ORI GIN AL PA PER

Surface breaks along the coastal plain of Ciro (IonianCalabria, southern Italy): geophysicaland paleoseismological insights

Paolo Galli • Sabatino Piscitelli

Received: 2 July 2013 / Accepted: 25 October 2013 / Published online: 6 November 2013� Springer Science+Business Media Dordrecht 2013

Abstract On July 28, 2004, the coastal plain of Ciro (Calabria, Ionian Sea) was inter-

ested by the sudden opening of a *5-km-long fracture, paralleling the coastline. All the

buildings, roads, and pipelines crossed by the fracture were damaged, inducing several

inhabitants to abandon their houses. The crack was 1–2-cm wide, downthrowing the

seaward block up to 1–2 cm. This phenomenon is known for having already hit this area at

least in the past century, both concurrently or not to earthquakes with epicentre far away

from Ciro. In order to investigate the subsurface geometry, and the nature of the crack, we

performed 5 electrical resistivity tomography and two paleoseismological trenches across

it. The two methods provided evidences for the whole displacement of the local coastal

succession, with offsets of several metres cumulated during the late Holocene. Giving the

radiocarbon age of samples collected in trenches, we have constrained the dates of a couple

of offset events which match some paleoearthquakes caused by the Lakes Fault, in the

neighbouring Sila Massif. Excluding other possible causes (i.e. anthropic or tectonic), we

are inclined to interpret these phenomena as the westernmost, surficial expression of a

submarine deep-seated gravity sliding.

Keywords Electrical resistivity tomography � Paleoseismology � Coastal

plains � Deep-seated slides � Calabria � Ionian Sea

P. Galli (&)Dipartimento Protezione Civile, Rome, Italye-mail: paolo.galli@protezionecivile.it

P. GalliIGAG, Consiglio Nazionale delle Ricerche, Montelibretti, Rome, Italy

S. PiscitelliIMAA, Consiglio Nazionale delle Ricerche, Tito Scalo, Potenza, Italy

123

Nat Hazards (2014) 71:291–313DOI 10.1007/s11069-013-0914-5

1 Introduction

On the evening of July 28, 2004, about forty buildings of Ciro Marina (Ionian coast of

Calabria, southern Italy, Fig. 1), both public (a school) and private, besides roads, walls,

and pipelines, suffered severe damage (Fig. 2) due to the sudden opening of a NNE–SSW

fracture across the ground surface of the flat coastal plain of Ciro (*5 m a.s.l.). The

fracture was *5-km long, with a rough rectilinear trend paralleling the coastline towards

Punta Alice (Fig. 1). Typically, on asphalted roads, walls, and buildings inside the Ciro

Marina settlement, the fracture was few millimetres, up to 1–2-cm wide; in some places,

the seaward side was both downthrown by 1–3 cm and displaced horizontally by 1–2 cm,

with a dextral component. Some concrete walls exhibited a set of microfractures spread

along 10–20 m of length, which likely represented the brittle response of the wall to the

ductile deformation of the terrain beneath the foundations.

A similar phenomenon had occurred at dawn of August 17, 1999, when roughly the

same buildings that were damaged in 2004 experienced analogous effects. According to

both documents retrieved in the archive of the Ciro Marina municipality, and to the

accounts of the inhabitants, others surficial breaks formed in 1990, 1980, and in the 40s of

the twentieth century. Likely, the same occurred also on September 8, 1905, when con-

temporary to the 120-km-far Sant’Eufemia Gulf earthquake (Mw 7.5; Galli and Molin

2007) a *1-km-long fracture opened ‘‘near Punta Alice’’.

Interferometric studies (PSInSAR, Permanent Scatters analysis of images acquired by

satellites ERS1-2 and Radarsat in the periods 1992–2002 and 2003–2005, respectively)

have depicted very well the areal effects of the 2004 event (Farina et al. 2007). Indeed,

these show that the fracture fits with the western border of a wide zone which has lowered

at a rate of 1.5–3 mm/year since 1992 and that recorded an abrupt increase due to the July

2004 event. All the permanent scatters (PS) located east of the fracture inside Ciro Marina

recorded a subvertical downthrow of 5–10 mm (Fig. 1), with a growing horizontal com-

ponent going eastward (up to 45� near the coast line). On the other hand, the PS time series

across the fracture north of the settlement show a high constant rate (up to 10 mm/year)

without any important acceleration due to the 2004 event.

In this paper, we summarize our attempt to investigate the nature of this fracture by

means of geophysical and paleoseismological methodologies, with the aim of evidencing:

1. The shear plane at depth (i.e. its geometry and kinematics);

2. The dynamics of the 2004 (and previous) slip (i.e. slow/fast/alternating);

3. The amount of previous offsets (if any);

4. Their age and recurrence.

As in the cases of active faults studies (e.g. in Galli et al. 2006, 2013a; Vanneste

et al. 2008; Giocoli et al. 2011), geoelectrical analyses (electrical resistivity tomography:

ERT) permitted to individuate the (eventual) existence and rough geometry of the shear

plane at depth in the open field, both in the lack of geomorphological indication (e.g. a

scarp), and in places where the fracture was not (more) visible. Following the ERT

results, we opened two paleoseismological trenches north of Ciro Marina, i.e. far from

the inhabited settlement, which allowed us to identify de visu, and to investigate the

fracture at depth.

It is worth noting that the terms ‘‘fault’’, ‘‘faulting’’, footwall, and hangingwall that we

use in the following paragraphs are only indicative of the physical displacement affecting

the geological layers, and not necessarily of the tectonic nature of this phenomenon.

292 Nat Hazards (2014) 71:291–313

123

2 Seismotectonic and geological background

The Alpine crystalline-metamorphic backbone of the Calabrian Arc occupies the southern

tip of the Italian boot, resting above a NW-dipping subduction slab (Ionian oceanic lith-

osphere) which is the most relevant geodynamic feature of the entire (southern) Apennines.

Approaching the Calabrian coast from SE, the slab—which is almost horizontal in the

Ionian domain—plunges steeply into the mantle beneath Calabria, bending then to almost

horizontal in the transition zone. It fits with a ‘‘Benioff plane’’ (Amato et al. 1993)

extending at least 500 km into the asthenosphere, below its related backarc basin (i.e. the

southern Tyrrhenian basin; Malinverno and Ryan 1986).

Extension of the imbricate systems of the Calabrian thrust belt was active since Upper

Miocene time (Moretti and Guerra 1997), causing elongated N–S and NE–SW trending

basins on the inner margin of the Arc (Crati and Mesima graben, Gioia Tauro, Crotone,

Fig. 1 Satellite view of the Ciro-Marina-Punta Alice coast. Coloured dots represent the average velocitiesdistribution (mm/year) of the Permanent Scatterer Radarsat (2003–2005 period, ascending. Modified fromCampolmi 2007). Yellow-dotted line is the 2004 fracture; dashed line is the smoothed scarp on the northerncontinuation of the fracture)

Nat Hazards (2014) 71:291–313 293

123

Sant’Eufemia, and Messina Strait basins, mainly end of Lower Pleistocene), bordered by

primary high-angle normal faults (Ghisetti 1981; Tortorici et al. 1995; Galli and Bosi 2002,

2003; faults 2, 6, 8–10 in Fig. 3). At least since Middle Pleistocene, Calabria was strongly

uplifted (0.6–1.3 mm/year-rates, respectively, from north to south; e.g. in Molin et al.

