The contribution of regional uplift and coseismic slip to ...prev.enea.it/ponte stretto - Antonioli...

The contribution of regional uplift and coseismic slip to the vertical

crustal motion in the Messina Straits, southern Italy: Evidence from

raised Late Holocene shorelines

Luigi Ferranti,1 Carmelo Monaco,2 Fabrizio Antonioli,3 Laura Maschio,1 Steve Kershaw,4

and Vladimiro Verrubbi3

Received 22 April 2006; revised 13 December 2006; accepted 5 January 2007; published 7 June 2007.

[1] Detailed mapping and dating of raised Late Holocene shorelines in southernCalabria, central Mediterranean region, reveals that the superposed shoreline record ofuplift has both steady and abrupt components. Analysis reveals quantitative constraintsmay be applied to displacement partitioning between regional and fault-relatedsources in a context dominated by forearc uplift and extension above a retreating slab.Rapid displacements of arguable coseismic origin occurred at �1.9 and �3.5 ka andpossibly at �5 ka and show a consistent site value, pattern of along-strike variation, andrecurrence time (�1.6 ka). The source of the rather large (�1.5–2.0 m) slip per eventbased on the raised shoreline is not directly known and tentatively coincides with theScilla extensional fault, which is inferred to run largely offshore. Although largeuncertainties exist on the trace location, length, and seismogenic potential of the fault,our findings suggest that a substantial fraction of Holocene displacement isaccommodated by coseismic footwall uplift. Precise compensation for sea level changesconstrains Late Holocene steady uplift during the interseismic intervals at �1 mm/yr, avalue consistent with long-term (0.1–1 Ma) estimates of regional uplift. Thus, LateHolocene total uplift of a �20-km stretch of coastline at �1.6–2.1 mm/yr is nearlyequally balanced between regional and coseismic components. Appraisal of the presentelevation attained by a suite of 125 ka and younger marine terraces indicate that rapid netuplift occurred in two episodes: (1) �100–80 ka and (2) after �5 ka; given theconstancy in regional uplift rate, the two episodes are attributable to enhanced fault sliprate. Efficient seismic strain release was clustered in intervals of 10–20 ka andintercalated with a �80-Ka-long period of fault quiescence.

Citation: Ferranti, L., C. Monaco, F. Antonioli, L. Maschio, S. Kershaw, and V. Verrubbi (2007), The contribution of regional uplift

and coseismic slip to the vertical crustal motion in the Messina Straits, southern Italy: Evidence from raised Late Holocene shorelines,

J. Geophys. Res., 112, B06401, doi:10.1029/2006JB004473.

1. Introduction

[2] The net vertical displacement of the Earth’s crustresults from the summed contribution of different sources,which can be regarded either as regional or local. Withinplate boundaries and mobile belts, the most obvious localsources are represented by faults, which, opposite to regionalstrain, accommodate instantaneous displacements. Whereasthrust faults account for dominant uplift in contractionalbelts, subsidence is a common product of normal faults,

which, within plate convergence zones, typically occurs inthe overriding plate above retreating slabs [e.g. Elsasser,1971; Funiciello et al., 2003; Schellart et al., 2003; Stegmanet al., 2006]. Within extensional settings, however, sedi-ments or water infill often prevent a direct observation of thedisplacement record. On the other hand, in extensionalprovinces which experience regional uplift, the syntectonicrecord might be exposed and offers a chance to characterizethe sign and magnitude of motion accommodated on localstructures. Even under this favorable circumstance, accuratequantification of the relative contribution of far-field andfault-related sources to the net vertical displacement of theregion is not obvious. The issue is further complicated by theambiguity inherent in the timescale of comparison betweendisplacements on crustal faults, which may suffer frequenttemporal fluctuations [e.g., Wallace, 1984; Slemmons anddePolo, 1986; Grant and Sieh, 1994; Marco et al., 1996;Friedrich et al., 2003], and regional strains, which aretypically sustained over longer time spans.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B06401, doi:10.1029/2006JB004473, 2007ClickHere

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1Dipartimento di Scienze della Terra, Universita di Napoli Federico II,Naples, Italy.

2Dipartimento di Scienze della Terra, Universita di Catania, Catania,Italy.

3Ente per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA),Casaccia, Rome, Italy.

4Department of Geography and Earth Sciences, Brunel University,Uxbridge, Middlesex, UK.

Copyright 2007 by the American Geophysical Union.0148-0227/07/2006JB004473$09.00

B06401 1 of 23

http://dx.doi.org/10.1029/2006JB004473

[3] Within the central Mediterranean area, the Calabrianarc, which includes southern Calabria on peninsular Italyand the northeastern part of Sicily Island (Figure 1a),experienced large surface uplift since �0.8 Ma [Westaway,1993; Miyauchi et al., 1994; Monaco et al., 1996]. Themagnitude of Calabrian uplift is among the largest in theMediterranean setting, and the �300 km wavelength ofthe uplifting province, in addition to its spatial coincidencewith the location of a NW-dipping lithospheric slab(Figure 1a), clearly outlines its regional significance.Although located within a plate convergence zone, muchof the Calabria topography has been acquired duringextension [Ghisetti, 1984; 1992, Monaco et al., 1996],but the contribution of faulting to surface uplift is contro-versial [e.g., Valensise and Pantosti, 1992; Westaway,1993; Catalano et al., 2003].[4] Regional uplift, local slip rates, and macroseismic

intensities are the greatest around the Messina Straits, thenarrow sea arm between Sicily and Calabria (Figure 1b),where destructive pre- and historic earthquakes and devas-tating tsunamis have left their record in the Scilla and Cariddimyth [Virgil Marone, 1994]. In the last decade, displacedHolocene shorelines have been investigated in several

places around the Messina Straits [Firth et al., 1996;Stewart et al., 1997; De Guidi et al., 2003; Antonioli etal., 2004], and the computed average uplift rates appearconsistently higher than longer-term rates [Antonioli et al.,2006]. Although evidence exists for significant coseismicuplift at coastal sites in northeastern Sicily [Stewart et al.,1997; De Guidi et al., 2003], the role and magnitude offault-induced versus regional, steady displacement duringHolocene uplift is, however, still poorly understood.[5] In this paper, we present a detailed study of raised

Holocene shorelines on the eastern side of the MessinaStraits, which offers an unprecedented opportunity to quan-tify the relative contribution of local and regional sources tototal uplift and to characterize the absolute displacement offault blocks. Comparison of the Holocene uplift pattern witha longer (�125 ka) uplift record, drawn from a flight ofmarine terraces, allows characterization of the temporalvariations of uplift rates and provides vital insight into theprocess of fault clustering [Slemmons and dePolo, 1986;Marco et al., 1996; Friedrich et al., 2003]. Resolution of themode and magnitude of partitioning of vertical crustalmotion into local and regional components on the veryshort timescale contributes to the understanding of the

Figure 1. (a) Tectonic setting of southern Italy. Solid black line: Front of the contractional orogen in theApennines and Sicily, solid teeth toward the orogenic belt [after the work of Bigi et al., 1992] and belt ofcontractional earthquakes in northern Sicily (empty teeth [after the work of Oldow and Ferranti, 2006]);dotted black lines: Depth (km) to the Benioff-Wadati zone of the Ionian slab [lines contoured after thework of Giardini and Velona, 1988]; gray patches bounded by thick dashed lines: Parts of the TyrrhenianSea with Moho shallower than 15 and 10 km [after the work of Cassinis et al., 2003]; thin, solid graylines: Uplift and subsidence rates (mm/year) in the Late Pleistocene [adapted from the work of Ferranti etal., 2006]. (b) Current deformation of the Calabrian Arc. Active faults (barbs on down-thrown side) afterthe studies of Stewart et al. [1997],Monaco and Tortorici [2000], and Catalano et al. [2003]; the double-arrowed line shows extension direction derived from fault kinematic analysis [after the work of Monacoand Tortorici, 2000] and contraction direction offshore northern Sicily based on fault-plane solutions.Focal mechanisms of moderate to large earthquakes (M > 4) after Harvard CMT [1976–2006] (http://www.seismology.harvard.edu/CMTsearch.html) and Mednet RCMT [1997–2006] (http://mednet.ingv.it/events/QRCMT/Welcome.html) catalogues [Pondrelli et al., 2002, 2004], Gasparini et al. [1985], andAnderson and Jackson [1987]. Epicenters of 1981–2002 instrumental seismicity from the IstitutoNazionale di Geofisica e Vulcanologia (INGV) database (Castello et al., 2005, CSI, Catalogo dellasismicita italiana 1981–2002, versione 1.0. INGV-CNT, Roma, http://www.ingv.it/CSI/). Solid dots aretide stations at Tropea (T) and Reggio Calabria (RC).

B06401 FERRANTI ET AL.: REGIONAL AND COSEISMIC UPLIFT, ITALY

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seismogenic potential in the area and places constraints onmodels of Calabrian arc uplift. This study also has widersignificance because it provides clues to understanding thedevelopment of topography in extensional portions ofconvergent settings and may impact models of the seismiccycle and fault behavior in fast uplifting regions.

2. Tectonic Setting

[6] The Calabrian arc straddles the area between theApennines and Sicily contractional belts (Figure 1a), andwas emplaced to the southeast during Neogene northwesterlysubduction of the Ionian slab [Malinverno and Ryan,1986; Gueguen et al., 1998; Faccenna et al., 2001;Rosenbaum et al., 2002]. Today, the slab is imaged byseismic tomography and by earthquakes which deepen tothe northwest down to �500 km beneath the southeasternTyrrhenian Sea [Figure 1a; Giardini and Velona, 1988;Amato et al., 1993; Selvaggi and Chiarabba, 1995; Worteland Spakman, 2000]. The �30-km-thick Calabrian crust[Cassinis et al., 2003] is thought to rest directly on anasthenosphere wedge emplaced above the Ionian litho-spheric slab, and delamination of the lower crust issuggested by residual topography and gravity [Gvirtzmanand Nur, 2001].[7] Since �10 Ma [Gueguen et al., 1998; Faccenna et al.,

