new active faulting offshore se spain (alboran sea): implications...

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Earth and Planetary Science L

Active faulting offshore SE Spain (Alboran Sea): Implications for

earthquake hazard assessment in the Southern Iberian Margin

Eulalia Gracia a,*, Raimon Pallas b, Juan Ignacio Soto c, Menchu Comas c,

Ximena Moreno a,b, Eulalia Masana b, Pere Santanach b, Susana Diez a,

Margarita Garcıa d, Juanjo Danobeitia a

HITS scientific party 1

a Unitat de Tecnologia Marina, Centre Mediterrani d’Investigacions Marines i Ambientals-CSIC, 08003 Barcelona, Spainb RISKNAT Research Group, Dpt. Geodinamica i Geofısica, Facultat de Geologia, Universitat de Barcelona, 08028 Barcelona, Spain

c Instituto Andaluz de Ciencias de la Tierra (CSIC)-Universidad de Granada, 18002 Granada, Spaind Institut de Ciencies del Mar, Centre Mediterrani d’Investigacions Marines i Ambientals-CSIC, 08003 Barcelona, Spain

Received 17 May 2005; received in revised form 30 October 2005; accepted 7 November 2005

Available online 27 December 2005

Editor: V. Courtillot

Abstract

The southern margin of the Iberian Peninsula hosts the convergent boundary between the European and African Plates. The area

is characterised by low to moderate magnitude shallow earthquakes, although large historical events have also occurred. In order to

determine the possible sources of these events, we recently acquired swath-bathymetry, TOBI sidescan sonar and high-resolution

seismic data on the Almerıa Margin (Eastern Alboran Sea). The new dataset reveals the offshore continuation of the NE–SW

trending Carboneras Fault, a master fault in the Eastern Betic Shear Zone, and its associated structures (N150 and NS faults). These

structures are active since they cut the Late Quaternary sedimentary units. The submarine Carboneras Fault zone is 100 km long, 5–

10 km wide, and is divided into two N045 and N060 segments separated by an underlapping restraining stepover. Geomorphic

features typically found in subaerial strike-slip faults, such as deflected drainage, water gaps, shutter ridges, pressure ridges and benechelonQ folds suggest a strike-slip motion combined with a vertical component along the submarine Carboneras Fault. Considering

the NNW–SSE regional shortening axis, a left-lateral movement is deduced for the Carboneras Fault, whereas right-lateral and

normal components are suggested for the associated N150 and NS faults, respectively. The offshore portion of this fault is at least

twice as long as its onshore portion and together they constitute one of the longest structures in the southeastern Iberian Margin.

Despite the fact that present day seismicity in the Almerıa margin seems to be associated with the N150 to NS faults, the

Carboneras Fault is a potential source of large magnitude (Mw ~7.2) events. Hence, the Carboneras Fault zone could pose a

0012-821X/$ - s

doi:10.1016/j.ep

* Correspondin

Marıtim de la B

E-mail addre1 The HITS sc

Alpiste (IACT-C

Spain), P. Blond

P. Terrinha, J. G

etters 241 (2006) 734–749

ee front matter D 2005 Elsevier B.V. All rights reserved.

sl.2005.11.009

g author. Unitat de Tecnologia Marina-CSIC, Centre Mediterrani d’Investigacions Marines i Ambientals (CMIMA). Passeig

arceloneta, 37-49, 08003 Barcelona, Spain. Tel.: +34 93 230 95 36/+34 93 230 95 00; fax: +34 93 230 95 55.

ss: [email protected] (E. Gracia).

ientific party: R. Bartolome, M. Farran, (CMIMA-CSIC, Barcelona, Spain), M. Gomez (ICTJA-CSIC, Barcelona, Spain), M.J.R.

SIC, Granada, Spain), G. Lastras, V. Wilmott (DEPGM-Universitat de Barcelona, Spain), H. Perea (DGG-Universitat de Barcelona,

el, O. Gomez (University of Bath, UK), L. Bullock, C. Jacobs, I. Rouse, D. White, S. Whittle (National Oceanography Centre, UK),

afeira, C. Roque (Universidade de Lisboa, Portugal).