2004; Dumas and Raffy 2004), as suggested by the staircase of marine terraces which

border the coasts of both seas (see Bigazzi and Carobene 2004; Miyauchi et al. 1994 and

reference therein) and by the deposition of thick sandy and conglomeratic bodies of deltaic

or littoral facies directly overlaying marine clays (Moretti and Guerra 1997). These

deposits outcrop today at 400 m a.s.l. within the extensional basins (for instance, in the

Crati half-graben basin), whereas Upper Pliocene–Pleistocene sediments and contemporary

Fig. 2 View of one of the several houses which were damaged by the surficial break opened in July 2004

294 Nat Hazards (2014) 71:291–313

123

continental paleosurfaces may reach 1,400 m a.s.l. in the raised blocks of Sila, Serre, and

Aspromonte.

Calabria has been struck by some amongst the most catastrophic earthquakes of Europe

(Fig. 2; see an overview in Galli et al. 2007) which were mainly caused by the normal

faults that controlled the opening of the extensional basins along the Tyrrhenian side

(Cotecchia et al. 1969; Galli and Bosi 2002; faults 8–10 in Fig. 3). Moreover, Galli and

Bosi (2003) and Galli and Scionti (2006) hypothesize the existence of a *NW–SE Sila

active fault system, responsible for all the largest earthquakes of the Ionian side of central

Calabria (faults 4–5 in Fig. 3), whereas to the north, the E-W Rossano fault (3 in Fig. 3),

besides driving the definitive downthrow of the crystalline Sila Massif northward, was

responsible for repeated strong earthquakes during the historical period (Galli et al. 2010).

Fig. 3 Seismotectonic framework of Calabria, with Mw [5.5 earthquakes (modified from CPTI11 2011)and primary seismogenetic faults (red = certain, i.e. investigated by paleoseismological analyses). 1 Mt.Pollino Fault; 2 W-Crati Fault System; 3 Rossano Fault; 4 Cecita Fault; 5 Lakes Fault; 6 Savuto FaultSystem (Piano Lago-Decollatura Fault); 7 Feroleto-Sant’Eufemia Fault; 8 Serre Fault System; 9 CittanovaFault; 10 Reggio Calabria Fault System. Green earthquakes symbols derive from paleoseismic and/orarchaeoseismic studies (see in Galli et al. 2008)

Nat Hazards (2014) 71:291–313 295

123

2.1 Local geology

The Ciro Marina-Punta Alice coastal plain is located within the northernmost part of the

Neogene Crotone basin (Roda 1964; Fig. 3) which, in turn, lays over the downthrown

crystalline-metamorphic basement of the eastern Sila Massif Unit (Barone et al. 2008). The

Crotone basin is part of a larger Neogene forearc basin, and it mainly consists of a suite of

continental, paralic, shallow-marine, and deep-marine deposits organized to form uncon-

formity bounded stratal units (Zecchin et al. 2012).

In the investigated area, an eastward-dipping sedimentary succession has been evi-

denced by some deep exploration wells ([2,000 m b.s.l.; see ViDEPI 2013) which

encountered the Argille Variegate group (Eocene–Cretaceous-coloured clays and shales,

sandstones, and marls) at 1,500 m b.s.l., unconformably overlaid by the Monte Cacio-

cavallo clays and sandstones (Oligocene–Lower Miocene). In turn, these are unconform-

ably mantled by the grey-blue, marly clays of Cutro (Roda 1964. KCR in Fig. 4.

Piacenzian-Calabrian; *500 m b.s.l.) which on the one hand thicken seaward, and on the

other outcrop *1 km west to Ciro Marina, below the Madonna del Mare syntheme (CMD

in Fig. 4). The latter is made by polygenic, massive conglomerates in reddish sandy matrix

(Upper Pleistocene), which unconformably cut all the underlying formations.

Fig. 4 Simplified geological map of the investigated area. KCR, Cutro clays (Piacenzian-Calabrian); CMD,Madonna del Mare conglomerates (Upper Pleistocene); NEL, aeolian sands, interfingered with b, alluvialdeposits; d, beach deposits (Holocene). RIF-1 is a seismic reflection line (in Sorriso-Valvo et al. 2005). Redline is the 2004 fracture. ERT1-5 and T1-2 are the electrical resistivity tomographies and thepaleoseismological trenches (this work). Section a–a’ is in Fig. 18. Black dots, deep boreholes

296 Nat Hazards (2014) 71:291–313

123

As a matter of fact, all the deposits affected by the fracture outcrop on a NNE–SSW

strip confined between the coastline and the western foothill. They are made by aeolian

sands (Marinella dunes; NEL in Fig. 4), interfingered westward with alluvial deposits,

mainly Holocene sandy gravels and silts (b in Fig. 4). This environment is enriched by the

presence of a marsh, which mainly develops during the winter months behind the coastal

dune north of Ciro Marina. To the west, the marsh is bounded by a seaward-facing scarp

that parallels the coastline and that resulted aligned with the 2004 surface break.

3 Geoelectrical tomographies

The electrical resistivity tomography (ERT) is a fast, non-invasive, and inexpensive sur-

ficial geophysical survey that has been widely applied to obtain two-dimensional images of

subsurface resistivity patterns. As aforementioned, it has proven to be useful to provide

both the exact locations of buried faults, and the delineation of the internal architecture of

fault zones and also of the associated sedimentary basins.

We have performed ERT surveys by using a Syscal R2 resistivity meter (Iris Instru-

ments), coupled with a multielectrode acquisition system (32 electrodes), with a constant

spacing ‘‘a’’ between the adjacent electrodes (e.g. from 2 to 5 m). Along each profile, we

applied different array configurations (Wenner–Schlumberger and dipole–dipole), and

different combinations of dipole length (i.e. 1a, 2a, 3a) and ‘‘n’’ numbers of depth levels

(n B 6), obtaining investigation depths ranging from about 10 m (for a = 2 m) to about

25 m (for a = 5 m). To obtain two-dimensional resistivity images of the subsurface, the

Wenner–Schlumberger and dipole–dipole apparent resistivity data were inverted using the

RES2DINV software (Loke 2001). The inversion routine is based on the smoothness-

constrained least-squares inversion, implemented by using a quasi-Newton optimization

technique (Loke and Barker 1996). The optimization method adjusts the 2D resistivity

model trying to iteratively reduce the difference between the calculated and measured

apparent resistivity values. The root-mean-squared (RMS) error provides a measurement of

this difference. Generally, the best results were obtained by means of the Wenner–Sch-

lumberger array, which showed a higher signal-to-noise ratio, a greater investigation depth,

and a better sensitivity patterns to both horizontal and vertical changes in the subsurface

resistivity (Loke 2001). In all cases, the root-mean-squared error was less than 10 %.