2001, and references therein], extension within the hinter-land of the Apennines, Calabria, and Sicily stretched thecontinental crust and resulted in the local formation ofoceanic crust beneath the southern Tyrrhenian Sea, wherethe Moho is found at depths as shallow as 10 km just to thenorthwest of the Eolian volcanic arc (Figure 1a). Extensionis typically regarded as a back-arc spreading process abovethe retreating slab [Malinverno and Ryan, 1986; Lonerganand White, 1997; Gueguen et al., 1998; Faccenna et al.,2001]. Although the extensional hinterland experiencednet subsidence during formation of the Tyrrhenian basin,the western margin of the Apennines [D’Agostino andMcKenzie, 1999; Ferranti and Oldow, 2005] and Calabriarecords sustained Late Neogene to Quaternary upliftcoeval to extensional faulting. Thus not all of the normalfaults in the interior of the orogen need to accommodateback-arc subsidence, and the post-0.8 Ma extension inCalabria has been viewed as a result of uplift [Westaway,1993; Wortel and Spakman, 2000] or partly attributed toplate boundary reorganization [Goes et al., 2004].[8] Today, an array of active normal faults is traced along

the axis of the mountain belt in the Apennines and Calabriaand along the Ionian coast of eastern Sicily (Figure 1b).The extension direction, determined by fault slip analysis[Tortorici et al., 1995; Monaco and Tortorici, 2000], focalmechanisms of crustal earthquakes [Frepoli and Amato,2000; Neri et al., 2005; Harvard and Mednet CMT Cata-logues], and global positioning system (GPS) geodeticvelocities [D’Agostino and Selvaggi, 2004], is �NW-SE(Figure 1b). Residual GPS velocities suggest that theMessina Straits are extending in a NW-SE direction at�3 mm/yr (Figure 2). Regional GPS velocity fields alsopoint to a reduction in the rate of Ionian slab retreat andTyrrhenian back-arc extension with respect to the geologicrates [Hollenstein et al., 2003; D’Agostino and Selvaggi,2004; Goes et al., 2004; Oldow and Ferranti, 2006] and

together with seismicity depict an � E-W trending belt ofcontraction offshore northern Sicily (Figures 1a and 1b).[9] The recent uplift of the Calabrian arc is spectacularly

documented by displaced Middle Pleistocene and youngerflights of marine terraces around the Messina Straits[Ghisetti, 1984; Dumas et al., 1982, 1988, 1999; Westaway,1993; Miyauchi et al., 1994]. In particular, well-developedand preserved markers of the last interglacial, equated tothe Marine Isotope Stage (MIS) 5.5, dated at �125 ka,provide the best constraint to evaluate the regional uplift(Figure 1a).[10] Various mechanisms have been invoked to explain

the Calabrian arc uplift. Within one class of models, uplift isviewed as an isostatic response to removal of a high-densitydeep root, either through slab break-off [Westaway, 1993;Wortel and Spakman, 2000] or through decoupling of theupper crust from the underlying slab and convective flow inthe mantle wedge [Gvirtzman and Nur, 2001; D’Agostinoand Selvaggi, 2004]. Alternatively, uplift may have beeninduced by stalling in the roll-back process and trapping ofCalabria between the buoyant continental landmasses ofAdria and northern Africa [e.g., Goes et al., 2004]. Recentwork in extensional settings elsewhere (Corinth Gulf,Western Turkey, etc. [Westaway, 2002; Westaway et al.,2004; 2006]), has highlighted the thermal response tosediment load in promoting crustal uplift through lowercrustal flow directed beneath regions of prevailing erosion.This conjecture might apply to Calabria as well and issupported by the temporal coincidence between the estab-lishment of the �100-ka Milankovitch forcing and the onsetof Calabrian uplift (R. Westaway, work in progress, 2006).[11] Maximum cumulative uplift rates averaged since the

Middle Pleistocene are estimated at 1.7 mm/yr [Westaway,1993; Catalano et al., 2003]. Attendant extension is sus-pected to contribute substantially to the magnitude of uplift[Westaway, 1993; Catalano et al., 2003]. According toWestaway [1993], 1.67 mm/yr of post–Middle Pleistoceneuplift of southern Calabria is partitioned into �1 mm/yrregional processes and the residual to distributed displace-ment on major faults [Scilla fault (SF), Reggio Calabriafault (RCF), and Armo fault (AF), Figure 2] and mostlyresult in footwall uplift. Alternative interpretations hold thatnormal faults in the Messina Straits accommodate long-termsubsidence in the general uplift context [Valensise andPantosti, 1992] or result from differential plate motion[Goes et al., 2004].[12] A coseismic uplift component might be embedded in

displacement of Late Holocene beaches, marine terraces,and tidal notches, which, along the coast around the straits,occurred at rates of between 1.4 and 2.4 mm/yr (Figure 2).Detailed leveling survey of raised Late Holocene notchesand deposits at Taormina, along the Sicily coastline south ofthe Messina Straits (Figure 2), suggests meter-scale coseis-mic uplifts, possibly associated with slip on a potentialoffshore fault [De Guidi et al., 2003].[13] Leveling campaigns in the Messina Straits area

during 1970–1982 established a differential uplift of themountain ridges with respect to the coastline at 1 mm/yrand, based on a scanty tidal gauge record, was interpreted asreflecting absolute surface uplift [Mulargia et al., 1984].The contemporary vertical deformation pattern, however,was attributed by Mulargia et al. [1984] to a combination of


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steady uplift and episodic subsidence during large exten-sional earthquakes.

3. Crustal Seismicity and Active Faults

[14] Crustal seismicity in the central Mediterraneanattains its highest level in the Messina Straits, as attestedby the �2-ka record of devastating earthquakes andtsunamis [Tinti et al., 2004] (CPTI Working Group, Cata-logo Parametrico dei Terremoti Italiani, INGV, Bologna,http://emidius.mi.ingv.it/CPTI/, 2004). Instrumental and his-torical seismicity spatially coincides with the belt of Qua-ternary normal faults, which have northeast strike andtypically northwest dip in southern Calabria, but in easternSicily, they swing to a more northerly strike and dip to theeast (Figures 1b and 2).[15] On the basis of displacement of Middle and Upper

Pleistocene wave-cut platforms and marine terraces, long-term vertical fault slip rates are estimated at�0.1–0.3 mm/yr[Ghisetti, 1992; Westaway, 1993] or up to 0.7 mm/yr[Monaco and Tortorici, 2000]. Many of these faults dis-place uppermost Pleistocene and Holocene sediments, andcoseismic ground rupture has occurred during large histo-rical earthquakes [e.g. Monaco and Tortorici, 2000; Jaqueset al., 2001; Galli and Bosi, 2002]. Holocene and LatePleistocene recurrence time of large earthquakes (1783 and1908 events, maximum moment magnitude (M) � 7,Figure 2) established from trenching [Galli and Bosi,

2002] and geomorphology [Valensise and Pantosti, 1992],is 1350–1800 and 700–1500 years for a 1783-type and a1908-type earthquake, respectively.[16] Little information is available on the offshore faults.

In front of the study area, the NW-dipping Scilla fault isinferred to run north of the seismogenic sources for the1783- and 1908-type earthquakes (Figure 2; [Bousquet et al.,1980]; [Westaway, 1993]; [Monaco and Tortorici, 2000];[Jaques et al., 2001]). Source parameters and even the traceof the Scilla fault are poorly established because of the lackof strong historical earthquakes and of marine geophysicalsurveys. In regional compilations, several investigators havetraced the fault both onland and offshore (Figure 3), butdetailed mapping and structural analysis are lacking. Esti-mates of fault length range from �10 km [Ambrosetti et al.,1987; Tortorici et al., 1995] to �15–20 km [Ghisetti, 1992;Miyauchi et al., 1994] and up to �30 km [Westaway, 1993;Monaco and Tortorici, 2000]. The structure would becapable of generating a maximum moment magnitudesimilar to the M � 6–6.5, 6 February 1783 earthquake[Jaques et al., 2001; CPTI Working Group, 2004]. No otherhistorical earthquake is attributed to the Scilla fault.

4. Holocene Raised Shorelines

4.1. Methods

[17] Beach deposits and wave-cut platforms were previ-ously observed a few meters above the modern shoreline at

Figure 2. Seismotectonic map of the Messina Straits region. The Messina Straits proper is the narrowestsea arm between the two landmasses. Faults are thick solid lines barbed on the down-thrown side, dashedwhen inferred (sources as in Figure 1): CF, Cittanova Fault; SEF, S. Eufemia Fault; SF, Scilla Fault; RCT,Reggio Calabria Fault; AF, Armo Fault; TF, Taormina Fault. Double-arrowed line is extension direction(rate indicated) from residual GPS velocities between two sites (gray dots) in the Sicily and Calabria sideof the Straits, respectively [after the work of D’Agostino and Selvaggi, 2004). White boxes aremacroseismic epicenters of historical earthquakes, width of box proportional to Meq., the equivalentmagnitude [after the work of the CPTI Working Group, 2004]. White dots with flag show site-averagedHolocene uplift rates (sites G, M, SA, and T after the work of Antonioli et al. [2006]; sites S, B,and P after this work). Place names: S, Scilla; P, Palmi; B, Bagnara; G, Ganzirri; M, Milazzo; SA,S. Alessio; T, Taormina.


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this coast [Miyauchi et al., 1994], and the Late Holoceneage of two distinct outcrops near Scilla village was assessedthrough radiometric dating of shells [Antonioli et al., 2004].Detailed inspection revealed two distinct paleoshorelines atboth locations and at few other outcrops spanning the wholecoast between Scilla and Palmi villages (Figure 4). Theupper and lower shorelines are dominantly represented byfossiliferous marine deposits and wave-cut terraces and by aprominent barnacle band, respectively (Figures 5a–5g).[18] The shorelines were mapped by measuring at each

outcrop the maximum elevation of relevant morphologicand sedimentary features such as inner margins of terraces,upper and lower surfaces of beach deposits, algal rims,range of the barnacle band, and material collected forradiometric dating (Tables 1 and 2). The elevation wasmeasured by using a tape referenced to the observed sealevel. A measurement uncertainty of 10 cm arising fromimprecise tape positioning was determined from randomrepetition at each site. In order to avoid the larger effects oftidal range and sea-level range due to air pressure variation,measurements were repeated sequentially at single localitiesand at the same spot.[19] An additional source of measurement error ensues

from a poorly identified marker position, which is variabledepending on marker type and preservation. We chose spotswhere lateral outcrop continuity gave reliable identificationof morphological sea-level markers, therefore with mini-mum uncertainty on elevation of past sea levels. Themeasured marker elevation and uncertainty are listed inthe fourth column of Table 1, where the uncertainty quan-

tifies the cumulative contribution of measurement (±5 cm)and positioning (±5–10 cm) error, the latter assigned on asite-by-site basis.

Figure 3. Proposed models for the location and length of the Scilla fault. Town labels as in Figure 2.V.S.G., Villa San Giovanni.

Figure 4. Map showing the site distribution of LateHolocene shoreline marker elevation along the Scilla-Palmicoast (elevation range given in meters a.s.l.).


