359-07 1 of 12

INTRODUCTION

Liquefaction, the temporary loss of shear strength ingranular sediments, is usually regarded as an indicator ofpaleoseismicity, although it may have other causes, such aslithostatic loading, cyclic wave-induced (storm) loading, andslumping, which can be difficult to identify with certainty(Ricci Lucchi, 1995). Nonetheless, establishing a causal linkbetween the deformation and paleoseismic events is useful inunderstanding the paleotectonic regime of ancient basins.

Among others, Sims (1973, 1975) specified criteria forcorrelating deformation with earthquakes: The basin should be

located in a tectonically active region; the sediments should besusceptible to liquefaction; the deformation structures should beconfined to a specific stratigraphic interval; the structuresshould occur over a wide area of the sedimentary basin; and,there should be no slopes or slope failures.

This paper describes pillow horizons in the GuadagnoloFormation, a calcareous, marly succession of Miocene age(Burdigalian to Langhian), in the transition area between theLatium-Abruzzi carbonate shelf and the nearby Sabina basin ofcentral Italy (Fig. 1). Satisfying the aforementioned criteria,these pillows are interpreted to be seismically induceddeformation structures related to liquefaction. In the following

Geological Society of AmericaSpecial Paper 359

2002

Indicators of paleoseismicity in the lower to middle MioceneGuadagnolo Formation, central Apennines, Italy

Goffredo MariottiLaura Corda

Marco BrandanoGiacomo Civitelli

Dipartimento di Scienze della Terra, Università degli studi di Roma “La Sapienza,” 00185 Rome, Italy

ABSTRACT

Convolute bedding—pillow horizons—of likely seismic origin are identified in abioclastic carbonate succession, the Guadagnolo Formation, in the central ApennineMountains of Italy. These sediments, which were deposited in a carbonate-ramp envi-ronment, are from Burdigalian to Langhian (Relizian) in age. The lower part, about500 m thick, consists of marlstones, marly limestones, and calcarenites, representingcyclic, shallow-water, coarsening-upward sequences. The second part, about 100 mthick, is dominated by prograding bodies of clinoform calcarenites. The horizons con-taining the pillow beds are in the topmost of the lower part, about 30 m below thebase of the overlying calcarenites. They are present at the same stratigraphic positionfrom the Prenestini to the Ruffi mountains across a distance of about 20 km. Pillows,20 cm to more than 1 m thick, are present in all the deformed layers and consist ofmarly calcarenites, which differ texturally from the enclosing matrix. They areregarded as the product of deformation ensuing from liquefaction of a denser layeroverlying a lighter, silty layer that is richer in clay.

These structures are interpreted to reflect liquefaction processes induced by seis-mic shocks, and they correlate well with coeval Miocene tectonism in this sector of theApennines.

Mariotti, G., Corda, L., Brandano, M., and Civitelli, G., 2002, Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation, centralApennines, Italy, in Ettensohn, F.R., Rast, N., and Brett, C.E., eds., Ancient seismites: Boulder, Colorado, Geological Society of America Special Paper 359,p.___

1

discussion, we use the geometric and textural characterization ofsedimentary structures to support interpretation of them aslikely indicators of paleoseismicity.

