of 
the stretch of the fault indicated by an alignment of bore-
holes: it is therefore probable, as suggested in ENEL 
(1984), that the Lucedio fault might reach the areas 
north-east of Crescentino and of Salera, south-east of 
Tricerro. 

A seismic line crossing the faults north of the RIT 
(ENEL, 1984) shows that both the Cavourrina and 
Lucedio Faults match the thrust fronts evidenced by the 
SGd’I (1969a) (Fig. 1). Here the Cavourrina Fault could 
partly fit in with the youngest thrust front reported by Bigi 
et al. (1990). 

On the other hand, ESE and WSW of Crescentino, 
where many authors placed the Monferrato thrust front 
(SGd’I, 1969a; Pieri & Groppi, 1981; ENEL, 1984; Cas-
sano et al., 1985; Dela Pierre et al., 2003), at least down 

to the depth of about 200 m, any of the available bore-
hole logs account for the existence of faults similar to 
the Lucedio one. The Pliocene and Lower Pleistocene 
marine sediments dip 10-15° to the NNW and are de-
formed by a flexure. The flexure starts just east of Cres-
centino near the western termination of the Lucedio 
Fault. 

The change of the tectonic features of the thrust 
front east of Crescentino implies the presence of a fault 
crossing the front (Crescentino Fault) which could match 
the NW-SE lateral ramp hypothesized by Costa (2003). 
Indeed, the Crescentino Fault (Fig. 3B) reaches the Po 
river bed in a place where outcropping Tertiary marine 
sediments show NW-SE fault planes. 

In the area between Pontestura and Morano Po, the 
river bed is almost completely carved in Tertiary bed-
rock (Fig. 3B): the presence of calcareous marl sug-
gests that it belongs to the Eocene terms of the 
“Ligurian” units, the same reported by Dela Pierre et al. 
(2003a) in the Po bed south of Trino. In the river bed NE 
of Pontestura, nearly vertical marl strata, running N-S, 
outcrop, while to the east strata dip very irregularly and 
are displaced by faults. Undeformed NNW-SSE marl 
outcrop in the river bed SW of Morano Po, that is, east 
of the area where the sediments are displaced by faults. 

Also near Casale Monferrato, in the river bed, Eo-
cene clay and calcareous marl of the “Ligurian” units 
outcrop, although a few dozen metres north of the river 
bed, Pliocene marine sediments (subzone MP14 and 
MP15a) have been found in boreholes (Violanti & Sas-
sone, 2008). The boundary between Eocene and Plio-
cene sediments is not exposed, but strongly deformed 
outcropping sediments suggest the presence of an un-
conformity or a tectonic contact. 

The geological structure of the Casale Monferrato 
area matches that of the Castel Verrua area, South of 
Crescentino, where Pliocene sediments unconformably 
overlie the deposits of the “Complesso Indifferen-
ziato” (“Ligurian” units; Zappi, 1961; Dela Pierre et al., 
2003a,b). At Casale Monferrato, the contact could corre-
spond to the projection at the surface (Fig. 1C) of a NW-
SE thrust front (evidenced in ENEL, 1984) or of another 
front (Fig. 1D) hypothesized in Bigi et al. (1990). 
 
4.2. Geomorphology and Quaternary stratigraphy of 
the Vercelli Plain 

The Vercelli Plain is quite homogeneous, especially 
in the north-western and central-northern areas (Fig. 
2A). According to all previous works (SGd’I, 1966; 
SGd’I, 1969a; GSQP, 1976; Carraro et al., 1975; 
Giraudi, 1998; Dela Pierre et al., 2003a; Gianotti et al. 
2008) it is mainly formed by glaciofluvial and fluvial sedi-
ments dated between the Mindel glaciation and the 
Holocene. 

Despite the scarcity of exposures, the stratigraphy of 
the sediments is fairly well known thanks to boreholes 
drilled for water and stratigraphic surveys. The strati-
graphic data enable the thickness of the Quaternary 
sediments to be evaluated and also to differentiate the 
areas in which sedimentation prevailed from others 
where erosion and sedimentation phases occurred. 

Based on the abundance of terraces formed by the 
main streams, (Fig. 4) the Vercelli Plain can be divided 

 
 

9 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 



 

   

 

into four parts: the north-western area, formed by some 
terraced surfaces, is a narrow strip surrounding the hills 
of the SE Ivrea morainic amphitheatre. The central-
northern area, extending over about two-thirds of the 
studied plain, forms the main surface of the plain. The 
southern area is formed by seven different terraces 
while the last well recognizable area is the belt formed 
by three terraces parallel to the river beds.  

The four older terraces (S1 to S4) are only in the 
southern area, while the others (S5 to S8 and T9 to 
T11) are more diffuse. The stratigraphy of the sediments 
forming the terraces will be described from the oldest to 
the most recent. However, some parts of the Vercelli 
Plain are formed by terraces shaped by local streams 
(L1-2), and will be described separately. 

The relationship between sediments that form ter-
races and moraines of the Ivrea amphitheatre indicates 
the glaciofluvial origin of sediments and suggests the 
age of some terraces. 

The bottom of sediments forming the oldest terrace 
is carved into the Tertiary bedrock, while the bottom of 
other glaciofluvial deposits cuts into older sediments 

and sometimes into the Tertiary bedrock. As determined 
in the whole of the Mediterranean basin by Macklin et al. 
(2002), I have assumed that, if the phases of coarse 
sedimentation predominantly correspond to periods of 
glacial expansion, the phases of prevailing erosion 
mainly correspond to interstadials or interglacials. The 
terraces (Fig. 4), due to their characteristics, can be 
divided into groups. One group (S1-S3) includes only 
the terraces that form the RIT, relating to a landscape 
that was significantly different to the modern one. Con-
versely, the distribution of younger terraces (S4-T11), 
the inclination of their surfaces, and the direction of their 
scarps enable the identification of their own stream. In 
this group of terraces a first subgroup (S4-S8) can be 
distinguished: this includes terraces shaped by rivers 
that flowed, at least in certain parts, in areas away from 
the current river beds. The terraces form the eastern 
portion of the river Dora Baltea glaciofluvial fan, and the 
area, oriented approximately W-E, between the RIT and 
the Monferrato hills. A second subgroup includes ter-
races (T9-T11) lying along the modern river beds.  

Several exposures and the stratigraphy and lithology 

 
 
10 

 
 

Giraudi C. 

Fig. 4 - The terraces of the Vercelli Plain. S1-S3: terraces forming the Trino isolated hill (RIT). S4-S8: terraces shaped by Alpine rivers 
when their bed was far from the modern ones. T9-T11: terraces forming a belt near the modern day Alpine river beds. L1-L2: terraces 
shaped by local streams.  



 

   

 

of sediments obtained from boreholes show that some 
terrace surfaces are formed by sediments of different 
ages. 

 
Terrace S1 - Sediments that form terrace S1 (“a” in Fig. 
5) are described in SGd’I (1969a), GSQP (1976) and 
ENEL (1984) as directly overlying the Oligocene marine 
bedrock, 8-9 m thick, and formed, at the bottom, by 
glaciofluvial sandy gravel. Sediments are very weath-
ered (colour 2.5-5 YR of the Munsell Soil Color Chart, 
MSCC). The degree of weathering of sediments is also 
similar to that of deposits partly outcropping on a terrace 
scarp eroded by the Dora Baltea river (“a” in Fig. 5), not 
far from the morainic front, and assumed to be formed 
before the Mindel glaciation (SGd’I., 1969a). A layer of 

pedogenized loess (coloured 5YR, MSCC) lays above 
sandy gravel, and it is covered by a younger, pedoge-
nized loess (coloured 7.5YR, MSCC). According to the 
SGd’I (1969a), the older loess sedimented during the 
Mindel glaciation, while the second one is dated at the 
Riss glaciation. Another thin and discontinuous loess 
horizon, (pedogenized and coloured 10YR, MSCC), 
ends the stratigraphic sequence. 

The S1 glaciofluvial sediments are weathered and 
pedogenized to the same degree as some morainic 
deposits in the Northern Ivrea amphitheatre reported by 
Gianotti et al. (2008). According to Carraro et al. (1991) 
the moraines with soils coloured 2.5YR (MSCC) are the 
oldest and, according to their palaeomagnetic character-
istics, can be dated to the late Early Pleistocene. Other 

 
 

11 

Fig. 5 - Geological map of the Vercelli Plain. Legend- m1-m2: moraine ridges of the Serra Alloformation; a-h: late Early Pleistocene to 
late Upper Pleistocene glaciofluvial sediments; a: late Early Pleistocene (MIS 22-?); b: late Early Pleistocene to Middle Pleistocene (MIS 
22?-MIS 12); c: Middle Pleistocene (MIS 10); d: Middle Pleistocene (MIS 8); e: late Middle Pleistocene (MIS 6); f: late Middle Pleistocene 
or early Upper Pleistocene; g: early (?) and middle Upper Pleistocene (MIS 4?); h: late Upper Pleistocene (MIS 2); i, l, m: Late Holocene. 
L1: sediments from Valdora temporary stream and other local streams (MIS 4? - MIS 2?); L2: sediments of the local streams (MIS 2?-
Late Holocene). 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 



 

   

 

moraines, early Middle Pleistocene in age (Gianotti et 
al., 2008), contain soils coloured 5YR (MSCC). The S1 
glaciofluvial sediments, being the oldest and most 
weathered, could have the same age as the oldest mo-
raines and date back to late Early Pleistocene.  