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[20] Each time-annotated measurement was further cor-rected for tidal fluctuations and for sea-level changesresulting from air-pressure fluctuations. Tidal correctionswere applied using the nearest hour-tide elevation providedby nearby gauges (http://www.flaterco.com/xtide/). Unfor-tunately, the closest tide gauge to the study area (�6–22 kmto the west depending on outcrop location) is at Villa SanGiovanni within the Messina Straits (Figure 4) and thusexperiences strong tidal currents. Another tide gauge islocated at Tropea north of the study sites (Figure 1b) andis similar in terms of tidal regime to the field localitiesbecause it faces the open sea. However, the Tropea site wasconsidered too far away (�38–54 km) to provide reliable

tidal estimates for the study area on its own; therefore acompromise of both tide gauges was used.[21] Monthly tidal ranges recorded at both sites may

exceed 1 m, with historical ranges of �1.5 m, but com-monly they are within 0.70 m, a value typical of the Medi-terranean Sea. During our observations (May and October2003; November 2004; September 2005, Table 1), dailytidal ranges were between 0.38 and 0.75 m at Villa SanGiovanni and between 0.37 and 0.72 m at Tropea. Sincedaily and monthly mean sea levels were found to vary by nomore than a few centimeters, we adopted the daily averagedmean sea level for correction. Because tidal variationsbetween the two gauges are nonharmonic, the main issue

Figure 5. (a) Site B, showing two terraces and related inner margins attributed to the upper (whiteupside-down triangles and dashed line) and lower (black upside-down triangles and dotted line)paleoshorelines. Angle of sight of picture in Figure 4. (b) Detail of the inner margin of thepaleoshorelines in Figure 5a. Dotted lines mark the vertical extent of the barnacle band. Dashed line inthe middle ground outlines the inner margin of the upper terrace. Backpack is about 60 cm tall. (c) Marinedeposit of the Holocene upper paleoshoreline from site A. Finger points to a gastropod of the Buccinidaefamily. (d) Close-up of the barnacle band (BB) in Figure 5b. AR is an algal rim underlying the barnacleband. Note the dense patches of barnacles, and compare to the present barnacle band in Figure 5f. (e)Detail of the fossil barnacle which is identified as the species Chthamalus depressus in light of itssymmetrical opening. Width of picture is about 3 cm. (f ) Present barnacle band at site B, with a thicknessof ~40 cm, with the sea level slightly below the mean tide level. White dashed line marks the upper limitof the dense band; only isolated individuals live above this line. Black arrows outline a submerged algalrim (or trottoir), whose upper part was emerging when the picture was taken. (g) Inactive pot holes carvedin the upper terrace, site B. (h) Thin section from upper part of the beach deposit at site A. An early,micritic cement rimming the grains and a second, predominant microsparitic cement are visible,suggesting deposition under seawater.


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Table

1.LocationandElevationDatafortheHoloceneMarkersMeasuredat

Individual

Sites,IncludingTideandAirPressure

Correctionsa

Site

UniversalTransverse

Mercator(U

TM)

Coordinates

(33S05,42)

Marker

Measured

Marker

Elevation

Measurement

Tim

e(yy/m

m/dd/hh)

Tide

Correction

Atm

ospheric

Pressure

Correction

Corrected

Marker

Elevation

Sea-Level

Constraint

Data

Uncertainty

Shoreline

Elevation,m

Upper

Shoreline

AMarinaS.Gregorio

WD

6042533898

Fossiliferousbeach

deposit

3.52±0.10

03/10/17/12

0.05±0.02

+0.05

3.62±0.12

Minim

um

+0.20

3.62�0.12

+0.32

Barrenbeach

deposit

3.95±0.10

03/10/17/12

0.05±0.02

+0.05

4.05±0.12

Maxim

um

�0.30

4.05�0.42

+0.12

BPunta

Paci

WD

6140534244

Barrenbeach

deposit

3.24±0.10

04/11/26/11

�0.05±0.16

+0.19

3.38±0.26

Maxim

um

�0.30

3.38�0.56

+0.26

Fossiliferousbeach

deposit

2.94±0.10

04/11/26/11

�0.05±0.16

+0.19

3.08±0.26

Minim

um

+0.20

3.08�0.26

+0.46

Algal

rim

2.47±0.10

03/10/17/10

0.06±0.12

+0.05

2.58±0.21

Minim

um

+0.10

2.58�0.21

+0.31

Platform

inner

margin

2.45±0.15

03/10/17/10

�0.09±0.17

+0.05

2.41±0.32

Minim

um

+0.50

2.41�0.32

+0.82

CS.Sebastiano

WD

7200140858

Barrenbeach

deposit

3.00±0.15

05/09/12/14

0.03±0.01

+0.02

3.05±0.16

Maxim

um

�0.30

3.05�0.46

+0.16

DPietraGalera

WD

7260544026

Barrenbeach

deposit

3.80±0.15

05/09/12/16

0.05±0.13

+0.03

3.88±0.28

Maxim

um

�0.30

3.88�0.58

+0.28

Fossiliferousbeach

deposit

3.20±0.10

05/09/12/16

0.05±0.13

+0.03

3.28±0.23

Minim

um

+0.20

3.28�0.23

+0.43

Platform

inner

margin

2.22±0.15

05/09/12/16

0.05±0.13

+0.03

2.30±0.28

Minim

um

+0.50

2.30�0.28

+0.78

EMarinadiPalmi

WD

7306845480

Fossiliferousbeach

deposit

2.21±0.10

05/09/13/12

0.02±0.14

+0.06

2.29±0.24

Minim

um

+0.20

2.29�0.24

+0.44

Platform

inner

margin

2.10±0.15

05/09/13/12

0.02±0.14

+0.06

2.18±0.29

Minim

um

+0.50

2.18�0.29

+0.79

Lower

shoreline

AMarinaS.Gregorio

WD

6042533898

Barnacle

band

1.70±0.10

03/10/17/12

0.05±0.02

+0.05

1.80±0.12

Minim

um

(shelt)

+0.20

1.80�0.12

+0.32

BPunta

Paci

WD

6140534244

Barnacle

band,platform

0.75±0.10

04/11/26/13

�0.09±0.17

+0.18

0.84±0.27

Minim

um

(shelt)

+0.20

0.84�0.27

+0.47

Algal

rim,lithophagaborings

1.29±0.10

04/11/26/13

�0.09±0.17

+0.18

1.38±0.30

Minim

um

+0.10

1.38�0.30

+0.40

Platform

inner

margin

0.74±0.15

04/11/26/13

�0.09±0.17

+0.18

0.83±0.32

Minim

um

+0.50

0.83�0.32

+0.82

Barnacle

band,channel

1.60±0.15

04/11/26/11

�0.05±0.16

+0.19

1.74±0.31

Maxim

um

(exp)

�0.20

1.74�0.51

+0.31

CS.Sebastiano

WD

7200140858

Barnacle

band

1.17±0.15

05/09/12/14

0.03±0.01

+0.02

1.22±0.16

Minim

um

(shelt)

+0.20

1.22�0.16

+0.36

DPietraGalera

WD

7306845480

Barnacle

band,platform

0.80±0.10

05/09/12/16

0.05±0.13

+0.03

0.88±0.23

Minim

um

(shelt)

+0.20

0.88�0.23

+0.43

Barnacle

band,channel

1.40±0.15

05/09/12/16

0.05±0.13

+0.03

1.48±0.28

Maxim

um

(exp)

�0.20

1.48�0.48

+0.28

Notch

1.50±0.10

05/09/12/16

0.05±0.13

+0.03

1.58±0.23

average

±0.05

1.58�0.28

+0.28

Platform

inner

margin

1.40±0.10

05/09/12/16

0.05±0.13

+0.03

1.48±0.23

Minim

um

+0.50

1.48�0.23

+0.73

aIndividual

markerssupply

maxim

um

(Max)orminim

um

(Min)constraintonshorelineelevationestimation.Theelevationconstraintprovided

bybarnaclesdiffers

accordingto

theirlocationin

exposed(exp)or

sheltered(shelt)settings(Figure

6).


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B06401

is represented by the proper tidal correction that should beadopted for the study sites. A conservative approach wasadopted by averaging the tide correction recorded at bothgauges, with the result of decreasing the correction andincreasing the uncertainty (Table 1). The resulting correc-tions to the observed elevations varied between �9 and+6 cm, with uncertainty ranging from 2 to 17 cm (Table 1).[22] The atmospheric pressure effect on sea level was

stipulated to allow for the difference in pressure betweenthe time of observation and the mean annual pressure forthe site. These corrections are based on the invertedbarometer assumption using meteorological data from thenearby Reggio Calabria station (Figure 1b) (http://www.wunderground.com/). Observations were done with relativehigh pressure, and thus corrections range between +2 and19 cm (Table 1). In the following, both in the text andfigures, elevations of relevant features associated to theHolocene paleoshorelines will be given with respect to themean sea level including tidal and air-pressure corrections.[23] Figure 6 shows the inferred relation of the mapped

forms and deposits with the coeval sea level both for theLate Holocene and the modern environment, and theassigned uncertainties on sea-level position estimationintrinsic to each marker are listed in the penultimatecolumn of Table 1. Depending on the specific type,

exclusive of the notch, the markers offer a lower or upperconstraint to the sea-level position, and thus the relateduncertainty may be additive or subtractive (Figure 6).[24] The modern shoreline benthic assemblage is char-

acterized by a band of living barnacles of the speciesChthamalus depressus that, in the mesotidal conditions ofthe central Mediterranean Sea, commonly marks the uppermesolittoral biocenosis [Peres and Picard, 1964]. Withinrelatively sheltered exposures like caves inside blocks orpocket bays, the denser part of the band is �40 cm thick(Figure 5f), probably reflecting the mean tidal range.Isolated individuals are found up to a few decimetersabove this line and possibly mark the monthly or longerpeaks. In more exposed settings, such as on open platformsand surge channels, the living barnacle band reaches athickness of �1 m or more and is shifted some decimetersabove the elevation found in sheltered exposures.[25] Thus, the thickness of the barnacle band reflects the

combined effect of the above-mean tidal range and of thelocally variable wave splash zone. However, the densepatch of barnacles has a limited range and is a sensitivemarker of sea level, which falls close to its base (Figure 5f).Uncertainty in sea level positioning for this marker isestimated at ±20 cm, depending upon its location onsheltered or exposed settings (Figure 6). Below the dense

Table 2. Radiocarbon Age, Material, Measured and Corrected Elevation, and Shoreline Attribution of Samples Listed by Location (Site

UTM Coordinate in Table 1)a

SampleNumber

LabNumberb Material Species

MeasuredElevation, m

CorrectedElevationc, m

14C Age,year

Calibrated 14CAges, 1s

Calibrated Error, year Attribution

Site A (Marina di S. Gregorio, Scilla)A4 R 2626 flowstone – 2.85 ± 0.05 2.95 ± 0.07 1936 ± 56 1889 ± 57 ContinentalA6 UTC 12274 barnacle Chthamalus depressus 1.69 ± 0.05 1.79 ± 0.07 3501 ± 35 3386 ± 42 Lower shorelineA5 UTC 12273 barnacle Chthamalus depressus 1.70 ± 0.05 1.80 ± 0.07 3530 ± 39 3409 ± 47 Lower shorelineA7 UTC 12656 mollusk Spondylus sp. 3.55 ± 0.05 3.65 ± 0.07 3610 ± 49 3504 ± 65 Upper shorelineA3 Gx 28331 mollusk Hexaplex sp. 2.90 ± 0.05 3.00 ± 0.07 3930 ± 40 3909 ± 60 Upper shorelineA8 R 3717 mollusk Spondylus sp. 2.20 ± 0.05 2.30 ± 0.07 4497 ± 69 4746 ± 51 Upper shorelineA1d Gx 28045 mollusk Spondylus sp. 2.52 ± 0.05 – 2930 ± 60 2710 ± 67 DisplacedA2d Gx 28332 mollusk Spondylus sp. 2.89 ± 0.05 – 3450 ± 40 3330 ± 50 Displaced

