Faulting and Ancient Earthquakes at Sybaris Archaeological Site, Ionian Calabria, Southern Italy by Francesca R. Cinti, Laura Alfonsi, Alessandro D’Alessio, Simone Marino, and Carlo A. Brunori INTRODUCTION The Sybaris archaeological site, founded by the Greeks in 720 B.C., is located within the Sibari Plain near the Crati River mouth (Ionian northern Calabria, southern Italy), in an almost flat and low-lying area (Fig. 1). The plain is bounded by the Pollino chain to the north and by the Sila massif and the northern Crati basin to the south and west. From a seismotectonic point of view, Sybaris is located in the northeastern Calabrian arc, the tectonic evolution of which is controlled by slow north-northwest/south-southeast conver- gence between the Eurasian and African–Adriatic continental plates (e.g., Gvirtzmann and Nur, 1999; Argnani, 2000; Jolivet and Faccenna, 2000). Throughout the Calabrian arc, complex dynamics associated with subduction and rollback have pro- duced back-arc extension, widespread uplift, and relative sub- sidence in the major tectonic basins, including Sibari, where mainly normal seismogenic faults accommodate internal defor- mation. The interior of the Sibari Plain has a high seismogenic potential, and recently, on July 2010, the Mt. Pollino chain area experienced a three-year seismic sequence with magnitudes up to 5.2 (Fig. 1), following 30 years of seismic quiescence. In con- trast, low to moderate seismicity characterizes the eastern half of the plain closer to the Ionian Sea, where the archaeological site of Sybaris is located (Fig. 1). Although not well constrained, there is evidence for active compression in this portion of northern Calabria and the Ionian Sea, where mostly strike-slip faults are mapped (e.g., Frepoli and Amato, 2000; Galadini et al., 2001; Pondrelli et al., 2006; Scognamiglio et al., 2009; Comerci et al., 2013; Fig. 1), but significant uncertainty exists on loca- tions, geometry, and age of these faults. The 2700-year long record of history stored in the archaeological site of Sybaris may have recorded the traces of earthquakes that occurred in the area by sealing their effects in the sediments and in the archaeological remains. An archaeo- seismic study of the site constitutes a unique means to deepen our knowledge of the seismotectonic of the area. The recognition and characterization of the coseismic de- formation affecting the structures of the Sybaris archaeological site is the objective of the present study. To identify past seis- mic deformation events at Sybaris, we proceeded with (1) a systematic survey of the deformed structures, (2) an analysis of the tectonic deformation, (3) the formulation of a hypothesis for tectonics and earthquakes inferences, and (4) constraints on the timing of the deformation based on archaeological stra- tigraphy and absolute dating. THE ANCIENT SYBARIS The Sybaris site hosted the development of the ancient Greek town of Sybaris from 720 B.C. until its decline in 510 B.C. The historical records allude to the foundation of Sybaris in a geographic position between the Crati and Sybaris (now known as Coscile) Rivers. The rivers today are joined about 10 km from the coast and show one single river mouth (Fig. 1). The first description of the actual configuration is in 1789 A.D. in a historical map (Carta Generale del Regno di Napoli, Foglio 26, Zecchi et al., 2003). After the demise of the Greek town, two other settlements arose in time, in part overlapping the previous ruins (Greco and Luppino, 1999): the Hellenist center of Thurii (443 B.C.) and the Roman Copia (193 B.C.). The exceptional archaeological stratification has made Sybaris one of the most important Mediterranean archaeological sites of the Archaic and Classical ages. Starting from the third cen- tury A.D., the settlement suffered a progressive decay until its final abandonment in the seventh century A.D. The Roman Copia remains currently are those that are outcropping as the first level in the excavated areas, and it is these remains that are investigated in the course of this work. Rarely, a few remains belonging to the phases preceding the Roman town foundation are exposed at different locations. The actual configuration of the archaeological park encloses distinctive archaeological sec- tors: Parco del Cavallo, Prolungamento Strada, Casa Bianca, and Stombi (Fig. 1, right inset). The traces of the three ancient towns (Sybaris, Thurii, and Copia), buried beneath a considerable thickness (more than 4 m) of fluvio-deltaic plain deposits, were initially unearthed by archaeologists in the early 1930s (Zanotti Bianco, 1960), who identified the circular wall belonging to the Roman thea- trum hemicycle at Parco del Cavallo. Not until the late 1960s was a systematic effort committed to identify the three super- posed towns throughout the site by prospecting, research, and excavations (Rainey and Lerici, 1967). A renewed effort at ex- cavations has occurred since the 1990s to gradually define the doi: 10.1785/02201401071 Seismological Research Letters Volume 86, Number 1 January/February 2015 245
Transcript
Faulting and Ancient Earthquakesat Sybaris Archaeological Site,Ionian Calabria, Southern Italy
by Francesca R. Cinti, Laura Alfonsi, AlessandroD’Alessio, Simone Marino, and Carlo A. Brunori
INTRODUCTION
The Sybaris archaeological site, founded by the Greeks in 720B.C., is located within the Sibari Plain near the Crati Rivermouth (Ionian northern Calabria, southern Italy), in an almostflat and low-lying area (Fig. 1). The plain is bounded by thePollino chain to the north and by the Sila massif and thenorthern Crati basin to the south and west.
