Int J Earth Sci (Geol Rundsch) (2003) 92:912–922DOI 10.1007/s00531-003-0366-3

O R I G I N A L P A P E R

K. R. Reicherter · A. Jabaloy · J. Galindo-Zald�var ·P. Ruano · P. Becker-Heidmann · J. Morales · S. Reiss ·F. Gonz�lez-Lodeiro

Repeated palaeoseismic activity of the Ventas de Zafarraya fault(S Spain) and its relation with the 1884 Andalusian earthquake

Received: 10 December 2002 / Accepted: 2 September 2003 / Published online: 14 November 2003� Springer-Verlag 2003

Abstract One of the most destructive historical earth-quakes (M �6.7) in Spain occurred in 1884 along thenormal Ventas de Zafarraya Fault located in the CentralBetic Cordilleras. Palaeoseismic and radiocarbon data pre-sented in this study are the first to constrain the timing ofthe pre-1884 fault history in the last 10 ka. These datayield a recurrence interval of between 2 and 3 ka for majorearthquakes, under the assumption of uniform return pe-riods along the normal fault. The Holocene slip rate isestimated to be in the order of 0.35€0.05 mm/year, whichis significantly higher than the mean slip rate of 0.17€0.03 mm/year since the Tortonian. Several of the mostimportant deformations and secondary features, such aslandslides and liquefaction, are related to strong groundmotion and document the Holocene activity of the Ventasde Zafarraya Fault.

Introduction

The most destructive earthquake of the Iberian Peninsuladuring the last 150 years occurred on 25 December 1884at 21:08 h (‘Terremoto de Andaluc�a’, Fern�ndez deCastro et al. 1885, in: Mu�oz and Ud�as 1980). More than800 casualties and several destroyed villages were

reported. The epicentre was probably located in thetriangle between Arenas del Rey, Alhama de Granada andVentas de Zafarraya according to the macroseismicinformation (Fig. 1). The maximum intensity was X(MSK scale) from which a magnitude of between 6.1(L�pez Casado et al. 2000) and 7 (Mu�oz and Ud�as1980) has been calculated. European commissions studiedthe geology of the region and the effects generated duringor after the earthquake (Orueta and Duarte 1885;Taramelli and Mercalli 1886; Kilian 1889; Mu�oz andUd�as 1980 and references herein). They described anarea of a complex pattern of surface cracks (Fig. 2),landslides, rock falls, liquefaction, and the change ofspring-water chemistry associated with the seismic event.The international collaboration resulted in the reconstruc-tion of the new village of Arenas del Rey with one of thefirst earthquake-safe city designs.

Although no unambiguous fault-related rupture at thesurface or coseismic movements along the fault planewere recognized, Mu�oz and Ud�as (1980) and Sanz deGaldeano (1985) concluded that the earthquake haspossibly been associated with several faults and tectonicblocks along the northern margin of the Sierra Tejeda(Fig. 3).

Here we characterize, palaeoseismologically, the Ven-tas de Zafarraya Fault (VZF) in order to establish itsrelationship with the 1884 earthquake and with previouscoseismic events along the same normal fault. Ourinvestigations include sedimentology, microstratigraphy,radiocarbon dating, as well as an evaluation of aerial andsatellite photos, and an assessment of the recent andhistorical seismicity. We applied high-resolution ground-penetrating radar (GPR), to describe and characterize thesub-surface expression of the VFZ in the hanging wall.

The Betic Cordilleras in southern Spain are locatedwithin the Eurasian–African Convergence Zone in anapproximately 500-km-wide region with a disperse seis-micity. In the last few years, intense work on thepalaeoseismicity of individual faults in the Betic Cordil-leras started. Several structures along active fault zones inthe Betic Cordilleras are related to coseismic surface

K. R. Reicherter ()) · S. ReissInstitut f�r Geophysik, Universit�t Hamburg,Bundesstraße 55, Hamburg, Germanye-mail: reicherter@dkrz.deFax: +49-40-428385441

A. Jabaloy · J. Galindo-Zald�var · P. Ruano · F. Gonz�lez-LodeiroDepartamento de Geodin�mica,Universidad de Granada,Campus Fuentenueva, Granada, Espa�a