E. Gracia et al. / Earth and Planetary Science Letters 241 (2006) 734–749 735

significant earthquake and tsunami hazard to the coasts of Spain and North Africa, and should therefore be considered in any

hazard re-evaluation.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Alboran Sea; Carboneras Fault zone; strike-slip faulting; submarine channels; seismicity

1. Introduction

The present-day crustal deformation of the south-

eastern Iberian margin, which includes the Iberian

Peninsula and adjacent offshore Mediterranean region,

is driven mainly by the NW–SE convergence (4–5 mm/

yr) between the African and Eurasian plates [1,2] (Fig.

1). This convergence is accommodated over a wide

deformation zone with significant seismic activity

south of the Iberian Peninsula [4,12,13]. Seismicity is

mainly characterised by low to moderate magnitude

events. Nevertheless, large destructive earthquakes

(MSK Intensity IX–X) have occurred in the region, as

has been revealed by historical records [8,14] (Fig. 1).

This may pose significant earthquake and tsunami

hazards to the coasts of Spain and North Africa.

The Neogene and Quaternary faulting activity in the

southeastern Iberian Margin is dominated by a large

left-lateral strike-slip system of sigmoid geometry re-

ferred to as the Eastern Betic Shear Zone (EBSZ)

[15,16]. The active fault system stretches over more

than 450 km from Alacant to Almerıa, and includes,

from north to south, the Carrascoy, Bajo Segura,

Alhama de Murcia, Palomares and Carboneras faults

[e.g. 15,17]. The Carboneras Fault and terminal splays

of the EBSZ extend further into the Almerıa margin in

the Alboran Sea [e.g. 18–20], towards the area where

the submarine epicentres of the historically recorded

earthquakes of Almerıa (1522), Dalıas (1804), and

Adra (1910) are located [8,9,21] (Fig. 1). Despite the

potential contribution of the Carboneras Fault zone to

the earthquake and tsunami hazard, little is known of its

detailed shallow structure and geometry offshore.

In order to investigate the offshore prolongation of

the Carboneras Fault and associated seismogenic struc-

tures, we carried out a high-resolution marine

geophysical survey of the Almerıa Margin in the NE

Alboran Sea (Fig. 1). The main objectives of this study

are 1) to image and characterise the seafloor geomor-

phology and the geometry of active tectonic structures

identified offshore Almerıa (Spain), such as the sub-

marine continuation of the Carboneras Fault zone; 2) to

study how these structures affect the present-day phys-

iography of the Almerıa Margin, such as the drainage

system of the Almerıa Canyon; 3) to investigate how

they accommodate the present-day strain regime along

the Eurasian-African plate convergence; and 4) to high-

light the relevance of the Carboneras Fault to seismic

hazard assessment of south Iberia, bearing in mind that

high magnitude earthquakes with long recurrence inter-

vals (104 years) have been documented in the EBSZ

[11].

2. Geological and geodynamical setting of the

southeastern Iberian Margin

The Betic and Rif Cordilleras linked by the Gibraltar

Arc constitutes the westernmost end of the Mediterra-

nean Alpine ranges at the boundary between the Afri-

can and European plates (Fig. 1). The Betic Cordillera

is an ENE–WSW–trending fold-and-thrust belt com-

posed of the External Zone, Mesozoic to Tertiary

rocks corresponding to the Iberian Plate paleomargin,

sedimented on top of the Variscan basement, and the

Internal Zone (or Alboran domain), consisting of a

thrust stack of metamorphic complexes (Fig. 1) [e.g.

16,22. Superimposed onto the previous structure, Neo-

gene to Quaternary sediments fill the intramontane

basins, limited by E–W and NE–SW faults [23]. Middle

Miocene to Pleistocene calc-alkaline through K-rich

volcanic rocks crop out in the Cabo de Gata area and

also in submarine structures, such as the Alboran Ridge

[24] (Fig. 1).