From a seismotectonic point of view, Sybaris is located inthe northeastern Calabrian arc, the tectonic evolution of whichis controlled by slow north-northwest/south-southeast conver-gence between the Eurasian and African–Adriatic continentalplates (e.g., Gvirtzmann and Nur, 1999; Argnani, 2000; Jolivetand Faccenna, 2000). Throughout the Calabrian arc, complexdynamics associated with subduction and rollback have pro-duced back-arc extension, widespread uplift, and relative sub-sidence in the major tectonic basins, including Sibari, wheremainly normal seismogenic faults accommodate internal defor-mation. The interior of the Sibari Plain has a high seismogenicpotential, and recently, on July 2010, the Mt. Pollino chain areaexperienced a three-year seismic sequence with magnitudes upto 5.2 (Fig. 1), following 30 years of seismic quiescence. In con-trast, low to moderate seismicity characterizes the eastern halfof the plain closer to the Ionian Sea, where the archaeologicalsite of Sybaris is located (Fig. 1). Although not well constrained,there is evidence for active compression in this portion ofnorthern Calabria and the Ionian Sea, where mostly strike-slipfaults are mapped (e.g., Frepoli and Amato, 2000; Galadini et al.,2001; Pondrelli et al., 2006; Scognamiglio et al., 2009; Comerciet al., 2013; Fig. 1), but significant uncertainty exists on loca-tions, geometry, and age of these faults.
The 2700-year long record of history stored in thearchaeological site of Sybaris may have recorded the traces ofearthquakes that occurred in the area by sealing their effects inthe sediments and in the archaeological remains. An archaeo-seismic study of the site constitutes a unique means to deepenour knowledge of the seismotectonic of the area.
The recognition and characterization of the coseismic de-formation affecting the structures of the Sybaris archaeologicalsite is the objective of the present study. To identify past seis-mic deformation events at Sybaris, we proceeded with (1) asystematic survey of the deformed structures, (2) an analysis ofthe tectonic deformation, (3) the formulation of a hypothesisfor tectonics and earthquakes inferences, and (4) constraintson the timing of the deformation based on archaeological stra-tigraphy and absolute dating.
THE ANCIENT SYBARIS
The Sybaris site hosted the development of the ancient Greektown of Sybaris from 720 B.C. until its decline in 510 B.C.The historical records allude to the foundation of Sybaris ina geographic position between the Crati and Sybaris (nowknown as Coscile) Rivers. The rivers today are joined about10 km from the coast and show one single river mouth (Fig. 1).The first description of the actual configuration is in 1789A.D. in a historical map (Carta Generale del Regno di Napoli,Foglio 26, Zecchi et al., 2003). After the demise of the Greektown, two other settlements arose in time, in part overlappingthe previous ruins (Greco and Luppino, 1999): the Hellenistcenter of Thurii (443 B.C.) and the Roman Copia (193 B.C.).The exceptional archaeological stratification has made Sybarisone of the most important Mediterranean archaeological sitesof the Archaic and Classical ages. Starting from the third cen-tury A.D., the settlement suffered a progressive decay until itsfinal abandonment in the seventh century A.D. The RomanCopia remains currently are those that are outcropping as thefirst level in the excavated areas, and it is these remains that areinvestigated in the course of this work. Rarely, a few remainsbelonging to the phases preceding the Roman town foundationare exposed at different locations. The actual configuration ofthe archaeological park encloses distinctive archaeological sec-tors: Parco del Cavallo, Prolungamento Strada, Casa Bianca,and Stombi (Fig. 1, right inset).
The traces of the three ancient towns (Sybaris, Thurii, andCopia), buried beneath a considerable thickness (more than4 m) of fluvio-deltaic plain deposits, were initially unearthedby archaeologists in the early 1930s (Zanotti Bianco, 1960),who identified the circular wall belonging to the Roman thea-trum hemicycle at Parco del Cavallo. Not until the late 1960swas a systematic effort committed to identify the three super-posed towns throughout the site by prospecting, research, andexcavations (Rainey and Lerici, 1967). A renewed effort at ex-cavations has occurred since the 1990s to gradually define the
doi: 10.1785/02201401071 Seismological Research Letters Volume 86, Number 1 January/February 2015 245
topographic urban layouts of the three settlements. CasaBianca, with harbor facilities, temples, and edifices, is the mostrecently unearthed area (since 1970).
Other than human intervention, the late Holocene geo-logical events played a role in the history and evolution of thethree settlements, because the site is in a geologically active sec-tor. Environmental and paleogeographic reconstructions(Cucci, 2005; Stanley and Bernasconi, 2009; Bernasconi et al.,2010) indicate an eastward migration of the Crati delta marineboundary in the area where the three settlements were succes-sively placed. Horizontal coastal progradation has been occur-ring at a rate of about 1 m=yr since Greek times (2.4 ka; Cucci,2005). The level of Copia lies 2 m below the water table, andnowadays the archaeological area is kept dry by a compositesystem of water pumps. Besides the uplift at the regional scale(mean value <0:6 mm=yr since 11.2 ka; e.g., Bordoni and Va-lensise, 1998; Cucci and Cinti, 1998), the site experiences localsubsidence (between ∼0:5 and ∼2:0 mm=yr over the interval0.8–3.5 ka; Cucci, 2005), which is likely caused by the fluc-
tuation of the shallow water table and by the compaction ofthe fine, highly compressible coastal and alluvial sediments. Ac-cording to Cucci (2005) and Ferranti et al. (2011), the signal ofsubsidence due to sediment compaction at the archaeologicalarea has slowed since the early Holocene, and it has definitivelyceased during historical times. Other than the local subsidence,flooding from the nearby Crati River repeatedly affected thearchaeological area through time. Among the natural factorsinfluencing the evolution of the sites are earthquake eventsin historical time, as documented by archaeological data(Marino, 2012). This study focuses on the collection and analy-sis of data supporting this paleoseismic issue.