P. Becker-HeidmannInstitut f�r Bodenkunde, Universit�t Hamburg,Allende-Platz 1, Hamburg, Germany

J. MoralesInstituto Andaluz de Geof�sica, Universidad de Granada,Granada, Espa�a

Fig. 2 Topographic map of the scarp of the Ventas de ZafarrayaFault. Topographic lines every 50 m; master topographic linesevery 250 m. Note locality of radar-lines in Fig. 6. Locality 1

cemetery of Ventas de Zafarraya, locality 2 Cort�jo del Barranco,locality 3 Pilas de Algaida

Fig. 1 a Geological setting. General map of the Betic Cordillera(legend see b). b Map of study area. 1 Upper Miocene–Quaternarysedimentary rocks; 2 Subbetic unit (the entire subbetic zone in a); 3Internal subbetic; 4 Prebetic; 5 Oligocene–Lower Miocene sedi-mentary rocks including flysch and olistostroms; 6 Campo deGibraltar Flysch; 7 Predorsalian, Dorsalian and Mal�guide Com-

plexes; 8 Alpuj�rride Complex; 9 Nevado-Fil�bride Complex; 10Iberian Massif with cover rocks; 11 isoseists of the 1884-earthquake; 12 macroseismic intensity of the 1884-earthquakesource; 13 unconformity; 14 fault; 15 normal fault; 16 reverse fault;17 syncline, 18 anticline. Inset shows locality of Fig. 2

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rupturing (see summary in Masana and Santanch 2001).The Alhama de Murcia fault zone was investigated bySilva et al. (1997), Mart�nez-D�az et al. (2001), andMasana et al. (2003). The Carboneras Fault Zone in theprovince of Almer�a has been studied by Bell et al. (1997)and Reicherter and Reiss (2001). A description of activefaults in the Granada depression was provided byReicherter et al. (1999), Alfaro et al. (2001) Reicherter(2001) and, recently, by Galindo-Zald�var et al. (2003).

The stratigraphic relationships along the active VZFpermit the reconstruction of the faulting history, includingthe number and relative size of faulting events, and thedetermination of recurrence intervals (e.g. Wallace 1986;McCalpin 1996).

Geological setting

The South Iberian Domain or External Zone is made up ofalmost 1,000 m of Liassic white limestones and greydolostones, followed by approximately 500 m of marlylimestones and limestones of Middle Jurassic to LateCretaceous age (Garc�a-Hern�ndez et al. 1980). Thekarstified Zafarraya Polje (Figs. 1, 2 and 3) is filled withalluvial and colluvial deposits of Quaternary age; under-lying Tortonian calcarenites have been drilled. The areaof subsidence within the Zafarraya Polje is asymmetric(Ollero and Garc�a 1984). The small basin is bound to thesouth by the normal VZF and forms a half-grabenassociated with an extensional roll-over structure, asindicated by seismic and gravimetric data (unpublisheddata of Galindo-Zald�var).

The Albor�n Domain or Internal Zone, is deformed byextensional detachments during the Mid-Miocene (Fer-n�ndez-Fern�ndez et al. 1992; Mart�nez-Mart�nez andAza��n 2002). Low- to high-grade metamorphosedschists and marbles form the Alpuj�rride Complex,whereas the Malaguide Complex includes Variscanbasement covered by Mesozoic sediments. The Internal

Zone is locally overlain by nappes of the Campo deGibraltar Flysch units (Fig. 1). The Internal–ExternalZone Boundary (IEZB) separates the Internal Zones fromthe External Zones. The IEZB forms a low angledetachment (N50�E strike and 25� dip to NW) in thestudied area with a top-to-the-W sense of movement(Galindo-Zald�var et al. 2000). Towards the west it bendsinto an E–W direction. In the studied area, the VZF cutsthe Internal–External Zone Boundary (IEZB) of the BeticCordilleras (Lonergan et al. 1994).

The normal VZF strikes WNW–ESE and dips towardsNNE at an angle of 60� and is associated with a prominentscarp in Jurassic limestones. The fault can be divided intotwo E–W-oriented sectors separated by a central NW–SE-oriented sector. The striations on the fault plane indicate amain normal slip component with a minor dextral strike-slip component (superposed striae with a rake of 12�E and27�E). The present-day stress field indicates a NW–SE-directed maximum horizontal compression direction(Herraiz et al. 2000), and a SW–NE-directed extension,which is in concordance to the observed kinematicindicators on the fault plane.