We made 5 ERT, as reported in Fig. 4 (ERT 1–5), with variable length (from 62 to

155 m), depending from electrodes spacing (i.e. 2–5 m). All the ERT have been coupled

with a topographic profile which we have performed ad hoc by using optical levelling

method.

3.1 Ert-1

This tomography (62-m long, with 2-m-spaced electrodes) is located in the northernmost

part of the investigated area, across the smoothed scarp facing westward the mentioned

ephemeral marsh. The scarp is 4-m high and 30-m wide, affecting partly fixed, and pe-

dogenized aeolian sands. Indeed, this ERT was designed in order to verify the eventual

matching between the scarp morphology and any subsurface feature. As a matter of facts,

both the dipole–dipole and Wenner–Schlumberger tomographies evidence a relatively

high-resistivity body at surface ([200 Xm), which likely represents the aeolian sands

standing above the water table (Fig. 5). At depth, the foot of the scarp does not match

Nat Hazards (2014) 71:291–313 297

123

clearly with lateral discontinuity, even if a faint plunge of the isoresistivity layers can be

traced as going eastward.

3.2 Ert-2

This tomography (62-m long, with 2-m-spaced electrodes) investigates 1 km to the south

the same scarp as in ERT-1 (Fig. 4), which is here 2.5-m high, and 20-m wide. ERT results

show an abrupt lateral discontinuity between deposits characterized by the different

resistivity values (i.e.[100 vs\10 Xm), just below the scarp edge (Fig. 6). In the eastern

side, these might fit with silty-clayey sediments, very rich with mineralized fluids (e.g.

brackish water), whereas they should match with sandy-gravelly deposits at west. At the

top of the section, the highest values of the entire ERT reasonably reflect the absence of the

water table.

The lateral discontinuity is almost vertical, although it occurs 2–3 m westward to the

scarp foot, as we would have expected in case of fault-related scarp. However, as the scarp

is here largely reworked by human activities, the scarp edge has artificially migrated

eastward, as the result of the dumping of material towards the marsh area (see the resistive

wedge between progressive 32–38 in Fig. 6).

3.3 Ert-3

We have designed this 155-m-long tomography near the Ciro Marina cemetery, across the

smooth scarp that accommodates here a level difference of 3 m within *30 m in length.

This is also the place where Sorriso-Valvo et al. (2005) performed a 96-m-deep borehole,

and another one was dug west to this ERT. Indeed, giving the larger electrodes spacing

(5 m), ERT-3 investigates a deeper portion of the subsoil. Similarly to ERT-2, also this

section evidences an abrupt, vertical discontinuity which is here located at the foot of the

scarp (Fig. 7). The contrast is sharp within the first 10 m of depth, where [100 Xm

resistivity terrains are juxtaposed against \20 Xm ones. More in depth, below 10 m, the

influence of the salt water table likely obliterates the subsoil image depicted by the ERT.

As a matter of facts, borehole S1 encountered clayey-sandy silts down to 6 m, passing

then into sands and sandy gravels, as evidenced also by the different resistivity of ERT

layers. Conversely, the other borehole (S2 in Sorriso-Valvo et al. 2005; outside ERT-3

profile) met, from the top, a prevailing gravelly sandy succession which fits well the high-

resistivity values revealed by ERT-3 in its western sector.

Fig. 5 ERT-1 (Wenner-Schulmberger), showing only a faint lateral discontinuity beneath the foot of thescarp at depth (arrows)

298 Nat Hazards (2014) 71:291–313

123

3.4 Ert-4

This tomography (62-m long, with 2-m-spaced electrodes) is located between the school

that has been cut and damaged by the fracture and the cemetery, where the scarp

accommodates a step of 2 m within a 20-m-wide belt (Fig. 8). Going eastward, the ERT

evidences at depth a vertical discontinuity between terrains with different resistivity

(*100 vs \50 Xm), whereas nearing the surface, the ‘‘hangingwall’’ shows a high-

resistivity body ([200 Xm) at the top of the succession. As in the previous case, the

vertical discontinuity occurs in the distal portion of the scarp and matches at surface with

the 2004 cracks both in the ground and across the adjacent buildings. Therefore, we have

decided to open here trench 2, the results of which will be presented later.

3.5 Ert-5

This tomography parallels with the concrete wall of the mentioned school in Scalaretto

Street and has been centred on the fracture affecting the structural joint of the building and

the wall itself (Fig. 9). The profile is 62-m long, with electrodes spaced by 2 m.

Also, in this case, the ERT shows the abrupt, subvertical contact between terrains

characterized by different resistivity values ([100 vs \30 Xm; Fig. 10), fitting exactly

with the 2004 fracture trace. The very low resistivity core (\10 Xm) visible in the

‘‘hangingwall’’ indicates the presence of clayey-silty deposits interbedded between coarser

ones (e.g. sands). In the footwall, the high resistive values likely indicate coarse and

granular deposits (sands and gravels). This site also has been considered suitable for

paleoseismological trenching (trench 1).

Fig. 6 ERT-2 (dipole–dipole). Note the subvertical discontinuity just beneath the scarp edge betweenterrains with different resistivity values (arrows). The mismatch between this limit and the foot of the scarpis due to artificial dumping of material over the natural scarp, as suggested also by the wedge of resistivedeposits visible at surface between progressive 32–38

Fig. 7 ERT-3 (dipole–dipole), located near the cemetery of Ciro Marina. Note the abrupt subverticalcontact between terrains characterized by different resistivity values, around progressive 100 (arrows)

Nat Hazards (2014) 71:291–313 299

123

Fig. 8 ERT-4 (Wenner–Schulmberger), located south of the cemetery. Note the subvertical discontinuitybetween terrains with different resistivity values around progressive 46 (arrows). In this site, we openedtrench 2 (black rectangle)

Fig. 9 View looking west of ERT-5, designed parallel to the northern wall of the school affected by 2004surface breaks

Fig. 10 ERT-5 (Wenner-Schulmberger, upper panel; dipole–dipole, lower panel), designed along thenorthern concrete wall of the school in Scalaretto Street. The centre of the ERT fits with the 2004 surfacebreak. As in the previous tomographies, note the abrupt, subvertical discontinuity between terrains withdifferent resistivity values (arrows). We opened here trench 1 (empty rectangle)

300 Nat Hazards (2014) 71:291–313

123

4 Paleoseismic analyses

Encouraged by the ERT results, we decided to open two trenches across the 2004 fracture,

in order to apply a paleoseismological approach in the study of the deformed sedimentary

succession. This allowed us to investigate de visu the geometry of the shear plane hypo-

thetically associated with the 1905, 1980, 1990, 1999, and 2004 surface breaks (and

previous unknown events) and to ascertain whether the past throws have always been

limited to few centimetres or more.