THE ARCHAEOSEISMIC DATA
We conducted an archaeoseismological field survey on theRoman Copia occupational phase (i.e., second century B.Cand sixth/seventh centuries A.D.) outcropping in Casa Biancaand Parco del Cavallo. Prolungamento Strada shows a diffuse
and intense restoration of the structures, thus preventing thepreservation of earlier deformed features. On the contrary, re-storations at Casa Bianca and Parco del Cavallo occur in a fewisolated spots, providing a quite continuous record of the de-formed features. Effects of local differential subsidence arepresent at the site, particularly concentrated at the thermal areaof Parco del Cavallo, as pavement waving and random tilting ofstructures. These were differentiated in our survey from thoseof clear seismic origin (i.e., fractures, faults, rotations, warping,and collapses). The fractures and the faults preserve continuityand homogeneous strike on different types of man-made struc-tures (different for material, orientation, and shape) and on theterrain. Moreover, the features are observed in the more stableparts rather than at particular weak points of the man-madestructures, and we record displacements of several centimetersof thick (>1 m) lime walls.
The description and the mapping of the coseismic featuresat the two survey locations are detailed in the following sec-tions (Figs. 2 and 3).
Parco del CavalloIn the map of Figure 2 are reported the recognized coseismicfeatures as identified on the Copia structures of Parco del Cav-allo. Consistently oriented fractures, tilting, warping, and clock-wise horizontal rotation of walls and patched up/dismantledwalls (photos 1–6 in Fig. 3a) are the elements characterizing thesurface seismic deformation at this study site.
The fractures affecting the walls of the residential build-ings’ area (aedes) of the middle Imperial age, northwest andsoutheast of the plateia B (Fig. 2; photos 1 and 2 in Fig. 3a),show a direction ranging between 40° N and 50° N (plot inFig. 2) and have prevalent right lateral displacements between20 and 30 cm. No vertical offset is observed. The fractures arearranged in bands that are similarly oriented, with a length ex-ceeding 30 m and width of 3 m (Fig. 2). Similar bands ofdeformation are inferred in the thermal area and just northof the theater complex (Fig. 2; photos 4–6 in Fig. 3a). Thebrittle deformation recognized at the site occurs in an area∼200 × 80 m wide.
▴ Figure 2. Locations of the coseismic features at Parco del Cavallo. The upper left inset is the plan of the site (based on a plan fromSoprintendenza per i Beni Archeologici della Calabria, Copyright 2007). The background image is available at www.ilgiornaledellarte.com(last accessed October 2014). In the upper right corner, a rose diagram shows the strikes of fractures. (1, open fracture and sense oflateral movement; 2, warping; 3, direction of tilting; 4, sense of rotation; 5, interpolation of closely spaced fractures; 6, zone of consistentcharacteristics of the deformation; 7, vast collapses; 8, TL sampling; 9, position of photos shown in Figure 3a.)
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▴ Figure 3. Selected images representing the types of deformation observed at (a) Parco del Cavallo and (b) Casa Bianca. In (a), Parcodel Cavallo images (1) and (2) show the laterally shifted walls of the aedes; image (3) shows the vast collapse of the theatrum wallsoverlying (yellow dashed line) thick alluvium, and images (4)–(6) show the tilting rotation and warping of walls. In (b), Casa Bianca image(1) shows one of the fractures in the Lungo Muro 1 m-thick wall (the inset shows the offset from above), and images (2) and (3) showfractures affecting the stairs and the portico of edifice M. Images (4) and (5) show sand-filled fractures in edifice N; the inset shows acloser view of the traces and a cut in the stratigraphy. Image (6) is the distortion of a conduit for sewage disposal in edifice M, image(7) shows the rotation of the perimeter wall of the small temple, and image 8 shows the toppled wall with elements still connected in frontof edifice M. The locations of the images are reported in Figures 2 and 4b for Parco del Cavallo and Casa Bianca, respectively.
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Major zones of severe collapses of vaults and buttress wallsare found lying over an alluvial deposit and are still visible atthe forum, thermae, and theatrum (Fig. 2; photo 3 in Fig. 3a).Ceramic shards within the alluvium right below the collapsedstructures have been sampled (TL1–TL4 in Fig. 2; see alsophoto 3 in Fig. 3a) for thermoluminescence (TL) dating (proc-essed by TecnArt S.r.l., Torino). The resulting ages are, fromthe oldest to the youngest, A.D. 43! 100 (TL2), A.D. 333!190 (TL4), A.D. 740! 99 (TL1), and A.D. 1230! 98(TL3). Assuming that all of the alluvium at the sample loca-tions (forum and theatrum) belongs to the same flooding event,the TL data would suggest an age constraint for the collapse ofthe man-made structures, as discussed in Tectonics and Earth-quakes Inferences section.