GEOLOGICAL SETTING

The Guadagnolo Formation (Fig. 2) is a lower to middleMiocene calcareous, marly succession deposited in shelf-to-basin transition areas along the western edge of the Latium-Abruzzi carbonate shelf (Civitelli et al., 1986a, 1986b). Theformation has a variable thickness, which may reach 1000 mas it approaches the basin to the north. Toward the shelf,however, its thickness decreases as some beds disappear,incomplete and/or condensed successions develop, and majorerosion results in the uppermost packstone-grainstone restingdirectly on Upper Cretaceous shallow-water carbonates. Thechief feature of the formation is a pattern of cyclic depositionthat occurred in slope and carbonate-ramp environments. Thebasal part is characterized by gravity-flow deposits (Fig. 3A),whereas the bulk of the unit, of Burdigalian and Langhian(Relizian) age, consists of a thick, monotonous stack ofcalcareous, marly deposits (Fig. 3B) that exhibit repeatedshallowing-upward sequences (average thickness about 0.5 to10 m) with a complex internal organization and numerousunconformities (Civitelli et al., 1986a, 1986b). Theseunconformities are thought to be mainly related to high-frequency eustatic cycles and, subordinately, to tectonics, thelatter being especially important in the topmost part of thesuccession (Madonna, 1996; Civitelli et al., 1996). Theshallowing- and coarsening-upward sequences consist ofargillaceous wackestone, commonly with a bioturbated base,gradually passing upward to wackestone-packstone and tobioclastic packstone-grainstone. These facies are organizedinto sequences (Fig. 4), which have been interpreted to besubtidal cycles deposited on the deeper part of a mid-ramp(sensu Burchette and Wright, 1992; James et al., 1999). In thispart of the Guadagnolo Formation, we have observed rare 15-to 20-cm-thick coarser layers with a major bioclasticcomponent (abundant bryozoans). They have a wide lateralextension, are normally graded and have a sharp, planar base;undulation, hummocky laminae are the main primarystructures. We have interpreted these layers as tempestites.

The uppermost part of the Guadagnolo Formation consistsof coarse-grained bioclastic grainstone-packstone and rests onthe underlying calcareous, marly part which in turn is above amajor unconformity (Fig. 2). In the lower part, these bioclasticcarbonates include a 10-m-thick horizon with abundant chertnodules. This is an important correlation horizon, which recursthroughout the Prenestini and Ruffi mountains. This uppermostpart forms a rather homogeneous unit, which caps theGuadagnolo Formation throughout the study area.

The pillow structures are located approximately 30 m belowthe cherty horizon in the uppermost part of the GuadagnoloFormation, and are located at the same stratigraphic position

throughout, from the Prenestini to the Ruffi mountains in thesouthern Sabina basin (Fig. 5).

PILLOW HORIZONS

The best exposures with pillow structures are in thenorthwesternmost sector of the Ruffi Mountains, along the roadlinking the Tiburtina state road with the village of Saracinesco(Fig. 1). There, at least four superimposed horizons can berecognized (Fig. 5).

The lower horizon (Fig. 6; A in Fig. 5) has a thickness ofabout 1 m. Within it, spheroidal structures can be seen; theyare either isolated or aggregated and consist of two or morelaterally or vertically packed spheroids (Fig. 7). In some cases,they are not completely separated, because the marl wedges,which appear to be injected between them from below, do notcross the entire layer. The pillows are more coarse grained andmuch more indurated than the surrounding marl. In the samehorizon, an elongate body extends for about 6 m and isbounded by a flat upper surface and by a more undulatinglower one. This body is composed of multiple spheroidalstructures, with diameters ranging from 30 to 40 cm, whichare separated by areas of calcareous marl with weaklamination that follow the contour of the pillows (Fig. 8). Thishorizon overlies a layer of highly bioturbated calcareous marland is topped by about 40 cm of marl with both horizontal andvertical traces of equally intense bioturbation.

Above this horizon, the succession continues with 1 m ofmore calcareous, bioturbated marl, followed by about 2 m ofmarly limestone. Above this is another 6 m of marlstone,bearing burrows with a basically subhorizontal pattern, mainlyrepresented by Planolites and Palaeophycus. The subsequentpillow layer (B in Fig. 5) is approximately 80 cm thick and iscomposed of ovoid bodies in marlstones. The width of thesebodies varies from 10 to 60 cm, and their lower and uppersurfaces are usually flat. The pillows are separated by marlsinjected from below.

The next level of deformation (C in Fig. 5) is above 2.5 mof marlstone and is very similar to B; it is less than 1 m thick,and the 20- to 50-cm-thick pillows, consisting of marlylimestones, are embedded in marl. Bioturbation is observed inboth the pillows and the marl, but never across the marl-pillowboundaries.

The uppermost pillow bed (D in Fig. 5) overlies 3.5 m ofcalcareous marlstone and intensely bioturbated marlstone. It iscomposed of two large composite bodies consisting of two ormore pillows (Fig. 9). The first is about 2 m long, and thesecond is 3.5 m long. Both bodies are about 1.5 m high. Thepillows inside these bodies generally have a spheroidal shape,but their lower and upper surfaces are fairly flat. They are madeup of marly limestone, but their host material has a dominantmarly component with cuspate geometry, apparently due toescaping fluids. This stratigraphically younger interval occursabout 30 m below the unconformity shown in Figure 2.