Indeed, even if paleoseismology typically investigates the surficial evidences of deep

seismogenic structures, its methodological approach has been successfully applied also to

deep-seated gravity landslide analysis (McCalpin and Irvine 1995; Galadini et al. 2001;

Onida et al. 2001; Gori et al. in press) and, more in general, it can be used to the study of

every recent, brittle/ductile mesoscale deformation. Moreover, the paleoseismic approach

may help in discriminating the dynamics of the rupture, i.e. slow versus fast slip, as is the

case of creeping vs an instantaneous offset.

4.1 Trench 1

This trench (4-m deep, 7-m long) has been dug north of the school affected by the 2004

vent, along the axis of ERT-5. The site matches with the buried thalweg of an ephemeral

NE-SW trending stream that, from the Pleistocene hills (sands and gravels) outcropping

the west of Ciro Marina, reaches the sea north of the port. Indeed, the main problem here

was to avoid trenching inside the monotone, massive sandy coastal deposits (i.e. mainly

aeolian dunes), hoping—conversely—to reach a layered stratigraphical succession that was

suitable for evidencing any possible deformation, as that potentially represented by stream

deposits. As a matter of fact, this site is almost totally flat, and it does not present the trace

of any scarp, whereas the path of the paleo-creek is only visible on 1950s aerial photos as a

faint shadow zone due to moisture differences. Therefore, the trench was designed mainly

on the basis of the information provided by the ERT, and following the crack on the school

wall.

A first trenching attempt along the school wall failed suddenly, as the exposed suc-

cession was made by massive, loose sand deposits which slid dangerously before letting us

recognize any possible feature. A second, successful attempt few metres away has, instead,

revealed a ‘‘faulted’’ stratigraphical succession composed, from the bottom to the top, by

four main units (Fig. 11). Unit 1 are alternating greyish gravels, with embricated flat

pebbles ([ 1–4 cm), and ochre coarse sands; upwards, it is capped by unit 1a, well-sorted,

layered, yellowish sands, passing upward to brownish gravels in sandy matrix. Unit 2 are

upward-coarsing ochre sands, laminated at the bottom, and truncated at the top by an

erosional surface. This latter is emphasized by a stone line made by fine clasts ([ 1–2 cm).

Unit 3 are mottled silty-clayey sands, with abundant organic material, passing upward to

unit 4, massive fine, clast-supported gravels. Unit 4 gradually passes upward to unit 4a,

silty sands, and sandy silts with sparse pebbles. Actually, unit 3 outcrops only in the

downthrown side, where it gradually passes to unit 4, the bottom of which still contain silty

organic material. Conversely, in the ‘‘footwall’’, unit 2 is directly overlaid by unit 4.

As far as the depositional environment of this succession, we can hypothesize that unit 1

represents beach deposits, covered by aeolian sand (unit 2). Unit 3 suggests a very low-

energy environment, likely a coastal marsh, whereas unit 4 is alluvial deposits related to

the activity of the mentioned paleo-creek. Likely, the age of the creek deposits is very

recent, as the Scalaretto area has been flooded several times in the last century (and

Nat Hazards (2014) 71:291–313 301

123

before). For instance, we have found an interesting coeval document in the Archive of the

Civil Protection Department in Rome which describes the 1957 flood: ‘‘…the immense

flood, which hit […] the Scalaretto [area] […] where all the first-storeys have been

overwhelm […] the vineyards, the orange-grooves, and the gardens […] are inundated

[…]’’. On the other hand, we obtained a 14C date at the top of unit 3 (sample CIRO-01),

which constraints the age of the entire succession to the Late Holocene (3,650–3,380 BP,

2r cal. age; see Table 1).

As aforementioned, the entire stratigraphical section is displaced by an apparently

normal fault. A first shear plane displaces units 1–1a and 2 (fault A in Fig. 11; see inset in

Fig. 12), dragging the horizontal strata of the footwall, tilting the hanging wall, and

causing the downslope alignment of pebbles along the plane. Upward, this fault branches

into several splays, which look very ‘‘fresh’’ (i.e. they are still opened) pointing to the

fracture surveyed across the school wall. A minor splay (B in Fig. 11) offsets the same

units just east of plane A.

Unfortunately, the nature of the contact between units 1–2 and 3 across the supposed

eastern fault C is not visible, as it extends below the water table level (here, 3 m below the

ground surface in August), making impossible any prolonged, autoptic examina-

tion.1However, as the contact is certainly subvertical, considering the lithology of the units

Fig. 11 Interpretative log of part of the southern wall of Trench 1. See text for the description of the unitsand of the offset events

1 During the excavation, a spring formed at the contact between the clays and the sands, causing severeinstability problems to the trench wall.

302 Nat Hazards (2014) 71:291–313

123

(loose granular deposits), it is highly improbable to relate it to erosional processes. On the

contrary, given the proximity of ‘‘faults’’ A–B, and the matching with a buried scarp (i.e.

the erosional surface carved over unit 2), we interpret the contact as due to fault C

(Fig. 11), which downthrows units 1–2 well below the trench bottom.

Table 1 Conventional and calibrated ages of samples from trenches 1–2 (Beta Analytic Inc. Miami, FL)

Sample Unit Analysis Dated

material

Conventional

radiocarbon age

(year BP)

Calibrated BP age

range (1r-68 %)

Calibrated BP age

range (2r-95 %)

Trench 1 CIRO-01 3 AMS Organic silt 3,290 ± 60 3,580–3,460 3,650–3,380

Trench 2 CIRO-02 2 AMS Organic silt 4,240 ± 60 4,850–4,820

4,750–4,720

4,870–4,780

4,780–4,600

CIRO-04 3 AMS Charcoal 2,900 ± 40 3,080–2,960 3,160–2,920

Fig. 12 View looking south of trench 1, dug near the damaged school in Scalaretto Street (background).Black arrows point to the cracks affecting both the concrete wall and the structural joint of the building.Vertical dotted lines in trench (red) indicate the faults affecting the aeolian–alluvial deposits. The insetshows a detail of the western displacement (A–B in Fig. 11; labels as in Fig. 11: net 0.5 m)

Nat Hazards (2014) 71:291–313 303

123

The entire offset of the units is not fully evaluable, because correlative layers exist only

across the western faults. For instance, faults A–B downthrow the bottom and the top of

units 1a by *0.65 m, whereas the bottom of unit 4 is displaced by *0.25 m across the

same faults. Actually, if we consider the original profile of the ground surface before the

erosion of the free-face edge which formed during the faulting event (see dotted line in

Fig. 11), the top of unit 2 is offset by at least 0.42 m. The different offset between units

1–1a (*0.65 m) and the erosional surface over unit 2 (*0.42 m) may be explained both

by the erosion of part of the footwall (i.e. of the top of unit 2) or by the existence of a

faulting event(s) during or after unit 2, and before unit 4 deposition. However, the lack of

the stone line in the footwall of fault A suggests that erosion occurred prior to the sedi-

mentation of unit 4, and therefore, these faults account surely for one faulting event

happened after the deposition of unit 4 and one or more after units 1–2, before the erosional

surface formation.

