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Tectonophysics 308 (1999) 143–170
www.elsevier.com/locate/tecto

The Holocene paleoearthquakes on the 1915 Avezzano earthquake
faults (central Italy): implications for active tectonics
in the central Apennines
F. Galadini a,Ł , P. Galli b
a CNR, Istituto di Ricerca sulla Tettonica Recente, Area di Ricerca di Roma-Tor Vergata, via del Fosso del Cavaliere, 00133 Rome, Italyb Servizio Sismico Nazionale, via Curtatone 3, 00185 Rome, Italy

Received 4 October 1998; accepted 27 November 1998

Abstract
Extensive paleoseismological research was conducted in the Fucino Plain (central Italy) in order to better understandthe seismogenic characteristics of the fault responsible for the 1915 Avezzano earthquake .Ms D 7:0/ and improve thegeneral knowledge regarding active tectonics in the central Apennines. Evidence for Late Pleistocene–Holocene surface
faulting events was obtained through the study of thirteen sites across four different fault branches. The paleoseismologicalanalysis outlined the occurrence of ten surface faulting events in the past 33,000 years, seven of which occurred during the
Holocene. Radiocarbon, thermoluminescence and archaeological dating permitted the definition of an event chronology andthe estimation of a recurrence interval for surface faulting events ranging between 1400 and 2600 years. On the basis of theobserved offsets it was possible to calculate vertical slip rates for the individual fault branches, ranging between 0.24 mm
yr 1 and 0.5 mm yr 1 and an extension rate across the Fucino Plain ranging between 0.6 and 1 mm yr 1 . The chronology ofsurface faulting events appears linearly distributed in time, and the observed recurrence times are similar to those inferredby other paleoseismological studies along different active Apennine faults. The general consequence of the large time span
between strong earthquakes is that even a 2000 year long historical record, such as the Italian earthquake catalogue, does
not cover the entire seismic cycle of all the active Apennine faults. A comparison of the extension rate across the Fucino
Plain with that across the entire central Apennines (as inferred from the sum of seismic moments of earthquakes which
occurred in the interval 1000–1992) shows a seismicity ‘deficit’ in the period indicated. This confirms that a number ofseismogenic faults were not active during the past 1000 years.  1999 Elsevier Science B.V. All rights reserved.
Keywords: active fault; paleoseismology; earthquakes; seismotectonics; Apennines

1. Introduction
The 1915 Avezzano earthquake (Ms D 7:0, according to Margottini et al., 1993), which struck the
Fucino Plain (central Italy), is one of the major seisŁ Corresponding author. Fax: C39-6-4993-4211; E-mail:galad@irtr.rm.cnr.it

mic events to have occurred in Italy over the last few
centuries. Due to its relatively recent occurrence, thecoseismic effects are well known in terms of intensity distribution (for example it was responsible fordamage in Rome) and descriptions and a map of surface ruptures are included in the fundamental workof Oddone (1915).
Although the occurrence of strong earthquakes

0040-1951/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 1 9 5 1 ( 9 9 ) 0 0 0 9 1 - 8

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

along the Apennine chain is described in the Italian
seismic catalogues (e.g. Boschi et al., 1997; Camassiand Stucchi, 1997), the seismogenic behaviour of thefaults responsible for these earthquakes is not wellknown. For the 1915 earthquake area, reliable dataon the recurrence intervals between large seismic
events and slip or extension rates across the Fucino
basin are lacking. According to seismic catalogues
the 1915 event occurred in an area where apparently
no other earthquakes had originated during the last
millennium. This observation is not surprising if one
considers that paleoseismological data from centralsouthern Italy (e.g. Pantosti et al., 1996) show thatcoseismic faulting within the Apennine chain may
be characterised by long recurrence intervals (1000years or more along the same active fault). The lackof other large historical earthquakes in the Fucino
Plain may therefore be due to the long recurrence
intervals for 1915-type events.
Extensive paleoseismological research has been
performed during 1992–1996 to better understandthe seismogenic behaviour of the structure responsible for the 1915 earthquake. The paleoseismologicalanalysis was based on diverse investigations: (1) the
study of twelve trenches excavated ad hoc along the
major Holocene fault branches; (2) the study of thedisplacements of Holocene sediments in two quarries located at the eastern edge of the plain; (3)the survey of excavations dug for the laying of apipeline and an aqueduct (in the northeastern andsouthwestern sectors of the basin, respectively); (4)the survey of some drainage channels in the central
part of the basin; (5) the examination of hundreds ofshallow boreholes (3–4 m deep); and (6) the analysis
of coseismic deformations affecting archaeologicalremains. Collected data have already been publishedin several papers (Galadini et al., 1995, 1996, 1997;
Galadini and Galli, 1996).
The paleoseismological investigation was preceded by the reconstruction of the Quaternary geological and tectonic evolution of the region throughdetailed stratigraphic, geomorphological and structural work (Galadini and Messina, 1994). Particularattention was also given to the geological evolutionof the Late Pleistocene and Holocene through thestudy of the lacustrine terraces and related deposits
which surround the Fucino Plain (Giraudi, 1988).
Based on the large amount of available data, thepresent paper addresses active-faulting problems inan effort to understand the characteristics of thepresent tectonic regime and to provide insight forseismic hazard assessment in the central Apennines.
All data on the active tectonics of the Fucino Plaincollected during the last 10 years have been synthesised in the present paper. The results of the paleoseismological analysis are presented in the article
in different sections, with each section relating to amajor Holocene fault branch within the Fucino Plain.
The implications derived from the paleoseismological analysis (e.g. slip rates, recurrence intervals forlarge seismic events, inferred 1915 surface-faulting,etc.) are discussed in specific sections.

2. Geological framework
The structure of the central Apennines is mainly
due to Cenozoic compressive tectonics which produced intense shortening across NW–SE trending
thrust faults (e.g. CNR-PFG, 1983), the most important of which placed Meso–Cenozoic carbonates incontact with Miocene flysch. Since the Pliocene, theextensional regime related to the numerous 10–20
km-long, NW–SE trending normal faults has been
responsible for the formation of the main intermontane basins (Fig. 1). These faults affect Quaternary
continental deposits (mainly lacustrine and fluvial
facies) and show spectacular carbonate bedrock fault
scarps. Outside the intermontane basins Quaternaryfault activity is observed in the displacement ofslope-derived breccias or scree deposits. Slip rates
calculated on the basis of the displacement of Early
Pleistocene formations (along the VF, SVFZ and PF
of Fig. 1) are less than 1 mm yr 1 (e.g. Galadini and
Messina, 1994).
Bosi (1975) used a mainly geomorphological approach to define the faults reported in Fig. 1 as being‘probably active’. Recent works (e.g. Galadini and
Messina, 1994 and references therein; Carrara et al.,
1995; Chiarini et al., 1997), however, provide better
constraints on their activity (Fig. 1). Active faults
are present throughout this sector of the Apennine
chain and are characterised by the clear displacementof Late Pleistocene–Holocene deposits. In contrast,some faults which show geomorphic evidence ofrecent activity are sealed by middle Pleistocene de-F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

145

Fig. 1. Fault map of the Fucino Plain and surrounding areas. The rectangle encloses the study area of Fig. 2. PF D Pescasseroli fault;
SVFZ D Sangro Valley fault zone; VLF D Vallelonga fault; LVF D Liri Valley fault; SBGF D San Benedetto dei Marsi–Gioia dei Marsi
fault; MHF D Marsicana Hwy fault; TMF D Tre Monti fault; VF D Velino fault; OPF D Ovindoli-Pezza fault; CFF D Campo Felice
fault; MDF D Monti della Duchessa fault; SVF D Salto Valley fault.

posits and landforms, and as such they are no longer
considered to be active (e.g. the Liri Valley fault
and the Monti della Duchessa fault; LVF and MDF,
respectively, in Fig. 1).
The Fucino Plain (Fig. 2), one of the major intermontane basins of the central Apennines, is filled
by more than 1000 m of lacustrine and fluvial Plio–
Quaternary deposits and surrounded by mountains(average 2000 m) made of Meso–Cenozoic carbonate formations. Several terraces, which range in age
from Pliocene to Holocene, are found at different
elevations around the basin. Some of them represent

the top surfaces of lacustrine sedimentary units whileothers are carved into older deposits.
According to Galadini and Messina (1994) the
tectonic evolution of the Fucino basin started during the Pliocene, when NE–SW faults (TMF and
its northeastern prolongation in Fig. 1) along thenorthern border formed a half-graben basin. Since
the Late Pliocene, however, activity started on NW–
SE trending fault branches located along the easternborder of the basin (Marsicana Hwy fault and San
Benedetto dei Marsi–Gioia dei Marsi fault, MHF
and SBGF, respectively, in Figs. 1 and 2) form-