Seismological setting

The present-day stresses in the studied area and theGranada depression (Fig. 1) were determined by focalmechanism solutions. It is characterized by a NE–SWextension (Galindo-Zald�var et al. 1993, 1999). However,the stress field in the area is heterogeneous as documentedby permutations of the stress axes. Essentially, radialextension, NE–SW extension, and NW–SE subhorizontalcompression are observed; the latter is parallel to theshortening direction active under the regional tectonicstress field (Buforn et al. 1988; DeMets et al. 1990;Galindo-Zald�var et al. 1999).

The seismic activity in the Granada depression andsurrounding areas is characterized by frequent micro-

Fig. 3 Digital elevation modelof the study area showing the1884 rupture (Fig. 2). AD Al-bor�n Domain; IEZB internalexternal zone boundary; ZPZafarraya Polje; SID SouthIberian Domain. Note landslideof Pilas de Algaida and localityof Fig. 8. The trace of the IEBZis covered by Quaternary de-posits and projected, hence, itseems not to be displaced by theVZF

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earthquake activity (MW �3.0, Fig. 4). The occurrence ofseries and seismic swarms is frequently observed, affect-ing the depression (Vidal 1986; Posadas et al. 1993;Serrano 1999; Saccorotti et al. 2001). The depth of thisshallow activity ranges between 5 and 15 km to amaximum of 20 km and includes earthquakes withMW �5 or more. The last moderate event occurred tothe south of the Granada depression with MW =5.0 in1984 (Morales et al. 1996). The lower cut-off of seismicactivity in 15–20-km depth has been interpreted byMorales et al. (1997) as the brittle–ductile transition in thecrust.

The Andalusian earthquake of 1884 is the most recentdestructive major event in southern Spain, followed byseveral aftershocks with intensities of up to MSK=VIIIduring 1 year (Mu�oz and Ud�as 1980). Depending on themode of calculation, magnitudes for this event rangessignificantly between 6.1 (L�pez-Casado et al. 2000) and6.5. to 7.0 (Mu�oz and Ud�as 1980, 1982); recently,Iba�ez et al. (2003) have estimated a MS of between 6.3and 6.8 based on intensity/magnitude relations. Duringthe EC-project FAUST (faust.ingv.it) a magnitude of 6.2,a length of 17.5 km and a strike of 89� were calculated forthe VZF and the 1884 event.

Palaeoseismological analysis

Although coseismic surface ruptures or cracks were notlikely to survive human activity, we searched for evidenceof strong ground motion in the geological record.Contemporaneous historical drawings and etchings ofunknown authors (Courtesy National Information Servicefor Earthquake Engineering, University of California,Berkeley, USA; see gallery of pictures at http://nisee.berkeley.edu/kozak/index.html) show the damage,destruction and ground failures in the areas of Zafarraya,

Alhama de Granada and Arenas del Rey (Fig. 5). Thedescribed cracks clearly delineate the WNW–ESE-trend-ing VZF and its prolongation towards the east (L�pez-Arroyo et al. 1980; Mu�oz and Ud�as 1980; Figs. 2 and5). The total rupture length observed was ~16 km,partitioned into two individual segments (Douville 1906).The rupture area, with a complicated system of fractures,extends in an E–W-elongated area of approximately20 km length and 4 km width (Ud�as and Mu�oz 1979).Partly, the ‘cracks’ indicate normal displacement of theQuaternary sediments with respect to the Jurassic lime-stones. On the other side, cracks formed in the Polje area(Fig. 5). This and other features related to the earthquake

Fig. 4 Historical seismicity inAndalucia (after Reicherter2001). Recent seismicity fromNEIC data (http://neic.usgs.gov/neis/epic/epic.html)

Fig. 5 Historical drawing of the 1884-earthquake in Zafarraya.Note ground failure with open cracks, which are probably drawnexaggerated (Courtesy National Information Service for Earth-quake Engineering, University of California, Berkeley; see galleryof pictures at http://www.nisee.berkeley.edu/kozak/index.html)

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Fig. 6 Radar sections and lineinterpretation of the Ventas deZafarraya Fault (locality seeFig. 2). All radar lines obtainedwith 200-MHz antennae. Thicklines normal faults; thin linesbedding (B) and cracks (C), (L)liquefaction; dashed line groundwater table; arrows counter-clockwise rotation of the hang-ing wall block; TWT two-traveltime; ns nanoseconds; orienta-tion left side is south, right sideis north

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of 1884 have been described by Taramelli and Mercalli(1886) and Douville (1906, see summary in Reicherter2001).The length of the rupture displays approximatelythe mapped fault length.