Casa BiancaThe mapping of the main coseismic effects is shown in Fig-ure 4a,b. Most of the effects in Casa Bianca are fractures cross-ing both artifacts (prevalently of Copia age) and soft terrainaffecting the whole excavated area (photos 1–5 in Fig. 3b).Other deformation of structures, such as distortions, clockwisehorizontal rotations, and southeastward collapses, are observed
(Fig. 4b; photos 6–8 in Fig. 3b). Collapsed walls are overturnedon the floor (photo 8 in Fig. 3b). The fractures on structuresand in the terrain have a prevalent strike of 55° N (plot inFig. 4b), with a general high-angle dip; secondary directionsare also present, likely due to the different material crossed(soft sediment versus man-made structure). When an openingis observed, it reaches a maximum of 5 cm; several data pointsshow horizontal displacements that are mainly right lateral andgenerally less than 30 cm. No vertical offset is observed. Thissense of movement is also reflected by the distortion of a con-duit for sewage disposal in edifice M (photo 6 in Fig. 3b). Someof the fractures surveyed in the soft occupational level withinedifices M and N, a few of them mentioned also in the archaeo-logical documents (Marino, 2012), are clearly distinguishablebecause they are filled by coarse grayish sand (photos 4, 5 inFig. 3b). We interpret the surface fracturing with sand infill aspaleoliquefaction features. Liquefaction occurs when a sandbody at depth under conditions of water saturation passes toa liquid state when stressed by shaking and the opening of over-lying fractures allows the sand to reach the surface (e.g.,Wangand Manga, 2010). Being characterized by these hydrogeo-logical conditions and a very shallow sand body, the Sybaris
▴ Figure 4. Locations of the coseismic features at Casa Bianca. The upper right inset shows the plan of the site (redrawn from Vitti andVoza, 2012); (a) comprises a photomosaic of the site, the position of the deformed features is reported as in the legend, and capital letterscorrespond to the edifices shown in the plan of the site; and (b) provides a map of the zones with homogeneous bands of deformation. Inthe upper right corner of (b) is a rose diagram of the strikes of the fractures. The deformation features use the same symbols as in thelegend but in black. (1, open fracture and sense of lateral movement; 2, collapse direction; 3, sense of rotation; 4, deformed section; 5,fracture location as described in archaeological report (Marino, 2012); 6, zone with homogeneous characteristics of the deformation; 7,sampling for 14C dating; and 8, position of photos shown in Figure 3b.)
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site is prone to liquefaction in a strong ground shaking. Thesandy filled fractures affect the structure of the edifices and theoverlying enriched ceramic shards layer, and they continue up-ward into an alluvial deposit (Marino, 2012; photo 4 inFig. 3b). At the time of the first excavation, the fractures weresealed by the soft material constituting the upper level of thealluvium. This upper level, filling edifice N, was sampled forradiocarbon dating (sample C1; Fig. 4b), and the resultingage is Cal A.D. 685–885 (2 sigma calibrated results; processedby Beta Analytic Radiocarbon Dating, Florida). These dataprovide an age constraint on the paleoliquefaction that is dis-cussed in the Tectonics and Earthquakes Inferences section.
The consistency of the orientation and deformation ofthe fractures as surveyed, along with their continuity cuttingthrough edifices, serves to define a system of subparallel align-ments of brittle deformation. This system occupies an area ofabout 180 × 40 m, with a strike of 55° N.
TECTONICS AND EARTHQUAKES INFERENCES
We surveyed the areas of Parco del Cavallo and Casa Biancaand found that brittle deformation and shaking effects are ex-pressed as homogeneous bands within and across the sites. Thehomogeneity of the data consists of the characteristics of thefractures (strike, alignment, opening, and slip direction), thepresence of clockwise rotations, and the directions of collapsesof singular elements. Merging the characteristics of the obser-vations at the two distinct sites, we infer a 50° N striking (about1 km long zone of coseismic brittle deformation; i.e., a faultzone), along which opening and right-lateral movements witha maximum displacement of 30 cm are observed. The faultzone crossing the site, hereinafter called Sybaris fault zone,is a tectonic rupture. It does not necessarily represent a primarysurface faulting, that is, the projection of the earthquake faultplane to the surface. It could be the rupture occurring along asecondary fault, branching off or subordinate to the primaryseismic fault (Yeats et al., 1997) and acting to locally accom-modate the regional coseismic deformation from the nearbymain fault. The type and homogeneity of the surveyed brittledeformation along the fault zone, which affects structures andsoils, and the local flat topography allow us to exclude the con-clusion that the zone of fractures is associated with surficial soilfailure mechanisms such as soil slumping, landsliding, lateralspreading, or local subsidence. These soil failure mechanismswould imply the action of gravitational forces (i.e., topographicrelief ) and/or the presence of abrupt lateral stratigraphicchanges, circle-shaped arrangement of the cracks, and verticaldisplacements along the cracks. Given the seismotectonic ori-gin of the fracturing, the other elements of damage (rotation,wall tilting, and collapses at the site) were likely caused by thesudden shaking of the ground.
From the solely archaeoseismological data surveyed at thepark area, we cannot discriminate between the primary or sec-ondary nature of the Sybaris fault zone. No paleoseismologicaldata are available in the Sybari fault area, and few papers are
published on the active tectonics of this portion of Calabria(the coastal Ionian side; Ferranti et al., 2014).