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

Fig. 2. Study area map showing site locations and the surface faulting pattern of the 1915 earthquake inferred from historical reports andthe present paleoseismological study.

ing a new half-graben which was superimposed on
and perpendicular to the pre-existing one. Data fromreflection seismic surveys (e.g. Mostardini and Merlini, 1986) show the present half-graben structurewith fill sediments which clearly pinch out along thewestern border of the basin and the listric geometry(typical of growth-faults) of the MHF and SBGF.
The basin is also affected by secondary faults, themost important of which are the Trasacco and theLuco dei Marsi faults (TF and LMF, respectively, inFig. 2).
The attempts to drain Lake Fucino have been aleitmotif of the last two millennia, beginning withthe partial drainage of the lake by the ancient Romans (1st–2nd century A.D.). They constructed an

impressive hydraulic system, consisting of a tunnel excavated in Mt. Salviano and open channels
in the plain (Fig. 2), which ceased to operate during the decadence of the Empire (5th–6th century
A.D.). Recent detailed stratigraphic and geomorphological investigations allowed Giraudi (1998) toreconstruct lake level oscillations for the last 30,000
years. Data related to the last two millennia showthat the level has increased significantly only sincethe 14th century, culminating in peak levels during
the 19th century when the lake was finally drained
for agricultural purposes (1862–1875). Presently, theFucino area is an essentially flat, intensely cultivatedplain (Fig. 3) which is cut by many E–W and N–Strending drainage channels.

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

147

of which is reported in Fig. 2) and about 400,
4-m-deep hand-boreholes have been used to reconstruct the stratigraphic succession of the inner andwestern portions of the basin over the last 30,000
years. Four main sedimentary units have been distinguished, separated by erosional surfaces and datedby means of radiocarbon or archaeological analysis(Fig. 4). In contrast, a complete Late Pleistocene–
Holocene stratigraphic record is not available for theeastern border of the basin, which is affected by
the SBGF and MHF. This is due to lateral facies
variability, as well as the abundance of erosional
episodes and colluvial deposition along the Lake
Fucino paleoshoreline.
Due to the evidence of recent tectonic activity
along the above-mentioned faults, and the presenceof very recent lacustrine sediments (up to the 19th
century A.D.) which allow the characterization of
displacement events, the Fucino Plain appears to be
an ideal place for paleoseismological analysis.

3. The 1915 earthquake

Fig. 3. Aerial photograph of the SE portion of the Fucino basin.
Large arrows highlight the Trasacco fault (TF in the text), visibleon the photograph as a faint lineament affecting the plain. The
location of the study sites is reported along the fault. Small
arrows indicate the trace of the Roman channel built in the 1st–
2nd century A.D. to partially drain the lake.

The survey of the aqueduct trench in the southwestern portion of the basin (Fig. 2) and of thewalls of the present drainage channels (the main

On January 13, 1915 a strong earthquake .Ms D
7:0/ struck the villages in the Fucino basin and surrounding areas, causing more than 30,000 casualties
and strong damage over an area of 500 km2 . According to the Italian seismic catalogues (Boschi et al.,
1997; Camassi and Stucchi, 1997) the main shock
epicentre was located between Gioia dei Marsi and
Ortucchio and the hypocentre occurred at a depthof 8 km. The earthquake was also responsible forthe damage of some monuments in Rome, affecting
22 old churches, 20 old palazzi, several parts of the
Aurelian walls and parts of the Claudius aqueduct.
The earthquake was recorded in several seismic
stations world-wide; three proposed focal mechanisms based on first arrivals have been published forthis earthquake, each showing totally different solutions: NE–SW normal faulting (Micci et al., 1975);
NE–SW left-lateral strike-slip faulting (Gasparini etal., 1985); NW–SE left-lateral strike-slip faulting(Basili and Valensise, 1991). None of these solutions
is sufficiently constrained because of the low qualityof the original seismic records (for a detailed discussion, see Basili and Valensise, 1991). Moreover,
all the proposed solutions clearly contrast the known

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

Fig. 4. Stratigraphic columns and related ages of lacustrine sediments (mainly silts and clays) in the western and inner portions of theplain.

structural framework of the Fucino area, which ischaracterised by NW–SE active normal faults.
A few days after the earthquake, Oddone (1915)
provided a detailed field-based report of the surface
ruptures (Fig. 5), he described the main scarp along
the eastern border of the basin, with a maximum
height of 1 m and lack of horizontal componentof movement. According to Oddone, as well as to
Alfani (1915) and other historical sources (including press reports), the main fault scarp affected theMarsicana Hwy between Cerchio and Pescina at two
different locations. To the south, the main NW–SE
scarp roughly followed the border of the historicallake (up to the Gioia dei Marsi area). Although Oddone’s map clearly shows the presence of scarps also
in the inner portion of the basin, no precise description of these features is reported in the text. As amatter of fact, Oddone’s map (Fig. 5) highlights analmost continuous rupture with the downthrown side
always located towards the centre of the plain. Other
geologic effects affected the most damaged areas,
including landslides in the southeastern part (close to
Gioia dei Marsi), differential settlements in the inner
portion and liquefactions along the eastern border ofthe basin (Galli and Ferreli, 1995).
More recently, Oddone’s data were interpreted byServa et al. (1986) using eye-witness accounts ofthe earthquake and new field surveys. The authors
concluded that the two easternmost fault branches
slipped in 1915: the Marsicana Hwy fault (MHF) andthe San Benedetto dei Marsi–Gioia dei Marsi fault(SBGF) (Figs. 1 and 2). Using new historical andgeologic data Galadini et al. (1995) confirmed thisconclusion but pointed out that the surface faulting
pattern of the 1915 earthquake — as reconstructed— could be still incomplete due to the lack of

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

149

Fig. 5. Map of surface ruptures produced by the 1915 earthquake and damage distribution, from Oddone (1915). Arrows represent thedirection of the seismic wave propagation; surface breaks and isoseismals are reported with hatched and black lines, respectively.

observations for possible faulting in the inner andwestern portions of the basin. In fact according toOddone’s report and other historical sources surface
faulting may also be expected along the Trasacco
fault (TF).
No clear evidence of the 1915 scarps are presently
found along the MHF due to intense agricultural cultivation, and therefore reconstruction of the surface
faulting pattern in the area between Cerchio andPescina is based on the above-mentioned historical
data. Precise field-based recognition of the rupture is
therefore not possible, and the only certainty is that

(according to historical sources) it was located at thebase of the 70 m-high scarp which affects the middle
Pleistocene deposits and landforms along the MHF.
In contrast, a retreated fault scarp affects the area
between S. Benedetto dei Marsi and Venere along
the SBGF, where historical reports locate the 1915
surface. This NW–SE trending scarp is about 0.5–
0.7 m high and affects lacustrine sediments related
to the last depositional phases of Lake Fucino along
an approximately 3 km-long branch. As in the caseof the MHF, more than 80 years of farming has
made it very difficult to detect the scarp in the field,

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

and only a preliminary survey of the oldest available
aerial photographs (made by the R.A.F. in 1943) allowed the precise location of the rupture. The scarp
appears to be very fresh on the R.A.F. photographs
and therefore there is little doubt that it was formed
as a result of the 1915 earthquake. A fault scarp
about 5 km long and 3–4 m high is also present in
the area between Venere and Gioia dei Marsi, affecting a Holocene lacustrine wave-cut terrace partly
carved on the carbonate bedrock (Giraudi, 1988).
Available paleoseismological data (Galadini et al.,1997) clearly indicate that part of this scarp (whichis en-echelon with the previously described scarp,
see Fig. 2) formed in 1915. Southeast of Gioia dei
Marsi a bedrock fault scarp affects the southernslope of Mt. Serrone (dashed line in Fig. 2). Oddone (1915), Alfani (1915) and newspapers released
immediately after the earthquake reported the occurrence of ruptures along this slope; the descriptions donot, however, allow to discriminate between tectonic
and gravitational movements.
No scarps are related to the long-term activityof the Trasacco and Luco dei Marsi faults (TF and
LMF, respectively, in Fig. 2), and these faults appear
on aerial photographs as very faint NW–SE trending
lineaments affecting the lowest areas of the basin(see Fig. 3 and sections below). No evidence of
1915-related activity is therefore available from thesurface for these two branches.
One of the geologic effects of the 1915 event
was the subsidence of the plain, as shown by thegeodetic levelling made by Loperfido (1919). The
benchmarks included nine monuments of the Virgin,eight pillars and one memorial stone, all placedalong the shore of the lake in 1862 at the beginningof the most recent drainage works. The displacement
measured in 1917 varied between C5 cm and 54
cm. The inversion of the geodetic data allowed Wardand Valensise (1989) and Amoruso et al. (1998) toinfer that the 1915 earthquake fault is a SW dipping
normal fault, bordering the eastern side of the basinin agreement with the surface observations.

