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Geomorphological fragility and mass movements of the archaeological area of “Torre di Satriano” (Basilicata, Southern Italy) Stefania Pascale1, Jessica Bellanova2,Lucia Losasso1, Angela Perrone2, Alessandro Giocoli2,3, Sabatino Piscitelli2, Beniamino Murgante1 & Francesco Sdao1 1

School of Engineering, University of Basilicata, 85100 Potenza (PZ), Italy 2 CNR-IMAA, Tito, Potenza, Italy, 85100 Potenza (PZ), Italy 3 ENEA, 00196 Rome, Italy Stefania Pascale, [email protected]

Abstract This paper describes the results of geomorphological and stability studies carried out in the archaeological site of Satriano di Lucania (Basilicata, Southern Italy), where an important sanctuary was built during the 4th Century B.C. This study is based on a mutidipliscinarity approach including accurate interpretation of aerial photos, geomorphological and geoelectrical surveys , and stability analyses. A description of the stability condition of the archaeological site with reference to the landslide that affects the sacred complex is provided in this work. Keywords: Slope instability; Landslide hazard; Lucanian sanctuary; 4th Century B.C.; Basilicata (South Italy)

1. Introduction Basilicata Region (Southern Italy), due to geological, geomorphological, climatic and seismic characteristics, is one of the Mediterranean basin regions most subject to geomorphological instability, taking form by different kinds of landslides, evolution, mechanisms and processes of intense and selective erosion. In particular, in some areas of Basilicata Region, landslides are so intense to generate sometimes extensive and serious damages to people and properties. In the last years, recent geomorphological studies have shown that many archaeological sites of Basilicata Region, especially in the Apenninic areas, are characterized by widespread and intense landslides which damage valuable historical and archaeological remains. Such situations can be observed, for example, in the archaeological area of Rossano di Vaglio ([1] and [2]), where the shrine of the goddess Mephitis falls within a large and ancient landslide; in the "Parco Storico Naturale delle Chiese Rupestri del Materano", in which there are numerous medieval testimonials characterized by a serious state of collapse due to landslides [3], [4] [5] and in the Satriano di Lucania area, which represents the study area of this article [6]. This work reports the main results of accurate geological, geomorphological and geophysical studies of "Torre di

Stefania Pascale, Jessica Bellanova, Lucia Losasso, Angela Perrone, Alessandro Giocoli, Sabatino Piscitelli, Beniamino Murgante & Francesco Sdao

Satriano" archaeological area, supplemented by analysis and interpretation of aerial photos, which allowed the definition of the geomorphological instability and subsequent drafting of landslide inventory. Researches and surveys previously carried out both in the investigated area and the neighbour zones have been also considered [6]. In particular, it was analyzed the area on which a worship place arises and where there are the remains of the Lucanian Sanctuary structures [7]. Wall structures of the sanctuary, unearthed during various archaeological excavations, show progressive deformations which led the local population to repeatedly restructure the sacred building between the fourth and first centuries B.C.. Since its total abandonment a subsequent fossilization of the area has been caused by the deposition of detrital and colluvial materials. As a whole, the settlement of Lucanian age located downstream of the “Torre di Satriano”, is configured as a space-time unity with specific lithological, morphological characteristics and well-define anthropogenic activities [8]. Finally, environmental and/or socio-cultural changes have influenced the local population to definitively abandon the place of worship during the first century A.D..