The Sybaris archaeological site falls within an area with alocal topography that is almost flat and affected by a high sed-imentation rate in Pleistocene–Holocene time and by activesubsidence. In this kind of environmental condition, any directevidence of faulting on the ground would be easily hidden (dis-couraging paleoseismological trenching studies). In additionto the archaeoseismic evidence, we used the analysis of high-resolution topographic profiles and anomalies of riverbedsto acquire indirect data, such as anomalies in the geomorphol-ogy that point to the presence of the Sybaris fault away fromthe site. Profiles in Figure 5a,b show the topographic setting ofthe Sybaris fault zone area. Profile 1 crosses the Casa Biancasite, located about 2 m below sea level. We may interpret the2–3 m high-relief defined in profiles 2–4 as a structural highbordered by two northeast–southwest-striking pre-existing tec-tonic lineaments, named the Crati and Timparelle faults (Cfand Tf in Fig. 5b; Lanzafame and Tortorici, 1981) and by thepaleorivers of themodernCrati River andCoscile River (Fig. 5a).The Cf and Tf, with similar strike with respect to the Sybarisfault, are as old as the Pliocene–early Pleistocene, are buried be-low the alluvial plain coverage, and are poorly constrained,mapped only through geophysical investigations (Lanzafame andTortorici, 1981; Comerci et al., 2013). The Sybaris fault zone isfound on the slight topographic high where the Crati River pres-ently flows (Fig. 5a,b). The Sybaris fault activity is dismantlingthe topographic relief that served as a drainage divide betweenthe Crati and Coscile Rivers, thus it is controlling the recentlocal morphology and the present Crati River course.
Recent evidence for the presence of a fault zone northeastof the archaeological site is furnished by electrical tomographyperformed within the ongoing Project PON AMICUS01_02818 (Cianflone et al., personal comm., 2014). Thesenew data support the presence of a tectonic discontinuity atdepth that would be congruent with the prolongation of theSybaris fault that has been inferred within the archaeological site.
Based on direct and indirect data, we deduce that the Syb-aris fault zone likely extends outside of the study area (Fig. 5a).The fault is presently activated with an oblique normal-dextralmechanism, compatible with the present-day east–west to east-northeast/west-southwest compressional deformation active inthe Ionian offshore (Fig. 5c). This regime, differing from thealmost pure extension ongoing to the west along the axis ofthe Apennines chain, is suggested by the focal mechanisms ofthe available earthquakes in the area (Fig. 5c) and by geodeticdata (Ferranti et al., 2014). Consistent with this tectonic inter-pretation, other active faults in the surrounding coastal Ionianarea are east–west- to west-northwest/east-southeast orientedwith left lateral motion (Galadini et al., 2001; see also Fig. 1).
To set age constraints on the activation of the fault zone atthe site, we used two key data points surveyed at edifice N inCasa Bianca (photos 4 and 5 in Fig. 3b), both consisting ofsand-filled fractures. The sand-filled fractures affect artifactsdated at the first half of the second century A.D. and continueup to the lower portion of the alluvial deposits (photo 4 in
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▴ Figure 5. (a) Topographic map of the Sibari Plain. The dashed red band locates the inferred Sybaris fault zone as recognized within thearchaeological site (black polygon). Other fault traces close to the archaeological site (red lines for Cf and Tf show the Crati and Tim-parelle faults) are from the ITHACA database (Comerci et al., 2013; available at http://sgi.isprambiente.it/geoportal/catalog/content/project/ithaca.page, last accessed October 2014). Dashed blue lines are the fossil river beds of the Coscile River (to the north) and CratiRiver (to the south) (redrawn from Pagliarulo, 2006). Black lines are the traces of the elevation profiles shown in (b). (b) Elevation profilesinclude the position of the Sybaris site, the Sybaris fault zone, the Cf and Tf faults, and the Crati River bed. (c) Focal mechanisms of recentearthquakes available in the area (red, Scognamiglio et al., 2009; blue, Pondrelli et al., 2006) are shown, with arrows indicating thedirection of the major active horizontal stress (green, compression in the coastal area Ionian side; and purple, extension in the internalsector of the Apennines and Calabrian arc). The open circle indicates the location of Sybaris.
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Fig. 3b). The organic-rich layer topping the fracture wassampled (C1 in Fig. 4b). The resulting 14C age is Cal A.D.685–885. Based on the upper termination of the fractures withrespect to the archaeological age stratigraphy and the radiocar-bon dating, we infer the occurrence of an earthquake (event 1)that caused fracturing and liquefaction and occurred after thesecond half of the second century and before the ninth century,with possibly a maximum limit of the seventh century A.D.The upper part of the time interval for the date of this earth-quake is preferred, considering the sample location with respectto the fracture termination. Another event (event 2) is sug-gested by archaeologists who analyzed the widespread collapsesat Casa Bianca. The age of these collapses is constrained by thefinding of a stela nscription and coin within the destroyedstructure that provides a terminus post quem for event 2 atthe first half of second century A.D. (Marino, 2012), withan upper age limit not yet determined. The time constrainton event 2 allows the possibility that event 2 is synchronousto event 1. However, the archaeological data mark a phase ofreconstruction at the site between an older evidence of destruc-tion (event 2) and a younger one (event 1) and point to theoccurrence of two distinct earthquakes. Neither of the events(events 1 or 2) is present in the current historical seismicitycatalog for the area (Rovida et al., 2011), although they oc-curred before the limit of the period of catalog completeness(last 0.5 ka for M >6) in southern Italy.