Active deformation in the southeastern Iberian Mar-

gin is revealed by earthquake mechanisms derived from

moment tensor inversion, covering both onshore and

offshore regions [4–7] (Fig. 1). In the central Betics and

southern Spain, focal mechanisms are heterogeneous

and faulting style ranges from normal to reverse, where-

as along the EBSZ and Alboran Sea, strike-slip faulting

dominates [6] as corroborated by geological and geo-

physical data [11,15,17–19,25,26] (Fig. 1). Regional

seismicity in the Ibero-Maghrebian region is diffuse

and does not clearly delineate the present-day Europe-

an-African plate boundary [4,13]. In the southeastern

Iberian Margin, instrumental seismicity is characterized

by continuous, shallow seismic events of low to mod-

erate magnitude (Mwb5.5) [4,6,8].

Although large earthquakes (MSK IntensityNVIII)

are relatively infrequent, they have occurred in the

Fig. 1. Regional bathymetric map of the southeastern Iberian Margin (contour interval: 200 m) constructed from the predicted bathymetry of [3].

Fault plane solutions of small to moderate earthquakes are from [4–7]. The largest historical earthquakes (MSK IntensityN IX) that occurred in the

region are located and depicted by a white star [8]. Location and moment tensor solution obtained for the 1910 Adra Earthquake (mechanism plotted

in gray) is based on [9]. Oppositely pointing grey arrows show the direction of convergence between the Eurasian and African plates from NUVEL1

model [1,2]. Geological domains of the eastern Betic Cordillera with the main Neogene faults are summarized from [10,11]. Indicated fault

movements correspond to late Neogene. CRF: Crevillente Fault, AMF: Alhama de Murcia Fault, PF: Palomares Fault, CAFZ: Corredor de las

Alpujarras Fault Zone, CF: Carboneras Fault. The black outlined rectangle depicts the study area corresponding to Fig. 2. Inset: Plate tectonic

setting and main geodynamic domains of the south Iberian Margin along the boundary between the Eurasian and African Plates. The black outlined

rectangle corresponds to the area depicted in this figure.

E. Gracia et al. / Earth and Planetary Science Letters 241 (2006) 734–749736

region [8,11,21]. Historical and archaeological records

of events suggest that this region has been affected by

at least 50 destructive earthquakes over the past 2,000

years, providing evidence of a significant seismic haz-

ard [21]. The town of Almerıa was devastated by earth-

quakes in 1487, 1522 (IX MSK), 1658 (VIII MSK), and

1804 (IX MSK), and Vera was destroyed in 1518 (IX

MSK) and 1863 (VII MSK) [4,8,21] (Fig. 1). These

events have been attributed to motion along the Carbo-

neras and Palomares fault systems [27]. On the other

hand, the 1910 Adra Earthquake (Mw=6.1, MSK

I0=VIII in Adra) occurred offshore (Fig. 1) probably

generated by N120–N130 trending faults consistent

with moment tensor calculations [9].


At a regional scale, the Carboneras Fault system is

straight and continuous: its northern end links with the

NS trending Palomares Fault [15,17,18,27,28], and its

southern end, to the east of the town of Almerıa and near

Cabo de Gata, enters the Mediterranean Sea [15,18,20]

(Fig. 1). The Carboneras Fault is probably the largest

brittle structure in the EBSZ, and it could link with other

faults to form the Trans-Alboran Shear Zone, connecting

the Betics with the North African Rif [18]. The exposed

portion of the Carboneras Fault zone is about 50 km long

with a width ranging from 1.4 to 2.5 km [27,29]. Three

main segments (northern, central, and southern) have

been distinguished along the Carboneras Fault on land

based on relationships between geomorphic and tectonic

features [30]. Paleostress analysis indicates that the Car-

boneras Fault has been affected by a rotation in the

maximum horizontal stress direction from NW–SE to

N–S, which took place at the end of the Miocene [31].