The loess dating is based mainly on the presence of 
prehistoric artefacts. The younger loess covers some 
Upper Palaeolithic artefacts and can be dated at the 
MIS 2. The intermediate loess covers Lower Palaeolithic 
artefacts and includes at the top some Middle Palaeo-
lithic Mousterian artefacts. Thus, the top of the loess 
may be dated to the late Middle Pleistocene or Upper 
Pleistocene (Fedele, 1976), that is, at MIS 6 - MIS 3. 
The older loess is, therefore, older than MIS 6 and 
dated at least at MIS 8. 
Terrace S2 - The terrace surface S2 is separated from 
that of S1 by a scarp that reaches a height of approxi-
mately 10 m. The stratigraphy of the sediments forming 
the terrace ( SGd’I, 1969a; GSQP, 1976; ENEL, 1984), 
is very similar to that of S1. Glaciofluvial sandy gravel 
and very weathered sand (coloured 2.5-5YR, MSCC), 
(“b” in Fig. 5) form the main sedimentary body. The S2 
sediments, assumed to be older than the Mindel glacia-
tion by SGd’I (1969a), can be correlated to the moraines 
having the same degree of weathering and can be 
dated to the late Early Pleistocene or the early Middle 
Pleistocene. They are covered by two loess horizons, 
the older and more weathered one (colour 5YR) being 
covered by a less weathered one (colour 7.5YR). At the 
top of the younger loess, Middle Palaeolithic Mousterian 
artifacts have been found (Fedele, 1976). We can as-
sume, therefore, that the loess horizons correspond to 
those described for the S1 surface and that they are of 
the same age (MIS 6- MIS 3 and MIS 8). On the whole, 
the sediments are 15-16 m thick.  
Terrace S3 - Terrace surface S3 is separated from that 
of S2 through a scarp that reaches a height of approxi-
mately 10 m. The stratigraphy sediments (GSQP, 1976; 
ENEL, 1984), is made by gravelly sand and sandy 
gravel, with interbedded sand and silty sand layers, 
weathered at their top and coloured 5YR (MSCC). Also 
these sediments are originally glaciofluvial, but interbed-
ded fine sediments are colluvia that originated from the 
S2 terrace scarp. The glaciofluvial sediments can be 
correlated to moraines having the same degree of 
weathering and, consequently, dated to the early Middle 
Pleistocene. As on terrace S2, the pedogenized gla-
ciofluvial sediments are capped by two loess horizons: 
the older one is more weathered (5YR in colour) than 
the younger one (7.5YR). The loess horizons can be 
correlated, therefore, to those lying on terraces S1 and 
S2. On the whole, the thickness of sediments forming 
the terrace S3 can be around 15-17 m.  
Terrace S4 - The terrace S4 has been observed in 
three places, north of the RIT and north of Crescentino. 
Here the S4 surface is preserved in two small, isolated 
flattened heights which are surrounded by younger ter-
races. The first, larger one (nearly divided into two parts 
by a small valley with a flat bottom) lies near San Gri-
sante, while the second one is near Lamporo. Sedi-
ments forming the San Grisante terrace (GSQP, 1976; 
ENEL, 1984), are glaciofluvial sandy gravel covered by 
silt and sandy silt. Glaciofluvial sediments (“b” in Fig. 5) 

are very weathered and there is a truncated palaeosoil 
at their top. Therefore, between the end of the glacioflu-
vial sedimentation and the onset of the deposition of top 
silts, a strong pedogenetic phase occurred which was 
followed by an erosion. The degree of weathering of 
San Grisante glaciofluvial sediments is similar to that of 
sediments forming terraces S2 and S3 and of moraines 
dating back, according to Carraro et al. (1991) and 
Gianotti et al. (2008), to the late Early Pleistocene or the 
early Middle Pleistocene. According to GSQP (1976) the 
soil on the top of the glaciofluvial sediments is the so-
called “ferretto”, which developed during the interglacial 
between the Mindel and the Riss glaciations, that is 
during the MIS 11. The glaciofluvial sandy gravel should 
therefore have been sedimented during the MIS 12 or 
earlier.  

Silt and sandy silt sediments, overlying the top of 
glaciofluvial sandy gravel, form a layer of variable thick-
ness (from 3.6 to 6 m) and are capped by a soil col-
oured 10YR/7.5YR (“d” in Fig. 5). Silt is similar to that 
forming the top of the Torrazza-Rondissone terrace, 
lying W of the Dora Baltea river, described by GSQP 
(1976). Silt sedimented on a flood plain or in a palus-
trine basin, but at its top it consists of loess-derived 
deposits. In the Torrazza-Rondissone terrace, interbed-
ded between the silty deposits, some 0.1-0.5-m-sized 
polished and striated pebbles form some stone-lines. 
According to GSQP (1976) pebbles could have been 
carried there by floating ice chunks stemming from the 
tongue of the Dora Baltea glacier. The sin-glacial origin 
of sediments assumed by SGd’I (1969a) is therefore 
confirmed. In a quarry of the Torrazza-Rondissone ter-
race, interbedded in the upper silt sediments, a horizon 
containing volcanic glass was sampled. Mineralogical 
characteristics of glass suggest that it originated from 
the M. Amiata volcano (ENEL, 1984), which was active 
between 300 and 180 ka BP (Bigazzi et al., 1981), that 
is, in a period including the MIS 8 and the early MIS 6. 

North of the RIT, top sediments forming the surface 
are made by 4-to-6-m thick silt, very similar in its lithol-
ogy and sedimentary facies to that described above and 
containing remnants of the tephra layer. Silt covers un-
weathered sandy gravel (“d” in Fig. 5), about 8 m thick. 
Below the sandy gravel, a colluvium of a soil formed by 
very weathered silty clay coloured 2.5YR, was sampled 
in a borehole. It follows that the colluvium derives from 
the top of the pedogenized sandy gravel forming S1, 
and that the sandy gravel was probably sedimented 
during the same cold stage just before the silt. As the 
top of terrace S4 is higher than the S5 (dated at the MIS 
6; see below), it was formed in a cold stage preceding 
the MIS 6. Based on the volcanic glass chronological 
framework, the cold stage is, therefore, the MIS 8 (280-
240 ka BP). The loess-derived palustrine sediments 
could therefore be correlated with the oldest loess, 
which overlies soils coloured 2.5-5YR, identified on ter-
races S1, S2 and S3. 
Terrace S5 - This forms the NW part of the Vercelli 
Plain and derives from the melting of remnants of differ-
ent terrace surfaces that can be distinguished only near 
the moraine hills. 

The terraces consist of glaciofluvial sediments 
weathered by a soil coloured 7.5YR. They outcrop dis-

 
 
12 

 
 

Giraudi C. 



 

   

 

continuously and, generally, are limited in extent, form-
ing an apron around the moraines. In turn, the moraines 
lying at the NW boundary of the study area are formed 
by two differently preserved series of ridges (m1 and m2 
in Fig. 5). The presence of a series of terraces and mo-
raine ridges shows that the evolution of the glacial front 
in this area was very complex. 

According to Gianotti et al. (2008), both moraines 
and glaciofluvial sediments, dated to the Riss glaciation 
in former geological maps and papers (SGd’I, 1966; 
1969a; Carraro et al., 1975), pertain to the “Serra Allo-
formation” dated to the late Middle Pleistocene, that is, 
the MIS 6. 

To the south and SE the different surfaces join to 
form a single surface (S5, Fig. 4). 

Above the contour line 170 m a.s.l. (Fig. 5), surface 
S5 is formed mainly by sandy gravel sediments, some-
times covered by a thin silt layer, weathered by a soil 
coloured 7.5YR. At a lower altitude, surface S5 devel-
ops on sediments having different ages and origins. 

In the area NE of Lamporo, glaciofluvial sandy 
gravel, heavily weathered (coloured 2.5-5YR) down to a 
depth of 10-12 m (“b” in Fig. 5), is both exposed and 
sampled in some boreholes; this is very similar to that 
underlying the silt that forms the S4 surface near San 
Grisante. The degree of weathering of sediments is 
similar to that of S2 and S3 terraces and of the mo-
raines dating back to the late Early Pleistocene or the 
early Middle Pleistocene (Carraro et al., 1991; Gianotti 
et al., 2008). In the area NE of Lamporo, pedogenesis 
lasted for a longer period than in the San Grisante and 
RIT area, and has continued till the present day. Ardu-
ino et al. (1984), studying the relationships between the 
age of soils, the presence of iron oxides and the red-
ness of soils, evidenced that the pedogenesis did not 
stop during cold periods. 

Other boreholes showed that at the northern and 
eastern boundaries of the area with strongly weathered 
sandy gravel, there are sandy gravelly sediments a few 
metres thick, less weathered and coloured 7.5YR (“c” in 
Fig. 5). These sediments are covered by the younger 
glaciofluvial sediments that were described above, 
dated to the MIS 6. 

In some places surface S5 is capped by discontinu-
ous layers of silt, 2-3 m thick, alluvial in origin, formed 
by the sedimentation of material derived from the ero-
sion of soils developed on glaciofluvial deposits. The silt 
can be both stiff and weathered by a soil coloured 
7.5YR, or less stiff, but less pedogenized (soil coloured 
10YR). The latter sometimes overlaps the more weath-
ered one. In profiles 1 and 2 (Fig. 6) it can be noted that 
the boundaries between the different sedimentary units 
described above are evidenced by small changes in the 
slope of the plain: the places where the most weathered 
sediments are exposed are the flattest. 
Terrace S6 - This terrace is only in the western plain 
(Fig. 4). A scarp 3-4 m high separates it from S5 but it 
becomes less clear and nearly disappears towards the 
SE. The terrace is made by sandy gravel (“f” in Fig. 5), 
the thickness of which is unknown, younger than the 
MIS 6 glaciofluvial sediments forming S5. 
Terrace S7 - The surface of terrace S7, surrounding 
both the RIT and the S4 terraces, is well represented in 

the area. The scarp that separates the terrace from S6 
is higher to the west and becomes smaller towards the 
east, and the boundary between surfaces S7 and S5 is 
not a real scarp, but only a slight break in the slope of 
the plain (profiles E, F, in Fig. 6). 