2 G. Mariotti et al.

359-07 2 of 12

In the same stratigraphic position, about 20 km to the southin the Prenestini Mountains, similar pillow horizons wereidentified. The best outcrops are near the villages ofGuadagnolo and of Capzanicia (Fig. 1). Below the rock onwhich Guadagnolo village rests, the topmost pillowed intervalcan be seen (D in Fig. 5). This interval is about 2 m thick andhas simple and composite pillows that range from 30 to 60 cm

in width. At the northern entrance of Capzanicia the samedeformed horizon (D in Fig. 5) crops out for a few tens ofmeters. The horizon, more than 1.5 m thick, displaysspheroidal- to elliptical-shaped pillows with 2 main diameter ofmore than 1 m.

Finally, other exposures with similar pillows at a similarstratigraphic position were identified in the Cicolani mountains,

Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation 3

359-07 3 of 12

Figure 1. Location of the study area in central Italy.

359-07 4 of 12

Figure 3. Interpretative diagrams illustrating the evolution of the platform-basin zone in the Sabina area during the Oli-gocene to mid-Miocene interval 1—Shallow-water carbonate of Latium Abruzzi platform; 2—pelagites; 3—gravity flowdeposits in basal part of Guadagnolo Formation; 4—calcareous , spiculitic marly deposits of middle-upper part ofGuadagnolo Formation; 5—coarse-grained bioclastic limestones of uppermost part of Guadagnolo Formation; 6—sili-ceous sponges and spicules. (After Civitelli et al., 1986b).

Figure 2. Outcrop of the Guadagnolo Formation in the Prenestini Mountains. The topmost part consists of coarse-grained bioclastic grainstones overly-ing a predominantly marly, calcareous deposit separated by a major third-order unconformity (arrow). The arrow also indicates a cliff about 20 m high.

about 50 km to the north. These are still being investigated.Because of the discontinuous exposure, only the youngestpillow horizon can be correlated from exposure to exposure.

MICROANALYSIS

In the studied horizons, both the pillows and the enclosingmaterial were analyzed with scanning electron microscopy andenergy-dispersive spectrometry (SEM-EDS) to bettercharacterize their texture and composition. The pillows consistof a grain-supported fabric with scarce intergranular spacesoccupied by small amounts of clay. The individual grain sizesrange from 50 to 200 µm. Rounding and sorting are poorlydeveloped (Fig. 10A). Large bioclasts are rarely present and arealmost exclusively represented by fragments of echinoids,bivalves, bryozoans, benthic and planktic foraminifers, andsiliceous sponge spicules (Fig. 11).

In contrast, the marl squeezed between pillows is matrix-supported, in that bioclasts are not in contact with each other.The individual grains are between 10 and 150 µm in diameter(Fig. 10B), and sorting is even less developed. The biogeniccomposition, however, is not significantly different from that onthe pillow sediments (Fig. 12).

The different density of packing and thus the differentmatrices are also shown by semi-quantitative chemical analysis(SEM-EDS). The samples taken from the pillows have a highcalcium content, whereas silicon is subordinate and aluminum iseven scarcer (Fig. 10D). By contrast, the analyses conducted onan equivalent surface area of a rock sample collected from aninjected marl show a higher silicon content and the presence ofaluminum, potassium, and iron (Fig. 10E). The difference inpillow and nonpillow is due only to the different amount of claymatrix. The elemental chemical composition of the interparticlematrix (Fig. 10c) proves to be consistent with the presence ofclay minerals (Fig. 10F). Insoluble-residue analysis, by meansof X-ray diffraction, indicates an abundance of clay minerals ofthe smectite group and subordinate quartz. Carbonatepercentages were also determined by analysis of calciumcarbonate. Both pillows and injected marl from differentdeformed horizons were analyzed. The percentage of theCaCO3 is consistently about 75% within the pillows versus 70%in the surrounding marl. These values show a weak but constantdifference in all analyzed horizons.