Keller et al. [27] suggested that since the Burdigalian,

left-lateral strike-slip motion has been in the range of 30–

40 km and vertical offset in the range of 5–6 km.

The study area is located in the Adra-Almerıa Mar-

gin, comprising the offshore continuation of the Carbo-

neras Fault and associated structures to the NE Alboran

Sea (Fig. 1). The Almerıa continental shelf is narrow

(4–6 km) along much of this margin. Its main geomor-

phologic features have been recently revealed by swath-

mapping in the frame of the Program of Spanish Con-

tinental Shelf Cartography (ESPACE) [32]. This margin

is characterised by deeply incised canyons with a com-

plex pattern of tributary valley systems [33]. The

Almerıa Canyon drains from the shelf edge to the

deep-sea fan deposits in the Alboran Basin, which

exceeds 2000 m in depth [34,35]. The lowermost part

of the Almerıa Canyon was insonified using the MAK-

1 sidescan sonar system disclosing individual elements

of its channel morphology [36]. The Plio-Quaternary

sedimentary architecture of the NE Alboran Sea, based

on sparse single-channel seismic profiles, shows a cy-

clic pattern of deposition with alternating terrigenous

input into the basin related to sea-level oscillations

[34,35]. Deep multichannel seismic reflection data to-

gether with commercial wells and ocean drilling

revealed the regional tectonic-sedimentary evolution

and crustal structure of the margin and the eastern

Alboran Basin [19,20,26,37–39].

3. Data and methods: The HITS cruise

The present study results from an integration of dif-

ferent types of data: deep-towed sidescan sonar back-

scatter, swath-bathymetry, and high-resolution seismic

profiling, acquired during the HITS cruise (bHigh Res-

olution Imaging of Tsunamigenic Structures of the

Southern Iberian MarginsQ) on board the Spanish RV

Hesperides (Fig. 2). High-resolution sidescan sonar data

were collected using the Towed Ocean Bottom Instru-

ment (TOBI) [40] from the National Oceanography Cen-

tre, Southampton (UK) as part of the programme

European Access to Seafloor Survey Systems (EASSS

III). The TOBI sidescan survey consisted of six parallel

tracks, 6-km wide swath insonifying most of the area

bounded by latitude 36817V–36840VN and longitude

3805V–2810VW (Fig. 2b). The acoustic response (intensi-

ty of the backscattered signal) depends on the incidence

angle, roughness/topography and on the nature of the

seafloor. Reflective surfaces, such as high relief areas,

rock outcrops and landslides are depicted as light-grey to

white, whereas less reflective surfaces, such as low-relief

and fine-sediment covered areas, are dark-grey. Acoustic

shadows are black. The TOBI sidescan data, with an

along-track resolution of 6 m [40] enabled us to recog-

nise the seafloor superficial features in detail.

The swath-bathymetric data were collected by using

the Simrad EM12-S multibeam system covering an area

of about 35�100 km (Fig. 2a). Data gaps have been

filled using the Simrad EM300 bathymetric grid ac-

quired by the bInstituto Espanol de OceanografıaQ forthe Spanish Fisheries Office. Water depth ranges from

80–100 m at the top of the banks and shelf break down to

more than 1800m at the base of the slope. Simultaneous-

ly acquired and amounting to about 450 km of profiles,

high-resolution (1–5.5 kHz) Simrad TOPAS (TOpo-

graphic PArametric Sonar) seismic profiler provides de-

tailed stratigraphic information on the uppermost tens of

metres below the seafloor (50 to 80 m at an assumed

sediment velocity of 1.5 km/s). These data provide new

insights into the control of neotectonic structures over

the Plio-Quaternary sedimentary architecture of the mar-

gin. The seismic units recognised in the high-resolution

profiles correspond to Quaternary-age sediments based

on correlation with oil exploration wells and single-

channel seismic reflection profiles of the Almerıa Mar-

gin [19,20,35,36]. Similar high-resolution methodolo-

gies proved to be useful in exploring submarine

earthquake geology in other active areas along the Eur-

asian-African plate boundary, such as the Marmara Sea

[41] and the southwestern Iberian Margin [42].