4. Previous paleoseismological studies
Paleoseismological studies have been conductedsince 1988 in the Fucino area.

On the basis of a geomorphological study, Giraudi (1988) inferred the age of some fault scarps
located along the eastern (SBGF) and northern(TMF of Fig. 1) borders of the basin which werein good agreement with archaeologically determinedcollapse events that occurred in caves surrounding
the Fucino area. Four different events were identified
in the last 20,000 years: the oldest occurred approximately between 20,000 and 13,000 years B.P., thesecond between 5500 and 5000 years B.P., the third
between 3500 and 3000 years B.P., and the mostrecent during the Middle Ages.
Michetti et al. (1996) collected data from two
trenches excavated along the SBGF and recognised
the effects of two paleoevents, the oldest having
occurred between the 6th and 9th century (HighMiddle Ages Event) and the second between the
9th and 14th century (Low Middle Ages Event).
Evidence for the latter event is questionable and will
be discussed in a specific section below in the lightof more recent paleoseismological data.
Coseismic effects related to a High Middle Ages
Event were determined also by Galadini and Galli(1996) in a preliminary analysis of four trenches
excavated at the intersection of the TF and a Roman
drainage channel built in the 1st–2nd century A.D.
(site 11 in Fig. 2). One of the trenches showed that
displacement of the channel-fill sediments occurredin the second half of the 1st millennium A.D.
The data obtained through the extensive paleoseismological study of the Fucino Plain have beenreported in Galadini et al. (1997), while specificobservations along the TF (sites 7, 8, 9 and 11
in Fig. 2) are described in Galadini et al. (1996).
An updated report of the basic paleoseismological
data is in preparation. All the available data will besummarised in the next sections.

5. Paleoseismological analysis
5.1. Trench investigation and dating methods
As reported in the introduction, paleoseismologyof the investigated area has been allowed by trenches
excavated ad hoc across the major Holocene fault
branches, quarries, long excavations dug for the laying of pipelines and the walls of the present drainage

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

channels. Paleoseismological data have been obtained from sites 1–14 (Fig. 2) while sites 15 and 16
did not give any evidence for faulting affecting Late
Pleistocene–Holocene deposits and site 17 is related
to speleothem ruptures in a cave.
In the following sections we summarise the geological and paleoseismological data available for thedifferent fault branches.
All laboratory dates (14 C and thermoluminescence) and sample site locations are reported inTable 1. Radiocarbon dating of samples collectedfrom peat levels and paleosols, as well as lacustrine
Table 1
Laboratory ages obtained by means of the radiocarbon (samples UD and BO) and thermoluminescence methods (on pottery
shards, samples T)
SampleAge, B.P.

Site

UD449
UD437
UD438
UD440
BO393
UD452
UD436
BO387
UD451
UD433
UD434
UD455
UD453
UD450
UD435
UD439
BO391
BO332
BO390
UD441
BO354
T1
T2
T3
T4
T5
T6
T7
T8
T9
–

1,450 š 100
3,390 š 70
3,490 š 70
3,760 š 70
5,060 š 90
5,340 š 100
5,670 š 90
6,170 š 140
7,120 š 120
8,660 š 100
9,260 š 100
9,730 š 140
9,950 š 140
10,400 š 140
10,790 š 110
10,990 š 120
12,100 š 50
19,100 š 650
23,420 š 280
27,230 š 450
32,520 š 500
661 š 46708 š 59730 š 56766 š 100789 š 78
1,444 š 142
1,547 š 142
2,783 š 213
4,670 š 430
14,180 š 260

4
10
10
2
12
4
13
2
4
13
13
*
*

4
8
13
8
1
8
7
5
5
5
5
5
5
2
2
5
5
**

* Site not reported in Fig. 1 (west of and close to Bacinetto).
** Kieffer(1979) in reference to Mt. Etna and used fortephrachronology by Narcisi (1993).

151

Table 2
Laboratory and calibrated ages a
SampleLaboratory age,
B.P.

Calibrated age,
B.C. .2¦ /Description

UD449
UD440
BO393
UD452
UD436
BO387
UD451
UD433
UD434
UD455
UD453
UD450
UD435
UD439
BO391

1,450 š 100
3,760 š 70
5,060 š 90
5,340 š 100
5,670 š 90
6,170 š 140
7,120 š 120
8,660 š 100
9,260 š 100
9,730 š 140
9,950 š 140
10,400 š 140
10,790 š 110
10,990 š 120
12,100 š 50

426–782 (A.D.)
2,203–1,857
3,944–3,618
4,248–3,773
4,541–4,218
5,217–4,545
5,979–5,576
7,588–7,196
8,255–7,885
9,003–8,323
9,156–8,393
10,231–9,055
10,729–10,053
10,921–10,353
12,415–11,876

peat
organic silt
colluviumorganic siltorganic siltorganic siltorganic silt
peat
peat
peat
peat
paleosolorganic silt
peatorganic silta Calibration was made using a standard program (Stuiver andReimer, 1993). Calibrated ages are reported in the text as calendar years A.D. and B.C. (limits of the 2¦ interval derived fromthe probability distribution).

or colluvial organic silts and sands, was conducted
at two different laboratories (ENEA – Bologna, andCRAD – Udine). To account for CO2 variation in
the atmosphere the laboratory ages were calibratedusing a standard program (CALIB 3.0 by Stuiver andReimer, 1993) which permits the calculation of ages
up to 18,400 years B.P. (Table 2).
Thermoluminescence analysis was made by the
Department of Physics at the University of Milan on
pottery shards of different ages (since about 3000
B.C.) using the fine-grain technique (see Zimmermann, 1971).
In some cases archaeologists were able to obtain archaeological dates for pottery fragments byanalysing the pottery grain, the form of the fragment,
the thickness of the pottery and the characteristics ofdecorations.
When it was possible to compare the thermoluminescence dates obtained from the pottery witharchaeological dates for the same fragments, the former method consistently gave younger dates and thedifference between the two dating methods increased
with the age of the pottery. For example, at site 6,
thermoluminescence dating gave 833š213 B.C. on apottery fragment dated at 1700–1200 B.C. by means

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

of archaeological analysis. At site 3, pottery fragments of the 1st–2nd century A.D. (archaeologicalanalysis) were dated at 550š147 A.D. and 447š142
A.D. by means of thermoluminescence. In contrast,
these dating problems do not affect another pottery
fragment sampled at site 6, as thermoluminescence
defined an age of 2720 š 430 B.C. while archaeological analysis gave 2800–2600 B.C.
However, the investigated area is characterisedby an abundance of archaeological sites which havebeen studied by means of stratigraphic archaeological criteria. For this reason, when dates are available
both through thermoluminescence and through archaeologists’ expertise, we consider the latter as thepreferred age.
Some other chronological constraints were also
derived, in particular for the inner and western portions of the basin, from the stratigraphic frameworkof the Late Pleistocene–Holocene lacustrine units(see geological framework section). Detailed stratigraphic correlations between the different studied
sites were performed by surveys along drainage
channels walls (representing an almost continuous
network of exposures), surveys of the trench excavated for the aqueduct between Trasacco and Avezzano and by examination of a few hundred handboreholes. On these grounds it was possible to relatespecific lacustrine units observed in the trenches
across the TF and LMF to the stratigraphic columns
reported in Fig. 4.