Having occurred during the life of the site, events 1 and 2left traces on the development of the Sybaris urban topography.At the time of event 2 (after the first half of the second centuryA.D.), the site was fully occupied, and after this event life con-tinued in the settlement; collapses were not removed, religiousceremonies were conducted directly over the sanctuary rubble(edifice M in Fig. 4), and the site underwent remodeling. Theperipheral areas were deserted, thus reducing the urbanizedterritory, and some portion of the city changed in its use(Marino, 2012). Some other postearthquake data are the nar-rowing of major urban streets and the restoration of civil struc-tures (the theatrum and thermae area). In Sybaris, as in otherancient Greek and Roman settlements in the Apennines af-fected by earthquakes (e.g., Galli and Galadini, 2003; Galadiniet al., 2010), a persistent resilient behavior is observed. Thisattitude took place particularly when the site had peculiar fa-vorable and strategic environmental conditions (water supply,communications, soil fertility, and territory defense). The ef-fects of the earthquakes are generally not removed, but insteadbecome part of the archaeological stratigraphy, as observed atSybaris (Marino, 2012).
The preferred timing for the occurrence of event 1 (prob-ably in the younger part of the interval between the second andseventh–ninth centuries A.D.), based on dating and geologicalinference, would indicate that event 1 may have happened dur-ing the life of the site. Less-constrained independent archaeo-logical reports hypothesize an earthquake at about the first halfof the fourth century A.D. (compatible with the event 1 esti-mated age interval) that caused the extensive ruins of the col-lapsed walls of the theatrum at Parco del Cavallo and that was
responsible for the definitive abandonment of the theater. Thearchaeological studies point to a progressive abandonment ofthe settlement during the fifth–sixth centuries A.D., with asporadic frequentation of the site up to the sixth century A.D.After this date, there are indications only for occasional occu-pation of the site up to the late antique/high medieval period.Tentative evidence to support the archaeological age determi-nation of the extensive collapses at Parco del Cavallo was madethrough theTL dating of four ceramic samples collected withinthe alluvial deposits under the widespread collapses at the thea-trum and at the forum (TL1 to TL4 in Fig. 2). The age of TL3(the youngest among the collected samples) sets the terminuspost quem for the alluvial deposition at A.D. 1230! 98, andconsequently the collapses are younger than this age. However,this constraint is very preliminary and is based on some as-sumptions that are yet to be validated. One assumption is thatthe alluvium containing the samples is coeval at the differentlocations of sampling. The other assumption is that the depositand the embedded samples did not undergo changes over time,with consequent impact on the estimate of the annual dose ofadsorbed radioactivity and thus on the accuracy of the resultingage determination. Additional data are required to resolve thespecific uncertainties on the nature and effective time of theoccurrence of the Parco del Cavallo collapses and thus to serveas an age constraint for event 1.
DISCUSSION AND CONCLUSION
The archaeoseismic analysis of ancient Sybaris described in thispaper shows the following: (1) There is an oblique normal-dextral fault zone (the Sybaris fault zone) composed of subpar-allel breaks, observable for a minimum length of ∼1 km,45° N–55° N striking, with maximum right-lateral motion of30 cm. The fault activity at ancient Sybaris occurs within thecompressional stress regime acting at a regional scale on theIonian Sea side (Fig. 5). (2) A damage scenario produced bya seismic event (event 1) occurred between the second halfof the second and the seventh–ninth centuries A.D. (youngerpart of the interval preferred), and a possible individual olderevent (event 2) occurred after the first half of the second cen-tury A.D. The effects on the structures, including the lateralmotion of solid and thick walls, imply high-intensity shakingat the site and suggest a magnitude for these events equal to orlarger than 5.5.
The Sybaris fault zone may be either interpreted as aprimary earthquake source or, alternatively, may slip as a sec-ondary fault to accommodate coseismic deformation fromfaulting away from the site. We do not have sufficient evidenceto discern whether we are looking at the seismotectonic frac-turing and effects of ground shaking induced by large events(M ≥6) farther away from the site or by moderate (aroundM 5.5–6) on-site events, that is, with an epicenter at or closeto the archaeological site.
Among the farther strong earthquakes with potential fordamaging the study site and with timing comparable with thatof the event 1 Sybaris event, there is the A.D. 951–1004 earth-
252 Seismological Research Letters Volume 86, Number 1 January/February 2015
quake (Mercalli–Cancani–Sieberg intensity IX), reported withlarge uncertainty on epicenter location by the catalog of strongItalian earthquakes (Boschi et al., 1995) in the offshore areaabout 15 km from the Sibari coastal zone (Fig. 1). Moreover,within the time interval of the event 1 occurrence, paleoseis-mological studies indicate the occurrence of a large (M ≥6:5)earthquake between the fifth–sixth and tenth centuries A.D.that originated within the seismogenic area in the vicinity ofthe town of Castrovillari and the Pollino Range (approximateepicentral location marked with dashed white box in Fig. 1;Cinti et al., 1997, 2002, 2013; Michetti et al., 1997), 20–25 km northwest of the Sybaris site. This event, although witha somewhat distant epicenter, would have had the potential forproducing the shaking effects (collapses, rotation, and liquefac-tion) observed at the Sybaris site. The available focal mecha-nisms (Pondrelli et al., 2006; Scognamiglio et al., 2009; Totaroet al., 2013) of the earthquakes (Fig. 5c) indicate that the Sibaricoastal area represents a transition zone between the exten-sional (internal sector) and the compressive regime (externalsector) with an east–west to east-northeast/west-southwestmaximum horizontal stress (Fig. 5a,c). The Sybaris fault is ac-tive in this latter area.