West of the Lamporo area, sediments forming the 
terrace (“g” in Fig. 5) are mainly glaciofluvial sandy 
gravel, while to the East, in places where the surface is 
less eroded by local streams, a layer of alluvial silt, 2-3 
m thick, pedogenized by a soil coloured 7.5YR, covers 
the sandy gravel. In a few places, the top silt is capped 
by another layer of silt not so stiff, with a less evoluted 
soil coloured 10YR, which can be correlated to the 
younger silt layer lying on terrace S5. The sediment 
thickness is on the whole about 15 m. 

Near the SW slope of the RIT, below the silt that 
forms surface S7, sandy gravel weathered by a soil 
coloured 5YR has been found. These sediments are 
probably remnants of the sandy gravel forming also 
terrace S3, only eroded at the top during the shaping of 
terrace S7. 

The terrace correlates with that evidenced by 
Gianotti et al. (2008), outside the moraine amphitheatre, 
on the right of the Dora Baltea river, and formed by gla-
ciofluvial deposits of the Piverone Alloformation. The 
terrace sediments, therefore, can be dated to the period 
following the MIS 6 glacial maximum (which ended 
about 140 ka BP) and preceding the MIS 2 glacial maxi-
mum (which started about 30 ka BP), named MIS 4? in 
this paper. 

Surface S7 was eroded by local streams. West of 
the RIT, these streams caused mainly the erosion of the 
summit silt, while north and NE of the RIT, the terrace is 
cut by a complex network of small valleys, the bottom of 
which lies between 1-2 m and 7-8 m below the terrace 
surface. 
Terrace S8 - The scarp dividing S7 from S8 is lower 
towards the west and higher towards the east: it is this 
feature that makes it different from those that separate 
the terraces S5 from S6, and S6 from S7. In the plain 
south of the Po river, terrace S8 has been observed 
only west of Castel Verrua and east of Casale Monfer-
rato, but is lacking in the intermediate area. 

Sediments forming the terrace (“h” in Fig. 5) mainly 
consist of sandy gravel, overlain by a soil coloured 
10YR. The sediment thickness, which is known only in 
the Trino and Palazzolo area, does not exceed 10 m. 

The terrace correlates with that evidenced by 
Gianotti et al. (2008), outside the moraine amphitheatre, 
on the right of the river Dora Baltea, and is formed by 
glaciofluvial deposits of the Ivrea Alloformation. Inside 
the amphitheatre sediments of the Ivrea Alloformation 
are dated to the last glacial maximum, around 21 ka BP, 
according to Gianotti et al. (2008), or are younger, be-
cause they also lie upstream of the terminal moraines. 
The sediments forming S8 can be dated, therefore, to 
the late Upper Pleistocene, between 21 and 14-15 ka 
BP. 
Terraces T9, T10, T11 - These are the most recent 
terraces and form a discontinuous strip along the river 
beds. It should be noted that starting from the area 
south of Fontanetto Po down to Trino, the strip formed 
by terraces T9, T10 and T11 is narrower than in the 

 
 

13 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 



 

   

 

western and eastern areas (1.2 to 2.5 km 
wide, against the 2.5-5 km near Cres-
centino and 3-3.5 km east of Morano Po). 
In the plain south of the Po, between Ver-
rua Savoia and Casale Monferrato, only 
terrace T11 is present.  
Alluvial sediments forming terraces T9, T10 
and T11 are mainly of sandy gravel lithol-
ogy (i, l, m in Fig. 5). Their thickness, visible 
only between Fontanetto Po and Trino, 
does not exceed 6-8 m. In the sediments 
that form terrace T9 some useful dating 
elements have been found. In a borehole 
drilled near Fontanetto Po an iron nail con-
tained in the sandy gravel came to light, 
similar to those used by Romans for the 
Ivrea harbour in the Dora Baltea river (F. 
Gambari, personal communication). In a 
quarry South of Villanova Monferrato, tree 
trunk remnants have been exposed, dated 
380-600 AD, 115-725 AD and 440-640 AD 
(2σ calibrated 14C age; Tropeano & Olive, 
1989). It follows that terrace T9 should be 
dated to the Roman and the Early Medieval 
periods. 

On the Po banks, near Palazzolo, Trino 
and Morano Po, where sandy gravel form-
ing terraces T10 and T11 lie directly on the 
Tertiary bedrock, at the bottom of the allu-
vial sediments, bronze axes and swords 
from the Bronze Age have been found 
(Janigro D’Aquino,1979; Fozzati & Giraudi, 
1983; Facchin, 1997; Giraudi, 1998). Near 
the Po bed, north of Camino, the T11 sedi-
ments cover the remains of a medieval 
building and contain remnants of poles, 
from the Middle Ages (1225-1400 and 1325
-1460 AD), and trees, dated to the Renais-
sance (1410-1620 AD) (2σ calibrated 14C 
age; Giraudi, 1998). On the whole we can 
state that sediments forming the three most 
recent terraces date back to the last 3-4 
millennia. 
 
Terraces shaped by small local streams - The Ver-
celli plain has been shaped also by local streams mainly 
fed by water from springs sited along the “risorgive” 
area (De Luca et al., 2005). Fig. 4 shows two areas 
shaped in a different way by said streams.  
Surface L1 - This is the surface, lower than S5 and S7, 
that forms the central and Northern Vercelli Plain, 
formed mainly by sandy gravel. L1 is fairly regular but in 
the eastern part it appears cut by small valleys with flat 
bottoms, 1 to 3 m deep, produced by smaller local 
streams. 

The scarp between S5 and L1, well recognizable in 
the NW area, becomes difficult to identify towards the 
SE, but NW of Ronsecco it is again well recognizable. In 
the north-western plain, L1 narrows and enters an aban-
doned river bed, produced by a glacial meltwater 
stream, which cut into the MIS 6 glaciofluvial sediments. 
The stream that shaped the L1 surface, therefore, came 
from the former stream bed (Fig. 4), called Valdora. 

According to Gianotti et al. (2008) the glacial meltwater 
stream was linked to the Piverone Alloformation glacial 
phase, doubtfully attributed to MIS 4, and was therefore 
contemporaneous with the glaciofluvial sedimentation 
forming the S7 terrace. However, the surveys carried 
out for this paper have evidenced that the bottom of the 
former Valdora bed, formed by sandy gravel having a 
homogeneous grain size and lithology, is cut across by 
a gently sloping scarp a few metres high. The surface 
L1 begins east of the scarp, therefore it is younger than 
the Piverone Alloformation. In the southern Vercelli 
plain, surface L1 cuts surface S7, which is correlated 
with said Alloformation, confirming that L1 was younger. 
The scarp, which crosses the former Valdora bed, can-
not have been produced by lithological discontinuities or 
tectonic displacements, because these would also have 
affected the surrounding areas formed by older sedi-
ments. It seems reasonable to believe the bottom of the 
former bed was partly modified by the water of a large 
spring, which formed near the base of the gently sloping 
scarp, and was active for a period following the 

 
 
14 

 
 

Giraudi C. 

Fig. 6 - Profiles along the Vercelli Plain. 6A: terrace map with the position of profiles; 
1, 2: profiles reported on Fig. 6B; a,b,c,d,e,f: position of the profiles reported in Fig. 
7; 6B: profiles showing the slope of the plain, the boundaries between terraces and 
stratigraphic units and thickness of glaciofluvial sediments lying on Early Pleisto-
cene fluvial and lacustrine deposits.  

 



 

   

 

 
 

15 

Piverone Alloformation glacial maximum.  
Surface L2 - L2 represents a cluster of surfaces shaped 
by local streams. In fact, the different surfaces are diffi-
cult to map because the very low scarps separating 
them are very difficult to follow and have been partly 
erased by agricultural works. L2 forms also the bottoms 
of the small valleys cutting into fluvial terraces and L1 
surfaces. The sediments forming L2 are generally silty 
sand, sand and sandy gravel; their thickness, that 
reaches 2.5 m, is known only in the Trino area because 
some trenches some hundreds of metres in length have 
been made for a channel. 
 
4.3 - Thickness of glaciofluvial sediments according 
to borehole data 

The stratigraphy of sediments lying well below the 
terrace surfaces in the area North of the Lucedio and 
Cavourrina Faults and the Crescentino Flexure has 
been evidenced by boreholes that reached a maximum 
depth of 200 m (Fig. 7). Based on the borehole align-
ments, some geological sections have been drawn, 
revealing the thickness and the relationships between 
both the glaciofluvial sediments and the underlying older 
deposits, as also the presence of possible tectonic 
structures. 

Three different glaciofluvial and fluvial units (FAU) 
have been identified, mainly formed by sandy gravel 
overlying, through a sharp contact, thinner fluvial and 
lacustrine sediments or the older FAU deposits. The 
fluvial and lacustrine sediments are dated at the Lower 
Pleistocene, and are mainly made by sand, silt and clay, 
with vegetation remnants and small pieces of wood 

interbedded with thin sandy gravel and peat layers 
(ENEL, 1984; ARPA Piemonte, 2014; Varalda et al., 
2006). 

 
The 1st FAU includes units “a” and “b” which form the 

terraces, and overlies Lower Pleistocene sediments 
through an erosion surface and has a maximum thick-
ness of about 70 m. The top of the 1st FAU is in general 
eroded and covered by later sediments. When the top of 
the 1st FAU reaches the surface (on terrace S5) or is 
exposed in quarries (below the silts forming terrace S4 
near San Grisante) sediments are heavily weathered 
(soils coloured 2.5YR or 5YR). As discussed above 
regarding terraces S4 and S5, pedogenesis occurred 
probably during MIS 11 and the top of the glaciofluvial 
sediments is dated to the MIS 12 or is older. 