6. The main fault branches
6.1. The Marsicana Highway fault (MHF)
The Quaternary activity of the MHF (about 11 kmlong) is recorded by the displacement of Pliocene
lacustrine sediments and Pleistocene fluvial and lacustrine sediments, with offset amount increasing
with age. The fault is highlighted by a 70 m highscarp which affects Pliocene–middle Pleistocene fluvial deposits. These deposits and related terraces
clearly appear to be suspended over the more recent deposits and the bottom of the historical lake
(Fig. 6A). In line with the SE extent of the MHF,
a minor fault branch along the SW slope of Mt.
Parasano (Bosi et al., 1993; Blumetti et al., 1993) ishighlighted by a continuous carbonate bedrock scarp(Fig. 6B).
As already pointed out, besides Oddone’s mapping no direct geological evidence of the 1915 surface faulting or, more generally, of Holocene scarps
can be recognised along this fault, probably due tothe planation of the area related to intense agricultural work. The excavation of a long gas pipeline
trench, which by chance crossed the MHF and aminor fault branch at sites 1 and 2, was therefore aunique possibility to collect paleoseismological data
related to this fault.
At site 1 two fault planes (separated by 35 m)
were observed affecting Late Pleistocene–Holocene
deposits up to the level of the ploughed soil (Fig. 7).
The pipeline trench crossed another fault at site 2.
This site is exactly located on a ca. 1 km-long fault
scarp (reported in Giraudi, 1988) which is parallel tothe MHF. This scarp is interpreted as being the resultof the activity of a minor fault branch, structurally
related to the MHF.
The investigations at site 1 and, secondarily, atsite 2 allowed the recognition of at least four displacement events which affected the MHF. The identified succession is represented by:(1) an event, recorded at sites 1 and 2, which
occurred after 2500 B.C. (this was likely the 1915
event, at least at site 1, considering that historical
reports indicate ruptures in this area); the verticaloffset at site 1 is 0.8 m, while at site 2 it is 1 m;
(2) an event which occurred between 19; 100 š
650 years B.P. and 2500 B.C. (recorded at site 1);
the vertical offset related to this event is 0.36 m forthe westernmost of the two faults at site 1, while
a cumulative offset of 1.6 m can be calculated forthe units affected by this and the subsequent events
across the easternmost fault;(3) another event which occurred between
19; 100 š 650 years B.P. and 2500 B.C. (recorded
at site 1); a minimum total vertical offset can becalculated either for the westernmost fault (1 m), orfor the easternmost one (2.2 m);(4) one event which occurred approximately
19; 100 š 650 years B.P. (recorded at site 1); deposits affected by all the reported events (unit 7 inFig. 7) have been found at the hanging wall of thewesternmost fault and 150 m to the northeast of theeasternmost one (with a horizontal attitude); it has

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

153

Fig. 6. Geological section (A) across the Marsicana Hwy fault (from Messina, 1996, modified) and aerial view (B) of the Mt. Parasano
fault.

been possible to measure 7.5–9.5 m of vertical offset
affecting this unit across the two faults.
6.2. The San Benedetto dei Marsi–Gioia dei Marsi
fault (SBGF)
The activity along this fault branch was determined by analysing two trenches (sites 3 and 5) andtwo quarry exposures (sites 4 and 6).
The SBGF (about 12 km long) is composed by
NW–SE trending fault scarps which affect a Late
Pleistocene soft-rock pediment, a Holocene wavecut terrace and the historical lacustrine deposits (Giraudi, 1988). The scarps usually occur in fluvial andlacustrine gravels or in lacustrine silts (Fig. 8A). In
some places between Venere and Gioia dei Marsi,
however, the Holocene wave-cut terrace is carved
into the carbonate bedrock and the SBGF appears as
a discontinuous, strongly weathered, few-metre-highcarbonate bedrock scarp. Close to Casali d’Aschi
the SBGF steps to the east (Fig. 2) and displaces
Early and middle Pleistocene slope-derived breccias(Galadini and Messina, 1994). Southeast of Gioia
dei Marsi the fault is easily detectable along thesouthern slope of Mt. Serrone (dashed line in Fig. 2)
because it forms an impressive carbonate bedrock
scarp (Fig. 8B). The fault plane is usually exposed
along the scarp showing dip-slip kinematic indicators (mainly striae) and place the carbonate bedrockin contact with Late Pleistocene slope deposits.
In contrast to the MHF, the SBGF fault scarps aredetectable on aerial photographs and recognisable
in the field. This recognition become very difficult
when the scarp affects silty lacustrine sediments,
as at site 5 (Fig. 9), because the scarp is almost
completely bevelled due to intense farming. In thiscase several 4-m-deep hand-boreholes were necessary to exactly define the position of the fault. The

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

Fig. 7. Geological cross-sections of the gas pipeline trench at site 1 (southern wall). Section (b) is located 35 m to the west of section (a).
Small stars indicate the event horizons; the triangle represents the sampling site. The older date is obtained by means of the radiocarbon
method; unit 1 is a colluvium which buries an archaeological settlement close to this area, dated back to 2500 B.C.

hand-boreholes were dug 20–30 cm apart along lines
perpendicular to, and crossing, the general trend of
the SBGF (Galadini et al., 1995). In some cases
the vertical displacement affecting sedimentary units
was defined, based on the interpretation of the obtained sections.
The scarp is more easily recognisable at sites 3
and 4 because it affects the carbonate bedrock. The
trench location at site 3 was identified without further
surveys, while the southern wall of an abandoned
quarry was logged at site 4 (located 20 m north ofsite 3).
Several quarries are present in the area close to
Casali d’Aschi and many of them show displacements affecting slope deposits. In the quarry at site 6
it was possible to define a succession of displacement events and obtain chronological constraints forthem. Analyses using aerial photographs and geomorphological surveys, however, showed that thisarea is clearly affected by deep-seated gravitational
movements. This has been carefully considered in
the interpretation of paleoearthquakes at this site.

On the basis of the analyses performed at sites 3,
4, 5 and 6 it is possible to summarise the successionof displacement events which have occurred along
the SBGF:(1) the 1915 event (at all sites); the offset related
to this event ranges between 0.30 m (site 6) and morethan 0.60 m (site 3);(2) an event which occurred shortly after 426–782
A.D. (at all sites); the offset related to this eventis larger than 0.30 m at site 3; deposits affected bythis event and that which occurred in 1915 show aminimum total offset of 1.20 m at site 4; the 6 mvertical offset calculated at site 6 is the result of agravitational component;(3) an event contemporaneous with the depositionof sediments dated at 833 š 213 B.C. using the thermoluminescence method, or at 1700–1300 B.C. witharchaeological methods (site 6); the large value of vertical offset associated to this event at site 6 (1.5 m) is
probably the result of a gravitational component;(4) a probable event not much younger than
10,231–9055 B.C. and much older than 5979–5576

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155

Fig. 8. Geological section (A) across the San Benedetto dei Marsi–Gioia dei Marsi fault (from Giraudi, 1988, modified) and aerial view(B) of the Mt. Serrone fault.

B.C. (site 5); the deposits affected by this and themore recent events at site 5 show a minimum total
offset of 3 m;(5) an event which occurred between 20,000 years
B.P. and the limit Late Pleistocene–Holocene (site6); the vertical offset is larger than 0.7 m;(6) an event which occurred between 32; 520 š
500 years B.P. and about 20,000 years B.P. (site 6).
Evidence of displacement older than that occurredshortly after 426–782 A.D. has been observed at site
3, but because of the lack of correlative deposits
across the fault zone they cannot be defined.
An event has been observed at site 6, occurred
between the limit Late Pleistocene–Holocene and2720 š 430 B.C. which may be related or subsequent
to the event observed at site 5 between 10,231–9055
B.C. and 5979–5576 B.C.
6.3. The Trasacco fault (TF)
This NW–SE trending, 7.5 km-long branch runs
across the inner portion of the basin, i.e. the flat areathat was occupied by the central part of the historicallake. No field-based geomorphological features canbe directly attributed to the TF, and this branch isonly visible on aerial photographs or satellite images
as a straight lineament representing the sharp contact
between soils with different lithologies and moisture
contents (Fig. 3). Giraudi (1986) hypothesised historical activity for the TF because of the freshnessof the lineament, as shown by the lack of sediments
sealing the contact between different soils.
About 300 hand-boreholes were necessary to precisely locate the fault in the field. Boreholing could
easily reach a depth of 4 m in the soft (silts andclays) lacustrine sediments of the inner part of thelake (Figs. 10 and 11). The boreholes, dug 20–30
cm apart along lines perpendicular to and across theTF, permitted in some cases the reconstruction of
fault geometry and related offsets. In particular it
was possible to define a fault plane dipping 60º to
70º towards the southwest and a displacement generally larger than 1 m affecting the top of complex
D of Fig. 4. Sedimentary units related to the top ofcomplex D are easily detectable through boreholing
due to their typical yellowish colour.