Finally, this study revealed the great potential of thearchaeological Sybaris site to contribute information concern-ing the reconstruction of the earthquake history of this sectorof southern Italy and to provide new knowledge about theactive tectonics of the coastal Ionian sector of the northernCalabria region. The brittle zone mapped at ancient Sybarisrepresents the first direct evidence for surface faulting in Hol-ocene times in this portion of the Ionian territory. We mappedthe effects of earthquakes affecting an ancient site for which noother records of earthquakes have been available up to now.
The activity of the Sybaris fault implies a high seismic vul-nerability of the Sybaris archaeological site, with the potentialfor the seismic shaking damage and fracturing of the remainingarchitecture. Moreover, the presence of clay- and sand-richsediments and of the particular hydrological setting amplifiesthe seismic shaking and increases the vulnerability of the site.The seismic issue is a threat to the preservation of this majorcultural heritage site.
AKNOWLEDGMENTS
This research and our special thoughts are dedicated to SilvanaLuppino, the Director of Museo Nazionale Archeologico dellaSibaritide, who recently passed away. To her goes our admira-tion for her total commitment to the archaeological study andto the managing of the Sybaris archaeological site. She uncon-ditionally sustained us in the developing of this work andshared her deep knowledge and fruitful insights on the historyof the site. We are also grateful to Luigi Cucci and GuidoVentura for their constructive suggestions provided on thema-nuscript. Many thanks also to those who were occasionally in-volved during the survey. We are indebted to the anonymousreviewer for the detailed and insightful comments that substan-tially improved the clarity of the paper. This study has ben-
efited from funding provided by the Italian Presidenza delConsiglio dei Ministri-Dipartimento della Protezione Civile(DPC). This paper does not necessarily represent DPC officialopinion and policies.
REFERENCES
Argnani, A. (2000). The southern Tyrrhenian subduction system: Recent evo-lution and neotectonic implication, Ann. Geofisc. 43, no. 3, 585–607.
Bernasconi, M. P., J. D. Stanley, and C. Caruso (2010). Sybaris-Thuri-Copia deltaic settings in Calabria, Italy: Molluscs, associated bio-genic components, and ecobiostratigraphy applied to archeology,J. Coastal Res. 26, no. 2, 377–390.
Bordoni, P., and G. Valensise (1998). Deformation of the 125 ka MarineTerrace in Italy: Tectonic Implications, in Coastal Tectonics, I. S.Stewart and C. Vitafinzi (Editors), Geol. Soc. London Spec. Publ.,London, Vol. 146, 71–110.
Boschi, E., G. Ferrari, P. Gasperini, E. Guidoboni, G. Smriglio, and G.Valensise (1995). Catalogue of Strong Italian Earthquakes from461 B.C. to 1980, Istituto Nazionale di Geofisica and Storia Geo-fisica Ambiente, Bologna, Italy.
Cinti, F. R., L. Alfonsi, C. A. Brunori, and G. Ventura (2013). Archaeo-seismic field survey, chapter 4, in Parametrization of Active Faults inthe Calabria-Lucania Region, Final Report, Deliverable Number25/c2, Project S1 INGV-DPC 2012–2013.
Cinti, F. R., L. Cucci, D. Pantosti, G. D’Addezio, and M. Meghraoui(1997). A major seismogenic fault in a ‘silent area’: The Castrovillarifault (southern Apennines, Italy), Geophys. J. Int. 130, 595–605.
Cinti, F. R., M. Moro, D. Pantosti, L. Cucci, and G. D’Addezio (2002).New constraints on the seismic history of the Castrovillari fault inthe Pollino gap (Calabria, southern Italy), J. Seismol. 6, 199–217.
Comerci, V., A. M. Blumetti, P. Di Manna, D. Fiorenza, L. Guerrieri, M.Lucarini, L. Serva, and E. Vittori (2013). ITHACA Project andcapable faults in the Po Plain (northern Italy), Ingegneria Sismica,1–2 January–June 2013, 36–45.
Cucci, L. (2005). Geology versus myth: The Holocene evolution of theSybaris plain, Ann. Geophys. 48, 1017–1033.
Cucci, L., and F. R. Cinti (1998). Regional uplift and local tectonic defor-mation recorded by the Quaternary marine terraces on the Ionian coastof northern Calabria (southern Italy), Tectonophysics 292, 67–83.
Ferranti, L., R. Pagliarulo, F. Antonioli, and A. Randisi (2011). Punish-ment of the Sinner: Holocene episodic subsidence and steady tec-tonic motion at ancient Sybaris (Calabria, southern Italy),Quaternary Int. 232, 56–70.
Ferranti, L., M. Palano, F. Cannavò, M. E.Mazzella, J. S. Oldow, E. Gueguen,M. Mattia, and C. Monaco (2014). Rates of geodetic deformationacross active faults in southern Italy, Tectonophysics 621, 101–122.
Frepoli, A., and A. Amato (2000). Fault plane solutions of crustal earth-quakes in southern Italy (1988–1995): Seismotectonic implications,Ann. Geofisc. 43, no. 3, 437–459.