Based on the age and the weathering, we assume 
that the 1st FAU can be correlated to the strongly weath-
ered glaciofluvial sediments of the RIT. However, while 
on the RIT sediments form three different terraces and 
sedimentary units with a bottom gradually at lower alti-
tudes, north of the Lucedio Fault the 1st FAU formed 
during conditions of prevailing sedimentation. 

There are no direct data that can suggest the real 
age of the base of the 1st FAU, but the abrupt increase 
in sediment grain size at the base of the 1st FAU corre-
sponds to the grain size increase that occurred, after the 
sedimentation of thinner Early Pleistocene sediments, in 
the Po plain and around the Alps. Studies carried out by 
Muttoni et al. (2007) demonstrate that at the mouths of 
the Alpine valleys in Lombardy (east of the study area), 
a sharp grain size change occurred during the MIS 22 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 

Fig. 7 - Stratigraphic sections of the sediments forming the Vercelli Plain obtained from ENEL (1984) boreholes. 



 

   

 

(starting ca. 870 ka BP). Moreover, Valla et al. (2011) 
have reported that around 800-900 ka BP, in the French 
Alps, erosion phases stronger than before started. The 
increased erosion probably produced an increase in the 
volume and grain size of the debris carried by rivers in 
the plains surrounding the Alps.  

Since the grain size increase is a general trend, and 
its age agrees with the chronological framework of the 
1st FAU, we assume that the sharp transition from fluvial
-lacustrine to glaciofluvial sediments occurred during the 
MIS 22. 

The sections reported in Fig. 7 show that the 1st 
FAU sediments are not in contact with the Lucedio 
Fault. However, the sediment dip changes nearing the 
fault. In the northernmost area, the 1st FAU sediments 
dip towards the south and SE, as one would expect for 
sediments produced by Alpine rivers flowing from north 
and NW, while near the Lucedio Fault they dip towards 
the northern quadrants.  

The 2nd FAU lies on an erosion surface carved in the 
1st FAU, is mainly of sandy gravel, and reaches a maxi-
mum thickness of 20 m. Its top is exposed on the S5 
terrace surface (“c” in Fig. 5) and, as discussed above, 
is covered by the MIS 6 glaciofluvial sediments. The 2nd 
FAU has been identified also in a borehole made near 
the Lucedio fault (Fig. 7, section c) embedded between 
the 1st FAU and the glaciofluvial sediments dated MIS 6. 
Interbedded within the sandy gravel of the 2nd FAU, a 
tephra layer has been found. Its age, obtained by the 
fission track method, is 350±100 ka BP (ENEL, 1984). 
As sediments are of glaciofluvial origin, the tephra fall 
could be dated to the MIS 10 (ca. 380-340 ka BP) or 
MIS 8 (ca. 280-240 ka BP). However, the stratigraphic 
framework and the tephra age indicate that the tephra 
was deposited during the MIS 10, because the sedi-
ments of the 2nd FAU are older than the deposits form-
ing terrace S4, dated MIS 8. As the 2nd FAU is dated at 
MIS 10, the erosion surface that separates it from the 1st 
FAU is probably dated MIS 11. 

The 2nd FAU is very near to, or in contact with the 
Lucedio Fault plane (Fig. 7, section c). However, its 
deposits are not faulted, but overlie an erosion surface 
cut into the Early Pleistocene lacustrine and fluvial sedi-
ments which are displaced by the fault. This implies 
that, during the MIS 10, a river was flowing just north of 
the Lucedio Fault. 

The 3rd FAU includes all the sediments younger than 
that forming the 2nd FAU. The contact between its base 
and the older sediments occurs through an erosion sur-
face. The older sediments forming this FAU are dated to 
the MIS 8 in terrace T4. 

On the whole, the stratigraphy of the sediment evi-
denced by boreholes shows that in the area north of the 
Lucedio Fault sedimentation prevailed, while south of 
the fault erosion and depositional phases alternated. 
The difference between the northern and southern ar-
eas, however, disappeared during the sedimentation of 
the 3rd FAU. 
 
4.4. Summary of the stratigraphic data 

The combination of morphological and stratigraphic 
data indicates the chronology of sediments that form the 
Vercelli Plain. 

The deposition of the older glaciofluvial sediments form-
ing the 1st FAU, the highest terraces and part of the 
S5 surface (“a” and “b” in Fig. 5) started during the 
MIS 22 (ca. 870 ka BP) and ended before the MIS 11 
(ca. 400 ka BP). 

The glaciofluvial sediments of the 2nd FAU, forming also 
part of surface S5 (“c” in Fig. 5), are dated to the MIS 
10 (ca. 380-340 ka BP). 

The glaciofluvial and lacustrine sediments (“d” in Fig. 5) 
forming terrace S4 can be dated to the MIS 8 (ca. 280
-240 ka BP). 

The glaciofluvial sediments (“e” in Fig. 5) which form a 
large part of surface S5 and the terraces (5a, 5b, 5c, 
5d) in the area near the moraines are dated to the MIS 
6 (ca. 180-130 ka BP). 

The glaciofluvial sediments (“g” in Fig. 5) that form ter-
race S7 could have been deposited during the MIS 4 
(MIS 4?) but their chronological framework is definitely 
bracketed between the end of the MIS 6 glacial maxi-
mum (ca. 140 ka BP) and the beginning of the MIS 2 
(ca. 30 ka BP). Nearly in the same period, or later, in 
the northern plain, surface L1  was shaped. 

The last glaciofluvial sediments (“h” in Fig. 5) forming 
terrace S8 are dated to the MIS 2 (ca. 30-14 ka BP). 

The most recent sediments (i, l, m, in Fig. 5) forming 
terraces T9, T10, T11 are dated to the late Holocene 
(ca. 4 ka BP to the present). 

 
5. CONSIDERATIONS ON THE DIFFERENT THICK-
NESS OF GLACIOFLUVIAL AND FLUVIAL SEDI-
MENTS 
 

Data show that in the study area the thickness of 
glaciofluvial and fluvial sediments, dated between 870 
ka BP and the Late Holocene, can be quite different 
(Fig. 8). In general the thickness is greater (reaching 70 
m) north of the thrust fronts (which match the Lucedio 
and Cavourrina faults and the Crescentino and Morano 
Po flexures). South of the thrust front, the thickness of 
the glaciofluvial and fluvial sediments is always less 
than 20 m. In particular, between Fontanetto Po and the 
area just East of Trino, along the younger terraces, the 
sediment thickness is less than 10 m. 

Because the boreholes are mainly sited in the area 
between Trino, the RIT and Crescentino, the thickness 
of the glaciofluvial and fluvial sediments forming the 
south-eastern Vercelli Plain is less known. In order to 
evaluate the sediment thickness of the eastern plain, the 
thickness of the sediments containing phreatic ground-
water reported in hydrogeological studies (Regione 
Piemonte, 2004; Varalda et al., 2006) has been used. In 
fact, the hydrogeological studies carried out by ENEL 
(1984) indicated that the base of the phreatic groundwa-
ter matches the base of glaciofluvial sediments. 

Glaciofluvial sediments are thickest in the plain be-
tween Lamporo and the area NW of the RIT (Fig. 5; 7; 
8) where the very weathered sediments of the 1st FAU 
are exposed. In the area NW and W of the RIT, the 
isopachs are nearly parallel to the Lucedio fault and 
show that the bottom of the 1st FAU forms two depres-
sions, elongated SW-NE, divided by a small ridge.  

The northernmost depression (ND in Fig. 8) lies 
near the axis of the syncline in the Pliocene and Pleisto-

 
 
16 

 
 

Giraudi C. 



 

   

 

 
 

17 

cene marine sediments, and its depth 
increases from East to West, in a 
direction opposite to that of rivers. 
The southernmost depression (SD in 
Fig. 8) lies near the Lucedio fault and 
is closed to the SW. North of Cres-
centino and near Tricerro, the 
isopachs are transversal to the 
Lucedio fault and Crescentino flexure 
and assume a direction approximately 
N-S. In the plain east of Trino, the N-
S isopachs are nearly parallel to the 
eastern branch of the Cavourrina 
fault. Lastly, starting from the area 
just west of Morano Po and as far as 
Casale Monferrato, the isopachs have 
a direction nearly parallel to the flex-
ure and to the northern slope of the 
Monferrato hills. 

Profiles 1 and 2 in Fig. 6 and A-D 
in Fig. 9 show the variations in the 
sediment thickness. In the profiles A-
D (Fig. 9) it can be observed that 
there are increases in sediment thick-
ness both west and east of the area 
between Fontanetto Po and Trino. 
Moreover, west of Fontanetto Po, the 
bottom of the sediments dips to the 
west, therefore in a direction opposite 
to the slope of the plain. The west-
ward dip of the bottom of the sediments forming the 
older terraces is greater than that of the most recent 
deposits. The base of the sediments of terrace S7 lies 
ca.18 m below that reached east of Fontanetto Po, while 
the base of the sediments of terrace T8 is 2 m below. 
 
6. DATA ON MINOR MORPHOLOGICAL FEATURES 
 

In the Vercelli Plain other secondary morphological 
evidence can be analyzed and taken into account, such 
as the change of the inclination of the terrace surfaces. 
Some observations about small changes of the terrace 
surfaces, due to the presence of different sedimentary 
units, were reported above. In this chapter some 
anomalous slope inclinations observed in the southern 
part of the plain will be discussed. 

Each profile in Fig. 9 refers to the surface of a single 
terrace. Profile D represents the surface of terrace S7, 
profile B that of S8, profile A that of terrace T9, and pro-
file C that of surface L2. On the profiles the thickness of 
the sediments forming the terraces is also reported. 

All the profiles show anomalous slope inclination 
values in the area between Trino and Morano Po (Fig. 
9), where the terrace surface inclination is around 0.22 
% while in the area west of Trino it is between 0.09 and 
0.15% and East of Morano Po between 0.12 and 0.17%. 