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

Fig. 9. Geological cross-section of the trench excavated at site 5 (S wall). Small stars indicate the event horizons.

On the basis of these preliminary surveys weselected sites 8, 9 and 11 (Fig. 2) as suitable for paleoseismological analysis. At site 11 the TF crosses
the Roman drainage channel excavated in the 1st–
2nd century A.D. Preliminary boreholing gave someevidence of the displacement of the channel bottom
and trenching at this site was also performed becauseof the possibility to obtain precise chronologicalconstraints about displacement events.
Further exposures are from a long, EW-trending
trench excavated for the laying of an aqueduct thatcrossed the TF at site 7 (about 50 m north of site8) and from site 10 which is located along the bankof one of the main drainage channels of the Fucino
Plain (Fig. 2). The banks of the channels are usually
covered by vegetation, but periodic cleaning is necessary to maintain the drainage system operational.
Cleaning conducted at the beginning of 1996 allowed

a paleoseismological analysis to be performed at thissite.
Paleoseismological analysis allowed the identification of seven Holocene displacement events along
the TF plus an older displacement event (which occurred approximately 15,666–14,397 B.C.) that was
found only at site 11.
The Holocene events can be summarised as follows:(1) the 1915 event (sites 7, 8, 9 and 11); thevertical offset ranges between 0.15 m (site 11) and
0.7 m (site 7);(2) an event after or possibly during, the 5th–6th
century A.D. (sites 7, 8, 9 and 11); the vertical offset
ranges between 0.2 m (site 11) and more than 0.3 m(site 7);(3) an event approximately during the 16th–15th
century B.C. (sites 8, 11 and possibly 9); a mini-

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

157

Fig. 10. Geological cross-section of the SE wall of the trench excavated at site 8. Small stars indicate the event horizons; the triangle
represents the sampling site. The date is obtained by means of the radiocarbon method.

mum total offset of 0.7 m can be calculated for the
sedimentary unit which was affected by this and the
youngest events at site 8;(4) an event which occurred about 3944–3618
B.C. (sites 9, 11, probably 10 and possibly 8); a
minimum total vertical displacement can be calculated for the deposits affected by this and subsequent
events at site 9 (0.9 m) and site 11 (0.6 m);(5) an event more recent than 10,729–10,053 B.C.
and preceding 5979–5576 B.C., possibly close to thelatter date (sites 8, 9, 11 and probably 10); a minimum
total vertical displacement can be calculated for thedeposits affected by this and subsequent events at site
8 (3 m), site 9 (1.3 m) and site 11 (0.78 m);(6) an event between 10,729–10,053 B.C. and
5979–5576 B.C. (sites 10 and 11); a minimum total
vertical displacement can be calculated at site 11(0.86 m);(7) an event after 10,729–10,053 B.C. but close tothis date (sites 9, probably 10 and possibly 11); the158
F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170
Fig. 11. Geological cross-section of the trench excavated at site 9 (SE wall). Small stars indicate the event horizons; triangles represent the sampling sites for radiocarbon
analysis. Tephra 1 is one of the Late Pleistocene volcanic levels, the youngest of which has been found at site 1 and dated back at 19; 100 š 650 years B.P. As for tephra 2,
Narcisi (1993) related this level to an eruption of Mt. Etna (Sicily, southern Italy) which has been studied by Kieffer (1979) and which occurred about 14; 180 š 260 years
B.P.

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

minimum total vertical displacement is 1.8 m at site
9 and 1.2 m at site 10.
6.4. The Luco dei Marsi fault (LMF)
Like the TF, the ca. 4.5 km-long LMF is also visible on aerial photographs as a lineament due to thecontact between soils with different lithologies andmoisture contents. It was originally recognised by
Giraudi (1986) for a length of about 1 km in the area
close to the village of Luco dei Marsi. The investigation of the aqueduct walls, where it was expected
to cross the LMF (see site 13 in Fig. 2), has revealed that this branch continues towards the north.
Unfortunately, a very thick cover of reworked deposits is present at this site and thus the sedimentary
succession which is suitable for paleoseismologicalanalysis is only 1 m thick (Fig. 12).
The location of LMF and related displacement
were also identified by digging hand-boreholes, augured perpendicular to a lineament which was observed on aerial photographs at site 12.
Analysis at site 12 only permitted to define 0.15
m of vertical offset affecting sediments deposited
after the 4th century A.D. without distinction of
displacement events.

159

Data obtained from site 13 allowed the identification of two displacement events, namely:(1) the 1915 event, to which a vertical offset lower
than 0.1–0.2 m is related;(2) an event subsequent to the Roman drainageof the lake (1st–2nd century A.D.); the total verticaldisplacement related to this event and to the 1915
one across the investigated structure is 0.1–0.2 m.
6.5. The Tre Monti fault (TMF)
The TMF is a NE–SW trending, ca. 5 km-long
branch of a longer fault which borders the northern sector of the Fucino basin, between Avezzano
and the Aielli area. Galadini and Messina (1994)
demonstrated, however, that the portion of the fault
northeast of the basin has to be considered inactive,
as it is sealed by middle Pleistocene slope-derived
breccias. Since the middle Pleistocene the only active
portion of this structure is thus the TMF, probably
acting as a ‘release fault’ (sensu Destro, 1995).
The fault is located along the southern slope of the
Tre Monti Mountain and appears at the surface as acarbonate bedrock fault scarp which consists of fourmain en-echelon segments. The TMF is responsible
for the displacement of Pliocene lacustrine sediments

Fig. 12. Geological cross-section along the aqueduct trench (S wall) at site 13. Small stars indicate the event horizons.

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

and Pleistocene slope deposits. At the base of theslope affected by the fault some NE–SW fault scarps
are present (up to 0.5 km long) which affect the depositional surface of Late Pleistocene gravels. The
prolongation of these scarps towards the west-southwest coincide with an impressive scarp which affects
the upper surface of a Late Pleistocene alluvial fan.
Trenching and paleoseismological analysis performedon this feature (site 16) did not, however, show any
evidence of faulting or other kind of deformation.

7. The paleoseismic events in the Fucino PlainAs already pointed out, the presence of a continuous Holocene sedimentary record in the inner part ofthe lake provided a unique opportunity to reconstruct
the Holocene seismic history of the Fucino basin (inparticular that of the TF), whereas only discontinuous information is available for the period between
32,000 years B.P. and the beginning of the Holocene.
As indicated in the geologic framework, the Fucino structure appears to consist of a primary fault
system (SBGF–MHF) with secondary branches (TF
and LMF). Movement along the latter faults has
to be considered as the result of sympathetic slip
accommodating part of the coseismic slip. Largemagnitude events originated from the primary fault
system and were responsible for the activation of theentire Fucino structure.
Available paleoseismological data are summarised in Fig. 13 and Table 3. The different events

Fig. 13. Age ranges of the observed coseismic displacement events (recognised through the study of trench and quarry exposures andthrough the collapse of speleothems). The dashed part of the interval represents the less probable time span of occurrence. Numbers
besides the segments indicate the studied sites (Fig. 2).

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

161

Table 3
Summary table of the Late Pleistocene–Holocene displacement events
Event
E1

Age of displacement
1915
1915
1915
1915
1915
1915
1915
1915
1915
1915

Vertical offset

Fault

Site

>0.6
>0.3
¾0.6
0.3
¾0.7
>0.4
>0.4ˆ
¾0.15
<0.1–0.2
>0.3

2
2
2
2
3
3
3
3
4
–

3
4
5
6
7
8
9
11
13
14

E2

2nd–15th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)¾426–782 A.D. (508 A.D.?)833 š 213 B.C.–3th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)
2nd–15th cent. A.D. (508 A.D.?)>0.3[>120]–
0.2; 6 [6.5]
>0.3
>0.25
[>0.7]ˆ
¾0.2[0.1–0.2]

2
2
2
2
3
3
3
3
4

3
4
5
6
7
8
9
11
13

E3

¾833 š 213 to 1300–1700 B.C.
¾15th–16th cent. B.C.
15th cent B.C.–2nd cent. A.D.
¾15th–16th cent. B.C.