DISCUSSION

The analyzed pillows consist of bioclastic packstone-grainstone with fine-sand and coarse-silt grain sizes. They aresurrounded by injected marls represented by wackestone-packstone with medium to fine silt grain sizes. The presence oftwo main granulometric classes, medium- to fine-grained sandsand medium to fine silt (with 30% clay), increases the potentialof selective liquefaction and better preserves the resultingdeformation (Ricci Lucchi, 1995).

The pillows are characterized by upward-cuspate contactsat the base and by an internal lamination that, if present, followsthe external structure. In our opinion, the pillow beds of theGuadagnolo Formation can be interpreted as soft-sedimentdeformation structures related to the liquefaction processes in anunconsolidated two-layer system. Furthermore, the grain sizesinvolved in this phenomenon are those that have a highliquefaction potential (Seed and Idriss, 1982). Moretti et al.(1999a) reported some experiments on earthquake-inducedliquidization processes in unstable, two-layer, density-gradientsystems. Liquefaction caused the loss of shear resistance in bothstrata; the triggered deformation consists of large load casts.Only in the experiment where Moretti et al. (page 377) used “avery soft silty clay with very low shear strength” as theunderlying layer, did the overlying sands collapse inside thethixotropic silty clay. The cuspate form of the clay-rich siltsqueezed between the pillows was probably due to a lessereffective viscosity of the upper layer compared with the lowerone ( after Alfaro et al., 1997).

Our analyzed structures formed in a reverse-density gradientsystem in which a medium fine sand layer, showing greater bulk

Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation 5

359-07 5 of 12

Figure 4. A shallowing, coarsening-upward, subtidal cycle consisting ofargillaceous wackestone passing upward to wackestone-packstone andto bioclastic packstone-grainstone.

density as a function of particle concentration, overlies a lightsilty layer. After liquefaction, the denser layer was completelydisrupted, having been reduced to a series of isolated pillowsembedded in the lower, less dense underlying layer. Theoverlying, denser layer, although composed of angular bioclasticgrains, was capable of liquefaction because of its watersaturation; the underlying layer, however, shows evidence oflower viscosity, owing to its higher percentage of clay.

Liquefaction processes, as we mentioned above, may havedifferent causes; thus, it is important to review the main causesor processes capable of generating structures similar to the oneswe investigated.

Slumping

The possibility of slumping can be discounted for at leasttwo reasons. First, the pillowed horizons do not show folds, andthe geometry of the pillows fails to indicate vergence, whichwould suggest re-sedimentation due to lateral movement of thematerials. The geometry of the escape structures does notindicate any lateral translation, and the deformed horizons are

never joined with re-sedimented deposits that would indicate anenvironment conducive to slumping processes.

Second, the paleogeographic setting for the analyzed partof the Guadagnolo Formation, reconstructed on the basis of aphysical and sedimentological stratigraphic study (Civitelli etal., 1996), is a middle ramp with bathymetries of some tens ofmeters, where the sediments were remobilized by waves andsignificant tidal currents. The low angle of the ramp was suchthat it probably did not permit, without an external trigger,slumping and gravity flows. In this connection, we note that incontrast, in the lower part of the succession, where gravity-flowdeposits are common and unequivocally indicate sedimentationover a shelf-basin slope pillow structures are never found.

Loading

Unequal loading by density contrast (Dzulynski, 1996) canbe responsible for deformational structures similar to the oneswe studied. Depending on sedimentation rate, some lithologiesmay develop nodules floating within more muddy materials.Moretti et al. (1999b) described pillow structures from Miocene

6 G. Mariotti et al.

359-07 6 of 12

Figure 5. Measured lithostratigraphic sections. Locations shown in Figure 1.