2. Historical notes on the Satriano archaeological site From the archaeological point of view, the Torre di Satriano represents one of the most interesting areas of the Basilicata Region, due to the anthropogenic presence, starting as early as the Bronze Age to the Middle Ages [6]. Over the years human settlement has been involved in a complex evolution characterized by abandonment and subsequent reorganization of the territory differently distributed in space. The first abandonment has been recognized between the Late Bronze Age and the Iron Age followed by a repopulation during the eighth century B.C., as evidenced by burials found in the area. The major phase of growth of the pre-Lucanian indigenous settlement took place from the sixth century B.C. that coincides with the implantation of a settlement with its necropolis, along the southern side of the Torre di Satriano. In the IV-III century B.C., the area was involved in great transformations corresponding with the arrival of people from Basilicata. It dates at this time the Lucanian Sanctuary which is located over a large area close to a spring and not far from a sheep track that favored the interaction between people, and represented a road network linking the Tyrrhenian and the Ionian sectors of the peninsula. The Sanctuary activity developed in a large enough time span, also characterized by quite long periods of scarcity of documentation, such as the period between the second century and the beginning of the first century B.C., until the complete abandonment occurred in the first century A.D. ([6] and [9]). During its period of activity, the Sanctuary was characterized by repeated renovations, especially between the third and the first century B.C., when, due to the damage of the seabed structures, the abandonment of the lower shelf, on which stood one of the buildings in favor of the upper one, occurred. The disappearance of the Lucanian settlement started at the end of the third century B.C., probably as a result of the Romanization phenomenon of the area that led to the emergence of new urban realities as Potentia. In the Middle Ages, finally, there was a restocking with the birth of Satrianum that became an important bishopric in the twelfth century A.D..

Geomorphological fragility and mass movements of the archaeological area of “Satriano Torre” (Basilicata, Southern Italy)

3. Geomorphological fragility and landslides of “Torre di Satriano“ archaeological site.

3.1

Geological setting of the study area

The study area, located in the central sector of the Campano-Lucano Appennines (Fig. 1), represents a high morphological and structural, standing as a small relief with a convex morphology and with steep slopes.

Fig. 1. Location of the study area.

The ridge on which the ruins of Torre di Satriano stand, is a close alignment NWSE oriented (Fig. 2), which acts as both geographical and hydrographic watershed between two great morpho-tectonic depressions, respectively known as the TitoPicerno intermontane basin at north and the Pergola-Melandro at south, that over the past two million years were filled by coarse clastic sediments [10]. The recent tectonic uplift rate occurred in this part of the chain during the last 730 ka, with speeds estimated in the order of 0.6-1 mm/yr, has increased erosional activity exerted by the water courses that has profoundly affected the hundreds of meters of clastic sediments, filling the intermontane depressions [10]. Lateral erosion, alternated to the vertical one, has produced a widening and, sometimes, a decrease in the slope of the river valleys, up to the current configuration of the landscape. From a geological point of view, in the examined area outcrop the terrains belonging to the Ceno-Mesozoic pelagic successions of the Lagonegro Units, the Tortonian pelitic-arenaceouscalcareous alternations of the “Monte Sierio” Formation (sensu [11]), and the middleinferior Pliocene sands (Fig. 2).


Fig. 2. Geological map of the study area (Geological Map of Italy at 1:100,000 scale, Servizio Geologico D’italia (1971) - Carta Geologica d’Italia scala 1:100.000. F. 199 “Potenza”, Roma; modified by [6].

The Lagonegro Units are, in particular, represented, from the bottom to the top, by “Monte Facito”, “Calcari con Selce”, “Galestri” and “Flysch Rosso” formations. “Monte Facito" formation (Lower-Middle Triassic) is subdivided in a) a terrigenous (siliciclastic) unit, made up of a succession of quartz-rich calcarenites and mudstones, marls, shales and green micaceous sandstones, strongly deformed and frequently associated with gravels; and b) an organogenic unit, made up of grey massive limestones and heavily fractured black limestones and marls. “Calcari con Selce” formation (Upper Triassic), conformably lying on the "Monte Facito" formation, consists of centimetres-to-decimetres-thick layers of grey limestones with beds and nodules of black and white chert, marls and calcareous