GPR visualization of the Ventas de Zafarraya Fault

Ground penetrating radar (GPR) is applied here tovisualize sedimentary structures related to coseismicdeformation (SIR 10B GPR system by GeophysicalSurvey Systems Inc. with antenna model 5106). Several200-MHz GPR-profiles perpendicular to the VZF wereanalysed, allowing a resolution of objects, discontinuitiesor strata in a dm/cm range (200 MHz approx. 20 cm). Avariety of filter tools were applied during processing withREFLEX-software (Sandmeier 2000): background re-moval, Butterworth bandpass, energy decay and fk-filtersas well as migration based on diffraction stack. The reliefof the section can be modelled with the 3-D topographycorrection later (Fig. 6a, b). Maximum interpretablepenetration was around 5 m in the present study.

In mainly arid regions, fault-related displacements inalluvial fans were mapped successfully with GPR (Bassonet al. 1994; Cai et al. 1996; Marco et al. 1997). High-resolution GPR-profiling provides not only the possibilityto trace active normal faults (Meschede et al. 1997;Reicherter and Reiss 2001), but also to visualize theassociated sedimentary hanging-wall patterns such asheterogeneous grabens and half-grabens including coarse-grained clastic wedges. Quantitative and qualitative GPRevaluation of these wedges yield the possibility ofestimation of palaeomagnitudes and slip rates on activenormal faults (Reiss et al. 2003). This study showed,however, that application of the georadar method incoarse-grained sediments and caliche covered fans islimited due to weak penetration and diffraction hyperbo-lae. Along the selected profiles, Quaternary unlithifiedsediments and palaeosols provide good contrasts againstwell-bedded Jurassic limestone of the footwall (Fig. 6).

The hanging wall of the VZF forms half-grabens thatare generally characterized by internal asymmetric con-cave, displaced reflectors or wedge-like features compa-rable to sedimentary structures observed in adjacentoutcrops (Fig. 7a). A GPR section was obtained perpen-dicular to the main scarp of the VZF where both foot andhanging wall consist of Jurassic limestones (Fig. 6a). Themain fault trace in the central part of the radargram can beprojected approximately 40 m E into the outcrop section(Fig. 7a). Reflectors are interrupted and displaced by thefault. Within the upper part of the hanging wall,continuous reflectors show a significant change intoconcave patterns, which are interpreted as dragged, fault-related sediments of Holocene age (Fig. 6a). Pinching-out features are interpreted as coarse-grained colluvialwedges.

A second GPR line was obtained about 80 m N of themajor scarp (Figs. 6b and 8). The interpretation of radarpattern revealed significant evidence for a secondary

normal fault within the hanging wall: the reflectors areinterrupted and an apparent change in dip is observableand, again, a concave filling is related with the fault. Wealso suggest a coseismic origin of the scarplet in 1884,because of its topographic expression.

Apart from this, secondary features have also beeninvestigated to distinguish between mass movements(landslides), liquefaction and aseismic fault creep. Ap-proximately 200 m N of the major scarp, within in theplane of the Polje (Fig. 2), a radar line exhibits verticalcracks and completely distorted layers within horizontalbeds (Fig. 6c). We interpret these observations ascoseismically induced cracks, as documented in historicaldrawings (Fig. 5), and as liquefaction. The characteristicpeculiarities observed in high-resolution GPR images(Reiss et al. 2003) help to distinguish fault-relatedsedimentary hanging-wall patterns from fluvial channelfills or anthropogenic filling, which may produce similarconcave patterns.