4. Results

The main morphostructural elements of the Almerıa

Margin are identified in Fig. 2a. They correspond to 1)

the Almerıa Canyon and Channel, a meandering turbi-

Fig. 2. (a) Colour shaded relief bathymetric map of the Almerıa Margin surveyed during the HITS 2001 cruise on board the RV Hesperides. Contour

interval is 50 m. Main morphostructural features are identified. (b) High-resolution TOBI sidescan sonar of the same area. The white outlined boxes

depict the areas presented in Figs. 3a and 4a.


dite system confined between large topographic highs,

2) a dense tributary valley network, 3) a N045–N060

prominent lineation, which corresponds to the subma-

rine continuation of the Carboneras Fault, and 4) the

Cabo de Gata, Sabinar, and Chella Banks.

4.1. The Almerıa Canyon and Channel

A high-resolution map of the northern part of the

Almerıa Canyon is illustrated in the TOBI image (Fig.

3a). The northern Almerıa Canyon is more than 3 km

wide (talweg width of 380 m) and shows abrupt west

flanks (up to 300 m high), well developed meanders

and terraces (Fig. 3a). Some portions along its path

show high reflectivity, probably due to the presence

of coarse-grained talweg deposits. The net direction of

the Almerıa Canyon is roughly parallel to the subma-

rine continuation of the Carboneras Fault, located fur-

ther west (Fig. 3a). To the west and to the east of the

Almerıa Canyon there is a network of tributaries,

Fig. 3. (a) TOBI sidescan sonograph of the northern part of the Carboneras Fault zone and Almerıa Canyon. The canyon talweg deepens from 550 to 1050 m from the top to the bottom of the image,

with a mean slope of 2% and sinuosity of 1.51. Thick dashed line depicts location of (b). TVS: Tributary Valley System. (b) High-resolution seismic profile TA6 across the northern part of the

Almerıa Canyon and Carboneras Fault. Vertical scale in m is calculated by applying a velocity of sound propagation in water of 1500 m/s. Vertical exaggeration ~40.

E.Gracia

etal./Earth

andPlaneta

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ceLetters

241(2006)734–749

739


corresponding to the Dalıas and Gata Tributary Valley

Systems [33], respectively. The denser Dalıas Tribu-

tary Valley System is composed of tens of linear

gullies and channels, which depart from the shelf

edge, mostly following the straight-line slope of the

margin, trending N150 to N170. At their intersection

with the Carboneras Fault lineation, the tributaries

show abrupt changes in stream direction (e.g. gullies

A to D, Fig. 3a).

A high-resolution seismic profile crossing the

northern part of the TOBI image illustrates the shallow

structure and architecture of the upper stratigraphic

units (Fig. 3b). To the west, the Dalıas Tributary

Valley System depicts channel-levee systems and

gullies showing different degrees of incision, ranging

from a few metres to 45 m deep. The profile shows a

gentle upwarp which is bounded to the west by the

Carboneras Fault. It also shows how the Carboneras

Fault cuts and folds the sedimentary succession up to

the most recent units. A thick (~18 m) mass-wasting

deposit characterised by chaotic seismic facies is lo-

cated at the base of the surface break, and is thinly

Fig. 4. (a) TOBI sidescan sonograph of the southern part of the Almerıa C

Canyon, the talweg deepens from 1030 to 1220 m with a gentle slope of 1.8%

sinuosity of 1.95, with the talweg deepening from 1220 m to more than 1630

dashed lines depict the locations of (b) and (c). (b) High-resolution seismic p

is imaged. C-L: Channel-levee system. (c) High-resolution seismic profile

applying a velocity of sound propagation in water of 1500 m/s. Vertical ex

draped by the uppermost sedimentary units (Fig. 3b).