0.15 [8][>0.7]
–
–

2
3
3
3

6
8
9
11

E4

¾3944–3618 B.C.
−5979–¾3550 B.C.
5979–¾3550 B.C.

[>2][>0.9]ˆ
[>0.6]

3
3
3

8
9
11

E5

−10,729–5576 B.C.
10,729–5576 B.C.
10,729–5576 B.C.

[>3][>1.3][0.78]

3
3
3

8
9
11

E6

10,729–5576 B.C.
10,729–5576 B.C.

–[>0.86]

3
3

10
11

E7

10,231×5576 B.C.
¾10,729–10,053 B.C.
10,729–5576 B.C.
10,729–5576 B.C.

[>3]
[1.8]ˆ
[1.2]
[¾1]

2
3
3
3

5
9
10
11

Undefined

after 2nd cent. A.D.
after 19,100 š 650 B.P.
after 19,100 š 650 B.P.
after 2500 B.C.
after 2500 B.C.
5979 × 2nd cent. B.C.
20,000 B.P. to Holocene–L. Pleist. limit−Holocene–L. Pleist. limit × 2720 š 430 B.C.
−10,729–10,053 to 3944–3618 B.C.
after 5979–5576 B.C.

¾0.15[>2.2]* [>1]**[1.6]* 0.36**
0.4* 0.4**
[¾1]
–
>0.7
[10?]
–
–

4
1
1
1
1
2
2
2
3
3

12
1
1
1
2
5
6
6
10
10

E8

¾15,666–14,397 B.C.

E9

19,100 š 650 B.P.

E10

¾32,520 š 500 to 20,000 B.P.

–

3

11

[7.5–9.5]

1

1

–

2

6

− D age much younger than that reported; × D age much older than that reported; ¾ D age close to that reported; > D minimum
offset that can be evaluated; [] D cumulative offset (including all the events between En and 1915); ˆ D total deformation (fragile plus
continuous).
* , ** D site 1 (Fig. 7b), site 1 (Fig. 7a), respectively.
Italic points out low confidence events.

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

are reported in the text as E1 (the most recent) toE10 (the oldest).
7.1. The Holocene events
Seven displacement events are recorded during
the Holocene.
The most recent displacement event (E1), whichclearly ruptured all the studied faults, is related to
the 1915 earthquake.
The penultimate displacement event (E2), detectable in most of the studied sites with the exception of sites 1, 2, 10, 12, occurred shortly after
426–782 A.D.; Michetti et al. (1996) assume that
this event is the 801 A.D. earthquake, whereas Galadini and Galli (1996) hypothesise that it is either the508 A.D. or the 618 A.D. earthquake reported in the
catalogues of historical seismicity.
Based on archaeological dating the previous displacement (E3), clearly recognised at sites 6, 8 and11, probably occurred close to the 16th–14th century B.C. E3 may also have been responsible forthe collapse of caves between 1800 and 1100 B.C.
(Radmilli, 1981).
Another event (E4), observed at sites 9, 11 andprobably 10 along the TF, occurred about 3944–3618
B.C. This event may also have been responsible forthe collapse of caves between 3500 and 2200 B.C.
(Radmilli, 1981).
Three further displacement events (E5, E6 and E7)
are recorded along the TF between 10,729–10,053
B.C. and 5979–5576 B.C. The E5 event, closer to thelatter date and recorded at sites 8, 9, 11 and probably 10, may be the same as the one responsible forthe ruptures of speleothems that occurred between
6000 and 4000 B.C. at the Continenza Cave (site 17
in Fig. 2; Giraudi and Frezzotti, 1998). The oldest
Holocene event (E7) occurred about 10,729–10,053
B.C. and it is recorded at sites 9, 11 and probably 10.
The two oldest events at site 5 and the fourth
event back at site 6 are chronologically overlapping
within the E4–E7 succession of events and there isno basis to associate them to one or the other.
7.2. The Late Pleistocene events
The youngest Late Pleistocene event (E8) isrecorded by a displacement which occurred about

15,666–14,397 B.C. at site 11, while an older
event is recorded at site 1 which occurred about
19; 100 š 650 years B.P. (E9). The oldest displacement event (or group of events; E10) occurred between 32; 520 š 500 years B.P. and about 20,000
years B.P. (site 6).

8. Time span between events
The time spans between the five most recent
displacement events are given in Table 4. The timespans vary from about 1400 (between E1 and E2
events) to 2100–2600 years (between E3 and E4).
It was not possible to define the time interval
between the E5–E7 events, due to poor age constraints. Three events, however, did occur between
about 10,500 B.C. and about 5500 B.C. and thus,
assuming they occurred at equal time intervals, one
can calculate an average recurrence interval of 2500
years.
Available time intervals (Table 4) highlight aquasi-periodic distribution of the surface faulting
events during the Holocene.

9. Slip and extension rates
A vertical slip rate of 0.4–0.5 mm yr 1 can becalculated for the MHF at site 1 by considering the
cumulative offset (7.5–9.5 m) across the two fault
planes observed at this site and recorded by deposits
dated at 19; 100 š 650 years B.P.
A lower value (0.24–0.29 mm yr 1 ) was calculated for the SBGF by considering the vertical offset(3–3.3 m) which affects the top surface of unit 18
at site 5 (Fig. 9), whose age is close to 10,231–
9055 B.C. This slip rate, however, represents a minimum value, because it was obtained by calculating
the vertical offset separating the top of unit 18 at
the southernmost portion of site 5 from that at thenorthernmost portion (Fig. 9). Considering that theupthrown side underwent erosion at this site, testified by the number of colluvial episodes which affectthe downthrown side, it is clear that the actual vertical offset and related slip rate are larger than theabove-reported values.
Unfortunately, only observations on single sites

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163

Table 4
Time span between Holocene events a
Age of consecutive events
E1

1915 A.D.

E2

508 A.D. (?)

E3

1500–1300 B.C.

E4

¾3944–3618** B.C.

E5

¾5979–5576** B.C.

E6

10,729–10,053 to 5979–5576** B.C.

Time span between events

Mean time span

1400
1800–2000

1900

2100–2600

2350

1600–2400

2000

5000
5000
E7

¾10,729–10,053** B.C.

a Due to the poorly-defined age of E6, the time span between E5 and E6 and between E6 and E7 is reported as the maximum possible
interval, i.e. that deriving from E6 being very close to E7 or very close to E5.
** Calibrated radiocarbon ages.

are available for the MHF and the SBGF, therefore
nothing can be said regarding slip variability along
the faults.
In contrast, the more extensive data collectedalong the TF infers that the slip rate varies along thisfault branch. A minimum slip rate of 0.27–0.29 mm
yr 1 was calculated at site 8 (Fig. 10) by considering
the minimum vertical offset (about 2.2 m) which
affects the top surface of unit 9 (dated at 5979–5576
B.C.). To the north, however, the slip rate decreases.
At site 9 the vertical slip rate is 0.14–0.15 mm
yr 1 , calculated on the basis of the vertical offset(1.76 m) which affects the top of unit 10, dated at
approximately 10,729–10,053 B.C. (Fig. 11). The
slip rate at site 10 is 0.09 mm yr 1 , calculated on thebasis of the vertical offset (1.13 m) which affects thesame unit mentioned for site 9. This unit is affectedby a vertical offset of 1 m at site 11, for which aslip rate of 0.08 mm yr 1 is calculated. This trend
is probably related to the increasing depth of the
carbonate bedrock below the plain from south tonorth, resulting in a kind of ‘absorption’ of verticalmovement due to the presence of unconsolidated
sediments (see Bray et al., 1994). If this is true, themost realistic measure of the slip rate for the TF isthat calculated at site 8.
In regard to the LF, vertical offset data have beencollected at site 13, where the surface separating
units 5 and 6 is displaced by 0.1–0.2 m across thetwo faults detected at this site (Fig. 12). Consideringthat this surface formed not much after 3944–3618
B.C., the slip rate ranges between 0.017 and 0.036
mm yr 1 . However, considering that the paleoseismic record for the LMF only covers a short timespan and that only one trench is available for thisstructure, this value is not considered completely
reliable.
On the basis of the slip rate data collected at
different sites along the four fault branches, it ispossible to hypothesise the extension rate across theentire Fucino structure by summing the contributionof each investigated fault branch. A crucial point isrepresented by the variable dip caused by listric fault
geometry (e.g. Mostardini and Merlini, 1986). Observed faults generally dip 60º towards the southwest
at the surface, while their dip at depth is much lower.
Amoruso et al. (1998) calculated a dip of 55º š 10ºfor the seismogenic fault responsible for the 1915
earthquake by re-evaluating available seismologicaland geodetic data. Therefore, considering fault dip
values between 45º and 60º, the total extension rate
ranges across the whole Fucino basin between 0.6
and 1 mm yr 1 .
This may be a minimum value, however, considering that it was obtained using the vertical slip
observed at the surface and that this value may belower than the average subsurface slip (i.e. Wells andCoppersmith, 1994).