Site B (Punta Paci, Scilla)B2 UTC 12271 barnacle Chthamalus depressus 1.80 ± 0.05 1.91 ± 0.17 2274 ± 34 1881 ± 47 Lower shorelineB5 UTC 12654 barnacle Chthamalus depressus 0.88 ± 0.05 0.99 ± 0.17 2549 ± 38 2230 ± 58 Lower shorelineB1 R 2625 mollusk Spondylus sp. 2.01 ± 0.05 2.12 ± 0.17 2683 ± 45 2376 ± 60 Lower shorelineB3 UTC 12272 barnacle Chthamalus depressus 1.80 ± 0.05 1.92 ± 0.17 2744 ± 34 2427 ± 73 Lower shorelineB9 Poz 13000 barnacle Chthamalus depressus 2.73 ± 0.05 2.87 ± 0.21 3410 ± 40 3290 ± 52 Lower shorelineB4 UTC 12652 barnacle Chthamalus depressus 1.81 ± 0.05 1.92 ± 0.17 3609 ± 42 3500 ± 58 Lower shorelineB11 Poz 13005 mollusk Conus sp. 2.50 ± 0.05 2.59 ± 0.22 4760 ± 40 4933 ± 84 Upper shorelineB12d GX 28042 barnacle Chthamalus depressus 2.00 ± 0.05 – 1340 ± 40 879 ± 50 DisplacedB13d GX 28043 vermetid – 1.50 ± 0.05 – 420 ± 40 160 ± 50 DisplacedB14d GX 28044 vermetid – 2.10 ± 0.05 – 106.63 ± 0.53 pmc Modern DisplacedB/E15d GX 28041 coral Parazoanthus sp. 1.20 ± 0.05 – 106.63 ± 0.53 pmc Modern Displaced

Site D (Pietra Galera, Palmi)D6 Poz 13010 barnacle Chthamalus depressus. 2.12 ± 0.05 2.20 ± 0.18 2785 ± 35 2529 ± 80 Lower shorelineD5b Poz 13001 coral – 3.20 ± 0.05 3.28 ± 0.18 1670 ± 40 1232 ± 43 DisplacedD5c Poz 13002 mollusk Chlamys sp. 2.49 ± 0.05 2.57 ± 0.18 1680 ± 35 1242 ± 73 Displaced

Site E (Marina di Palmi, Palmi)E2 Poz 13011 mollusk Gastrana fragilis 1.67 ± 0.05 1.75 ± 0.19 4430 ± 40 4587 ± 68 Upper shoreline

aAt each site, samples are ordered by increasing age for the upper and lower shorelines. All age determinations are by accelerator mass spectrometry(AMS) 14C. Samples were calibrated after the work of Stuiver et al. [2005], CALIB 5.0. Program and Documentation, http://www.calib.qub.ac.uk/. Areservoir age of 400 years was added following Siani et al. [2000] values for southern Italy. Modern elevations are relative to present sea level.

bGx, Geochron Laboratories, USA; R, Physics Department of La Sapienza Roma University, Rome, Italy; UTC, Utrecht Laboratories, Netherlands; Poz,Poznan Radiocarbon Lab (Poland).

cCorrection for tide and atmospheric pressure fluctuations (see Table 1).dAfter Antonioli et al. [2004].


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part of the barnacle band, a rim or trottoir (organic bench)composed by coralline algae (predominantly Lithophyllumtortuosum) is found in some locales and marks withnegligible uncertainty the lower mesolittoral environmentbetween the mean and the low tide (Figures 5f and 6).[26] Conversely, marine terraces and wave-cut platforms

are less accurate sea-level markers. Depending on the localwave energy, the inner margin of platforms forms�0.5–1 mor more beneath the sea level. Because the study sites aremostly sheltered, so that Holocene outcrops are preserved,we adopt the lower boundary as uncertainty on shorelineposition (Figure 6). On the contrary, beach sediments, whichare included in displaced terraces, may have been partly laiddown above the sea level because of storms and waves.Under these circumstances, �30 cm is applied as depositionuncertainty (Figure 6). On the other hand, where evidenceexists that the marine deposit was not reworked, as in the case

of fossiliferous sand with fossil ages consistently decreasingwith sampling elevation, an average uncertainty of +20 cm isestimated. Tidal notches (Figure 6) give accurate sea-leveluncertainty (±10 cm), but they are rare in the crystalline rocksof Calabria; notches develop only in minor carbonate depos-its within fractures and neptunian dykes.

4.2. Shoreline Features and Elevation Distribution

[27] The two Holocene paleoshorelines at the Scilla-Palmi coast have different morphological and biologicalattributes. The upper shoreline is represented by a fossilif-erous beach deposit and locally by a wave-cut platform(Figures 5a–5c). The deposit is formed by crudely sortedcoarse sand and conglomerate placed in small pockets orfilling caves and includes intact or fragmented bioclasts(mollusks and subordinate bryozoans, corals, algae, andforaminifers; Figure 5c).[28] Thin section observations support a marine origin of

the deposit at site A, which shows a moderately sorted, finesandy bioclastic matrix size, the good preservation ofseveral fossils, and the lack of clear continental cements,such as meniscus or stalactite (Figure 5h). Two types ofcalcite cements occur, the older being a dark rim of possiblemicrobial origin around the grains and the younger being anequidimensional, white microsparite filling intergranularvoids (Figure 5h). Although not wholly restricted to themarine environment, these cements are unlikely in vadoseconditions.[29] Intact shells and a smooth depositional surface are

also found at other sites, and we conclude that this deposit isundisturbed; no significant reworking above the subtidalzone has occurred. Thus, the maximum height of the beachdeposits sets an upper limit for the shoreline elevation(Table 1 and Figure 4). On the other hand, deposition belowa substantial water depth seems unlikely, based on themorphological setting of the deposit, which is commonlypreserved within sheltered caves and gently dipping pocketbeaches.[30] Morphologic features associated with the upper

shoreline provide additional constraints on the maximumallowable depositional depth. In several instances, a wave-cut platform hosts the base of the sedimentary package andhas inner margins ranging between�2.2 and 2.4 m (Figure 4and Table 1), thus providing a lower limit for the paleosealevel. At site B, the platform consists of a �10-m-wide and�80-m-long terrace, which sharply abuts against an ancientcliff (Figure 5a). Here remnants of an algal rim, probablyrepresenting an ancient trottoir, are found at �2.6 m a.s.l.and, together with the platform inner edge at �2.4 m a.s.l.,mark a minimum height for the paleoshoreline (Figure 4 andTable 1). The difference in elevation between erosionalinner edges of the wave-cut platforms and depositionalinner edges of the beach deposits typically ranges between�0.5 and 1 m (Figure 4).[31] The lower shoreline is characterized by a prominent

barnacle band and locally by a wave-cut platform (Figures 3,4a, and 4d). The occurrence of the mesolittoral species C.depressus (Figure 5e), as at the modern shoreline (Figure 5f),offers a tighter constraint on the paleosea level associatedwith the lower shoreline. The width of the fossil barnacleband is typically �1 m (Figure 5e), except at site A,a sheltered environment, where it is �0.5 m (Figure 4).

Figure 6. Morphology and ecology of Holocene andmodern shorelines encountered in southern Calabria,showing the relation with coeval sea level, and theuncertainty in sea level positioning (positive and negativenumbers). The upper diagram shows benthic rims mainlyconnected to tidal excursion and applies to the lower LateHolocene paleoshoreline discussed in the text. Whereas thewavy distribution of the mesolittoral barnacle Chthamalussp. depicts lateral thickness variations related to waveenergy in exposed or sheltered settings, the regular grayband shows the thickness of the dense barnacle patch relatedto the tidal range. M.s.l., mean sea level; h.t.l., high tidelevel; l.t.l., low tide level. The tide range is generalized anddoes not show monthly, annual, nor secular changes. Thelower diagram shows sea-level relations for marine terracesand wave-cut platforms and chiefly applies to the upperLate Holocene paleoshoreline. Dashed line within beachdeposits separates fossil-bearing sediments, with stratigra-phically ordered fossils, from overlying barren sands. Not toscale.


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B06401

Although this thickness may have been reduced by erosion,its consistency with the observed width of the modernbarnacle band and with the average tidal excursion calls forits overall integrity.[32] The band lies at different elevation between sites,

and its base ranges between �0.8 and �1.8 m a.s.l.(Figure 4). This variability reflects both differences inenvironmental energy and lateral variations in tectonicdisplacement. At site B, the elevation markedly changesacross a few tens of meters from �0.8–1.9 m a.s.l. on arelatively sheltered platform to �1.7–2.9 m a.s.l. within asurge channel (Figure 4). At the platform site, an algal rimbored by Lithophaga holes is found at �1.4 m a.s.l. belowthe denser patch of the barnacle band, and only isolatedindividuals are found beneath (Figure 5b). Similarly, at siteD, the band varies in elevation from �0.9–1.8 to 1.5–2.5 ma.s.l. across a short distance (Figure 4).

4.3. Radiometric Ages

[33] Extensive radiometric dating allows tight constraintsto be placed on the age of the two shorelines. Most of theupper shoreline ages comes from site A, where shells weresampled at different elevations within the beach deposit andyielded calibrated ages in the range �3.5–4.7 ka (Table 2and Figure 7). The ages young toward the top of the depositaccording to the stratigraphic polarity (from bottom to top:samples A8, A3, and A7, Table 2 and Figure 7), furthersupporting the lack of substantial reworking.[34] At sites B and E, two mollusks sampled from the

beach deposit have calibrated ages of �4.9 and �4.6 ka(Table 2 and Figure 7), respectively, and reflect the oldestspan of the upper shoreline. Two samples (a mollusk and anindividual coral) from site D, sharing the same elevation,have nearly identical radiometric ages of �1.2 ka (Table 2).

Although their elevation falls within the range of the uppershoreline, their age is younger than in other sites, and weconclude they were simultaneously displaced during a laterevent.[35] Radiometric dating from the barnacle band of the

younger shoreline is distributed between �1.9 and 3.5 ka(Table 2) and is in good agreement with the cessation of theupper shoreline sedimentation. Whereas at site A only theoldest portion of the shoreline has been sampled, the wholeage distribution is found at site B and also includes a shell(Table 2 and Figure 7). An age consistent with the othersites is also found for a barnacle from the lower shoreline atsite D (Table 2).[36] Finally, a flowstone which seals both the upper and

the lower shoreline at site A is dated at �1.9 ka, in perfectagreement with the youngest barnacle age at site B (Table 2).[37] Table 2 also includes four dates from material

sampled in displaced blocks at sites B and B/E (a smallinlet about 100 m east of site B) by Antonioli et al. [2004],which postdate the ages of the raised paleoshorelines.

4.4. Summary

[38] Table 3 summarizes the best estimation of ages andpresent elevation of the two shorelines. At each site,individual markers offer minimum and maximum elevationconstraints for the upper and lower shorelines, and theircombination gives a nominal shoreline elevation and relateduncertainty.[39] At site A, the upper shoreline is conservatively

estimated at �3.8 m a. s. l. midway between the upperlimit of the beach sands and the upper limit of fossil shellsobserved in the deposit (Figure 4). Conversely, the avail-ability of several elevation constraints allows a robustelevation estimate at �2.9 m a.s.l. for the upper shorelineat site B, although the nominal uncertainty is quite large(Table 3). On the coastline between Palmi and Bagnara, theupper shoreline lies at a comparable elevation of �3.0–3.2 m a.s.l. at sites C and D but sharply decreases to �2.3 ma.s.l. at site E.