As far as fault C is concerned, we can only observe that it downthrows units 1–2 below

the trench bottom with a minimum offset of 0.4 m (bottom of unit 2). Indeed, by projecting

the mentioned profile of the ground surface at the top of unit 2 from the footwall of fault A

to the hangingwall, the minimum offset is 1.6 m. Moreover, we can reasonably hypoth-

esize that the erosional surface carved on unit 2, together with its top stone line, belongs to

the scarp developed successively to the first, visible faulting event. This caused the

downthrown of units 1–2, inducing the formation of a marsh that was progressively filled

by the silty clays (units C).

Basing on all the above, we hypothesize the following chain of events:

1. Between the paleoshore line and the dune behind, units 1–2 deposited before *4 ka,

when a first ‘‘faulting’’ event displaced them by *0.2 m across faults A–B, and by an

unknown value across fault C. The downthrown block was then occupied by a coastal

marsh which developed before and at least up to 3,650–3,380 BP.

2. Successively, the top of unit 2 was dismantled by erosive processes, with the steps that

formed on faults C–B–A progressively evolving onto a scarp which retreated

westward. On this surface, which was characterized also by a stone line, the alluvial

deposits of unit 4 began to accumulate in the most depressed portion, mantling the

stone line and interfingering with the marsh deposits.

3. A time after 3,650–3,380 BP, all deposits were offset by a new event that faulted units

3–4 against units 1–2, with a not-evaluable throw (fault C). The scarp profile

previously carved on unit 2 was cut by less than 0.25 m by faults A–B, and likely a

new scarplet begun to retreat in the footwall. The area was then progressively buried

by units 4–4a, which filled definitively also the eastern depression.

4. This slip history proceeded with the creep observed during the past decades, as it is

indicated by the open cracks surveyed on the trench wall and across roads and

buildings at surface.

4.2 Trench 2

This trench has been opened 0.5 km north of Trench 1, across a smooth scarp carved in an

abandoned field, following the robust evidences provided by ERT-4 (Fig. 8). Here, the

deeper level of the water table allowed us to reach a higher depth (*5 m) with respect of

trench 1. In this excavation, apart from the presence of a clear shear zone, the strati-

graphical succession substantially differs from trench 1, as deposits are mainly sand with

thin lenses of gravel (Fig. 13). Above all, a 0.7-m-thick, blackish, stiff, sandy silt level

304 Nat Hazards (2014) 71:291–313

123

outcrops along the entire trench wall (unit 2; Figs. 13, 14), overlaying fine, massive, grey-

pink sands (unit 1). Unit 2 is truncated upward by an erosional surface and then mantled by

coarse, grey sands (unit 3), and layered gravelly sands (unit 3b). In the downthrown side

(east), below unit 3b, we observed massive, coarse reddish sands (unit 3a). Unit 4 is

massive pink sands, which mainly mantle the scarp facing the downthrown block, and lack

at all in the western side of the trench. Unit 5 is a wedge of coarse, mixed sediments, which

probably has slid along the scarp. Units 6 and 8 are massive, orange sands, whereas unit 7

are sands and gravels carved within unit 6, tapering towards the scarp.

As far as the depositional environment of this succession is concerned, unit 2 could

represent the deposits of a coastal marsh (e.g. as the one currently existing behind the dune),

which emerged post *4.5 ka, and was successively truncated by erosion, undergoing a

process of strong consolidation, being then definitely buried by aeolian sands (unit 3).

The age of the exposed succession has been partially constrained by the 14C dating of

two samples (CIRO-02, CIRO-04; Fig. 13; Table 1) collected within unit 2 (bulk) and at

the bottom of unit 3 (detrital charcoal). Both suggest a Late Holocene age of the deposits,

allowing the upper layers (units 4–8) to be dated within the past 2–3 ka.

As mentioned above, the entire succession is affected by a main shear plane that offsets

units 2–4, downthrowing the eastern block (Fig. 15). Unit 4 is affected by several sec-

ondary shear planes, likely due to gravity collapse, which is filled by light-grey sands, as

the larger wedge filled by unit 5. Small open cracks continue upward in units 6 and 8,

probably joining with the surficial breaks observed in 2004 on the road, and on some

abandoned houses in the neighbourhood.

Due to the lack of correlative levels across the two side of the fault, it has not been

possible to evaluate finite offsets. Nevertheless, the eroded top of unit 2 is displaced by at

least 2.2 m, as we did not encounter it at the bottom of the trench in the hangingwall.

Fig. 13 Interpretative log of the northern wall of Trench 2. See description of the units in the text

Nat Hazards (2014) 71:291–313 305

123

Moreover, if we assume that the minimum thickness of unit 2 is that measurable between

faults A and C (1.7 m), the minimum offset affecting this unit would exceed 3 m.

Analogously to trench 1, we hypothesize the following succession of events:

1. A marsh environment developed behind the coastal dune and over previous aeolian

sands (unit 1) during at least the 5th millennium BP, allowing the deposition of

blackish, organic silts (Unit 2);

2. The area is then affected by a sudden displacement, which cuts unit 2 by an unknown

offset. The footwall is then intensively eroded, with the formation of an undulated

erosional surface joining eastward with the steep scarp which evolved behind the fault

step.

3. Unconformably over unit 2, sands and gravels of unit 3 deposited onlap the scarp.

After an erosion phase, these are mantled than by aeolian sands (unit 4).

4. At this moment, a new faulting event occurred, causing the fall of material within open

cracks along fault (unit 5). The downthrown area has been then filled by sandy-

gravelly colluvia (units 6–7) and further aeolian deposits (unit 8), the latter reaching

more than 2 m of thickness.

5. In recent times, a centimetric slip occurred along some visible cracks, possibly

associated with the cracks surveyed at surface and affecting roads and wall close to the

trenching area.

Fig. 14 Panoramic view of the northern wall of trench 2 (net 1 m) dug along ERT-4

306 Nat Hazards (2014) 71:291–313

123

The first ‘‘faulting’’ event, probably the most relevant one, likely occurred during or a

time after the deposition of the marsh deposits of unit 2, the eroded top of which yielded a

radiocarbon age of 4,870–4,600 BP. It occurred necessarily before the deposition of unit 3,

the bottom of which contains a detrital charcoal dated at 3,160–2,920 BP. Considering that

the top of unit 2 is deeply truncated by erosion (it could also lack more than 1 m upward),

it is reasonable that the event occurred much more close to 3,160–2,920 BP than

4,870–4,600 BP. On the other hand, the successive ‘‘faulting’’ event occurred well after the

deposition of unit 3, and after unit 4, and thus in an undefined period during the past two–

three millennia. Tentatively, we could hypothesize that the great thickness of aeolian filling

in the downthrown block (unit 8) was due to the deflation processes under some cooler,

drier, and windier conditions during the Late Holocene (e.g. in Campbell et al. 2011), as in

the Little Ice Age (fifteen-to-nineteenth century) or in the Late Roman-High Middle Age

phase (sixth-to-tenth century). Therefore, in this case, the downthrow of the eastern side

could have tentatively occurred closer to these periods.