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

10. Discussion
10.1. The 1915 coseismic faulting
The investigations conducted in the Fucino area
yielded a reconstruction of the surface faulting pattern produced by the 1915 event more complete thanthat available from previous works (e.g. Serva et al.,1986). In addition to the MHF and SBGF (whose slip
is also suggested by Oddone’s map), slip occurredalso along the TF and LMF (Figs. 2 and 14).
Some unpublished historical data point to theformation of scarps along the TF (e.g. Saladino,
1915 in Galadini et al., 1995). However, 1915 slip
along the TF and LMF is inferred from:(1) displacement of the ploughed soil after themost recent drainage of the lake (site 7; Galadini etal., 1996);(2) displacement of the most recent lacustrine
sediments deposited just prior to the 19th drainageof the lake (complex A in Fig. 4) in areas (sites
8, 12 and 13; Galadini et al., 1996, 1997) whichwere submerged by the lake only during the last few
centuries of this millennium;(3) thickening of the ploughed soil across the TF(site 11; Galadini and Galli, 1996).
Unfortunately no geological data are available on
the northern sector of the basin, along the TMF(Fig. 1), even though historical data (Alfani, 1915)
point to the possible occurrence of surface faulting
in 1915.
In short, on the basis of paleoseismological data,
the fault branches reported in Fig. 2 represent thebest available picture of the 1915 surface faulting.
Fig. 14 highlights the surface slip distribution, thatshows a decreasing vertical offset along the TF to-

Fig. 14. 1915 vertical offset along the different fault branches (for quantification see the vertical bar).

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

wards the north and the en-echelon relationship between the SBGF and MHF.
10.2. One more earthquake during the Middle Ages?
Michetti et al. (1996) interpreted the attitude ofsome sedimentary units in their two trenches acrossthe SBGF as being the result of deposition on a
paleoscarp formed by erosion along a paleoshoreline
or by coseismic movement of the fault. Due tothe lack of shoreline deposits, the authors preferred
the second hypothesis and related the deposit to asurface faulting event that occurred during the Low
Middle Ages (LMAE). The authors hypothesise that
the LMAE may be the 1349 event, even though thedamage distribution of this earthquake does not seemconsistent with an origin in the Fucino area (e.g.
Boschi et al., 1995).
In contrast, we have not found any trace of the
LMAE at the different sites we analysed. At site
5, which is located along the same branch investigated by Michetti et al. (1996), we found many
sedimentary episodes and erosive traces related tothe evolution of the lacustrine shoreline, similar to
the exposure of Michetti et al. (1996). Therefore,
we prefer the paleoshoreline erosion hypothesis andfollowing a conservative approach we conclude thata LMAE did not originate, nor produced surface
faulting, in the Fucino basin.
10.3. The Fucino fault and adjacent structures
Galadini and Messina (1994) defined a main active structure in this sector of the Apennine chain,represented by a 80 km-long lineament consistingof en-echelon branches located between the upper
Sangro River valley and the town of L’Aquila. The
Fucino fault lies in the central part of this zone andits prolongation towards the north is represented by
the Ovindoli-Pezza and Campo Felice faults (OPF
and CFF, in Fig. 1), while the southern prolongationis represented by the Sangro Valley fault zone and
the Pescasseroli fault (SVFZ and PF in Fig. 1).
A paleoseismological study conducted along the
OPF by Pantosti et al. (1996) found the traces ofthree displacement events: the oldest occurred between 5000 and 3300 B.C.; the penultimate about
1900 B.C.; and the most recent between 860 and

165

1300 A.D. The recurrence interval between the last
two events ranges between 2760 and 3200 years.
These data suggest that although the OPF and theFucino faults are adjacent and they slip at similar
rates, the timing of their events is completely independent. Therefore, in the time period investigatedthere is neither evidence of ‘cascading’ rupture of the
OPF and Fucino fault, nor evidence of synchronous
activation responsible for larger-magnitude events.
Similarly, recent investigations carried out by Giraudi (1995) in the Campo Felice area (Fig. 1) showthat the most recent slip event along some faults
connected with the CFF probably occurred in the last
2500–3000 years.
The fault branches of the upper Sangro Rivervalley (SVFZ and PF in Fig. 1) are also in-line with
the SBGF. Published data only indicate post-Early
Pleistocene activity (Galadini and Messina, 1993);
more recent data (Galadini et al., 1999), however,highlight a post-26,000 years B.P. activity of the
PF. Recent activity in this area is confirmed bygeomorphological evidence such as the fresh fault
scarp affecting Early Pleistocene gravels along mostof the PF. In addition, data on active tectonics areavailable for a sector of the Sangro Valley, southeastof that reported in Fig. 1, where deposits of glacial
origin related to the last glacial maximum are clearlyfaulted (Giraudi, 1995).
However, evidence of strong (M > 6) historicalearthquakes are lacking in the Sangro Valley andtherefore it appears necessary to address future research at collecting paleoseismological data in this
sector of the Apennine chain.
10.4. Comparing the paleoseismological results andthe historical record
Recent paleoseismological research in the Apennine chain shows that the recurrence intervals of displacement events usually range between more than
1000 and 3000 years (Pantosti et al., 1993, 1996;
Giraudi and Frezzotti, 1995; Cinti et al., 1997). Data
regarding the time span between the surface faulting
events in the Fucino Plain are completely consistent with this trend and show that the behaviourof the Apennine seismogenic structures responsible
for surface faulting events is characterised by longrecurrence intervals.

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

The historical record of earthquakes in Italy covers a time interval of more than 2000 years (Boschi
et al., 1997), although it is obviously less complete with regards to older events. A comparison of
the length of recurrence intervals of strong eventsand the time span covered by the Italian seismic
catalogues reveals that the latter do not necessarily include records of all the Apennine seismogenic
structures. This observation, already stated by otherauthors (e.g. Pantosti et al., 1996), is also highlighted
by the fact that geologic data in the Apennines show
the presence of active faults that, according to historical records, did not rupture during the time interval
covered by the catalogues (examples are the Ovindoli-Pezza fault, studied by Pantosti et al., 1996, andthe Sangro Valley fault zone, both mentioned in theprevious section).
10.5. Extension rates and active fault sets in thecentral Apennines
The extension rate through the Fucino Plain (0.6–
1 mm yr 1 ) is consistent with that evaluated by
Pantosti et al. (1996) for the Ovindoli-Pezza fault,
north of the investigated area (0.4–1.1 mm yr 1 ).
These are the only direct data available from thecentral Apennines which can be used to discuss theseismic extension rate across this Apennine sector.
The geologically inferred extension has been
compared with that obtained by summing the seismic moments of the historical earthquakes which occurred in an area including the Fucino seismogenetic
structure. This approach is based on the equation:
vs D Mo=2¼H Lt
derived from Kostrov (1974), where vs is the velocity
of separation between two zone boundaries, Mo isthe sum of scalar seismic moments, ¼ is the rigidity
modulus, H the thickness of the brittle layer, L
the length of the considered region, and t the timespan covered by the catalogue. Since the extensional
eigenvector (sensu Kostrov, 1974) of the seismic
moment tensor is not subhorizontal for normal faults
with dip d 6D 45º, according to Westaway (1992) the
resulting relative velocity can be estimated as:vs D Mo sin.2d/=2¼H Lt
The magnitude values necessary for the evaluation of Mo have been taken from the two mostFig. 15. Seismicity of central Italy (1000–1992, according toCamassi and Stucchi, 1997, 1998). The bold line delimitates thearea selected for the evaluation of the extension rate through thesummation of the seismic moment tensor.