(Tortonian) turbidite deposits of the Guadix basin in southernSpain. These structures, cyclically repeated in the succession,are elliptical in shape (long axes between 20 cm and 2 m) andcommonly parallel to the paleoslope. According to Moretti etal., the probable triggering mechanism for the studied pillowswas the process of overloading induced by rapid mass

sedimentation. In the succession that we have analyzed for thisstudy, however, such structures occur only in limitedstratigraphic intervals within a succession many hundreds ofmeters thick that consists of hundreds of cyclically repeatedsequences with the same lithologic characters and thicknesses.It seems unlikely that the pillows we studied derive from

Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation 7

359-07 7 of 12

Figure 6. Lowermost pillow horizon (A in Fig. 5) at the Saracinesco site(Fig. 1). Note the numerous spheroidalstructures across a distance of about 6 m.These structures consist of marly, bio-clastic limestones embedded in calcare-ous marls. Note the flat surface thatbounds the top of the layer. Hammer is33 cm long.

Figure 7. Isolated or composite pillows,consisting of two or more verticallystacked spheroids, inside the pillowhorizon shown in Figure 6. Hammer is33 cm long.

8 G. Mariotti et al.

359-07 8 of 12

Figure 8. Two pillows separated by cal-careous marls with laminar structuresthat tend to parallel the shape of the pil-lows. Saracinesco site (A in Fig. 5). Ham-mer is 33 cm long.

Figure 9. The uppermost pillow horizon(D in Fig. 5, locality Saracinesco) consistsof pillows that may exceed 1 m in thick-ness and which are commonly ovoid, withflat bases. The first pillow on the left sideis about 120 cm wide.

Figure 10. Scanning Electron Microscope (SEM) micrographs and plots. A: Sample collected from the inside of a pillow; texturally, it is a bioclasticpackstone-grainstone, with grains varying in diameter from 50 to 200 µm and without matrix. B: Sample of wackestone-packstone surrounding the pil-lows; note the larger amount of clay matrix, the smaller average size of the grains, and the lower degree of sorting. C: enlarged image of the sample inB, with abundant matrix; Energy Dispersive Spectrometry and Scanning Electron Microscope (EDS-SEM) analyses on the same samples also reveal dif-ferences between the pillows and the surrounding material. D: Sample collected from a pillow. E: Sample from marl surrounding the pillows. F: Sam-ple from the interparticle matrix of the injected marl. The high amount of silica in all the samples is also probably related to the numerous spongespicules both in the pillows and in the embedding marl. EDS spectra represent a 30-s, counting-time acquisition.

359-07 9 of 12

359-07 10 of 12

Figure 11. Photomicrograph showingmedium-grained packstone, collectedfrom a pillow, with bryozoan and echi-noid fragments and benthic foraminifers.It shows poor sorting and a small per-centage of matrix.

Figure 12. Photomicrograph showingfine-grained packstone-wackestone, col-lected from marl injected between pil-lows, containing planktic and benthicforaminifers together with bryozoan andechinoid fragments. Sorting is poor, andthe matrix is abundant.

intrinsic processes or from the mere density contrast of differentlithologies. Otherwise, given the lithological homogeneity of thesuccession, we would expect a greater frequency in theoccurrence of such deformation. Because such a frequency isnot present, we assume an extrinsic cause, external to thedepositional system and capable of triggering a process that islatent in successions consisting of materials with differentdensity, packing, and fabric.

Storm waves

Many authors have ascribed convolute bedding to stormwaves, whose passage can liquefy cohesive and noncohesivesediments, giving rise to pillow structures. Liquefaction due tostorm waves has been analyzed in modern sediments (Henkel,1970; Okusa, 1985; Dormieux and Delage, 1988), but fewexamples have been identified in ancient storm deposits.Nevertheless, an association of soft-sediment deformationstructures with hummocky cross stratification is frequentlyreported (Molina et al., 1998).

In the upper part of the succession we studied, where thepillow horizons are, we did not find any coarser layer withdistinctive features we could attribute to storm waves. Thus,on the basis of our findings, the assumption of a possiblerelation between our deformation structures and storm-waveaction is untenable.

Seismicity

In view of the above assumptions, a seismic-shock originfor the pillows is most probable. One of the best argumentssupporting this hypothesis is that, in many hundreds of metersof a monotonous succession of cyclically repeated lithologies,the pillows are widespread, but only in the same well-definedstratigraphic interval, between 50 and 30 m below the base ofthe uppermost calcarenitic part of the Guadagnolo Formation.At the same stratigraphic level, in more northern sectors of theSabina basin, about 50 km north of the Prenestini Mountains inthe Cicolani Mountains, we identified pillow structures verysimilar to the analyzed ones.