Palaeoseismic evidence

The Ventas de Zafarraya Fault exhibits several typicalindicators of coseismic displacement. Sedimentologicalcriteria are constrained by a series of radiocarbon data, inorder to reconstruct the Holocene faulting history of thefault. Along the fault, a set of 15 palaeosol samples,which are displaced or cover displaced Quaternarycolluvial deposits, were sampled for 14C soil dating(Table 1). 14C activity was estimated by liquid scintilla-tion spectrometry (LCS). Low-carbon-containing palaeo-sols were dated with accelerator mass spectrometry(AMS). To avoid isotopic effects, all 14C ages werecorrected with the 13C/12C ratios, which lie in the rangebetween 19.5 and 25.9 d13C.

At the cemetery of Ventas de Zafarraya (36�570500N,04�070500W, Fig. 2) the normal fault plane is exposed inan artificial wall cut. Anthropogenic terracing destroyedpartly the coseismic scarp, the uppermost layer containsplastic material. The hanging wall contains three coarse-grained wedge-like deposits that thicken towards the faultplane (Fig. 7a). The formation of colluvial wedges isgenerally considered as typical for coseismic ruptures(McCalpin 1996). Fine-grained, relict, reddish-yellowishpalaeosols and wash-off sediments rich in carbonates,eroded from the Jurassic substratum, separate the wedges.Older beds generally dip steeper towards the N thanyounger strata. The main fault bifurcates and the twolower wedges are displaced by a syn-1884 minor normalfault (Fig. 7a). The distances between the wedges are inthe order of ~1 m for each and the inferred individualcoseismic slip rates are approximately in the same order.The two lower wedges are ~70 cm thick, the upper wedgeca. 50 cm. With McCalpin’s rule of thumb (1986): doublecolluvial wedge thickness is approximately coseismicslip, and we end up at similar coseimic slip rates. Agedating of the wedge bases resulted in 8,800€130 years b.p.

for the lower and 2,315€30 years b.p. for the middle base,

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whereas the uppermost base is related to the 1884 event.The cumulative offset is 2.96 m in 8,800€130 years b.p.,and includes two 1884-like rupture events during theHolocene. However, age dating of intercalated strata isinconsistent and suggests a complex mixture of wash-offsediments of the slope and palaeosols (Fig. 7a). Hence,we obtained not significant and palaeoseismically rele-vant 14C-ages.

Both, coseismic displacement and wedge thicknesssuggest earthquakes with M >6.5. Liquefaction, such assand blows, clastic dikes and deformed beds, shear planesand ruptured or aligned pebbles, reveal further evidencefor repeated strong ground shaking. A secondary fault

strand developed approximately 50 m north of the mainfault contact associated with a 0.5-m-high scarplet(Fig. 8), the hanging wall of which also shows concavecolluvial filling in GPR (Fig. 6b).

Near the Cort�jo del Barranco (36�570436N,04�070868W) approx. 300 m west of the cemetery(Fig. 2), the coseismic displacement of the 1884-rupturingis between 1.2 and 1.5 m, resulting in a vertical slip ofbetween 1.0 and 1.3 m on a polished fault plane ofJurassic limestone that is not karstified. In the outcrop, thefault surface is exposed and a palaeosol covers approx-imately 1.2 m of a coarse-grained breccia of Jurassiclimestone fragments. Below this, a reddish-yellowish

Fig. 7 b Outcrop sketch of theLlanos de la Dona Fault. Notethree rockfall wedges, and re-duced palaeosol formation andwash-off colluvium, including14C-age dating results. Topmostpile of rocks is supposed to begenerated by ground shakingduring the 1884-earthquake

Fig. 7 a Outcrop sketch of theVentas de Zafarraya Fault atthe cemetery. Three colluvialwedges are intercalated bywash-off colluvium and pa-laeosols. Sample strategy, partlyat the base of the wedges, andages of 14C-dating in years b.p.

Topmost colluvial wedge issupposed to be generated im-mediately after the 1884-earth-quake, probably modified byhuman activity.

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palaeosol overlying a fine-grained sand and clay yielded14C ages of 7,370€60 years b.p. We interpret this brecciaas a result of the rupture that triggered the formation ofthe intermediate colluvial wedge dated at the cemeteryoutcrop as 2,315€30 years b.p. The anatomy of the entirefault zone with its minor faults and the internal structureof the hanging wall is depicted in the model displayed inFig. 8, where also the effects of liquefaction and refilledvertical fractures are represented, which have historicallybeen observed.