Figure 7. Map showing the site distribution of calibratedradiocarbon ages (in years B.P.) for the Late Holoceneshorelines along the Scilla-Palmi coast.

Table 3. Nominal Elevation Above the Present Sea Level and

Duration of the Late Holocene Shorelines Obtained by Combining

the Individual Marker Elevation (Table 1) and Dated Samples

(Table 2)

SiteNominal

Elevation, mShoreline Onset,

years B.P.Shoreline End,years B.P.

Nominal Age,years B.P.

Upper shorelineA 3.84�0.33

+0.31 4746 ± 51(mollusk A8)

3504 ± 65(mollusk A7)

4933 ± 84(onset);

3500 ± 58(end)

B 2.86�0.77+0.78 4933 ± 84

(mollusk B11)<3500 ± 58(barnacle B4)

C 3.05�0.46+0.16 – –

D 3.15�1.13+1.01 – <2529 ± 80

(barnacle D6)E 2.29�0.24

+0.44 4587 ± 68 –

Lower shorelineA 1.80�0.12

+0.32 3409 ± 47(barnacle A5)

1889 ± 57(flowstone A4)

3500 ± 58(onset);

1881 ± 47(end)

B 1.20�0.80+0.78 3500 ± 58

(barnacle B4)1881 ± 47

(barnacle B2)C 1.22�0.16

+0.36 – –D 1.36�0.71

+0.85 <2529 ± 80(barnacle D6)

>2529 ± 80(barnacle D6)


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[40] The lower shoreline has its maximum nominal ele-vation of �1.8 m a. s. l. at site A. At the remaining sites, theestimated nominal elevation for the lower shoreline falls inthe narrow range of �1.2–1.4 m a. s. l. (Table 3). Noevidence of the lower shoreline is apparent at site E, but thissite is on an open platform, and thus evidence could havebeen destroyed.[41] The fairly regular age distribution, according to the

stratigraphic position of sampled shells in the beach depositassociated with the upper shoreline at site A, documentsmarine sedimentation between �4.7 and �3.5 ka (Table 3and Figure 7). The additional age from sample B11 at site Byields a nominal duration between 4.93 and 3.50 ka for theupper shoreline.[42] Duration of the lower shoreline is tightly constrained

by ages of barnacles. Inception of the shoreline is docu-mented at about 3.4 and 3.5 ka at sites A and B, respec-tively, and is in good agreement with cessation of marinesedimentation associated with the older shoreline (Table 3).Whereas only old ages have been determined at site A, siteB has a larger age distribution, indicating the shorelinepersisted at nearly the same elevation at least until �1.9 ka,the youngest determined barnacle age (Figure 7 and Table 3).This finding matches the age of the flowstone (Table 2)which covers the barnacle band at site A, suggesting thecessation of marine conditions along the whole coastalstretch.

5. Late Holocene Uplifts

5.1. Stick-Slip Uplift

[43] Since the global sea level never stood higher than thepresent during the last 10 ka [Lambeck et al., 2004], thecurrent elevation of the two shorelines must be attributed touplift. Furthermore, the occurrence of two distinct shorelinesand their abrupt temporal superposition indicate quasi-instantaneous uplift, which is arguably related to coseismicfault displacement. Abrupt and large displacements ofcoseismic origin are consistent with the preservation ofbarnacle bands and coralline algal rims, which normally areeroded if not shifted upwards to escape wave action.Whereascontinuous sedimentation between �4.9 and �3.5 ka shows

there was no significant fault activity, a major displacement(event I) is constrained at 3500 ± 58 years before present(B.P.), resulting in development of the lower shoreline. Upliftat each site is determined from the difference in nominalelevation between the upper and lower shorelines and variesbetween�2.00 at site A and 1.7–1.8m at sites B toD (Table 4and Figure 8). The uncertainty in displacement is locally high(e.g., sites B and D), but this arises from the combination oferrors from individual sources in the nominal elevationcomputation. Nevertheless, the nominal displacement isquite consistent among the various sites.[44] At site E, there is no evidence for the lower shoreline,

and thus separation of the individual events from the totalcoseismic uplift (�2.3 m) recorded here is not possible. Onthe other hand, based on the comparison with nearby sites, itis unlikely that uplift of the older shoreline occurred during asingle earthquake, and thus the present elevation embodiesthe contribution of both events. At this site, uplift duringevent I can be broadly estimated based on the comparisonwith the average displacement (�1.75 m) contrasted to theaverage total uplift (�3.0 m) recorded at the other sites,except for site A, which has a peak of uplift. On this basis, westipulate a nominal �1.3-m displacement at site E duringevent I (Table 4 and Figure 8).[45] Following event I, a relative stillstand is indicated by

the persistence of the lower shoreline from 3.5 to �1.9 ka(Table 3). The coastline was raised by sudden tectonicdisplacement at 1881 ± 47 years B.P. (event II), as con-strained by cessation of the lower shoreline and simulta-neous development of the continental concretions at site A.The amount of vertical displacement is yielded by thenominal elevation of the lower shoreline and is consistentlyof �1.20–1.35 m along the coastline spanning sites B, C,

Table 4. Age and Amount of Co-Seismic Vertical Displacement

During Events I and II as Constrained by the Difference in

Elevation Between the Upper and Lower Shoreline and Their

Chronological Relationsa

Site Vertical Displacement, m

Event I (3500 ± 58 years B.P.)A 2.04�0.33

+0.31

B 1.66�0.77+0.78

C 1.83�0.46+0.16

D 1.79�1.13+1.01

E 1.33

Event II (1881 ± 47 years B.P.)A 1.80�0.12

+0.32

B 1.20�0.69+0.58

C 1.22�0.16+0.36

D 1.36�0.71+0.85

E 0.96aFor site E, individual coseismic displacement (asterisk) is estimated as

discussed in the text.

Figure 8. Map showing the site distribution of the LateHolocene coseismic uplift during events I and II along theScilla-Palmi coast. Uncertainties on the uplift magnitude arelisted in Table 4.


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B06401

and D and, as during event I, abruptly increases at site A upto �1.8 m (Table 4 and Figure 8). At site E, uplift isestimated at �1.0 m as residual from the total upliftdetracted from the inferred displacement during event I.

5.2. Steady Uplift

[46] In order to correctly assess the total amount oftectonic uplift experienced by the coast during the LateHolocene, accurate corrections for sea level variations mustbe applied. Toward this end, we compare the elevation-agedata to the local curve of Holocene sea-level rise [Lambecket al., 2004]. Using model predictions calibrated againstdata from 30 sites in Italy, Lambeck et al. [2004] calculatedvertical motions of the crust caused by glacial and meltwa-ter loading/unloading during the glacial cycle in addition tothe global sea-level rise from the melting of the last icesheets (the eustatic change). Of these loading corrections,the glacial signature is caused by the subsidence of thebroad geoidal bulge which formed around the northern icesheets during the last glaciation, and the meltwater signatureis the subsidence induced by the weight of the meltwater onthe ocean and shallow seafloor including the shelves. Forthe locations considered here, these and the eustatic con-tributions are additive.[47] The total tectonic uplift is portrayed in Figure 9, where

the dated samples are grouped into two point clustersrepresenting the upper and lower paleoshorelines. Inspectionof Figure 9 shows at once that the dated samples have beenuplifted by an amount equivalent to their vertical distancefrom the sea-level curve. Ambiguity surrounds estimation oftrue surface uplift during the pre-3.5-ka history. The regulardecrease in elevation with fossil age of the older shorelinebetween �4.7 and �3.5 ka at site A provides a localsedimentation rate which has a linear best fit of 1.09 mm/yr.[48] During the 4.9–3.5 ka time span, the sea level rose at

�1.8 mm/yr, and different uplift scenarios might haveexisted. One of the possibilities is that sedimentation nearlykept pace with absolute sea-level rise, and no crustal upliftoccurred. This is possible, but given the longer-term uplifttrend, it seems unlikely. An alternative possibility is thatsurface uplift might have occurred at a rate equal to the sea-level rise, requiring local compaction subsidence at1.09 mm/yr to maintain the sea at the same relative position.Given the limited thickness and lateral extent of the deposit,significant compaction seems unlikely. Thus, a certainamount of tectonic uplift at a rate not less than the0.70 mm/yr difference between absolute sea-level rise andlocal sedimentation rate is realistic in order to maintainshoreline conditions.[49] A more precise constraint is available for the youn-

ger shoreline, which stood at almost the same elevationthroughout its active existence from 3.50 to 1.88 ka(Table 3). Thus, �2 m of surface uplift occurred at the1.25 mm/yr rate of absolute sea-level rise (Figure 9). In asimilar way, since there is no evidence that the modernshoreline was far from its present position following eventII, compensation for post-1.88-ka sea-level rise indicates1.45 m of surface uplift at 0.77 mm/yr (Figure 9).[50] We interpret these additional fractions of uplift as

occurring at a steady rate which, since 3.50 ka, was0.99 mm/yr. The possibility that some uplift occurredinstantaneously during the life-span of the upper, lower,

Figure 9. Total displacement of dated material. The upperpanel shows displacement above the modern sea levelattributed to coseismic events I and II (black-coloredsymbol). The gray-colored symbol represents materialdisplaced due to storms or tsunamis (italics labels afterthe work of Antonioli et al. [2004]). Horizontal size ofsymbols equals the maximum age uncertainty. Elevationuncertainty from Table 2. The dashed and dotted areasinclude samples from the lower and upper shoreline,respectively, but do not portray their nominal elevation.The dashed line in the upper shoreline field is thesedimentation rate calculated by linear regression analysis.The lower panel shows the sea-level rise curve (thick solidline) and related s1 uncertainty [gray band, based onrelation (1)] for Scilla constructed with the model ofLambeck et al. [2004]. Steps at 4.93, 3.50, and 1.88 ka areadditional uplift increments for the coeval material derivedfrom sea-level rise correction. Incremental sea-level riserates for various time intervals are listed.


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and modern shorelines can be ruled out, since no otherapparent break in sedimentary or geomorphic features arefound except for the abrupt steps between the threeshorelines.[51] The uncertainty on the steady uplift rate estimation

may be drawn from the predicted uncertainty stipulated forthe sea-level rise (gray band attached to the sea-level curvein Figure 9). Following Lambeck et al. [2004], the spatiallyaveraged predicted uncertainty for Italy is:

spred ¼ �0:13þ 0:24T þ 0:012T2; 1 > T > 14ka;

spred ¼ 0:12T ; T < 1ka:

[52] Since we are interested in the last 3.50 ka, the error isnegligible, so that 3.48 ± 0.16 m of uplift occurred at 0.99 ±0.04 mm/yr.