marls, mudstones and marly clays. This succession is well layered and strongly fractured. This formation, showing a clear stratification and an intense cracking, constitutes the ridge oriented towards NW-SE on which the medieval site of "Torre di Satriano" is located. "Scisti Silicei" formation (Jurassic), composed of thin – layered and fractured variegated cherty shales, partially cherty marls, green and red Radiolarites and graded pebbly limestones. This formation, well stratified and finely cracked, essentially emerges along the southern slopes of Mt. Caruso and near some reliefs in the area. "Galestri" formation (Lower-Middle Cretaceous), consisting of clayey and marly thinly bedded rocks, extensively emerges near the north-western and southern sector of the examined area. “Flysch Rosso” formation Auctt. (Upper Cretaceous – Eocene) is made up of marly clays and clayey marls finely scaly randomly, alternated with levels of mudstones, marly calcilutites, bioclastic calcarenites, cherty radiolarites, clays and marly clays. This geological unit, strongly fractured and severely deformed as a consequence of its severe tectonic history, is particularly prone to slope instability phenomena. This formation is present in the South-western sector of the examined area. “Monte Siero” formation (lower Miocene) consists of an arenaceous-pelitic alternation in flysch facies and emerges in the NW of the study area and mostly in the orographic left of the Tito river. Pliocenic conglomerates outcrop in discordant transgression on the Lagonegrese Unit. They are constituted by elements of different rocks and variable sizes, poorly stratified and poorly cemented. The rounded blocks, with a diameter ranging from some millimeters to some centimeters, are immersed in an abundant sandy matrix. These conglomerates outcrop in the sector of the study area, mainly on the left and right orographic of the Tito river. These geological formations, finally, are capped by Pliocene wedge-top deposits and by Pleistocene-Holocene alluvial sediments. Mass movements are widespread in the study area and play an important role in the present-day landscape evolution. In particular, very large ancient and recent landslide bodies can be observed and, mainly consist of calcareous-siliceous eterometric debris pieces in a yellow-brown sandy-clay matrix. Furthermore, the thickness of the detrital accumulations, produced by landslide activity, that has always involved the considered area, varies from a few meters to a few dozen meters (landslide of Lucanian Sanctuary, [6]).

3.2

The state of landslides of the examined area: methodological approach

The definition of the landslide state and the resulting geomorphological map are based on a methodological approach consisting in close synergy between the methods of applied and evolution geomorphology, the traditional techniques of landslides recognition (constituted of the analysis of aerial photos and satellite and of cartographic maps) and geomorphologic detection. Based on this methodology, the study has been divided into distinct and sometimes interconnected phases, summarized in fig. 3.


Acquisition and interpretation of basic elements

Preliminary geomorphological analysis

Bibliographic sources;Institutional sources; precipitation data, sismic data;Relief and geological analysis;Geological mapping;Geomorphological mapping;Hydrographic mapping.

Geomorphologic alanalysis and interpretation of aerial photos

Geomorphological and field surveys

Geomorphological map; Evolving landslide areas; Erosion areas; features of evolution of the slopes; active factors in the evolution of landslides; features of Activity of landslide; Types and mechanisms of landslide ; Extension of areas affected by landslide

Geomorphological mapping processing

GEOMORPHOLOGIC MAP OF LANDSLIDES

Fig. 3. Study methodology.

Studies have also taken into account the results obtained by geological, geomorphological and archaeological surveys previously carried out, concerning both the selected areas and the neighboring ones. For the definition of the geomorphologic and landslide characteristics of the area, accurate geological and geomorphological survey at 1:2.000 scale have been conducted in the years 2008 – 2013 and compared with aerial photos for the years 1956, 1977, 1982, 1991, 1994, 1997, 2004 and 2010. As far as the southern side of the relief of "Torre di Satriano" is concerned, and in particular for the area of the "Lucanian Sanctuary" and the nearby necropolis, also some archaeological and geophysical surveys have been conducted in recent years [6]. The current state of landslides has been schematically shown on a geomorphological map, in which each landslide has been reported and mapped. For the drafting of such a map a thematic legend based on scheme proposed by [12] has been adopted and used, suitably adapted to local geomorphological conditions and already applied in other situations similar to the one in examination. In particular, for each landslide mapped the main geomorphological elements, the type and direction of movement and activity status have been shown.

4. Features and distribution of landslides of the study area The intense and recurrent landslides characterizing the investigated area are well known and studied [6]. This geomorphological fragility, which is common in many areas of the Basilicata Region, is related to the peculiar lithological and geomechanical nature and to the widespread and intense cracking of the surface terrains (clayey-marly intensely fissured successions significantly predominate), the morphological configuration of the slopes, the applicants and intense event of rain,


the frequent earthquakes. The analysis of landslide inventory map (fig. 4) shows that the area of Satriano has widespread and perfectly visible traces of a lively gravitational dynamics, which is still clearly evident and manifests through mass movements, of various types, size and degree of activity.