5 Discussion and conclusions

The most relevant and reliable result that we have achieved through the geoelectrical and

paleoseismological analyses is that the 2004 surface break, as all the previous ones (known

or unknown) fit—at depth—with a ‘‘geological’’ displacement which repeatedly occurred

at least during the Late Holocene.

Fig. 15 View looking north of the fault zone within trench 2. The dark level represents marsh deposits ofthe 5th millennium BP, faulted against aeolian sands. Net is 1 m

Nat Hazards (2014) 71:291–313 307

123

The two methods have produced data that match and complete each other, providing the

indirect and the direct evidence for the existence of a shear plane at depth (Fig. 16).

In detail, we have individuated at least two net offset episodes that are both charac-

terized by the ultra-decimetric throws. Their age may be inferred by comparing, and cross-

matching the succession of geological events described in the two paleoseismological

trenches which, in turn, are constrained by the radiocarbon dating of the samples that we

collected there (Fig. 17). Therefore, bearing in mind the depositional/erosional history of

units 1–2 in trench 1, and unit 2 in trench 2, we can reasonably suppose that the first

faulting event occurred a time after 4,870–4,600 BP, and likely slight before

3,650–3,380 BP. In turn, the second faulting event likely occurred a long time after

3,160–2,920 BP, and—tentatively—a time before the High Middle Age.

However, as we know from the historical accounts that at least one episode of surface

breaking certainly occurred in concomitance with a strong seismic shaking (1905 earth-

quake in Fig. 3; Rizzo 1907), by analysing the regional seismic record we can make further

hypothesis on the age of these displacements. Indeed, in 1905, the nearest village was Ciro

(6-km-far away from the coast), where the seismic shaking induced effects of 7 MCS

degree (Galli and Molin 2007) that roughly equal to horizontal peak ground acceleration

(PGA) of 0.1 g (e.g. in Faccioli and Cauzzi 2006). If this PGA was enough for inducing a

noticeable surficial crack along the investigated structure (whatever the cause is), it is

reasonable that stronger shaking might have activated larger slip. The most important

seismogenetic structure near the Ionian coast is certainly the Lakes Fault, in the Sila Massif

(#5 in Fig. 3). In June 1638, this fault caused Mw 6.7 earthquake which induced here

intensity effects much higher than in 1905. According to Galli and Bosi (2003), villages

west to Ciro experienced 9.5 MCS degree and, considering the overall intensity distribu-

tion, intensity in the studied area would have been around 8–9 MCS, i.e. up to 0.3 g in

Fig. 16 Merging of the electrical resisitivity tomography carried out near the damaged school (ERT-5), andof the paleoseismological trench (T1). The bodies with different resistivity have been correlated with theterrain exhumed in trench and with the stratigraphy of neighbouring boreholes. Note the good matchingbetween the 2004 crack, the fault visible in trench and the subvertical discontinuity in the ERT

Fig. 17 Chronological diagram of the event windows (E1–E2) individuated in trenches 1–2. Sample arrowsindicate post (right) and ante (left) quem terms. Eq1–3 indicate the time-span relative to thepaleoearthquakes generated by the far Lakes Fault (Sila Massif. From Galli et al. 2007)

308 Nat Hazards (2014) 71:291–313

123

terms of PGA. Moreover, paleoseismological analyses across the Lakes Fault demonstrated

that this structure was responsible for similar earthquakes also around 4 kyr BP, 3 kyr BP,

and 1.4 ky BP (Galli et al. 2007). Therefore, our hypothesis—which makes no claim to

being conclusive—is that at least the two greater displacement events dated in trenches 1–2

might fit with the earliest earthquake of the Lakes Fault (Eq1 in Fig. 17), and with one of

the successive (Eq2 or, most probably, Eq3 in Fig. 17), which are both compatible with the

ages that we have deduced inside trenches.

The geometrical and kinematics characters of the investigated shear plane (e.g. planar,

subvertical normal fault type), the depositional and geomorphological context of the ter-

rains affected by faulting (alluvial/aeolian littoral deposits on a flat, coastal plain), and the

presence of buried, retreated fault scarps suggest, in the whole, an instantaneous faulting

style, which was followed by the typical erosive processes that model fault scarp after

surface faulting (e.g. in Wallace 1977; Galli et al. 2013b).

In addition to this faulting style, a slow creep undoubtfully exists, the evidence of which

are both currently quantifiable by PSinSAR analyses (up to 10 mm/year), and is testified by

the periodical opening of the surface cracks. The main difference is that in the first case,

the instantaneous offset might be also in the order of 1 m (or more), whereas in the second

case, it just accommodates some mm/year during short time spans. In other words, we can

hypothesize the existence of episodic, abrupt slips of this structure, separated by long

quiescence periods, during which creeping phenomena may occur desultorily. Both the

former and the latter can be triggered by seismic shaking, as that induced by far strong

earthquakes. Nevertheless, we do not know whether the creeping episodes (as the 2004 and

previous ones) are a warming sign of a paroxysmal event, or—as it would result from the

case histories (e.g. 1905, 1940, 1980, 1999)—only a transient, static arrangement of the

involved rock volume.

This implies some considerations concerning the nature of this phenomenon. Firstly, we

exclude any anthropic origin (i.e. related to water/gas/oil exploitation), as the largest

offsets are prehistoric in age, and at least one surface-break event is pre-industrial, and

surely related to the 1905 earthquake shaking.

Secondly, it is highly improbable that the structure we are dealing with might fit with an

active fault, even if aseismic, and even if possibly triggered by the far-field earthquake

shaking (e.g. in Tape et al. 2013). Indeed, faults are primarily the brittle response to an

oriented crustal stress, and a NNE–SSW-trending normal fault would imply here an ESE-

oriented r3. Conversely, all the known, active, capable, and seismogenetic faults of

northern Calabria (Lakes Fault, Rossano Fault, Mount Pollino Fault; e.g. in Galli et al.

2007, 2008) account for a NNE-oriented r3 which is rotated by 90� with respect to what is

necessary in our case.

To date, our preferred hypothesis is that the ground breaks and the investigated buried

displacements are the surficial expression of a deep-seated gravity sliding (e.g. in Hampton

et al. 1996; see also the megaslide hypothesized in the near Crotone area by Minelli et al.