5.3. Uplift History

[53] Integration of the evidence for sudden uplift provid-ed by shoreline superposition (Tables 3 and 4) with therecord of continuous uplift derived from the curve of localsea-level rise (Figure 9) leads to reconstruction of the LateHolocene displacement history of the Scilla-Palmi coastline(Figure 10).[54] Following a coseismic uplift event (which will be

discussed in a later section) inferred at �5 ka (Figure 10a),�1.0–1.4 m steady uplift occurs from 4.93 to 3.50 ka at arate ranging between the �0.70 mm/yr estimated for sedi-

Figure 10. Cartoon depicting the uplift history of the Scilla-Palmi coast during six distinct episodes ofsteady and abrupt displacement. The first panel refers to an inferred uplift event (see text). US, uppershoreline; LS, lower shoreline. The two values for coseismic uplift during events I and II refer to sitesA (upper value) and B to D (lower value).


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mentation compensation and 0.99 mm/yr inferred from boththe post-3.5-ka record and the regional trend (Figure 10b).During this time span, the paleoshoreline is represented bymarine sediments which overlay a wave-cut platform carvedin the crystalline bedrock.[55] At 3.50 ka, sudden coseismic uplift of �1.7–2.0 m

during event I results in down-cutting of the previousshoreline and formation of a second shoreline mainlymarked by a barnacle band (Figure 10c). From 3.50 to1.88 ka, �2 m of steady uplift is accrued at 1.25 mm/yr(Figure 11d). At 1.88 ka, a second abrupt uplift event of�1.2–1.8 m raises the second shoreline to nearly its presentelevation relative to present sea level (Figure 10e).[56] Finally, since 1.88 ka, 1.45 m steady uplift has

occurred at an average rate of �0.77 mm/yr (Figure 10f).No other coseismic uplifts are recorded at this coastline, butevidence for earthquakes does exist. Younger coseismicevents, namely the 853 A.D. M � 6.3 Messina earthquake[CPTI Working Group, 2004] and the related tsunami,which originated on the Sicily side of the straits (Figure 2),might have displaced samples D5b and D5c (Figure 9). In asimilar way, the A.D. 1783 and 1908 earthquakes and relatedtsunamis might have displaced samples B13 and B14 and

sample B15, respectively (Figure 9; see Antonioli et al.[2004] for a review).

6. Late Pleistocene Raised Shorelines

6.1. Methods

[57] In order to compare vertical displacements at differ-ent timescales, appraisal of the elevation of three terraces ofthe last interglacial (Figure 11), which reflects three high-stands during the MIS 5.5 (124 ka), 5.3 (101 ka), and 5.1(82 ka), seems appropriate. These terraces have beenextensively studied from Scilla village westward towardthe Messina Straits, and although radiometric constraints arefew, their chronological attribution has been firmly estab-lished based on geomorphologic correlations [Dumas et al.,1988, 1999, 2005; Miyauchi et al., 1994; Catalano et al.,2003]. Ages of terraces immediately south of Villa SanGiovanni (Figure 11) are bracketed based on amino-acid,thermoluminescence (TL), and infrared optically stimulatedluminescence (IR-OSL) determinations [Balescu et al.,1997], and correlations are robust [Dumas et al., 1988,2005; Catalano et al., 2003]. Conversely, only a generalized

Figure 11. Map of the Upper Pleistocene terraces with spot indication of the inner-edge elevation.Lower hemisphere equatorial projections show fault kinematics data collected at different stations(asterisks). Local extension direction computed using software Faultkin v.1.1 (Allmendinger R. W. [2001]available at ftp://www.geo.cornell.edu/pub/rwa/FaultKin/). Solid dots are epicenters of 1981–2002crustal (D < 30 km) seismicity (M = 1.5–3) from the Istituto Nazionale di Geofisica e Vulcanologia(INGV) database (Castello et al., 2005, CSI, Catalogo della sismicita italiana 1981–2002, versione 1.0.INGV-CNT, Roma, http://www.ingv.it/CSI/). Bathymetric contours (depth in meters) modified after thework of Selli et al. [1979] and implemented with data from the work of Nautical Chart of Italy [1993].Faults labeled as in Figure 2. MIS, Marine Isotopic Stage; CPBZ, Capo Paci Bridge Zone.


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knowledge of the terrace distribution exists for the coastalregion north of Scilla [Miyauchi et al., 1994].[58] Uncertainty in elevation estimates of the inner edge

or shoreline angle of the marine terraces stems from acombination of younger sedimentary cover and precisionin measurement. The 1:5000 Calabria regional maps used totrace the inner edges have 10-m contours locally supple-mented by 5-m contours and include many spot heights tothe nearest meter. Thus, uncertainty in elevation estimate isprobably within 10 meters. The thickness of sedimentarycover shedding the terrace inner edges is highly variable butcommonly within 10 m. Thus a +5/�15 m maximumuncertainty in elevation estimation appears reliable. Ourmeasurements of the inner edges of the marine terraces are,within the stipulated uncertainty range, in broad agreementwith previous works [Westaway, 1993; Miyauchi et al.,1994; Jaques et al., 2001; Catalano et al., 2003; Dumaset al., 2005].

6.2. Elevation Distribution: Regional and FaultDisplacements

[59] Within the sector between Scilla and Villa SanGiovanni, the three last interglacial terraces form threestrips elongated parallel to the coast. Here the MIS 5.5terrace is abruptly truncated at an elevation of �100–120 magainst a structural scarp characterized by triangular facets(Figure 12a), which corresponds to the onland section of theScilla fault mapped in previous studies (Figure 3). East ofVilla San Giovanni, the inner edge of the 125-ka terrace inthe footwall block is found at an elevation of �170 m a.s.l.(Figure 11), reflecting �50 m of minimum vertical slipsince then.[60] Our mapping of the fault trace slightly differs from

previous work (Figure 3) in that west of Scilla, the faultjumps offshore through an en-echelon overlap link (CapoPaci Bridge Zone, CPBZ Figure 11), leaving small remnantsof the Late Pleistocene terraces in the footwall block. AtScilla, the fault strikes again onshore and drops the �125-katerrace of �20 m from 145–155 m down to 125–135 m(Figure 11).[61] Kinematic analysis of slip lineations collected on

subsidiary fault surfaces exposed in the crystalline bedrock(Figure 12b) yields NW-SE trending tensile axes (Figure 11),

in good agreement with seismicity and regional stretchingmeasurement (Figure 1b).[62] North of Scilla, no major faults are found on-land,

and thus the fault might either terminate or lie offshore(Figure 11). It is possible that the fault follows a steepbathymetric gradient which nearly abuts the coastlinebetween Bagnara Calabra and Palmi villages. Here a dra-matic topographic expression of 1 km from the �600-ma.s.l. high coastal cliff down to the �400-m b.s.l. deep baseof a steep submarine escarpment might be the expression ofthe fault (Figure 11). The inner edge of the MIS 5.5 terraceat this coastline is found at an elevation of 110–140 m a.s.l.,reflecting a chiefly regional uplift at �1 mm/yr.

7. Discussion

7.1. The Earthquake Cycle at the Scilla-Palmi Coast

[63] The total uplift at each site incorporates compo-nents of seismic and interseismic displacements, whichcan be analyzed in terms of deformation-releasing models

Figure 12. (a) View of the onland section of the Scilla fault (angle of sight of picture in Figure 11). Thefault trace and the up to 70-m-high triangular facets marking the fault scarp are outlined with dashedlines. (b) Detail of the cataclastic zone in the crystalline bedrock associated to the Scilla fault, includingNW-dipping fault planes (location in Figure 12).

Table 5. Vertical Tectonic Displacement Data on the Scilla Fault

Since 3.5 ka Listed by Site

Sites Amount, m Rate, mm/year

Coseismic upliftSite A 3.84 ± 0.54 1.10 ± 0.15Site B 2.86 ± 1.41 0.82 ± 0.40Site C 3.05 ± 0.57 0.87 ± 0.16Site D 3.15 ± 1.85 0.90 ± 0.53Site E 2.29 0.65

Regional upliftConstant 3.48 ± 0.16 0.99 ± 0.04

Total upliftSite A 7.32 ± 0.70 2.09 ± 0.19Site B 6.31 ± 1.57 1.81 ± 0.44Site C 6.53 ± 0.73 1.86 ± 0.20Site D 6.63 ± 2.01 1.89 ± 0.57Site E 5.77 1.64

Percentage of displacement Coseismic Regional

Site A 52 48Site B 45 55Site C 47 53Site D 48 52Site E 40 60


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[Shimazaki and Nakata, 1980; Wallace, 1984]. Usingconstraints on age and amount of partitioned verticalmotion (Tables 4 and 5 and Figure 9), a cyclic alternationof steady interseismic and stick coseismic displacementsteps is apparent and defines a time-predictable path(Figures 13a–13d).[64] Seismic displacements occur at 3.50 and 1.88 ka,

and interseismic uplift is modeled at 1.25 and 0.77 mm/yrafter the first and second coseismic events, respectively.The steady uplift, averaged over 3.5 ka, would occur at0.99 mm/yr (Figure 9).[65] The seismic displacement derived from difference in

paleoshorelines elevation incorporates the effects of bothco- and postseismic slip, but our resolution clearly preventsseparation of the two components. Similarly, postseismicdisplacement may be embedded in the interseismic part ofthe cycle together with a broader, aseismic signal, but herealso it is difficult to segregate the two components. For thesake of simplicity, we refer the relative displacementsbetween the upper and lower shoreline to the temporallylimited events I and II, but we are aware that part of thedisplacement might have occurred over a decadal or longer

temporal scale. The large uplifts during the interseismic partof the cycle are of the same magnitude as coseismic slipsand are difficult to sustain as postseismic relaxation andprobably reflect, in large part, the regional signal.[66] At site A, 7.32 ± 0.70 m total uplift during the last

3.5 ka took place at an average rate of 2.10 ± 0.19 mm/yr,which given the limited uncertainty on age, shorelineposition and paleobathymetry of the deposit is reasonablywell-constrained (Figure 13a and Table 5). Large, compa-rable amounts of slip occurred during events I and II (�2.0and �1.8 m, respectively, Table 4). Steady uplift precedingthe first coseismic event likely occurred at a rate�0.70 mm/yr(Figure 13a). The �4.75-ka age of the oldest shell at thebottom of the marine deposit might suggest a previousabrupt displacement slightly before (Figure 10a). This eventcould have raised the platform now lying beneath depositsof the upper shoreline, which thus would have a polycyclicorigin, and stripped off any deposit older than �5 ka(Figure 10a). The range of reliable ages for this previousevent (event pre-I), and the ensuing steady uplift rate can beestimated as follows. Backward extrapolation of the totaland the steady uplift rate curve at �2.10 and �1.00 mm/yr,

Figure 13. Deformation release cycle at individual sites, showing steady uplift punctuated by coseismicevents. (a) Site A; (b) site B; (c) site C; (d) site D. Empty symbols are for age markers; solid symbols arefor markers of displacement. Minimum and maximum displacement markers are placed on the right andleft, respectively, of the seismic cycle curve. See text for discussion.