Between the two gently dipping sectors from the 
profiles in Fig. 9 a rough value of the scarp height can 
be estimated. By projecting the slope measured in the 
western surfaces eastward to the area with the anom-
aly, it is possible to evaluate the difference between the 
eastern ground surface and the virtual elevation of the 
western surface. This method allows us to obtain a 

height difference of ≥7 m for terrace S7, of ≥6 m for S8, 
and of about 2 m for terraces T9 and L2. 

The anomaly coincides with the area where the gla-
ciofluvial sediments thicken. It is worth noting that all the 
profiles show that, west of Fontanetto Po, even if the 
thickness of the sediments increases, no superficial 
anomaly can be observed. 
 
7. DISCUSSION 
 

Stratigraphy, facies, age and distribution of the sedi-
ments and terraces, are useful for the discussion of the 
geological evolution of the Vercelli Plain starting from 
the MIS 22. In the first part of the chapter the impact of 
climatic variations will be considered, and then the 
stratigraphic data will be analyzed in order to obtain 
useful information for assessing the tectonic activity that 
occurred during the last 870 ka. 
 
7.1. The impact of climatic variations and interac-
tions between sedimentation and tectonic activity 

The impact of climatic variations on the evolution of 
the Vercelli Plain is clear, as the plain was formed 
mainly by glaciofluvial sediments, dated between MIS 
10 and MIS 2, connected with the glacial advances and 
the shaping of the Ivrea moraine amphitheatre. Also the 
erosion surfaces that separate the different glaciofluvial 
sedimentary bodies can be ascribed mainly to the gla-
cial retreats that took place during the interglacials. Mut-
toni et al (2007) suggest that also the grain size in-
crease of the sediments dated to the MIS 22 was 
caused by climatic variations. 

Nevertheless the evolution of the sedimentary units 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 

 

Fig. 8 - Map of the isobaths of the base of glaciofluvial and fluvial sediments and tectonic 
structures active after the sedimentation of the 1st glaciofluvial and fluvial unit. 



 

   

 

 

 
 
18 

 
 

Giraudi C. 

Fig. 9 - Topographic profiles and stratigraphic outlines in the southern Vercelli Plain. The profiles are based on 5 m contour lines reported 
on the “Carta Tecnica Regionale” at a scale of 1:10.000 in the Piemonte Region. The stratigraphic data are from ENEL (1984) boreholes 
and from Regione Piemonte (2004). 



 

   

 

 
 

19 

and the terraces indicates that the climatic impact on the 
plain evolution changed through time. Starting from MIS 
10, the evolution of the plain is characterized by alter-
nating phases of aggradation (glaciofluvial sedimenta-
tion) and erosion and pedogenesis. Erosion and pe-
dogenesis occurred between the end of one glacial 
phase and the start of a new one. 

In the Mediterranean area (Macklin et al., 2002), 
also in places very far from the glaciers, during the inter-
stadials, the rivers incised the sediments deposited dur-
ing the preceding cold stages, while on the terraces 
surface the soils evolved.  

At least the alternating phases of aggradation and 
erosion of the late Holocene terraces were climatically 
driven, as evidence by Giraudi (1998). 

Therefore climatic variations have had a great im-
pact on the evolution of the Vercelli Plain during the last 
400 ka. For the period preceding the MIS 10, that is 
during the sedimentation of the 1st FAU, the comparison 
between the parts of the plain lying north and south of 
the Lucedio fault shows data that seem to be in contrast 
with the hypothesis of an evolution driven mainly by the 
climate.  

The plain north of the Lucedio fault is formed by 
sediments up to 70 m thick, without any evidence of 
erosion surfaces, heavily weathered at the top, which 
can be dated between MIS 22 and MIS 12. 

South of the fault, the sediments having a similar 
age have been eroded or form (on the RIT) three differ-
ent sedimentary bodies whose bases are cut into the 
tertiary bedrock at progressively lower altitudes. The 
entire thickness of the three sedimentary units is be-
tween 35 and 45 m. 

The difference in sedimentation between the areas 
north and south of the fault cannot be ascribed to cli-
mate variations. We believe that, to the north, no strong 
erosion phases occurred because subsidence prevailed, 
while to the south the alternating phases of limited ag-
gradation and strong erosion could have been produced 
by the interaction between tectonic uplift and variations 
in fluvial regime driven by climate changes. 

Michetti et al. (2012), using a boundary R-surface 
sequence obtained from the stratigraphic data of oil 
wells, evidenced that the surface (corresponding to the 
base of the 1st FAU of this paper) is uplifted and eroded 
at the top of the buried thrust fronts of the Northern Cen-
tral Po Plain, while in the basins lying outside the fronts, 
the surface lies below very thick sedimentary cover. 

It can be therefore assumed that the shape of the 1st 
FAU bottom enables the subsidence rate and the distri-
bution and geometry of tectonic structures in the study 
area to be assessed.  

Studies on the Tertiary and Quaternary sediments 
forming the Monferrato Hills and the basin north of the 
Monferrato thrust front (Dela Pierre et. al., 1995) show 
that phases of subsidence of the basin can be corre-
lated to the activity of the thrust front. Mariotti & Doglioni 
(2000) state that the subsidence in the foredeeps can 
be ascribed to the load of thrust sheets and/or to the 
slab pull effect.  

The Pleistocene subsidence of the area external to 
the thrust front is well known and appears to continue 
the Pliocene trend (SGd’I, 1969a; Bigi et al., 1990; Dela 

Pierre et al., 1995; Irace et al., 2009). 
 
7.2. Tectonic interpretation based on stratigraphic 
data 
 

Interpretation of the anomalous changes in thick-
ness and in altitude of the bottom of the 1st FAU and 
younger sediments makes it possible to evaluate the 
tectonic activity and the deformation rate of some areas 
of the plain. Elements showing tectonic deformations 
connected with the Monferrato thrust front, but also with 
structures crossing it are discussed below. 
 
7.2.1. Tectonic deformations connected with the 
Monferrato thrust front 

The thickness variations, the dip and the difference 
in the sedimentation of the 1st FAU are reported in Fig. 7 
and Fig. 8. As evidenced above, apart from the RIT, the 
1st FAU was not found south of the Lucedio fault and in 
the Tricerro area, probably because it was eroded. The 
thrust front, forming the boundary between the two geo-
logically different areas, therefore played a role in the 1st 
FAU deformation.  

The 1st FAU is formed by glaciofluvial sediments of 
rivers flowing from the northern and western quadrants, 
but its bottom dips in different directions. In the north-
ernmost area the 1st FAU dips gently to the south. The 
dip appears regular because the Dora Baltea river 
flowed from the N and NW. Near the Lucedio fault, the 
1st FAU changes its slope, dipping toward the northern 
quadrants and assuming a direction contrary to the river 
flow. 

The change of the inclination can be ascribed to 
tectonic deformations. The area where sediments dip-
ping to the north join those dipping to the south 
(sections of Fig. 7) is the place where sediments reach 
their maximum thickness. 

In the subsidence area W and NW of the RIT, the 
bottom of 1st FAU sediments (Fig. 8) shows the pres-
ence of two depressions (ND and SD) divided by a ridge 
(IR). The three features have a SW-NE direction nearly 
parallel to the Lucedio fault. 

The northernmost depression (ND) matches the axis 
of the syncline deforming also the base of the Pliocene 
marine sediments. The ND bottom cannot have been 
shaped only by rivers, having also been deformed by 
tectonic activity. In fact, the base of the 1st FAU dips to 
the WSW, in a direction opposite to the river flow. For 
the same reason the bottom of the SD depression, 
closed to the west, cannot have been shaped only by a 
river. Above the IR ridge the thickness of the sediments 
is 15-20 m less that in the ND and SD depressions. The 
change of the thickness could be explained by a differ-
ent degree of subsidence.  

The deformations of the 1st FAU bottom fit the hy-
pothesis of the presence of tectonic features (probably 
poorly developed folds) parallel to the Lucedio fault, 
which can therefore be linked to the activity of the Mon-
ferrato thrust front. 

The sediments of the 1st FAU do not cross the 
Lucedio and Cavourrina faults, and so it is difficult to 
demonstrate when the deformation ended. But if the 
subsidence implies thrust front activity, then the end of 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 



 

   

 

the subsidence could imply the end of the tectonic com-
pression. 

The end of the subsidence north of the Lucedio fault 
is shown by the heavily weathered top of the sediments 
of the 1st FAU that are exposed near the axis of the 
subsiding area. In fact, if the subsidence had continued, 
the (now) weathered sediments would have been com-
pletely covered by younger ones. It follows that the sub-
sidence ceased before the end of the 1st FAU sedimen-
tation (MIS 12 - ca. 400 ka BP). 

As far as the Cavourrina fault is concerned, it can be 
observed that its activity ceased before ca. 280-240 ka 
BP, because undeformed sediments of terrace S4 seal 
the fault. The fault lies not far from the western, northern 
and eastern scarps that form the boundaries of the RIT, 
while no isolated ridge is preserved in the longer and 
wider area uplifted by the Lucedio fault. The presence of 
the RIT, and the preservation of the 1st FAU sediments 
lying on it, suggest that the Cavourrina fault activity pro-
duced an uplift stronger than the Lucedio fault. We can-
not exclude that the Cavourrina fault activity continued 
also after 400 ka BP.  

Section b in Fig. 7 (in a SSE-NNW direction) shows 
that the difference in altitude of the base of the 1st FAU 
sediments between the area where the thickness is 
greater (ND depression, Fig. 8) and the uplifted area 
(RIT) can be estimated as about 80-85 m. Nevertheless, 
the real deformation should be higher because the RIT 
is situated further down the slope than the ND depres-
sion. 