Pillow features comparable to the ones from this study havebeen found in Spain by Roep and Everts (1992), who indicatedthese liquefaction features were of seismic origin, on the basisof their observed structures, grain sizes, and presence ofdewatering features. Hempton and Dewey (1993) ascribed thedeformational structures that they found in Lake Hazar (Turkey)to seismic events. There, the pillow horizons, which areseparated by undeformed intervals, are distributed over a widearea and limited to a specific stratigraphic level. Rosskopf et al.(1995) also referred the genesis of the pillow structuresencountered in the littoral sediments of Piana del Sele(Campania, Italy) to seismic shocks, given the extent of theaffected area and their environment, so far from the shoreline asto exclude lithostatic loading or storm-wave action.

CONCLUSIONS

Given the textural and geometric characters, the well-defined stratigraphical interval, the distance between theoutcrops, and the paleogeographic and environmentalreconstruction of the Guadagnolo Formation during the pillow-forming time (late Burdigalian), we suggest that these pillowsare seismically induced deformational structures. Thelithostratigraphic framework and the stratigraphic-physicalarchitecture of the succession containing the deformed horizonsis controlled not only by sea-level changes, but also by local andregional tectonics. The Guadagnolo carbonate ramp was part ofthe foreland basin of the Apennine chain during early Miocene(Burdigalian) time and evolved upward to a foredeep filled bysiliciclastic deposits of late Miocene (Tortonian-Messinian) ageCipollari et al. (1995). On the basis of stratigraphic data fromsynorogenic sediments deposited during the Miocene inforeland depositioncenters in front of the eastward-migratingApennine thrust belt, Cipollari et al. (1995) pointed out aBurdigalian thrust phase centered on the northern SabiniMountains, about 100 km northwestward. This considerationand the widespread areal distribution of the seismically inducedpillow horizons suggest that these paleoseismites may reflectthe distal effect of tectonics that affected the Apennineaccretionary wedge, even if the studied area does not clearlyrecord the presence of faults.

We maintain that the presence of seismically induceddeformation structures could help in identifying distal tectonicprocesses in areas that do not have other important tectonicindicators. In addition, singling out and correctly interpretingsuch soft-sediment deformation structures could provide usefulcriteria for timing the evolution of major tectonic stages.Analyses of the microstructure of the rocks indicate the natureof variations in lithology and fabric that could increase thepotential of liquefaction.

ACKNOWLEDGMENTS

We are grateful to B.R. Pratt and R. Van Arsdale for theirrigorous reviews of this paper and their helpful suggestions, andto F.R. Ettensohn, who provided insightful scientific and editorialcomments that improved the manuscript greatly. We also thankFaith Rogers and Salma Monani for their copy-editing.

REFERENCES CITED

Alfaro, P., Moretti, M., and Soria, J.M., 1997, Soft-sediment deformation struc-tures induced by earthquakes (seismites) in pliocene lacustrine deposits(Guadix-Baza Basin, Central Betic Cordillera): Eclogae Geologicae Helve-tiae, v. 90, p. 531–540.

Burchette, T.P., and Wright, V.P., 1992, Carbonate ramp depositional system: Sed-imentary Geology, v. 79, p. 3–57.

Cipollari, P., Cosentino, D., and Parotto, M., 1995, Modello cinematico-strutturaledell’Italia centrale: Studi Geologici Camerti, v. 1995/2, p. 135–143.

Civitelli, G., Corda, L., Madonna, S., Mariotti, G., Milli, S., Barbieri, M., andCastorina, F., 1996, I depositi miocenici di rampa carbonatica dei Monti

Indicators of paleoseismicity in the lower to middle Miocene Guadagnolo Formation 11

359-07 11 of 12

Prenestini (Appennino centrale): processi deposizionali e stratigrafiasequenziale: Atti riunione del gruppo di sedimentologia del ConsiglioNazionale delle Ricerche (Catania), p. 123–125.