Fig. 4. Geomorphological map of the archaeological area of “Torre di Satriano”.

In the study area, 50 different landslides were recognized and defined, on a total area of 22 km2 and about the 78% (17 km2)was investigated. The most mapped landslides are related to complex types, where the retrogressive and roto-translational mass movements dominate, evolving, often, in earthflows. These landslides often involve the whole slope, from the top of the reliefs to the underlying watercourses of the Melandro and of the Tito-Picerno rivers which are characterized, for this reason, by a markedly meandering configuration, with evident lateral deviation and partial occlusion of the riverbeds. The numerous mapped landslides show similar


geomorphological features: often modeled or degraded scarps, connected with the surrounding relief; landslide channels with modeled edges and linked with the landslide bodies; bulge, morphological depressions and surface landslide; extended accumulation zones with partial landslide reactivations caused by the excavation made to the foot by Melandro River. The thickness of such landslides is variable and can reach a maximum value of about 20-25 m. Multi-temporal aerial photo interpretation and field surveys allowed to distinguish between active and inactive landslides. In particular, the landslides that showed signs of activity after 2013 were considered active (e.g. bright light colors on the aerial photos, landslide area with no vegetation, evident cracks in the source area and by a distinct bulge at the toe). Fig. 5 shows the distribution of landslides for each lithological class, according to the landslide density (ratio of landslide area of each type of landslide in every lithological complex "Af" and the total area of this last “Al”). The figure and the map show that landslides are present with varying intensity in each geological formations.

Fig. 5. Landslides distribution for lithological classes.

The lithological formations most affected by landslides are clayey-marly ones belonging to the Lagonegro Unit and, in particular, to the formation of Monte Facito and Galestri. The same figure shows that the typology, geometry and evolutionary features of landslides in the examined areas are markedly affected by lithological and structural characteristics of the lithologies outcropping. Distribution and type of mass movements is closely related to the geological and morphological setting, including structural and stratigraphic factors (alternating weak and hard rocks), tectonic setting and fluvial undercutting ([13] and [14]). The interaction between landsliding and lithology showed that mass movements mainly affect slopes carved in the flyschoid rocks, sandy and conglomeratic deposits. In the areas, where flyschoid lithotypes crop out of various kinds and with different pelitic content, the landslide type is closely linked to the prevailing lithological nature and to their degree of fracturing. Moreover, a chaotic and a disorganized tectonic setting further promotes mass movements, because the structural discontinuities such as joints, faults, foliation and bedding planes form the pre-existing lines of weakness in the rocks and high local relief. These lines of weakness are likely to be areas with high permeability and deeply weathering of rocks, consequently, are areas with particularly high incidence of slope instability. Slide type mass-movements occur, where flyschoid rocks, sandy deposits and conglomeratic deposits crop out. Flow mass movements, that are closely related to concave surface topography and involved mainly a clayey-flysch bedrock covered by slope and/or old landslide deposits. The source area of many flow-type landslides


mapped was branched in several coalescent landslide scarps and show elongated accumulation zones, ending with fan-shaped toes. Many shallow landslides are active within the source areas. Rock falls, are predominantly located in the zones where steep slopes and more resistant rocks crop out (e.g. carbonatic complex). Rock fall source areas are often connected to fault scarps, joints, or multiple cleavage systems. Rock falls may be represented by single boulder falls or events that move large volumes of rock. The falling material is deposited at the base of the cliffs and often produces typical debris cones. Among the various recognized landslides, the great landslide of "Lucanian Sanctuary" is particularly significant (figs. 4 and 5). This is a great, articulate and ancient mass movement, consisting of rototraslational slidings evolving to earth flows. This large mass movement has already been the subject of study in the recent past by [6]. Another important archaeological site is the Anaktoron that is located on a countersloping terrace site at an altitude of about 775 m above sea level delimited by a detachment developing between the units 740 m and 780 m above sea level, with a maximum length of 238 m and a width of about 230 m (fig. 4).