Section E of Fig. 9 (direction ca. W-E) shows the 
base of the 1st FAU sediments between the area west of 
San Grisante and the RIT. It evidences that the base of 
the sediment is uplifted near San Grisante, subsiding to 
the east and uplifting again in the proximity of the 
Lucedio fault and of the RIT. Fig. 9 shows also that the 
uplift of the 1st FAU in the San Grisante area occurs in 
the area north of the fault. 

In the area between Morano Po and Casale Monfer-
rato, the thickness of the glaciofluvial and fluvial sedi-
ments younger than the MIS 22 increases towards the 
North and the isopachs lie parallel to the northern Mon-
ferrato slope. The trend of the isopachs is similar to that 
of the area S and SW of Crescentino. The two areas 
show the same geological characteristics already evi-
denced by the Tertiary bedrock. The similarity between 
the two zones enables us to assume that also the 
isopach trend between Morano Po and Casale Monfer-
rato was produced by a flexure that probably corre-
sponds to a blind thrust front (Fig. 1). 

 
7.2.2. Tectonic deformations crossing the Monfer-
rato thrust front 

The trend of the isobaths of the base of the gla-
ciofluvial and fluvial sediments indicates that independ-
ent tectonic deformations of the Monferrato front took 
place. 

In fact, in the areas N of Crescentino and NE of 
Trino, the isopachs assume an approximately N-S direc-
tion, crossing the Crescentino flexure and the Lucedio 
fault (Fig. 6, profiles 1-2; Fig. 8). In particular, in the 
Crescentino area the isopachs in a N-S direction con-
tinue also well to the North of the thrust front. The uplift 

of the 1st FAU base near San Grisante, pointed out 
above (section E, Fig. 9), seems to have been produced 
by N-S deformations. 

Both the RIT and terrace S4 north of Crescentino lie 
in the northern portion of the areas affected by N-S tec-
tonic deformations (Fig. 8). The southern boundaries of 
the areas affected by these deformations are near Cas-
tel Verrua and Camino, where the hills form headlands 
within the alluvial plain. The N-S deformations, possibly, 
affect the plain, both north and south of the Lucedio fault 
and Crescentino flexure, and the Monferrato hills. 

On terrace S4, north of Crescentino, the top of the 
1st FAU sediments, older than glaciofluvial and palus-
trine deposits dated to the MIS 8, is strongly pedoge-
nized, but the soil is eroded, at least in part. Probably 
the deformation phase along the N-S structure started 
before the sedimentation of the palustrine deposits and 
favoured the erosion of the soil. 

The tectonic deformations along the N-S structure in 
the Trino area seem to be dated at the MIS 8. In fact, 
the sedimentary facies of deposits forming the terrace 
S4 and the thickness of the top sediments (from ca. 4 to 
6 m) highlight a decrease of the river energy and the 
development of a wide marsh on the flood plain, which 
had never formed before. The changing sedimentary 
facies fits the hypothesis of difficult drainage to the east, 
most likely caused by the slow uplift of the area lying 
NNE or NE of terrace S4. 

In the area south of the RIT, the profiles in Fig. 9 
show that between Fontanetto Po and the Trino area, to 
the Monferrato hill slopes, the glaciofluvial and fluvial 
sediments are less than 10 m thick. West of Fontanetto 
Po, sediments become thicker and their base dips to the 
west, that is, against the river flow. Also east of Trino 
(Fig. 9), in the area where the terrace surfaces show an 
anomalous slope inclination, sediments become thicker, 
and the isopachs have a N-S direction. 

In the area where the glaciofluvial and fluvial sedi-
ments are less than 10-20 m thick the bedrock is of 
Tertiary marine sediments, while where the thickness 
exceeds 20 m the bedrock consists of Lower Pleisto-
cene continental sediments. Therefore in the area 
where the thickness of the glaciofluvial and fluvial sedi-
ments is less, the stratigraphic gap is greater due mainly 
to stronger erosion. 

The thickening of sediments to the west and east 
can be observed also near Tricerro, north of the Lucedio 
fault (Fig. 6, profiles 1, 2). Whole data suggests that an 
uplift occurred mainly in the area between Fontanetto 
Po and Trino, but the area is elongated to the south to 
the Monferrato Hills, and to the north at least to Tricerro. 

A tectonic structure could exist east of the uplifted 
area. In fact, the increase in the thickness of the gla-
ciofluvial sediments observed east of Trino, evidenced 
by the isobaths running ca. N-S and crossing the flow 
direction of rivers, cannot have been produced by rivers 
alone. 

Due to the lack of borehole alignments, it is not clear 
if the structure is a fault or a flexure. Thus, it can be 
assumed the presence of an undefined tectonic element 
(Salera Line), which drove the subsidence of the east-
ern area. Based of the isopach trend, the Salera Line 
could also reach Tricerro. 

 
 
20 

 
 

Giraudi C. 



 

   

 

 
 

21 

In the Salera area there is also a flow of saline water 
from the Tertiary bedrock (ENEL, 1984). 

According to the small-scale cartography reported in 
Irace et al. (2009), along a belt roughly corresponding to 
the Salera Line, also the isobaths of the Upper Pliocene 
base are in a direction ca. N-S and the Pliocene sedi-
ment thickness increases towards the east. 

Faults and lineaments running N-S have been ob-
served in the Monferrato Hills but are not so common. 
According to Dela Pierre et al. (2003), the paucity of N-S 
structures in an area having many faults, anticlines and 
synclines with different directions could be due to their 
recent (Pliocene and Pleistocene) age. 

The Salera Line seems the northern continuation of 
a strongly asymmetrical syncline lying ca. N-S, at the 
mouth of the Cerrina Valley in the Po Plain, pointed out 
by SGd’I (1969a). Furthermore, the hypothetical con-
tinuation southwards of the Salera Line would cross the 
Po river bed in the place where marine sediments are 
really strongly affected by tectonic deformation. 

West of the Salera Line, the Eocene marine sedi-
ments, lying below fluvial deposits or outcropping in the 
Po river bed, reach nearly the latitude of Trino, while 
east of the Line they reach only the latitude of Morano 
Po. Therefore, it is possible that the Salera Line pro-
duced oblique deformations or that its activity changed 
in the course of time. 

The Lucedio Fault ends eastward against the Salera 
Line or, alternatively, it could continue in the Salera 
Line. In other words, this latter might have played a role 
in the migration northwards of the thrust front and could 
correspond (although with a different direction) to the 
transcurrent or transpressive fault hypothesized by 
Costa (2003) in the same area. Nevertheless, starting at 
least from MIS 10, the Salera Line seems to have pro-
duced only the subsidence of the area East of Trino. To 
sum up, the Salera Line seems to be a ca. N-S fault with 
complex kinematics extending from Tricerro to the Cer-
rina Valley in the Monferrato Hills. 

All the structures active during the last 870 ka are 

reported in Fig. 10. 
 
7.3. Evaluation of the uplift rate 

As observed above, the geological and morphologi-
cal features show strong differences between the up-
lifted area south of the Lucedio-Cavourrina faults and 
those north of these. The features are the result of cli-
matic variations and two different phases of tectonic 
activity. 

The maximum difference between the elevation of 
the 1st FAU base (dated ca. 870 ka BP) in the two areas 
is more than 80-85 m, and may be estimated as ca. 115 
m (Fig. 7, section b); thus, considering that the activity 
of the Lucedio and Cavourrina faults ended before 400 
ka BP, the mean uplift rate of the southern area linked 
to thrust front activity was 0.25 mm/yr. However in each 
area differences can be observed in the elevation of the 
1st FAU base. 

The deformation produced by the N-S uplift area 
between Trino and Fontanetto Po can be estimated 
using the variations in the altitude of the base of the 
glaciofluvial and fluvial sediments where the base dips 
against upstream, that is, west of Fontanetto Po (Fig. 9). 
In that area, the base of the sediments dated MIS 4? 
lies at an elevation 22 m lower than east of Fontanetto 
Po. As without tectonic deformation the inclination of the 
base of the sediments should be from west to east, the 
area between Fontanetto Po and Trino underwent a 
minimum uplift of 22 m.  

Based on the age of the sediments (an interval be-
tween 140 and 30 ka BP), the uplift rate is thus >0.16 
mm/yr. 

If the deformation (more than 12 m) of the base of 
the sediments dated MIS 2, ca. 30-15 ka old (Fig. 9) is 
considered, an uplift rate >0.4 mm/yr can be calculated. 

The uplift rate of the sediments forming the T9 ter-
race, dated to the last 2-1.5 ka but whose base could be 
dated to 3-4 ka, can be obtained using two different 
data. The first is the value of the dip against upstream, 
and the second is the anomalous inclination of the ter-

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 

Fig. 10 - Active tectonic structures during the Quaternary. 



 

   

 

race surface. The inclination against upstream of the 
sediment base, west of Fontanetto Po, is about 2 m 
(Fig. 9) and therefore the uplift rate could be nearly 0.5 
mm/yr. The slope inclination anomaly of the S9 surface 
east of Trino is nearly 2 m in correspondence with the 
Salera Line, and the uplift rate of the area during the last 
2 ka should therefore be nearly 1 mm/yr. However, tak-
ing into account the uncertainty of the method, such a 
rate should be considered the maximum possible.  

On the whole, over the last 140 ka, we can estimate 
an uplift rate between 0.16 and 0.5 mm/yr. 

Studies carried out in the Torino Hills (Boano et al., 
2004), sited west of the Vercelli Plain, evaluate 1 mm/yr 
the uplift rate from the Middle Pleistocene to the pre-
sent. 

Within the uplift area between Fontanetto Po and 
Trino, the southward lowering of the altitude of the base 
of the glaciofluvial and fluvial sediments and of the ter-
races surfaces suggests that the northern area is up-
lifted more than the southern one. 
 