Civitelli, G., Corda, L., and Mariotti, G., 1986a, Il Bacino Sabino. 2. Sedimen-tologia e stratigrafia della serie calcarea e marnoso-spongolitica (Paleogene-Miocene): Memorie Società Geologica Italiana, v. 35, p. 33–47.

Civitelli, G., Corda, L., and Mariotti, G., 1986b, Il Bacino Sabino. 3. Evoluzionesedimentaria ed inquadramento regionale dall’Oligocene al Serravalliano:Memorie Società Geologica Italiana, v. 35, p. 399–406.

Dormieux, L., and Delage, P., 1988, Effective stress response of a plane sea-bedunder wave loading: Géotechnique, v. 38, p. 445–450.

Dzulynski, S., 1996, Erosional and deformational structures in single sedimen-tary beds: A genetic commentary: Annales Societatis Geologorum Poloniae,v. 66, p. 101–189.

Hempton, M.R., and Dewey, J.F., 1983, Earthquake-induced deformational struc-tures in young lacustrine sediments, East Anatolia Fault, southeast Turkey:Tectonophysics, v. 98, Letter Section, p. T7–T14.

Henkel, D.J., 1970, The role of waves in causing submarine landslides: Géotech-nique, v. 20, p. 75–80.

James, N.P., Collins, L.B., Bone,Y., and Hallock, P., 1999, Subtropical carbonatesin a temperate realm: Modern sediments on the southwest Australian shelf:Journal of Sedimentary Research, v. 69, p. 1297–1321.

Madonna, S., 1996, Analisi stratigrafico-sequenziale della successione miocenicamarnoso-calcarea di Guadagnolo (M.ti Prenestini, Appennino centrale)[Ph.D. thesis]: Roma, Università degli Studi di Roma “La Sapienza”, 178 p.

Molina, J.M., Alfaro, P., Moretti, M., and Soria, J.M., 1998, Soft-sediment defor-mation structures induced by cyclic stress of storm waves in tempestites(Miocene, Guadalquivir Basin, Spain ): Terra Nova, v. 10, p. 145–150.

Moretti, M., Alfaro, P., Caselles, O., and Canas, J.A., 1999a, Modelling seismiteswith a digital shaking table: Tectonophysics, v. 304, p. 369–383.

Moretti, M., Soria, J., Alfaro, P., and Walsh, N., 1999b, Soft-sediment deforma-tion structures in Tortonian turbiditic deposits (Guadix basin, southernSpain): Atti Geoitalia 1999, Bellaria, p. 124–126.

Okusa, S., 1985, Wave-induced stresses in unsaturated submarine sediments:Géotechnique, v. 35, p. 517–532.

Ricci Lucchi, F., 1995, Sedimentological indicators of paleoseismicity, in Serva,L., and Slemmons, D.B., eds., Perspectives in paleoseismology: Seattle,Washington, Association of Engineering Geologists Special Publication 6,p. 7–17.

Roep, T.B., and Everts, A.J., 1992, Pillow-beds: A new type of seismites? Anexample from a Oligocene turbidite fan complex Alicante, Spain: Sedimen-tology, v. 39, p. 711–724.

Rosskopf, C., Cinque, A., Ferreli, L., Michetti, A.M., and Vittori, E., 1995, Strut-ture da liquefazione Interpretabili come sismiti in sedimenti litorali storicidella Piana del Sele (Campania): Studi Geologici Camerti, Volume Speciale1995/2, p. 387–395.

Seed, N.B., and Idriss, I.M., 1982, Ground motions and liquefaction during earth-quakes: Berkeley, California, Earthquake Engineering Research Institute,p. 227–251.

Sims, J.D., 1973, Earthquake-induced structures in sediments of Van NormanLake, San Fernando, California: Science, v. 182, p. 161–163.

Sims, J.D., 1975, Determining earthquake recurrence intervals from deforma-tional structures in young lacustrine sediments: Tectonophysics, v. 29,p. 141–l52.

MANUSCRIPT ACCEPTED BY THE SOCIETY MAY 11, 2001

12 G. Mariotti et al.

359-07 12 of 12

Printed in the U.S.A.