2013), the main shear plane of which developed at depth inside the grey-blue, Cutro

Pliocene clays (e.g. along bedding planes). As aforementioned, the latter are encountered

by all the wells of the area only few dozens of metres b.s.l., and as they dip seaward, the

shear plane could flatten and compensate within the clay strata (e.g. in panel A in Fig. 18).

In other words, the gently regional dipping of this formation towards the Ionian sea might

favour the gravitational sliding of large volume of rock towards the deeper sectors of the

sea bottom, which reaches 250 m b.s.l. 5 km east to the Ciro Marina coast, exceeding

1,000 m b.s.l. 15 km east (e.g. in Rebesco et al. 2009). The local involvement of the Cutro

Clays is also suggested by the *10-m offset of some seismic reflectors visible in a

Nat Hazards (2014) 71:291–313 309

123

reflection line made by Sorriso-Valvo et al. (2005) which matches both the 2004 surficial

cracks and the ERT-3 results (panel B in Fig. 18).

The hypothesis of a translational sliding (Locat and Lee 2002) fits also well with the

growing horizontal component detected by the PSinSAR analyses as moving away from

the fracture towards the coastline (Farina et al. 2007). Indeed, by inverting the slip vectors

of each PS through the method of Carter and Bentley (1985), Farina et al. (2007) have

defined the possible sliding surfaces at depth that would best accommodate the surficial PS

vectors along several E–W sections (area of Ciro Marina port in Fig. 1;). These depict a

listric plane (panel C in Fig. 18) which is subvertical close to the surface break—as we did

Fig. 18 A Simplified WNW-ESE geological section of the investigated area (a–a’ in Fig. 4). The bold lineis the hypothesized sliding plane within the Piacezian-Calabrian Cutro clays (KCR). AV, Argille Variegategroup (Eocene–Cretaceous); ACV, Monte Caciocavallo clays (Oligocene-Lower Miocene); CMD, Madonnadel Mare syntheme (Upper Pleistocene); NEL, aeolian sands, and coastal deposits (Holocene). B Is a detailof a seismic reflection line (Sorriso Valvo et al. 2005; see location in Fig. 4), showing the possible offset(*10 m) of the top of the Cutro clays, and of other upper reflectors. The section contains also ERT-3, withthe strong lateral discontinuity fitting at depth the mentioned offset. Bold dashed line is the hypotheticalsurface splay of the deep-seated sliding. C Envelope (dashed area) of all the sliding surfaces obtained byinverting the PS vectors (upper arrows) along several profiles orthogonal to the 2004 crack (mod. fromCampolmi, 2007)

310 Nat Hazards (2014) 71:291–313

123

observe in trenches and through ERT—and then flatten at depth between 80 and 200 b.s.l.,

i.e. inside the Cutro clays.

As similar recent cases that originated nearshore (e.g. in Hampton et al. 1996), also the

Ciro Marina slides could retrogress back across the inner coastal plains, causing a prom-

inent impact on human life and activities. Therefore, we intend the information contained

herein as a starting point for investigating more in detail this case, with the aim of

mitigating the eventual effects of future coastal failures.

Acknowledgments T. Campolmi, C. Salustri Galli, I. Ilardo, and V. Spina participated in the survey andinterpretation of the paleoseismological trenches. V. Scionti participated in the ERT campaign. G. Marinosurveyed and mapped the entire 2004 surface crack, providing us the logistic support for ERT and trenchanalyses, and fighting against the landowners who ‘‘a sira ca si e ra matina ca no’’ (the evening they say yes,the morning no). M. Perri dug with consummate skill the two trenches. Field survey was performed duringsummer 2006. A. Bosman kindly provided us the bathymetry of the Ciro Marina offshore. The view andconclusion contained in this paper are those of the authors and should not be interpreted as necessarilyrepresenting the official policies, either expressed or implied, of the Italian government.

References

Amato A, Alessandrini B, Cimini GB, Frepoli A, Selvaggi G (1993) Active and remnant subducted slabsbeneath Italy: evidence from seismic tomography and seismicity. Ann Geofis 36:201–214

Barone M, Dominici R, Muto F, Critelli S (2008) Detrital modes in a late Miocene wedge-top basin,northeastern Calabria, Italy: compositional record of wedge-top partitioning. J Sediment Res78:693–711

Bigazzi G, Carobene L (2004) Datazione di un livello cineritico del Pleistocene medio: relazioni consedimentazione, sollevamento e terrazzi marini nell’area Crosia-Calopezzati in Calabria (Italia). IlQuaternario 17:151–163

Campbell MC, Fisher TG, Goble RJ (2011) Terrestrial sensitivity to abrupt cooling recorded by aeolianactivity in northwest Ohio, USA. Quat Res 75:411–416

Campolmi T (2007) Valutazione delle condizioni di dissesto dell’abitato di Ciro Marina (KR), medianteinterferometria radar ed applicazioni paleosismologiche. Unpublished Degree Thesis, University ofFlorence, pp 125

Carter M, Bentley SP (1985) The geometry of slip surfaces beneath landslides: predictions from surfacemeasurements. Can Geotech J 22:234–238

Cotecchia V, Melidoro G, Travaglini G (1969) I movimenti franosi e gli sconvolgimenti della rete idrog-rafica prodotti in Calabria dal terremoto del 1783. Geologia Applicata e Idrologeologia 4:1–24

CPTI11 (2011) Parametric catalogue of Italian earthquakes, 2011 version. In: Rovida A, Camassi R,Gasperini P, Stucchi M (eds) Milano, Bologna. http://emidius.mi.ingv.it/CPTI

Dumas B, Raffy J (2004) Late Pleistocene tectonic activity deduced from uplifted marine terraces inCalabria, facing the Strait of Messina. Quat Nova 8:79–100

Faccioli E, Cauzzi C (2006) Macroseismic intensities for seismic scenarios, estimated from instrumentallybased correlations. In: Proceedings of the first european conference on earthquake engineering andseismology, Geneva, Switzerland, 3–8 September, paper no 569

Farina P, Casagli N, Ferretti A (2007) How space-borne InSAR can provide insights into coastal instabilityproblems: the Ciro Marina case (Italy), EGU General Assembly 2007. Geophys Res Abstr 9:03486

Galadini F, Galli P, Cittadini A, Giaccio B (2001) Late quaternary fault movement in the Mt. Baldo-LessiniMts. sector of the Southalpine area (northern Italy). Geol Mijnbouw 80:187–208

Galli P, Bosi V (2002) Paleoseismology along the Cittanova fault. Implications for seismotectonics andearthquake recurrence in Calabria (southern Italy). J Geophys Res 107(B3):1–19

Galli P, Bosi V (2003). The catastrophic 1638 earthquakes in Calabria (southern Italy). New insight frompaleoseismological investigation. J Geophys Res 108(B1):1–20

Galli P, Molin D (2007) Il terremoto del 1905 della Calabria Meridionale. Studio Analitico degli effetti edipotesi sismogenetiche, 2nd edn. p 112. http://ilmiolibro.kataweb.it/schedalibro.asp?id=543242