5. Geomorphological and archaeological analysis of the Lucanian Sanctuary The area on which the Sanctuary was built is located along the southern foothills of the limy slope on which stands the Torre di Satriano, at around 1000 meters above sea level, and takes the form of a plateau with a lower slope than the rest of the slope located upstream which climbs to the summit from the SS 95. Downstream landscape, in a more or less constant way towards the watershed of a stream tributary orographic right of the Melandro River degrades with the exception of small flat areas constituting the ancient stabilized landslide counterslope terraces - interrupting the physic continuity. In the area there are also water points that the emergence and development of the Lucanian settlement have favored and among them a particular significance has a spring that comes from the southern side and that is generated, in all likelihood, by the tectonic contact between the limestone and more permeable rocks forming the relief of the Tower which are in the bed of the fault and the clayeymarly top that serve as relative waterproof. This spring, which currently at the Land Registry of the water bodies in the Basilicata Region is collected and recorded, shows a flow of approximately 0.750 l/s measured at the end of the summer and that allows to hypothesize water supplies of greater magnitude in winter In morphological terms, the natural landscape has been in antiquity an ideal site for the construction of the Lucanian age Sanctuary; to this is added the strategic geographical location of the area in terms of connection between different cultures, placed along routes joining the Tyrrhenian coast to the Ionian coast [6]. The landforms related to exogenous recently dynamics, analyzed with a aerial photo analysis and with field surveys (fig. 4), have revealed that the territory of the Lucanian settlement is affected by widespread landslides both ancient and recent consisting mainly of rototraslational landslide that evolve to earth flows and evolving in clayey-marly lithologies belonging to different geological formations that outcrop in the area. In relation to the morphological conditions and the stability of the landslide were identified inactive landslide without


obvious active signs of movement, dormant landslide characterized by an apparent stability but with well preserved forms of detachment and accumulation and characterized by active landslide movements and that often promptly the ancient landslide reactivate (fig.6) At a more detailed scale, the water outflow, along the southern slope of the place of Santuary, is divided into small streams with low degree of vertical depth and with an almost total absence of fluvial tributaries that determine above an elongated but not straightaway physiography with sinuous course and with small radius, due to the unstable conditions of the land. Throughout the southern slope, flat areas generated by the landslide terraces, locally present with signs of waterlogging forming small pools seasonally fed The entire slope is characterized by a large landslide (fig. 6) with complex kinematics in which roto-traslational movements, evolving to earth flows, are recognizable. The activation of these large landslides (fig. 6) precedes the colonization of the area by man and is likely to be placed at the post-glacial period, that is at the end of the last phase of the Wurm glacial expansion that starts about 10 ka due to the considerable supply of water resulting from melting snow. The sacred activity of the Santuary probably has not been continuously carried out but it has experienced more or less long periods of stasis - or of showy decrease ritual - witnessed by the absence of votive objects, as seems to be happening in the period between the second and first centuries B.C. [9]. After considering the environmental characteristics of the area (this term refers to all physical, biological and socio-cultural territory) the reasons that have produced this gap in the sanctuary activity, that was followed, in the first century A.D., by his final abandonment, is not entirely clear, or at least does not seem sufficient to justify these events only with the arrival of Roman culture that in the centuries following will grow with the birth of the ancient Potentia. It seems clear that the abandonment of the sacred place is not only to be related to socio-economic factors but also to biological and environmental factors that would have forced the local population, already prepared, to completely abandon the site.