East of Pilas de Algaida (36�570432N, 04�050852W), asmall village 2 km East of Ventas de Zafarraya, evidencefor a 1884-coseismic landslide have been found (Fig. 2).

The Jurassic/Quaternary fault scarp, including a 2-m-thickcataclastic zone, slid en-block downslope (Fig. 3). Anintensely folded and deformed palaeosol on top of thelandslide yielded 14C-ages of 1,775€30 years b.p., thishorizon is covered by a recent soil (50€30 years b.p.).

Approximately 8 km NE of the VZF, a minor scarp ofapprox. 1–2 m height is developed along a 4-km-longnormal E–W-trending fault (Llanos de la Dona,37�010401N, 04�030490W, Fig. 1), juxtaposing Jurassiclimestones against Quaternary colluvial sediments. Incontrast to the VZF, the hill behind the scarp consists ofintensely karstified Jurassic limestones of only ~50 maltitude. Almost no soil and vegetation cover is developed

Table 1 Radiocarbon data of Ventas de Zafarraya and Llanos de laDona. n.d. Not determined due to method of AMS radiocarbonmeasurement; age b.p. conventional radiocarbon age (Stuiver andPolach 1977), i.e. half life 5,568 years, calibrated for isotope effectsto d13C of 25‰, (this is no calibration to calender years); errorb.p. 1s standard deviation (2s=double deviation value); HAM-xxxxDates of Hamburg Radiocarbon Laboratory, Hamburg University,

Allende-Platz 2, 20146 Hamburg, Germany; KIA-yyyy dates ofLeibniz Laboratory for Radiometric Dating and Isotope Research,Christian-Albrechts-University Kiel, Max-Eyth-Str. 11-13, 24118Kiel, Germany; HAM-xxxx/KIA-yyyy samples prepared in Hamburglab and measured in Leibniz Lab, Color according to Rock ColorChart, GSA

Lab. no. Sample no. d13C(‰PDB)

Age b.p. Error b.p. Colour

HAM-3711.1 Z1 20.0 8,800 €130 2.5Y 8/4HAM-3712.1 Z2 21.2 10,070 €70 7.5YR 4/6HAM-3713.1 Z3 20.9 13,540 €100 10R 4/6HAM-3714.1 Z4 19.5 15,990 €120 7.5YR 4/4HAM-3715.1 Z5 20.8 11,540 €70 7.5YR 4/6HAM-3716.1 Z6 23.4 8,730 €70 5YR 4/8HAM-3751.1 ZAF A 25.9 50 €30 7.5YR 4/4HAM-3752.1 ZAF B 25.1 1,775 €35 10YR 5/6HAM-3753.1 ZAF C 24.5 7,370 €60 5YR 4/8HAM-3698/KIA9669 ZAF 1 n.d. 2,315 €30 7.5YR 4/6HAM-3699/KIA9670 ZAF 2 n.d. 2,940 €140 10R 4/6HAM-3717.1 Llanos 1 22.2 9,610 €90 5YR 6/8HAM-3718.1 Llanos 2 25.2 2,960 €45 5YR 3/2HAM-3749.1 Llanos A (3) 24.7 1,110 €40 5YR 5/3HAM-3750.1 Llanos B (4) 24.9 1,650 €35 5YR 2/3

Fig. 8 Sketch model of theVentas de Zafarraya Fault withassociated roll-over structure.Note three different deforma-tion styles with respect to thedistance of the major fault planeand locality of the radar-lines inFig. 6. Not to scale