8. TECTONIC INTERPRETATIONS BASED ON MOR-
PHOLOGIC ANOMALIES AND FLUVIAL DIVER-
SIONS 
 

Studies reported in recent papers on the tectonics of 
the Po Plain (Burrato et al. 2012a; 2012b; Michetti et al., 
2012) have used presumed morphological anomalies 
and changes in the course of rivers, jointly with struc-
tural data, to evaluate the modern tectonic activity and 
the deformation rates that can be ascribed to structures 
buried below alluvial sediments.  

The epicentral area of the recent seismic crisis 
(2012) of the Emilian Plain (Galli et al., 2012) matches 
one of the areas where, according to the previous hy-
potheses, the drainage was strongly conditioned by the 
buried tectonic structures. The use of the drainage 
variations for estimating the activity of structures buried 
below the alluvial sediments of the Po Plain, therefore, 
may sometimes give reliable results. 

The morphological anomalies, the presence of an 
anomalous number of terraces and the river diversions, 
analyzed in this paper, provide the palaeogeographic 
and chronological data needed in order to complete the 
observations on the Vercelli Plain presented, in a less 
detailed way, in some papers (GSQP, 1976; Burrato et 
al. 2012a; 2012b; Michetti et al., 2012).  

The areas with topographic anomalies and complex 
morphology lie between the axis of the syncline north of 
the thrust front and the Monferrato Hills (Fig. 2; 4; 5), i.e. 
the area where the stratigraphic data show the presence 
of Quaternary tectonic deformations. 

The presence of S8 (ca. 30-14 ka BP) south and 
north of the Po can indicate possible clues of tectonic 
activity. In fact between Trino and Casale Monferrato, 
S8 is not far from the Po bed, while NE of Casale Mon-
ferrato some small remnants of the S8 terrace are 8-10 
km north of the river. 

Also south of the Po the S8 terrace remnants sug-
gest an anomaly. The terrace is preserved only west of 
Verrua Savoia and east of Casale Monferrato. It is likely 
that the lack of S8 in the intermediate area was caused 
by the erosion linked to the migration of the river south-

wards produced by the uplift of the plain north of Cres-
centino and Trino. 

Many river diversions highlighted by the geometry 
and extent of terraces of the studied area can have 
been produced by sedimentary and erosion processes, 
determined by climatic variations or tectonic deforma-
tions. 

The dominant influence of the climate on the evolu-
tion of the plain has already been discussed and shows 
a strong link between sedimentation and erosion 
phases, and climatic changes. 

Certainly, in the NW Vercelli Plain, the Dora Baltea 
river bed migrated many times during the last 870 ka, 
due to the change of shape and extent of the glacial 
fronts and of the position of the glacial meltwater 
streams. During the same glacial stages, glacier melting 
produced more than one meltwater stream fed by differ-
ent glacial lobes (Carraro et al., 1975; Gianotti et al., 
2008). 

Some diversions of Alpine rivers and of local 
streams that took place in the last 2 ka were, or could 
have been, produced by human impact (rivers Cervo 
and Sesia in the Vercelli area). 

Many river diversions, recognized in the southern 
Vercelli plain, occurred during the same sedimentation 
phase and can have been produced by the change in 
the inclination of the river bed as a consequence of 
variations in the solid load transport. However most river 
diversions can have been produced by tectonic defor-
mations along the structures described above. 

During the period between MIS 22 and MIS 12 
(~0.87-0.4 Ma), the terraces show a diversion to the NW 
of the river, formed by the Dora Baltea and the DROS, 
which flowed south of the RIT (Fig. 11a). The diversion 
is compatible with the uplift of the area south of the 
Monferrato thrust front, produced by the compression 
that induced also the deformation of the 1st FAU sedi-
ments. In that period, the northern slope of the Monfer-
rato Hills should have been not very far from the RIT. 

During the period between MIS 10 and MIS 8 (~0.35
-0.25 Ma), in the Crescentino area, the river changed its 
course, bypassing San Grisante to the north (Fig. 11b). 
The age of the diversion is the same as the beginning of 
the deformation along the N-S structure. During the 
same period, north of the RIT, a diversion eastwards of 
the Dora Baltea and the migration of the confluence with 
the DROS river occurred (Fig. 11b). The diversion may 
have been produced by the uplift of the area east of 
Lamporo. 

Despite the climatic variations that occurred be-
tween MIS 8 and MIS 4?, the river continued to flow 
north of the Lucedio fault, showing that the climate did 
not produce river diversions. The river ran parallel to 
and partly overlapped the thrust front. The position of 
the river was determined by the presence of the gla-
ciofluvial fan, which limited the lateral variations toward 
the north, and by the presence of terraces (or of the 
hillslopes) to the south. The morphological situation was 
substantially equivalent to that which currently deter-
mines the position of the Po from Turin to Crescentino 
and from Morano to Casale Monferrato. 

During MIS 4? (~0.14-0.03 Ma), a series of diver-
sions occurred (Fig. 11c). Initially the river (Baltea + 

 
 
22 

 
 

Giraudi C. 



 

   

 

 
 

23 

 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 

Fig. 11 - Fluvial diversions and tectonic mobility of the Vercelli Plain during the period between MIS 22 and MIS 12 (11A), between MIS 
10 and MIS 6 (11B), during MIS 4? (11C), and between MIS 3 and MIS 1 (11D). 



 

   

 

DROS), which flowed north of the RIT, migrated slightly 
towards the south eroding the northern slope of the 
ridge, then underwent diversions that made it flow to the 
west and south of the RIT, and later to the west and 
south of the terrace S4 near San Grisante. These diver-
sions are compatible with the uplift along the N-S struc-
tures in the Trino and Crescentino area. 

During this period, in the area between Crescentino 
and Trino an anomalous situation began in the relation-
ship between the position of the river and the Monfer-
rato thrust front, because the river crossed the front and 
began to flow behind it, showing that the activity of the 
thrust had ceased. 

During the Upper Pleistocene a diversion also oc-
curred of the Po towards the plain north of the Monfer-
rato hills (Carraro, 1976; Carraro et al., 1995), whereas, 
previously, the river flowed to the south. The Po diver-
sion could have occurred during MIS 4?, just during the 
phase of continuous diversions of the river in the south-
ern Vercelli Plain. 

During MIS 2 - MIS 1 there was a continuous migra-
tion to the south of the Po and the Dora Baltea rivers 
(Fig. 11d) and a significant shift to the west of the con-
fluence of the two rivers. 

The river diversions that occurred during the MIS 2 - 
MIS 1 period are compatible with the uplift of the struc-
tures, with a N-S axis, of the Crescentino and Trino 
areas. 

The southward river migration, which produced a 
strong and continuous erosion of the northern hillslopes, 
implies that in the Crescentino and Trino uplifted areas, 
the uplift of the northernmost portion is greater than that 
of the southern one, confirming the interpretation based 
on the variations of the altitude of the fluvial sediment 
base. 

The extreme north-south reduction of the Po river 
drainage basin in the stretch between Crescentino and 
Trino, described above (Fig. 2), may be a consequence 
of the southward migration of rivers. In fact, by eroding 
the hillside they reduced the extent of the basins of the 
streams that drain into the Po. 

In the area between Fontanetto Po and Trino, ter-
races T9, T10, and T11 form a strip narrower that in the 
area upstream and downstream. This may be a conse-
quence of the late-Holocene uplift of the area, sug-
gested by the deformation of the fluvial sediment base 
(Fig. 9). 

In the Casale Monferrato area, after the formation of 
terrace S8, the Po underwent a diversion to the north 
(Fig. 11d). West of the town, the migration of the river 
from north to south can be explained by the greater 
uplift of the northern area of the Trino and Crescentino 
north-south structures; consequently it can be assumed 
that the northwards diversion of the river was caused by 
the uplift of the southern plain and/or by the subsidence 
of the plain north of the Po.  

In the Rive and Balzola area, some small-scale mor-
phological clues on the late Holocene terraces could 
suggest stream diversions. The natural origin of the 
diversions is uncertain, but, if the diversions had been 
natural, it could have been linked to the subsidence of 
the area NE of Casale Monferrato. 

The small valleys (forming surface L2) cutting the 

river terraces show that during the MIS 2 - MIS 1 period, 
also the local streams suffered many diversions (Fig. 
11d). In particular, in the area between Ronsecco and 
Tricerro, there are remnants of small valleys abandoned 
because the streams were diverted N and NE. The di-
version may have been produced by the uplift of the 
northernmost part of the N-S structure. 

In the area between Tricerro and Costanzana some 
morphological features linked to the northward migration 
of the Marcova stream have been observed. The diver-
sions may have been produced by the uplift of the N-S 
structure, but also by the uplift of a narrow area (Fig. 
11d) parallel to the buried Monferrato front. 
 
9. RELATIONSHIP BETWEEN TECTONIC DEFORMA-
TIONS 
 

In the Arca and Beretta (1985) paper, the uplift rate 
of some places located near Casale Monferrato and the 
Vercelli plain is reported. The uplift rate was obtained by 
means of the comparison between data from geodetic 
measurements carried out in 1897 and in 1957 AD. 

In particular, the points lying along a section from 
Casale Monferrato to Vercelli, that cross the Monferrato 
thrust front, indicate an uplift rate of 4.32 mm/yr in the 
area south of the front, 1.37 mm/yr at Villanova Monfer-
rato, located north of the Po, between the front and the 
syncline axis, 1.67 mm/yr at Stroppiana and 0.62 mm/yr 
at Vercelli, located north of the syncline axis. The area 
south of the Monferrato front has an uplift rate four times 
greater than in the area north of it. 

However, the section does not allow a three-
dimensional interpretation and it is therefore not possi-
ble to determine whether the deformation occurred ex-
actly on the flexure or on the front, or along other struc-
tures transversal to the front. 