Galli P, Scionti V (2006) Two unknown M [ 6 historical earthquakes revealed by paleoseismological andarchival researches in eastern Calabria (Southern Italy). Seismotectonic implication. Terra Nova18(1):44–49. doi:10.1111/j.1365-3121.2005.00658.x

Nat Hazards (2014) 71:291–313 311

123

Galli P, Bosi V, Piscitelli S, Giocoli A, Scionti V (2006) Late Holocene earthquakes in southern Apennines:paleoseismology of the Caggiano fault. Int J Earth Sci 95:855–870

Galli P, Scionti V, Spina V (2007) New paleoseismic data from the Lakes and Serre faults (Calabria,southern Italy). Seismotectonic implication. Boll Soc Geol Ital 126:347–364

Galli P, Galadini F, Pantosti D (2008) Twenty years of paleoseismology in Italy. Earth Sci Rev 88:89–117.doi:10.1016/j.earscirev.2008.01.001

Galli P, Spina V, Ilardo I, Naso G (2010) Evidence of active tectonics in southern Italy: the Rossano Fault(Calabria). In: Guarnieri P (ed) Recent progress on earthquake geology. Nova Science Publishers Inc.,New York, pp 49–78

Galli P, Giocoli A, Peronace E, Piscitelli S, Quadrio B, Bellanova J (2013) Integrated near surface geo-physics across the active Mount Marzano Fault System (southern Italy): seismogenic hints. Int J EarthSci (in press). doi:10.1007/s00531-013-0944-y

Galli P, Peronace E, Quadrio B, Esposito G (2013b) Earthquake fingerprints along fault scarps: a case studyof the Irpinia 1980 earthquake fault (southern Apennines). Geomorphology (in press). doi:10.1016/j.geomorph.2013.09.023

Ghisetti F (1981) Evoluzione neotettonica dei principali sistemi di faglie della Calabria centrale. Boll SocGeol Ital 99:387–430

Giocoli A, Galli P, Giaccio B, Lapenna V, Messina P, Peronace E, Romano G, Piscitelli S (2011) Electricalresistivity tomography across the Paganica-San Demetrio fault system (L’Aquila 2009 earthquake).Boll Geofis Teor Appl 52(3):457–469

Gori S, Falcucci E, Dramis F, Galadini F, Galli P, Giaccio B, Messina P, Pizzi A, Sposato A, Cosentino D(in press) Deep-seated gravitational slope deformations, large-scale rock failure and active normalfaulting intertwine along the Mt. Morrone south-western slope (Sulmona basin, central Italy): geo-morphologic and paleoseismological analyses. Geomorphology

Hampton MA, Lee HL, Locat J (1996) Submarine landslides. Rev Geophys 34:33–59Locat J, Lee HJ (2002) Submarine landslides: advances and challenges. Can Geotech J 39:193–212Loke MH (2001) Tutorial: 2-D and 3-D electrical imaging surveys. Geotomo Software, Malaysia, p 127Loke MH, Barker RD (1996) Rapid least-squares inversion of apparent resistivity pseudosections by a quasi-

newton method. Geophys Prospect 44:131–152Malinverno A, Ryan WBF (1986) Extension in the Tyrrhenian Sea and shortening in the Apennines as a

result of arc migration driven by sinking of the lithosphere. Tectonics 5:227–245McCalpin JP, Irvine JR (1995) Sackungen at the Aspen high-lands Ski Area, Pitkin County, Colorado.

Environ Eng Geosci 1:277–290Minelli L, Billi A, Faccenna C, Gervasi A, Guerra I, Orecchio B, Speranza G (2013) Discovery of a gliding

salt-detached megaslide, Calabria, Ionian Sea, Italy. Geophys Res Lett 40:1–5Miyauchi T, Dai Pra G, Sylos Labini S (1994) Geochronology of Pleistocene marine terraces and regional

tectonics in the Tyrrhenian coast of south Calabria, Italy. Il Quat 7:17–34Molin P, Pazzaglia F, Dramis F (2004) Geomorphic expression of active tectonics in a rapidly-deforming

forearc, Sila massif, Calabria, southern Italy. Am J Sci 304:559–589Moretti A, Guerra I (1997) Tettonica dal Messiniano ad oggi in Calabria: implicazioni sulla geodinamica del

sistema Tirreno-Arco Calabro. Boll Soc Geol Ital 116:125–142Onida M, Galadini F, Forcella F (2001) Application of paleoseismological techniques to the study of Late

Pleistocene-Holocene deep-seated gravitational movements at the Mortirolo Pass (central Alps, Italy).Geol Mijnbouw 80:209–227

Rebesco M, Neagu RC, Cuppari A, Muto F, Accettella D, Dominici R, Cova A, Romano C, Caburlotto A(2009) Morphobathimetric analysis and evidence of submarine mass movements in the western Gulf ofTaranto (Calabria margin, Ionian Sea). Int J Earth Sci 2009(98):791–805

Rizzo GB (1907) Contributo allo studio del terremoto della Calabria del giorno 8 Settembre 1905. Atti dellaReale Accademia Peloritana 22:3–86

Roda C (1964) Distribuzione e facies dei sedimenti neogenici nel bacino Crotonese. Geol Romana3:319–366

Sorriso-Valvo M, Gulla G, Antronico L (eds.) (2005) Indagini, studio e monitoraggio del dissesto in atto nelcentro abitato di Ciro Marina. Relazione finale CNR IRPI (Cosenza), pp. 139

Tape C, West M, Silwal V, Ruppert N (2013) Earthquake nucleation and triggering on an optimally orientedfault. Earth Planet Sci Lett 363:231–241

Tortorici L, Monaco C, Tansi C, Cocina O (1995) Recent and active tectonics in the Calabrian arc (SouthernItaly). Tectonophysics 243:37–55

Vanneste K, Verbeeck K, Petermans T (2008) Pseudo-3D imaging of a low-slip-rate, active normal faultusing shallow geophysical methods: The Geleen fault in the Belgian Maas River valley. Geophysics73. doi:10.1190/1.2816428

312 Nat Hazards (2014) 71:291–313

123

ViDEPI (2013) Project ViDEPI, visibility of petroleum exploration data in Italy. Internet site: http://unmig.sviluppoeconomico.gov.it/videpi/default.htm

Wallace RE (1977) Profiles and ages of young fault scarps, north-central Nevada. Geol Soc Am Bull88:1267–1281

Zecchin M, Caffau M, Civile D, Critelli S, Di Stefano A, Maniscalco R, Muto F, Sturiale G, Roda C (2012)The Plio-Pleistocene evolution of the Crotone Basin (southern Italy): interplay between sedimentation,tectonics and eustasy in the frame of Calabrian Arc migration. Earth Sci Rev 115:273–303

Nat Hazards (2014) 71:291–313 313

123