recent available Italian catalogues (Boschi et al.,
1997; Camassi and Stucchi, 1997, 1998) and theseismic moments have been calculated for the earthquakes falling inside the polygon reported in Fig. 15.
The chosen area represents a part of the Apennines
which is characterised by NW–SE normal and normal-oblique faults and related NE–SW extension.
Assuming m D 3 ð 1011 dyn=cm2 , H D 15 km
and L D 150 km, and considering fault dips ranging
between 60º and 45º, the obtained seismic strain forthe period 1000–1992 is between 0.8 mm yr 1 and 1
mm yr 1 using the catalogue by Camassi and Stucchi(1997, 1998) and between 0.5 mm yr 1 and 0.6 mm

F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

yr 1 using the catalogue by Boschi et al. (1997).
The discrepancy between the obtained seismic strain
values is due to the fact that the magnitudes reported
in the former catalogue are generally larger thanthose reported in the latter.
However, the choice of the period may affect theresults. In fact, historical information is not homogeneous throughout the entire interval 1000–1992,
being more scarce in the early centuries.
More homogeneous information is available forearthquakes with M ½ 6 (whose contribution to thetotal seismic moment is greater than 90%) in the
period 1300–1992. With this time interval, the extension rate is 0.9–1.1 mm yr 1 considering the catalogue by Camassi and Stucchi (1997, 1998) and 0.7–
0.9 mm yr 1 considering the catalogue by Boschi etal. (1997).
The obtained values are similar to the paleoseismologically inferred rate throughout the Fucino
structure (0.6–1 mm yr 1 ). However, at least anotheractive and seismogenic fault system affects the central Apennines, paralleling the Fucino structure to
the east (i.e. the Sulmona-Gran Sasso fault system;e.g. Vittori et al., 1995; Giraudi and Frezzotti, 1995).
Therefore, the similarity between the differently calculated extension rates points to a seismicity ‘deficit’in the central Apennines during the last millennium.
This is consistent with the conclusion of the previous
section, indicating that a number of active faults inthe central Apennines were not active during the past
1000 years.
10.6. Faulting behaviour of the Fucino seismogenic
structure
Offset-per-event data related to the primary faultsof the Fucino basin (the MHF and SBGF) are lacking. However, an evaluation of the MHF slip rate
(0.4–0.5 mm yr 1 ) is available at site 1, along withevidence related to vertical offset caused by the 1915
event. In fact, on the basis of historical data whichindicates that about 0.9 m of displacement (divided
into two adjacent scarps with comparable verticaloffset) occurred in 1915 close to site 1, it is conceivable that the displacement of about 0.8 m observedin unit 1 (due to both faults detected at this site) is
entirely related to the 1915 event. Considering theage of unit 7 (about 20,000 years B.P.) and the aver-167

age time interval for the Fucino events (about 1900
years), one finds that unit 7 was probably affected byten events. If the fault has a characteristic behaviour,
the 0.8 m displacement observed at this site due tothe 1915 event would yield a total displacement of
about 8 m. This is comparable to the total offset of
7.5–9.5 m observed at site 1.
Another interesting point is obtained by comparing the offset affecting units 1 and 2 along thewesternmost fault detected at site 1 (Fig. 7b). On
the basis of historical data, the 0.4 m displacement
affecting unit 1 may be entirely related to the 1915
event, while the offset due to the previous event
is 0.36 m. The similarity of the offsets producedby these two events, as well as evidence given by
the comparison of long-term slip rates and the slip
data related to the 1915 earthquake, may indicate aconstant ‘displacement-per-event’ over time.
Unfortunately, site 1 is the only site along theMHF, and thus there are no other data which canconfirm the characteristic behaviour of the Fucino
fault. In fact, as pointed out in the previous section, the vertical slip rate evaluated for the SBGF atsite 5 (0.24–0.29 mm yr 1 ) represents a minimum
value, and therefore reliable results cannot be expected from a comparison of the 1915 offset with thelong-term slip rate. However, historical data at site
5 indicates that 0.6 m of vertical displacement occurred in 1915. Deposits dated at 10,231–9055 B.C.,
which may have suffered all seven Holocene eventsin the Fucino basin, are displaced 3–3.3 m; this isabout 1 m less than that expected for characteristic
behaviour and assuming 0.6 m as characteristic slip.
At sites 3 and 4 only minimum values for the1915 offsets may be considered along the SBGF;
moreover, the evaluation of the slip rate at these sites
may be unreliable due to the unknown depositional
geometries of the sedimentary units affected by thefault. In addition, the displacements observed atsite 6 appear to be clearly affected by gravitational
components.
Vertical offset data and slip rates are available forsites 9 (0.14–0.15 mm yr 1 ), 10 (0.09 mm yr 1 )and 11 (0.08 mm yr 1 ) along the TF, while a minimum slip rate is available for site 8 (0.27–0.29 mm
yr 1 ). Available data show that an almost constantdisplacement-per-event may affect the fault branchin the inner sector of the basin. However, as the TF

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F. Galadini, P. Galli / Tectonophysics 308 (1999) 143–170

is a secondary fault, these data are inconclusive forthe assessment of seismogenic structure behaviour.
In short, the only reliable data related to the seismogenic behaviour of the Fucino fault were obtained
along the MHF at site 1. These data may infer acharacteristic behaviour of the fault, but the lack ofother sites with similar results means that conclusive
hypotheses cannot be presented.

11. Conclusions
The paleoseismological research conducted in theepicentral area of the 1915 Avezzano earthquake.Ms D 7:0/, represents the final step of a detailed
geological and structural study aimed at defining
the Holocene faulting pattern and Late Pleistocene–
Holocene geological evolution of the region (Giraudi, 1988; Galadini and Messina, 1994; Galadini
et al., 1995). Through the study of trench walls andexposures and the analysis of collected data it waspossible to:(1) reconstruct that the surface faulting pattern of
the 1915 event is due to slip on four different fault
branches over a 15 km ð 20 km large area;(2) identify the displacements due to ten seismic
events which occurred since 32; 520š500 years B.P.,
seven of which occurred during the Holocene;(3) define a recurrence interval for events responsible for surface faulting which ranges between 1400
and 2100–2600 years (average 1900 years);(4) calculate a slip rate of 0.4–0.5 mm yr 1 forthe MHF and minimum slip rates of 0.24–0.29 mm
yr 1 and 0.27–0.29 mm yr 1 for the SBGF and theTF, respectively, as well as an extension rate acrossthe Fucino Plain between 0.6 and 1 mm yr 1 ;(5) determine the quasi-periodic distribution of
surface faulting events over the Holocene.
Data on the Fucino area are consistent with recently published paleoseismological works on active
faults of the central Apennines (e.g. Pantosti et al.,1996). Moreover, these data improve our understanding of the seismogenic processes in this sector of theApennine chain, characterised by faults with slip
rates lower than 1 mm yr 1 responsible for large
earthquakes .M ½ 6:5/ each 1000–2000 years.
The comparison between the Fucino paleoseismological data and the paleoseismological data set

related to the Ovindoli-Pezza fault (north of the Fucino Plain; Pantosti et al., 1996) shows no apparent
chronological relationship between the events that
occurred along the two faults, due to the different
recurrence time of surface faulting events. In contrast, neither paleoseismological nor historical dataon M > 6 earthquakes are available for the southern prolongation of the Fucino structure (i.e. theSangro Valley fault zone), despite geomorphologicalevidence of the present tectonic activity.
Another implication derives from the similarityof the extension rate (paleoseismologically inferred)
across the Fucino Plain and that obtained by the summation of seismic moments related to historical earthquakes in the period 1000–1992, throughout the entire
central Apennines. Since at least two parallel systemsof active faults affect the central Apennines, the similarity of the differently calculated extension rates indicates that a number of faults were not active since 1000
AD. This is not anomalous, considering that the timespan between two large events related to an Apennine fault is usually larger than 1000 years. A generalconsequence (already stated by other authors, such as
Pantosti et al., 1996) is that the Italian seismic catalogues appear to be insufficient to record all the latest
events caused by the different seismogenic structures
affecting the Apennine chain, despite the long time
period covered by historical information. As a result
the activity of many faults may not be reported in
the seismic catalogues and, paradoxically, may havea major impact on seismic hazard assessment (due tothe lack of events in the last 1000 years). This observation clearly directs future geological and paleoseismological research towards the individuation andcharacterization of historically ‘silent’ active faults.

Acknowledgements
We are grateful to M. Meghraoui and D. Pantosti for helpful discussions; their review of themanuscript has greatly improved it.

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