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respectively, would place a previous coseismic displacementof 1.9 m, a characteristic value for the site, at �5.3 ka.Using a steady uplift rate of 0.70 mm/yr derived from theminimal difference between the eustatic sea-level rise andthe sedimentation rate, it would shift this previous event at4.88 ka, closer to the inception of sedimentation at this site(Table 3 and Figure 13a). Since commencement of theupper shoreline has a better constraint at 4.93 ka suppliedby shell sample B11 (Table 2 and Figure 9), either steadyuplift or event pre-I slip should have been just slightlylarger. The narrow time window of event pre-I (�4.9–5.3 ka) is in good agreement with an independent estima-tion of 5.14 ka based on the averaged 1.64-ka recurrenceinterval between the youngest events I and II. Thus, thisreconstruction suggests that uplift at over �2 mm/yr couldhave been sustained at this site since �5 ka and resulted in�11 m vertical displacement of the coastline.[67] At site B,�6.3 m total uplift took place at 1.81 mm/yr

during the last 3.5 ka and probably �9 m uplift cumulatedsince �5 ka (Figure 13b). Displacement age and amountfor events I and II are tightly constrained by the duration ofthe younger shoreline and by several sea level markers(Tables 1 and 3). Event pre-I must have occurred justbefore the 4.93-ka age of shell B11 and likely close to thatdate, since �1.7 m of vertical slip taken from event Iwould fit the steady (0.99 mm/yr) and total uplift curvesexactly at 4.95 ka (Figure 13b).[68] At sites C and D, inference about pre-3.5 ka dis-

placement history is not possible, but both sites do share asimilar uplift path at a cumulative rate of �1.9 mm/yr(Figures 13c and 13d). In light of the lack of record forthe lower shoreline at site E, reconstruction of the time-predictable earthquake history here is not possible. However,this site also has an old age for inception of the upper

shoreline (Table 2). Simultaneous commencement of theupper shoreline at sites A, B, and E strongly argues forsimilar histories and for the existence of event pre-I over thewhole coastline at the date inferred at sites A and B.[69] In summary, the paleoshoreline record along the

Scilla-Palmi coast indicates that Late Holocene uplift isalmost equally partitioned between the steady and stick-slipcomponents (Table 5). The 0.99-mm/yr steady uplift rateestablished based on the shoreline relations was sustainedsince 3.5 and probably�5 ka and perhaps continues today assuggested by scanty contemporary observations [Mulargiaet al., 1984].[70] Figures 13a–13d shows the position in the deforma-

tion cycle of the 6 February 1783 earthquake, whose sourcewas attributed by Jaques et al. [2001] to the Scilla fault. Nosignificant uplift during this event was observed by con-temporary reporters along the coast. The moderate magni-tude estimated for the event (M = 5.94, CPTI WorkingGroup [2004]; M � 6.5, Jaques et al. [2001]) and thepossible subsidence following the 5 February 1783 mainshock on the Cittanova fault (Figure 2) conspire to minimizeuplift of the Scilla coastline during the seismic occurrence.For a M � 6.5 normal fault earthquake, empirical relations[Wells and Coppersmith, 1994] predict �0.6 m of maximumvertical slip, which even if all expressed by footwall uplift,would go easily undetected in the shoreline uncertaintyband.[71] Earthquake recurrence constrained by radiometric

dating of raised beaches displays a remarkable cyclicity(Figures 13a–13d). Three events occurred during the last3.50 ka on the Scilla coast, including the 6 February 1783A. D. event, and define a recurrence of 1.66 and 1.62 ka,respectively (Table 5), in good agreement with the upperbound long-term estimate for the Messina Straits [Valensise

Figure 13. (continued)


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and Pantosti, 1992] and the Cittanova fault in southernCalabria [Galli and Bosi, 2002]. The occurrence of aprevious event around �5 ka, as suggested by chronostra-tigraphy of the upper shoreline, substantiates this finding.[72] The 1.88-ka age of event II has no counterpart in the

historical catalogue [CPTI Working Group, 2004]. Theclosest match to this event is the AD 374 (�1.6 ka)earthquake, which devastated a large area in southern Italyand is attributed by Galli and Bosi [2002] to slip on theCittanova fault (Figure 2). A correspondence with the AD374 event is ruled out by the flowstone which seals marineconditions at site A (Figures 9 and 13). Provided that thecompleteness of the catalog is weak for the pre–MiddleAge events [CPTI Working Group, 2004], an earthquakeand related tsunami which struck a vast region around Sicilyis reported by Baratta [1901] at A.D. 177 (1.83 ka), thusonly 10 years off the age uncertainty in Table 2. Baratta[1901] quoted a cascade of historical sources [Benincasa,1593; Bonito, 1691; Mongitore, 1743], but there are noexisting or preserved contemporary accounts for the event.

7.2. Source of Local Deformation

[73] Significant coseismic uplifts observed along theScilla coastline requires the existence of a nearby seismo-genic source. Coastline uplift is typically observed duringthrust earthquakes at convergent margins [e.g., Keller andPinter, 2002], and yet Calabria resides above a subductingslab (Figure 1a). The pattern of Quaternary deformation inCalabria, however, has been one of extension, and crustalearthquakes show extensional focal mechanisms (Figure 1b).Thus, the Holocene coseismic uplifts are best attributed tothe activity of a normal fault, and recognition of the Scillafault as the source is tempting. However, the fault is clearlymapped onland for �10 km length (Figure 11), and the lackof marine geophysical surveys prevent establishment andaccurate characterization of an offshore section.[74] Nevertheless, there is evidence of a northern exten-

sion of the fault beyond its �10-km outcrop between Villa

San Giovanni and Scilla. The distribution pattern of raisedHolocene shorelines is the most important (Figure 14). Theamount of coseismic uplift during events I and II differs atindividual sites but appears to follow a self-similar patternalong a �20-km-long stretch. During both events, upliftdecreases at Palmi (site E) and is larger west of Scilla(site A) but keeps almost constant along the interveningcoastal stretch (Figure 14). Inspection of Figure 14 revealsthat combination of the exposed fault strand with the lateralextent of coseismically uplifted deposits may account for a>25-km-long fault.[75] That this behavior is not restricted to the Holocene

only is suggested by similarity between the recent and thelong-term displacement pattern drawn from offset of theLate Pleistocene terraces (Figure 14). It can be argued thatthe elevation of the Late Pleistocene terraces betweenBagnara Calabra and Palmi is close to the predicted mag-nitude of regional uplift (�120 m) and thus requires noadditional contribution from faulting. However, seismicuplift of Holocene shorelines does require footwall upliftin the same location. Here the long-term morphologicalexpression of faulting may be envisaged in the �1000-m-high escarpment stretching from the coastal upland areadown to the continental slope (Figure 11). This escarpmentprobably developed over the whole inferred time duration ofCalabrian uplift, i.e., during the last �1 Ma. The differentrates of Holocene and Late Pleistocene uplifts suggest thatover the �100-ka scale, footwall uplift and hanging-wallsubsidence related to a different source nearly balance. Thissection of the fault resides in the hanging wall of the S.Eufemia and Cittanova faults (Figure 2). Unlike other faultsin southern Calabria, including the Scilla and S. Eufemiafaults, the Cittanova fault is thought to accommodate asignificant component of hanging-wall subsidence [Jaqueset al., 2001, Figure 7] and thus counteracts footwall uplifton the former faults. Both the Cittanova and S. Eufemiafault terminate westward at the longitude of Scilla (Figure 2),and thus larger fault-related uplift is not impeded west of

Figure 14. Projection, on a profile parallel to the coastline, of the inner edge of Late Pleistocene (upperpanel) marine terraces and Late Holocene (lower panel) shorelines preserved in the footwall (graysymbol) and hanging wall (black symbol) of the Scilla fault. A, B, C, and D, sites of Late Holoceneshoreline outcrops.


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there. At a larger scale, the fact that both the Late Pleisto-cene and Holocene uplift rates are larger on the Calabriathan on the Sicily side of the Straits (Figures 1a and 1b)supports the existence of a NW-dipping fault at the Scillalocation.[76] In summary, although we are aware that an accurate

characterization of the Scilla fault awaits more robustgeophysical investigations in the offshore area, the distri-bution and size of Holocene uplifts and the regional tectonicenvironment strongly candidate the fault as the main seis-mogenic source at this coastline. On the basis of anaveraged throw of �1.7 and �1.3 m for events I and II,respectively, derived from the central, more stable sites (B,C, and D), and a 60� fault dip taken from outcrop measure-ments, minimum slips of �2.0 and �1.5 m are derived forthe two events. Scaling relations for normal faults [Wellsand Coppersmith, 1994] predict that �1.5–2.0 m of slip perevent is broadly compatible with a �30-km length, whichwould imply an offshore extension of the fault. Bothmagnitude-length and magnitude-displacement relationspoint to M � 6.8–6.9 earthquakes as appropriate for theScilla fault, which, based on the regular recurrence and site-constancy of coseismic slip (Figure 14), might follow acharacteristic seismic behavior [Schwartz and Coppersmith,1984].[77] The fault was considered capable of generating

characteristic M � 5.9–6.5 earthquakes, corresponding tothe estimated magnitudes for the 6 February 1783 A. D.earthquake [Jaques et al., 2001; CPTI Working Group,2004]. Although in A.D. 1783, the Scilla fault was closeto the expected brittle failure conditions (Figures 13a–13d),it apparently did not rupture with the magnitude estimatedhere. This might suggest that the fault has not yet releasedits accumulated seismic energy since the previous greatevent at 1.88 ka.

7.3. Comparison Between Long- and Short-TermDeformation Rates

[78] The 0.99 mm/yr Holocene interseismic uplift rate ofthe Scilla-Palmi coastline arguably represents the regionalcontribution to total uplift and is in very close agreementwith longer-term estimates in the region [Westaway, 1993;Miyauchi et al., 1994]. The coseismic uplift rate is, how-ever, much larger than the Middle-Late Pleistocene 0.2–0.3 mm/yr slip rate established for the Scilla fault by Ghisetti[1992] and Westaway [1993]. These are averaged estimates,which can be obviously sustained by crustal faults only forsome time intervals whose duration is, however, rarelydefined [Wallace, 1984; Slemmons and dePolo, 1986; Swan,1988; Grant and Sieh, 1994;Marco et al., 1996; Friedrich etal., 2003]. On the basis of the differential elevation of upperPleistocene marine terraces across the Reggio Calabria fault(Figure 2), Catalano et al. [2003] have shown that the faultthrow rate changed from 1.65 mm/yr during 125–100 ka to abackground value of 0.2–0.3 mm/yr since then. A similarpattern is likely to suit the Scilla fault.[79] By integrating the record of differential elevation of

Late Pleistocene and Late Holocene shorelines in thefootwall and hanging wall of the Scilla fault in its westernsector (Figure 14), we contrast in Figure 15 the long- andshort-term displacement history and establish the relativecontribution of faulting and regional deformation to total

uplift. Within the footwall, the elevation distribution ofLate Pleistocene terraces, corrected for the eustatic contri-bution [Waelbroeck et al., 2002], reveals that the average1.3 mm/yr uplift rate (heavy gray solid line in Figure 15)ensues from the combination of rapid and slow netdisplacement intervals (dotted line). Two intervals of rapidnet uplift at �100–80 ka and since 5 ka are separated andpreceded by a �75-ka- and a minimum �25-ka-longperiod of slower uplift, respectively (Figure 15).[80] Since the steady uplift component (dashed line)

appears constant at �1.0 mm/yr during the Holocene asshown in this study and throughout the 125-ka time span, asrevealed by the attained elevation of terraces in the hanging-wall block (at �0.9 mm/yr; Figure 15), it can be subtractedby the net uplift curve to compute the fault-related upliftcomponent through time. This component is 0.5 mm/yrduring �125–100 ka and virtually null between �80 and�5 ka and thus documents tectonic quiescence (Figure 15).Conversely, the periods of high net uplifts have high faultthrows of 1.4 and 1.1 mm/yr during Late Pleistocene andHolocene, respectively.[81] Onset of the present period of rapid slip is not

precisely defined, but holding the steady uplift rate notlower than 1.0 mm/yr during Late Pleistocene places it wellwithin the Holocene and probably coinciding with theoldest event inferred at Scilla (Figure 15). This mightexplain why there is no apparent record of uplifted Holo-cene shoreline at elevation higher than the raised beachesdescribed in this study.[82] Changes in total uplift are thus controlled by varia-

tion in slip rates and suggest clustering of fault and seismicactivity on the Scilla fault during time intervals, which areshorter (10–20 ka) than periods of tectonic quiescence(�80 ka).