6. The large landslide of “Lucanian Sanctuary” The southern slope of Torre di Satriano is entirely covered by an ancient and complex rototranslational slide that evolved into a large earthflow (fig. 6) ([15] and [16]). It is approximately 2060 m long, from 150 to 725 m wide, and extends between 850 and 605 m a. s.l. with an average inclination of about 10°. As already highlighted, this large landslide has significantly influenced the historical evolution of this archaeological area [6] . In particular, the activation of this large landslide is certainly before the VIII century A.C., while the eastern sector remobilization of the rototraslational slide, occupied by the Lucan sacred Sanctuary settlement, took place after the renovation around the 1st century A.C.; this caused a rotation against Mount of approximately 13° of the same Sanctuary (fig. 7). The large landslide of "Lucanian Sanctuary" involves the formation of "Calcari con selce" (upper Triassic) and the Galestri formation (lower - middle Cretaceous); the landslide is essentially constituted by very degraded and plastic marly-clayey material; in the clay matrix calcareous and/or siliceous heterometric sharp-edged stone fragments can also be found. The


alleged thickness of this landslide body, assessed both on geomorphological basis and indirect investigation (geoelectrical survey), varies from 20 to 25 m. 6.1 Geomorphological survey In situ geological and geomorphological surveys and aerial photo-analysis allowed the description of the main geomorphological features and the evaluation of the state of activity of the three different landslide areas (source, channel and accumulation). Along the main body of the landslide there are several secondary scarps, morphological depressions, and minor surface landsliding; in addition, a wide countersloping landslide terrace and creeping evidence can be observed. The latter are fed by surface water runoff coming from precipitations and by the discharge of the water source upstream which drain towards the south-east and probably in the past have been used for religious purposes of the sanctuary. The main source area is referable to a multiple and retrogressive rototranslational slide. It is mostly emptied and has a concave shape. The main scarp (fig. 6), at an elevation of about 850 m a.s.l., is affected by rockfalls and small rockslides. The source area is almost entirely covered by debris deposits of disjointed limestone and marl blocks immersed in a fine-grained matrix. Within this landslide there are morphological depressions and countorslope terraces, one of these holds the Lucan sanctuary (fig. 5): especially the latter terrace shows evident signs of recent rimobilitation as confirmed by the presence of a clear cut plan highlighted by recent archaeological excavations (fig. 8).

Fig. 6. Geomorphological map of the Lucanian Sanctuary.


Since the area of the sanctuary Lucanian is frequented by humans since the eighth century B.C., as documented by the discovery of some burials, it is evident that the landslide terrace on which it was realized, was already present at the time of realization of the settlement so the activation of the landslide is the oldest of the eighth century B.C. configures the phenomenon - along with a low degree of conservation of landslide morphologies that is the scarps, flanks and accumulation areas from the drainage network - as old and inactive. The flow channel, which is probably placed on a preexisting drainage line, extends between 770 and 675 m a.s.l. and has an average slope of 6°. It is about 860 m long and the width varies from 150 m to 350 m. It is delimited by two evident flanks. The accumulation zone shows a typical fan shape with an average slope of 5°. It is about 700 m long and 750 m wide. The landslide toe is located in the bed of the Cammarara stream, tributary of the river.

Fig. 7. Photo detail of the rotation against Mount of approximately 13° of the same Sanctuary [6].

Fig. 8. Site plan of the sanctuary area with planimetric (dotted line) of the detachment surface deforming the lower left corner of the bottom structure. In the photo the sliding surface of the landslide.