The morphological features that suggest a possible 
tectonic activity in the plain near Casale Monferrato are 
dated to the Upper Pleistocene. No clues showing older 
deformations have been found. The age of the tectonic 
activity makes it unlikely that the uplift was produced by 
the Monferrato thrust front. 
 
10. SUMMARY OF TECTONIC INTERPRETATIONS, 
CONSIDERATIONS ON SEISMICITY AND ON ASEIS-
MIC MOVEMENTS IN THE AREA  
 

The stratigraphic and morphological characteristics 
of the Vercelli Plain allow us to assess the evolution 
during two periods, the first between 870 and ca. 400 ka 
BP, the second following 400 ka BP. 

In the older period, evolution was influenced by the 
subsidence of the axial area of the syncline lying north 
of the Lucedio fault and of the Crescentino and Morano 
Po flexures, while the area between the syncline and 
the fault and the flexures was less subsiding, and the 
area south of the fault and the flexures was subject to 
uplift. 

The Lucedio fault was active until ca. 400 ka BP 
while the Cavourrina fault could have been active also 
later, but before 280 ka BP. As discussed above, these 
faults constitute the thrusts front, and therefore we can 
conclude that the main compression in the Monferrato 

 
 
24 

 
 

Giraudi C. 



 

   

 

 
 

25 

front ended before or about 400 ka BP.  
During the thrust activity the Salera Line and the 

Crescentino fault acted as transcurrents or transpres-
sives, according to the Costa (2003) hypothesis. 

Because the thrust fronts are reported on maps at a 
scale lower than that of the maps in this paper, and 
there is uncertainty about their exact position (Fig. 1), it 
is difficult to establish in detail whether the Crescentino 
and Morano flexures lie on stretches of the Monferrato 
thrust front, but it is likely that the flexures are superficial 
effects produced by the blind thrust. 

Interpretation of the data suggests that the fronts 
corresponding to the Lucedio and Cavourrina faults and 
to the Crescentino and Morano Po flexures were active 
at least in the period between 870 and 400 ka BP.  

The deformation of the sediments shows that the 
tectonic compression acted in different ways on the 
various stretches of the front during the same periods. 
The dip of the sediments, the degree of deformation and 
the dip of the fault planes indicate a clear difference 
between the fronts corresponding to the Lucedio and 
Cavourrina faults (the farthest from the Monferrato Hills) 
and the front that produced the flexures. 

According to the published papers (SGd’I, 1969a; 
SGd’I, 1969b; Pieri and Groppi, 1981; Cassano et al., 
1985; Dela Pierre et al., 2003a; Festa et al., 2009), ex-
cluding the area of the Lucedio and Cavourrina faults, 
the buried thrust front of the Monferrato-Torino Hills is 
always near the northern hill slope. Moreover, the Terti-
ary and Quaternary sediments lying outside the thrust 
front show an inclination and dip very similar to that 
observed in the Crescentino flexure. 

It can be deduced that, although framed within the 
activity of the Monferrato thrust front, the Lucedio and 
Cavourrina faults and the other associated tectonic 
structures (Crescentino fault and Salera Line) acted in a 
different way. 

The anomalous tectonic evolution of this part of the 
thrust front started well before the Quaternary. In fact, 
the Balzola Fault (Fig. 4; 5), which is a lower Pliocene 
thrust front lying north of the Lucedio fault (SGd’I, 
1969a; Pieri & Groppi, 1981; Cassano et al., 1985; Bigi 
et al., 1990; ENEL, 1994; Dela Pierre et al., 2003a), is 
nearly parallel to the younger thrust front. Naturally the 
data on the Quaternary evolution are related to a short 
period, compared to the length of the tectonic phase, 
and cannot properly explain the tectonic anomaly of this 
part of the Monferrato thrust front. 

In the last 400 ka, the only possible tectonic motions 
affect N-S trending structures near Crescentino and 
Trino. The activity of these structures became stronger 
during the last 250 ka. According to the deformation of 
the base of the sediments dated at the last 140 ka, the 
uplift rate of the north-south Trino structure was be-
tween 0.16 and 0.5 mm/yr and the northern part of this 
structure uplifted more than the southern part. 

The N-S deformations were not found in other 
places north of the Collina di Torino-Monferrato. It fol-
lows that these deformations are anomalous, but corre-
spond to an area of anomaly since the lower Pliocene. 
As the Lucedio and Cavourrina faults are sealed by 
Middle Pleistocene sediments, the N-S deformations 
can hardly be connected with the thrust front activity. 

Is not clear whether the north-south uplifted areas 
are included between north-south striking faults or flex-
ures, but east of Trino lies the Salera Line, a very impor-
tant structure with a long and complex activity. The Line 
seems to continue from Tricerro to the Cerrina Valley, 
inside the Monferrato Hills, reaching a length of ca 20 
km. 

We cannot completely exclude the uplift, since MIS 
4?, of a short, narrow area east of Tricerro (Fig. 11c;d) 
parallel, but external, to the Lower Pliocene Monferrato 
thrust front. 

The seismic catalogues show, for the studied area, 
the absence of any earthquakes between 1000 to 2006 
AD (Rovida et al., 2011; RSNI, 2014a) and the pres-
ence, during the period covered by instrumental record, 
of only four events of ML ≥ 2 (RSNI, 2014 b) located in 
Trino, Camino and Gabiano, but the depth of the epi-
centres of two events near Trino has been assessed as 
more than 50 km below ground level. 

Because the area of Casale Monferrato, according 
to the Arca and Beretta (1985) geodetic data, was af-
fected between 1897 and 1957 AD by vertical move-
ments with values greater than 4 mm / yr -1 but there 
were no earthquakes, one must conclude that the area 
is characterized by significant aseismic movements. The 
aseismic uplift rate of Casale Monferrato is at least eight 
time greater than the maximum rate that can be as-
sumed for the Trino area on the basis of the geological 
data. 
 
11. CONCLUSIONS 

 
The study of the Quaternary geological evolution of 

the Vercelli plain shows complex morphological, strati-
graphic and tectonic variations. With reference to the 
main aim of the work, i.e. the validation of the seis-
motectonic interpretations and the associated seismic 
hazard implications made by various Authors, we can 
observe the following. 

 
- Only some stretches of the buried fronts, which were 

reported or assumed as active by various Authors 
(Fig. 1), have influenced or induced deformation in the 
Quaternary sedimentation and drainage. Among the 
buried thrust-fronts which were active in the past 870 
ka (i.e., Lucedio and Cavourrina faults), and the flex-
ures of Crescentino and Morano Po, only the first two 
produced the most appreciable deformation.  

- The Salera Line, along with another possible fault 
(Crescentino fault), may have played a key role in the 
northward shift of the thrust fronts of Lucedio and Ca-
vourrina. 

- Over the past 400 ka the Monferrato front has no 
longer been active, or its activity has been very low 
because the base of the II FAU seals it. Thus, starting 
at about 400 ka BP, the tectonic evolution of the thrust 
and of the foredeep basin differed substantially from 
that of the fronts of the Emilia and Ferrara Folds which 
are considered active and seismogenic. 

- From MIS 10 or before, the Crescentino and Trino 
structures, transversal to the Monferrato front contrib-
uted to the uplift of areas elongated approximately in a 
NS direction. The uplift affected both the northern 

 
 
Quaternary studies as a tool to validate assumptions about seismic hazard ... 



 

   

 

Monferrato slope and areas in the plain south and 
north of the thrust front. The uplifted Trino area was 
limited to the east by the Salera Line. There are no 
indications of structures (faults or flexures) located to 
the west of the Trino area or forming the limits of the 
uplifted Crescentino area, although their presence 
might be assumed. 

- It is possible that the aseismic uplift, geodetically re-
corded in the area of Casale Monferrato, is connected 
with a structure similar to those of Trino and Cres-
centino.  

- It is possible that there is a structure that produces the 
uplift of a small area to the east of Tricerro. The struc-
ture would lie outside of the oldest Monferrato front, 
but its trend is sub-parallel to this. 

- It is possible that the southern Vercelli Plain was af-
fected by tectonic deformation even in the late Holo-
cene. 

- For the period between MIS 4? and the present, the 
maximum uplift rate of the structure of Trino is evalu-
ated as between 0.16 and 0.5 mm/yr. 

- The most important identified structure, that was active 
also during the Upper Pleistocene and the Holocene, 
is the Salera Line, an unknown structure with a com-
plex kinematics, which might continue to the south, 
inside the hills, for a length of about 20 km. 

 
The presence of aseismic uplift (up to 4 mm/yr in the 

area of Casale Monferrato) in an area with very low 
seismicity, could justify the deformation of sediments 
and of terrace surfaces that occurred in the past thou-
sands of years. However, the aseismic uplift, tested only 
for a few tens of years, may not be significant or may be 
only one aspect of the long-term tectonic evolution. In 
addition, as elsewhere in the world, there is the possibil-
ity that the area is subject to earthquakes with very long 
return periods, not reported by the seismic compilations. 

The detailed study of the geological evolution of the 
Vercelli plain has therefore made it possible to charac-
terise the tectonic structures that were active during the 
Quaternary and to assess the uplift rate. 

The recent vertical movements of the surface, how-
ever, are not associable with the Monferrato thrust front, 
as suggested previously, but to north-south unknown 
structures, transversal to the front, which seem to affect 
both the plain and the northern portion of the Monferrato 
hills. 

As a concluding remark, it is unlikely that the seis-
micity of the easternmost Apennine fronts (Emilia and 
Ferrara Folds) can provide useful information to assess 
the seismic hazard of the Vercelli Plain and of the North-
ern Monferrato. 

 
AKNOWLEDGEMENTS: 
We thank Paolo Galli who greatly improved the manuscript 
with their accurate revision and Edi Chiarini for the english  
revision. 

 
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