To the east are the northern Almerıa Canyon and the

Gata Tributary Valley System, depicting well stratified

reflectors incised by channel-levee complexes.

The southern part of the Almerıa Canyon runs from

36831V to 36826.5VN, as revealed by the TOBI sidescan

sonar mosaic and the swath-bathymetric map (Figs. 2a

and 4a). The southern Almerıa Canyon is narrower

(average width of 1.5 km) and rectilinear, showing a

net N038 trend. Several terraces are identified on the

western flank of the canyon. The lower part of the

Dalıas Tributary Valley System drains into the southern

Almerıa Canyon, where some sections of the gullies are

rectilinear, developed along N150 trending lineations

(Fig. 4a). One of these lineations is visible at depth on a

high-resolution seismic profile crossing the southern

part of the Almerıa Canyon (Fig. 4b). The lineation

corresponds to a transparent-facies high-angle zone

which separates areas where the stratified units show

contrasting thicknesses, dipping attitudes and local an-

gular relationships. This lineation is interpreted as a

NE-dipping normal fault which deforms the whole

anyon and the Almerıa Channel. In the southern part of the Almerıa

, yielding a low sinuosity of 1.05. The Almerıa Channel shows a high

m and an average slope of 3.8%. TVS: Tributary Valley System. Thick

rofile TA3 across the Almerıa Canyon, where the ~N150 trending fault

TA1 across the Almerıa Channel. Vertical scale in m is calculated by

aggeration ~40.


sedimentary succession up to the surface, favouring the

development of a rectilinear channel of the Dalıas

Tributary Valley System (Fig. 4b). The prolongation

of this fault towards the southeast reaches the Almerıa

Canyon, and probably facilitates the sharp and straight

morphology of one of its meanders. The faults striking

N150, where Dalıas Tributary Valley System gullies

develop, are designated by the general term of bN150faultsQ (Figs. 3a and 4a).

The Almerıa Channel is the tight meandering agra-

dational channel-levee turbidite system [34–36] located

downstream from the canyon, characterised by a rela-

tively high acoustic backscatter (Fig. 4a). The new full

coverage high-resolution dataset reveals the following

features. Four large abandoned meanders are observed

on the eastern flank of the channel, while narrow

terraces and outside meander furrows are identified on

its western flank (Fig. 4a). South of 36822VN, the

Almerıa Channel changes orientation from a general

NS to N120 trend and varies in sinuosity, general

morphology and infill (Fig. 4a). Towards the lower

part of the image, the channel narrows, is less deeply

incised, and shows an asymmetric transverse profile,

with higher levees on its western flank (Fig. 4b, c).

Incised into well-stratified, non-disturbed sedimentary

units, chaotic facies at the axis of the channel are

interpreted as the effect of coarse-grained bedload

(Fig. 4b). At the eastern end of the profile, transparent

irregular deposits overlie the stratified units of the

Almerıa Channel, corresponding to a landslide deposit

sourced southwest of the Sabinar Bank (Fig. 4c).

4.2. The Carboneras Fault zone

The swath-bathymetric data allow us to identify a

more than 70 km long and 5 km wide lineation striking

N045–N060, which corresponds to the surface expres-

sion of the Carboneras Fault (Figs. 2a and 5a). We

distinguish two main segments along the lineation:

the northern (33 km long, N045-trending), and the

southern (26 km long, N060-trending). Between these

two segments of the Carboneras Fault there is an area of

complex morphology formed by a narrow (b1 km)

slightly up-slope concave arcuate ridge (referred to as

ridge AR) which defines an elongated depression to the

northwest and is flanked by an abrupt escarpment to the

southeast (Figs. 2a and 5b profile TA3).

North of 36836VN, the northern segment of the

Carboneras Fault is rectilinear showing a NW-facing

escarpment evidenced by the sharp backscatter contrast

on the TOBI sonograph, up to 10 m high (Fig. 3a).