Galadini, F., E. Ceccaroni, and E. Falcucci (2010). Archaeoseismologicalevidence of a disruptive Late Antique earthquake at Alba Fucens(central Italy), Boll. Geof. Teor. Appl. 51, nos. 2/3, 143–161.
Galadini, F., C. Meletti, and E. Vittori (2001). Major active faults in Italy:Available surficial data,Netherlands J. Geosci. 80, nos. 3/4, 273–296.
Galli, G., and F. Galadini (2003). Disruptive earthquakes revealed byfaulted archaeological relics in Samnium (Molise, southern Italy),Geophys. Res. Lett. 30, no. 5, 1266, doi: 10.1029/2002GL016456.
Greco, E., and S. Luppino (1999). Ricerche sulla topografia e sull’urba-nistica di Sybaris-Thuri-Copiae, Annali di archeologia e storia antica6, 115–164.
Gvirtzmann, Z., and A. Nur (1999). Plate detachment, asthenosphereupwelling, and topography across subduction zones, Geology 27,563–566.
Italian Seismological Instrumental and Parametric Data-Base (ISIDe)Working Group (2010). INGV - Italian Seismological Instrumental
Seismological Research Letters Volume 86, Number 1 January/February 2015 253
and parametric database, http://iside.rm.ingv.it (last accessed Octo-ber 2014) (in Italian).
Jolivet, L., and C. Faccenna (2000). Mediterranean extension and theAfrica-Eurasia collision, Tectonics 19, no. 6, 1095–1106.
Lanzafame, G., and L. Tortorici (1981). La tettonica recente della valledel fiume Crati (Calabria), Geografia Fisica e Dinamica Quaternaria4, 11–21.
Marino, S. (2012). Copia/Thurii: Aspetti topografici e urbanistici di unacittà romana della Magna Grecia, Tekmeria, Pandemos-Paestum 14,262 pp.
Michetti, A. M., L. Ferreli, L. Serva, and E. Vittori (1997). Geologicalevidence for strong historical earthquakes in an “aseismic” region:The Pollino case (southern Italy), J. Geodyn. 24, nos. 1/4, 61–86.
Pagliarulo, R. (2006). Coastal changes and the environmental evolutionof the archaeological site of Sybaris (southern Italy), Geografia Fisicae Dinamica Quaternaria 29, 51–59.
Pondrelli, S., S. Salimbeni, G. Ekström, A. Morelli, P. Gasperini, andG. Vannucci (2006). The Italian CMT dataset from 1977 to thepresent, Phys. Earth Planet. In. 159, nos. 3/4, 286–303, doi:10.1016/j.pepi.2006.07.008.
Rainey, F. G. and C. M. Lerici (Editors) (1967). The Search for Sybaris1960–1965, Lerici Editori, Rome, Italy, 313 pp.
Rovida, A., R. Camassi, P. Gasperini, and M. Stucchi (Editors) (2011).CPTI11, The 2011 Version of the Parametric Catalogue of ItalianEarthquakes, Milano, Italy, http://emidius.mi.ingv.it/CPTI (last ac-cessed October 2014) (in Italian), doi: 10.6092/ingv.it-cpti11.
Scognamiglio, L., E. Tinti, and A. Michelini (2009). Real-time determi-nation of seismic moment tensor for the Italian region, Bull. Seis-mol. Soc. of Am. 99, no. 4, 2223–2242, doi: 10.1785/0120080104.
Stanley, J. D., and M. P. Bernasconi (2009). Sybaris-Thuri-Copia trilogy:Three delta coastal sites become land-locked, Mèditerranèe 112,75–86.
Tertulliani, A., and L. Cucci (2014). New insights on the strongesthistorical earthquake in the Pollino region (southern Italy), Seismol.Res. Lett. 85, no. 3, 743–751, doi: 10.1785/0220130217.
Totaro, C., D. Presti, A. Billi, A. Gervasi, B. Orecchio, I. Guerra, and G.Neri (2013). The ongoing seismic sequence at the Pollino Moun-tains, Italy, Seismol. Res. Lett. 84, no. 6, doi: 10.1785/0220120194.
Vitti, P., and O. Voza (2012). Interventi a Casa Bianca nel quinquennio2007–2012, in Il santuario delle divinità orientali e i suoi predecessori(Sibari—Casa Bianca): Scavi 2007, 2009–2012 Annuario SAIA 2011LXXXIX, [Serie III, 11] Tomo II, ISBN: 978-960-9559-01–0.
Wang, C.-Y., and M. Manga (2010). Earthquakes and Water, Springer-Verlag, Berlin, Heidelberg, 223 pp. doi: 10.1007/978-3-642-00810-8.
Yeats, R. S., K. Sieh, and C. R. Allen (1997). The Geology of Earthquakes,Oxford University Press, New York, 568 pp.
Zanotti Bianco, U. (1960). La campagna archeologica del 1932 nellapiana del Crati, Atti e Memorie della Società Magna Grecia n.s. 3,7–20.
Zecchi, R., G. Giorgi, F. Francavilla, and A. Ronchi (2003). Tendenzeevolutive recenti del delta del fiume Crati (Calabria-Italy) sulla basedella cartografia sto-rica e delle immagini telerilevate, Atti 7° Confer-enza Nazionale ASITA, Verona.
Francesca R. CintiLaura Alfonsi
Carlo A. BrunoriIstituto Nazionale di Geofisica e Vulcanologia