6.2 Geoelectrical survey The Electrical Resistivity Tomography (ERT) is an active, non-invasive and effective geophysical technique that provides 2D/3D images of the subsurface resistivity pattern. ERT is widely applied in landslide areas in order to collect indirect information about the geometrical features (lateral extention, sliding surface, thickness, etc.)of the mass movements ([17], [18] and [19]). The instrumental units necessary to carry out electrical resistivity measurements are a voltage generator, through which a train of square waves of current is injected in the subsoil, by means of the current electrodes A and B, and a receiving system constituted by a digital millivoltmeter connected to a computer, which stores the values of voltage across the electrodes M and N. Resistivity data may be acquired through different electrode configurations (Wenner, Schlumberger, Dipole-Dipole, Pole-Pole, etc.) that are chosen considering: the array sensitivity to vertical and/or horizontal resistivity variations, signal/noise ratio, depth of investigation, horizontal data coverage, logistic problems. The final product of the data acquisition is the realization of a pseudosection of resistivity, which represents a cross-section of the subsoil showing apparent resistivity values distribution as function of pseudo-depths. Using ad hoc modelling and inverting software, apparent resistivities and pseudo-depths are subsequently inverted in true resistivities and depths, producing the ERT. The high resolution obtained by this technique allows to discriminate effectively resistivity contrasts existing in the subsoil, providing, thus, more reliable information on the physical conditions of the rocks, the presence of subsurface discontinuities, the lithologicalstratigraphic and/or structural setting (limits, faults, sliding surfaces, etc.), the presence of underground aquifers, etc. To characterize the large landslide of the "Torre di Satriano", three ERT were carried out (figs. 6 and 9); data were acquired through a multi-electrode system using a Syscal R2 (Iris Instruments) device and the apparent resistivity data were inverted by the RES2DINV software [20]. All the ERT were carried out using 48 electrodes with an electrode spacing of 10 m, having a total length of 470 m and reaching a maximum investigation depth of about 70 m. The ERT1 and ERT2 were performed across the main scarp of the landslide body, with longitudinal and transversal direction to the body, respectively. ERT 3 was carried out in WNW-ESE direction, near the SP12 road affected by the mass movement (figs. 6 and 9). Data inversion was performed obtaining 2D models with a RMS error variable between 2.5 (ERT 2) and 2.9 (ERT 3) after 3 iterations. The range of the electric resistivity values is between 8 and more than 81.2 Ω m. For the sake of brevity, only ERT 1, carried out with direction parallel to the main axis of the "Lucanian Sanctuary" landslide, is reported and analyzed (fig. 6). This tomography highlights the presence of both vertical and horizontal resistivity changes due to the different lithologies outcropping in the study area.


Fig. 9. Electrical resistivity image carried out longitudinally to the landslide body. Dashed white line represents the hypothetical sliding surface, whereas dashed red lines possible tectonic contacts (faults). MF: Monte Facito formation; FG: Galestri Formation; SS: Scisti Silicei formation.

In particular, the first 20 m of the ERT are characterized by relatively high resistivity values (15-20 Ω m) that could be associated with slide material (dashed white line). Between 0 and about 80 m from the origin of the profile it is possible to observe a sector relatively more resistive that can be associated with the Monte Facito formation (MF). In the central and SW sector, there is a low resistivity zone, about 40 m thick that can be interpreted as clayey of the Galestri Formation (FG) or a waterrich material zone. The vertical contrasts between the high-resistivity zone and the low-resistivity material could be related to the presence of tectonic contacts (dashed red lines). In the deeper part of the ERT, there is a relatively more resistive layer that could be associated with a lithological change, probably due to the presence of the Scisti Silicei formation (SS).

7.

Conclusions

A multidisciplinary geological, geomorphological and geophysical study of the Lucanian Sanctuary area has been presented. The Sanctuary is located on the foot of the southern ridge of “Torre di Satriano”, representing a sacred place from the fourth century B.C. up to the first century A.D. when it was completely abandoned The Sanctuary has been regularly damaged by natural disasters (i.e. landslides, earthquakes), The evolution of the landscape, in the study area, appears to be strongly conditioned by landslide activity. This generates small landslide counterslope terraces among which also the one where the sacred place was built. The presence in the north-eastern side of the site of a concave recess oriented in the direction of the Sanctuary, that drains water from the upstream, could have fed a small marshy area at the terrace of the landslide that generated a natural ideal pre- sanctuary for the realization of the sacred structure. Changes in the flow of the spring and/or small landslide reactivation could be also some of the reasons which have led the local population to achieve the surface drainage with the construction of canals recognized in the archaeological excavation The extreme vulnerability of the area and the lack of


a continuous water supply in time are, in our opinion, the causes which have led the local population to abandon the place of worship in the first century A.D.. Since the last renovation of the Sanctuary took place around the middle of the first century B.C. seems realistic to assume that among the natural disasters, landslide activity has been particularly intense because it would have caused the counterslope tilt of the sanctuary structure in the top shelf, just when the abandonment of the area occurred. The advent of new religious cults associated with the Roman culture and the emergence of new rural realities represented socio-cultural issues that may have favored the final disappearance of the Lucanian Sanctuary.

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