From 36836V to 36831VN, the Carboneras Fault inter-

sects the Dalıas Tributary Valley System producing a

sharp deflection of its channels and gullies (Figs. 2, 3a

and 5a). For instance, Gully D is deflected towards the

southwest at the Carboneras Fault and follows this

lineation for more than 2 km (Fig. 3a). Then, it

bends sharply at a right-angle towards the southeast

following, for more than 4 km, the superficial trace of a

N150 high-angle fault. Similar geometries and trends

are displayed by gullies A, B and C (Fig. 3a). The

southern segment of the Carboneras Fault shows a step-

like morphology to the west (Fig. 5b, profile TA1),

which gradually passes to a subdued irregular ridge to

the east (referred to as ridge SR, profile TA2 in Fig.

5b). East of ridge SR, the seafloor shows a series of

10–15 km long and ~6 km wide undulations consis-

tently trending N120–130 (Fig. 5a). Based on the

TOPAS seismic profiles (Fig. 5b), these are interpreted

as widely spaced folds affecting the sedimentary suc-

cession (Fig. 6).

The succession of six high-resolution seismic pro-

files across the Carboneras Fault lineation, from the

shelf to the base of slope, illustrates how its shallow

structure varies along-strike (Fig. 5b). Near the shelf

area, well stratified units are folded and cut by subver-

tical faults which separate blocks of different stratigra-

phy and structure forming a positive flower structure

(Fig. 5b, profile BA8). In the area intersecting the

Dalıas Tributary Valley System, the distinction of faults

is less clear-cut owing to the gully and channel inci-

sions which mask the structure at depth. However, the

general geometry of the Carboneras Fault zone also

coincides with a seafloor upwarp (Fig. 5b, profiles

TA4 and TA5). Profile TA3 crosses ridge AR where

stratified units are folded in anticline which we interpret

as a pressure ridge. To the west, a small basin is

underlain by a gently folded thick stratified succession.

This basin is separated from ridge AR by tightly spaced

high-angle faults, some of which appear to be reverse

(Fig. 5b, profile TA3). East of ridge AR, a 30 m high

escarpment coinciding at depth with a high-angle fault

limits with gently folded strata. Towards the base of the

slope, profiles TA2 and TA1 also show folded elevated

areas limited by subvertical discontinuities interpreted

as faults (Fig. 5b).

4.3. The Chella and Sabinar banks

Prominent highs, such as the Chella, Sabinar, Pollux

and Cabo de Gata spur dominate the physiography of

the margin (Figs. 2 and 5a). They are composed of a

Neogene volcanic basement topped by carbonate plat-

forms [19,24]. The banks, shallowing up to 80 m, are

Fig. 5. (a) Slope map overlain on top of the 3D swath-bathymetry data of the Carboneras Fault zone, view from the southwest. The white thick lines

depict location of profiles (BA8 to TA8) presented on (b). (b) Succession of high-resolution seismic profiles across the Carboneras Fault zone, from

the shelf to the base of the slope depicting along-strike morphostructural variability. AR: arcuate elevated ridge, SR: subdued ridge. Vertical scale in

m is calculated by applying a velocity of sound propagation in water of 1500 m/s. Vertical exaggeration ~40, except for profile BA8, which is ~55.


Fig. 6. Structural synthesis of the offshore Carboneras Fault zone with the main segments and associated structures identified, overlying a 10 m

contour bathymetric map. See text for explanation.


tens of kilometres in diametre and several hundred

metres higher than their surroundings, and are easily

identified on the TOBI sidescan image as very high

reflectivity areas (Fig. 2b). On the Chella Bank, the

circular shape of the old-volcanic edifice is distinguish-

able (Fig. 2). Moats mainly developed on the eastern

flank of the Chella Bank and the northern flank of

Sabinar provide evidence of contour currents. Of espe-

cial interest is the presence of deeply carved scars to the

south of the Sabinar and Pollux banks, suggesting

dismantlement of the margin by large and complex

mass movements (Fig. 5a). The scars, up to 200 m of

headscarp height, cover an area of about 20 km2 with

run out distances of more than 10 km. Steep slopes (up

to 25%, Fig. 5a) and friable lithologies of the volcanic

edifices may favour large mass movements along this

part of the margin. Localized individual slide lobes are

observed on the western flank of the Sabinar Bank and

on the southern flank of the Chella Bank. To the west of

the Chella Bank we identify several NS morphological

ruptures on the seafloor, showing prominent normal

fault scarps, based on swath-bathymetry and high-res-

olution seismic profiles (Fig. 5a).