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on the mountain flank, which could provide wash-offsediments as observed along the VZF. Sediment accu-mulation rates are higher along the VZF because thehinterland of the Llanos foot wall is of smaller extent,hence providing lesser or no wash-off sediments. Trenchlogging allows identification of three coarse-grainedclastic wedges intercalated by relict palaeosols(Fig. 7b). The origin of the clastic wedges is interpreteddifferently, as along the VZF, as ‘rockfall wedges’,induced by coseismic shaking. Dating of intercalatedpalaeosols bracket the timing of the rockfalls. In contrastto the VZF scarp, where we dated the faulting episodes,here the phase of seismic quiescence has been dated, i.e.the soil formation intervals. Reddish palaeosols yield 14Cages from the base to top of 9,610€90, 2,960€45 and1,650€35 years b.p. (Fig. 7b). Parts of the recent soilcolumn directly at the fault scarp are ~1,110 years old.This soil was affected by slip-faulting, but is not overlainby boulders of the 1884-rock fall deposits. Those weredeposited at some distance from the scarp toe due todownhill rolling of lose limestone debris and jumpingacross the scarp (see Fig. 9). Instabilities along steeptopographic slopes, like slides, slumps and falls, can betriggered by strong earthquakes with magnitudes of M>5(Keefer 1984). Other slope-failure effects such as frost orexceptional precipitation events happen spontaneously.Radiocarbon dating support earthquake triggering of therockfalls during the palaeoearthquakes along the VZF,rather than fault reactivation along the Llanos de la Donascarp, although slip along the fault plane is observed. Theclastic ‘rockfall wedges’ possibly provide a new palaeo-seimic indicator. In conclusion, the three major eventsdetected along the VZF can surprisingly also be foundalong the Llanos scarp (Fig. 9).

Discussion and conclusions

The palaeoseismological investigations along this seg-ment of the VZF demonstrate that not only during, butalso prior to the destructive 1884 earthquake, coseismicdisplacements occurred. Repeated colluvial wedges alongthe bases of fault scarps and their stratigraphic relationwith wash-off sediments and palaeosols preserved withinthe half-graben prove evidence for earthquake-relatedfaulting. Several of the most important deformations andsecondary features, such as landslides and liquefaction,are related to the activity of the VZF. Palaeoseismic andradiocarbon data indicate at least two pre-1884 rupturesalong the fault during the last 10 ka. If we take intoaccount the relationship for normal faults by Wells andCoppersmith (1994), the estimated 1884-rupture length(16 km) is typical of earthquakes with M=6.4€0.6. Takingthe relationship using the maximum vertical displacementfor normal faults (Wells and Coppersmith 1994), which ismax. 1.3 m at the Cortijo del Barranco, magnitudeestimates are M=6.7€0.1. Considering afterslip, whichseems likely on hardrock–softrock fault scarps, andcalculating with a reduced coseismic displacement of1 m, we end up at M=6.6€0.1. Our calculations, afterWells and Coppersmith (1994), agree with the magnitudeproposed by L�pez-Arroyo et al. (1980) based on palaeo-intensity maps ranging between 6.5 and 7. Palaeoseismicfield data favour a magnitude of around 6.5 for the 1884event. The two former events are apparently in the sameorder of M 6.5, with respect to maximum displacementrelationships and wedge-thickness vs scarp-height rela-tions (McCalpin 1996).

Our data yield supplementary information accordearthquake recurrence intervals along the VZF of between2 and 3 ka for major earthquakes of M>6.5, under theassumption of uniform return periods. Taking into accountthat the total slip of the fault is ~1,500 m, and consideringthat the fault system is probably post-Tortonian in age, it ispossible to estimate that the minimum mean slip rate ofthe fault is 0.17€0.03 mm/year. The Holocene slip ratewas estimated at ~0.35€0.05 mm/year along the VZF,including s1 error of the 14C-data (Table 1). The smallerLlanos de la Dona fault is characterized by Holocene sliprates of 0.25€0.03 mm/year. This is typical for a moderateactivity rate along both faults. In contrast to this, Pel�ezMontilla et al. (2001) calculated a slip rate 0.125 mm/yearfor the long-term slip without palaeoseismic data. If weconsider the Slemmons and DePolo (1986) relationship,these data suggest a mean recurrence interval of~2,000 years along the Ventas de Zafarraya Fault, whichis therefore one of the main active faults in southern Spain.

Acknowledgements We are thankful to both anonymous reviewersand to the associate editor for helpful and in-depth comments on thepaper. The German Science Foundation, DFG-project Re 1361/3-1,and the Spanish CICYT, projects BET2000-1490-C02-01 andREN2001-3378/RIES, REN2001-2418C04-04/RIES, are thankedfor financial support. 14C-dating was partly carried out at theLeibniz Labor (Univ. of Kiel).

Fig. 9 Comparison of the dating methods colluvial vs rockfallwedges (see text for an explanation)

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