7.4. Faulting and Uplift Model

[83] Displacements of �1.5–2.0 m estimated from foot-wall uplifts may be regarded as a conservative estimate ofthe total coseismic slip, since they do not incorporate anypossible component of fault subsidence. Limiting displace-ment values may be imposed by scaling relations [Wells andCoppersmith, 1994], which, for a �30-km-long fault, pre-dict the coseismic slip to be only 20–30% in excess of theobserved magnitudes. Thus for significant subsidence tooccur, the Scilla fault must be substantially longer toaccommodate top-down motion during M > 7 earthquakes.This hypothesis is unlikely, since it would require earth-quake magnitudes much larger than those shown by histor-ical catalogues for the central Mediterranean region (Figure2; CPTI Working Group [2004]).[84] A more plausible explanation calls for minor subsi-

dence during extensional earthquakes on the Scilla fault.Although large subsidence is commonly associated withnormal fault slips [King et al., 1988; Stein et al., 1988], thesubsidence-to-uplift ratio varies substantially as a functionof co- and postseismic slips, thickness, and thermomechan-ical behavior of the brittle layer and lower crustal flowinduced by sediment load redistribution [e.g., Westaway etal., 2004, 2006]. Thus appraisal of the acceptable geologicsubsidence accommodated on the faults cutting the Cala-brian coast of the Straits is pivotal to understanding theshort-term crustal motion.


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[85] On the basis of the differential elevation of the MIS5.5 (�125 ka) terrace relative to the regional uplift datum,Westaway [1993] computed a �0.1-mm/yr subsidence com-ponent along the Reggio Calabria-S. Eufemia fault system(Figure 2), but the same relations were not established forthe Scilla fault. Long-term slip on these faults, however,chiefly produces uplift of the footwall [Ghisetti, 1984;Catalano et al., 2003], and the subsidence-uplift ratio onthe Reggio Calabria-S. Eufemia and Armo-Cittanova faultsystems (Figure 2) during the last 125 ka ranges from 0.4 tovirtually zero [Westaway, 1993].[86] When the geologic relations are applied to the short-

term deformation cycle on the Scilla fault, a maximumcoseismic slip of �2.0–2.5 m, including �70% uplift and�30% subsidence would honor our geomorphologic obser-vations. These faults accommodate substantial footwalluplift rather than subsidence both at the short temporalscale considered here and at the longer (�100 ka) scalerecorded by the Late Pleistocene terraces. During steadyinterseismic uplift, homogeneous absolute elevation is ac-crued over the whole footwall region, including large part ofthe exposed Calabria forearc. The uplift record thus indi-

cates that earthquake deformation coupled to regional upliftoverwhelmed interseismic flexure due to purely elasticdislocation.[87] The fact that clear partitioning of the vertical crustal

motion into regional and local components is still resolvableon very short timescales (such as those of the earthquakecycle) bears significant implications for uplift models of thisregion and elsewhere. The issue centers on the role ofnormal faults and their relations with the background ofuplift. A traditional view holds that normal faulting in thesouthern Calabrian arc creates local subsidence patches in ageneral uplift context [e.g., Mulargia et al., 1984; Ghisetti,1992; Valensise and Pantosti, 1992]. Within this scenario,regional uplift and local faulting need not be strictlyrelated, and normal faults serve to accommodate forearccrustal extension induced by slab roll-back [Elsasser, 1971;Lonergan and White, 1997; Faccenna et al., 2001] or areviewed as part of a diffuse transfer zone linking the Calabriantrench and the recently formed contractional belt offshorenorthern Sicily [Figure 1a; Goes et al., 2004]. Of course, thisbehavior may well apply to some of the faults wheresubsidence has been observed during historical earthquakes

Figure 15. Long-term displacement rate history for the Scilla fault. Sea-level correction after the workof Waelbroeck et al. [2002].


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[Valensise and Pantosti, 1992]. On the other hand, a netcontribution from normal faults to total uplift of Calabriawas previously supposed at the long-term temporal scale[Westaway, 1993; Monaco and Tortorici, 2000; Catalanoet al., 2003], but the coseismic origin of uplifts wasdifficult to prove. Documentation of large coseismic foot-wall uplifts sustained over the current earthquake cycle atScilla, and probably at the �100-ka scale (Figure 15),indicates that local and regional processes are stronglyintertwined.[88] Because of the rapid regional uplift intervening

during and within earthquake cycles, the effects of coseismicslip and postseismic relaxation are unbalanced by sedimentloading and foundering of the brittle elastic layer, and thecoastline keeps uplifting. Probably, the narrow continentalshelf incised by active canyons and the steep bathymetricgradient toward the deep Tyrrhenian basin (Figure 5) com-bine with the background uplift to accommodate efficientsediment removal and minimize flexural subsidence. Thebathymetric pattern offshore of the Tyrrhenian coast ofsouthern Calabria does not provide evidence of thick Qua-ternary depocenters and significant sediment filling ofaccommodation space created by faulting.[89] Footwall uplift sustained over several earthquake

cycles coupled to a vigorous regional uplift could resultfrom corner flow in the asthenosphere beneath a delami-nated crust (e.g., Gvirtzman and Nur [2001]) or above adetached slab [e.g., Wortel and Spakman, 2000], or, alter-natively, from thermally enhanced readjustment of thebrittle layer in response to sediment redistribution andlimited footwall erosion [e.g., Westaway, 2002; Westawayet al., 2004, 2006; R. Westaway, work in progress, 2006].[90] In these scenarios, normal faults do not act against

the regional uplift but rather combine with it in buildingtopography. Although flanked to the west by a deeplysubsiding region beneath the Tyrrhenian Sea (Figure 1a),typical back-arc models [Malinverno and Ryan, 1986;Lonergan and White, 1997; Gueguen et al., 1998; Faccennaet al., 2001; Schellart et al., 2003; Funiciello et al., 2003;Stegman et al., 2006], where extension stems from slabrollback, appear inadequate for the present southern Cala-bria context. Geodetic and seismologic data point to weakor no current subduction underneath Calabria and rifting inthe Tyrrhenian Sea [D’Agostino and Selvaggi, 2004; Oldowand Ferranti, 2006], and yet Late Holocene uplift andnormal faulting occur in Calabria. Possibly, extensionaluplift sustained over the �1-Ma scale, perhaps supportedby surface-induced mass redistribution, may characterize awide portion of the central Mediterranean forearcs [e.g.,D’Agostino and McKenzie, 1999; Ferranti and Oldow,2005] before back-arc rifting prevails.

8. Conclusions

[91] Late Holocene �1.8–2.1 mm/yr coastal uplift on theeastern coast of the Messina Straits is equally partitionedbetween steady and stick-slip coseismic contributions.Steady uplift occurred during the interseismic intervals at�1 mm/yr, a value consistent with estimates of regionaluplift since the Middle Pleistocene [Westaway, 1993].Episodes of sudden motion reflect seismic rupture, whichis tentatively attributed to the Scilla normal fault. This fault

is exposed onland for 10 km but is not yet adequatelyinvestigated offshore.[92] Our current understanding of the displacement his-

tory and seismotectonics of the region can be summarizedas follows:[93] (1) At least two large earthquakes prior to the

6 February 1783 earthquake have occurred at this site at1.88 and 3.50 ka, and a previous one is plausibly inferred at�5 ka. The �1.5–2.0 m seismic displacements recorded byraised beaches indicates a recurrence time of �1.64 ka forM �6.9 earthquakes. Repetition of similar amounts ofvertical slip per event at different sites and at regularrecurrence intervals is consistent with models of character-istic earthquake behavior [Schwartz and Coppersmith,1984] for the putative seismogenic source.[94] (2) The established recurrence time, however, holds

true only for a short-time window, since temporal clusteringof slip characterizes the �100–80-ka and Holocene inter-vals, which are separated by an �80-ka period of tectonicquiescence. The present high slip rate at up to 1.1 mm/yrprobably commenced around �5 ka. Quiescence alsooccurred prior to �100 ka. During quiescence and withinthe interseismic part of the clustered earthquake cycle,the region experiences steady regional uplift.[95] (3) Published estimates of slip rates for the fault,

based on the long-term record [Ghisetti, 1992; Westaway,1993], are up to 30% less than those calculated in this paperduring intervals of high-strain release. Thus, investigation ofraised Holocene shorelines has important ramifications forseismic hazard assessment.[96] (4) Slip on the Scilla fault mainly results in footwall

uplift, and thus the contribution of normal faulting togrowth of subaerial relief may be substantial. Althoughfew constraints exist on the amount of coseismic subsi-dence, the Holocene and Pleistocene terraces record sug-gests minor flexural loads, perhaps enhanced by climaticallyforced mass redistribution. Regional and fault uplifts appearstrongly intertwined, and thus normal faults in southernCalabria are not the mere expression of back-arc extensionabove a retreating slab but rather contribute to dynamicallysustained uplift.

[97] Acknowledgments. This work was supported by University ofNaples funds to L. Ferranti and University of Catania funds to C. Monaco.We also acknowledge financial support from the Project MIUR-PRIN‘‘Analysis of the tsunami risk in Calabrian Arc and Adriatic Sea’’ (Resp.L. Tortorici). We thank G. Scicchitano for his expert boat piloting andlogistical support and L. Simone and F. Toscano for advice in thin-sectioninterpretation. P. Galli suggested the possible correlation of seismic event IIwith sources not included in the CPTI catalogue and is warmly acknowl-edged for this. We are indebted to K. Lambeck who supplied the data forconstructing the local sea-level rise curve. The careful review of R.Westaway, of two anonymous reviewers, and of W. Schellart were instru-mental in clarifying several aspects of the work.

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��F. Antonioli and V. Verrubbi, Ente per le Nuove tecnologie, l’Energia e

l’Ambiente (ENEA), Casaccia, Rome, Italy.L. Ferranti and L. Maschio, University Dipartimento di Scienze della

Terra, University of Naples Largo S. Marcelino 10, Naples, 80138, Italy.([email protected])S. Kershaw, Department of Geography and Earth Sciences, Brunel

University, Uxbridge, Middlesex, UB83PH, UK.C. Monaco, Dipartimento di Scienze della Terra, Universita di Catania,

Catania, Italy.


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