5. Discussion

5.1. Interplay between submarine channels and faults:

Control on the sedimentary architecture of the Almerıa

Margin

According to the bathymetric and high-resolution

seismic data, the superficial expression of the Carbo-

neras Fault zone mainly consists of an upwarped nar-

row area, bounded by subvertical faults at depth. The

elevation of the seafloor associated with this structure is

responsible for the deflection of the Dalıas Tributary

Valley System. Deflections to the southwest are inter-

preted as the result of drainage-blocking produced by

the Carboneras Fault seafloor upwarps, which act as

shutter ridges (see Section 4.1, Fig. 6). As pointed out

by [43], the deflection of streams should be approached

with caution when determining the direction of lateral

displacement along directional faults. Despite the mis-

leading impression of dextral fault bbayonetsQ (offset

drainage), the consistent deflections to the southwest

should be interpreted as resulting from the relationship

between the direction of the Carboneras Fault drainage-


blocking and the general slope of the margin. Along the

Carboneras Fault lineation, water gaps, the place where

drainage cuts through strike-slip faults between shutter

ridges [44], allow deflection of the gullies to the south-

east. In this case, the mode of deflection is conditioned

not only by the general slope of the margin but, in some

cases, by the structural depressions coinciding with

faults trending N150, which locally constitute prefer-

ential paths for the submarine drainage (Figs. 3a and 6).

Gullies and channels of the Dalıas Tributary Valley

System in the northern part of the Almerıa Canyon are

seafloor features present throughout the sedimentary

succession on high-resolution seismic profiles. They

maintain their morphology and position over time,

suggesting that these tributary valley systems are stable

features at least during the Quaternary, and that no

lateral migration of the submarine drainage network

is produced where the general slope conditions are

maintained.

5.2. Structural model of the Carboneras Fault zone in

the Alboran Sea: Evidence for strike-slip displacement

There are several lines of evidence supporting that

the submerged portion of the Carboneras Fault de-

scribed here is a strike-slip fault. Swath-bathymetry

and high-resolution seismic profiles show a consider-

able variation in the three-dimensional structural geom-

etry along the strike of the fault (Fig. 5), analogous to

those that have been documented in strike-slip faults

exposed on land [44]. For instance, the submarine

Carboneras Fault displays several geomorphological

characteristics, such as systematically deflected gullies,

shutter ridges, water gaps and incised channels parallel

to the main structure (Fig. 6). The shallow structure of

the Carboneras Fault consists of a series of upward-

splaying subvertical faults defining positive flower

structures in cross section (Fig. 5b), as previously in-

ferred by [20,35]. These high-angle faults probably

coalesce at greater depths and constitute part of a single

large-scale directional fault zone 5 to 10 km wide. This

is a typical geometry found in the shallow structure of

large strike-slip systems [44].

In agreement with evidence found onland [e.g.

15,27,29,30], there are structures which may indicate

that the submarine Carboneras Fault is a strike-slip fault

with a sinistral sense of motion (Fig. 6). Firstly, the

series of widely spaced obliquely trending folds

(N120–N130) observed in the southern segment are

compatible with the structural geometries predicted

under left-lateral shear deformation. Secondly, ridges

AR and SR show a series of undulations with ben

echelonQ arrangement observable in the 10-m contour

bathymetric map (Fig. 6). These elevated and folded

areas correspond to pressure ridges: Ridge AR is

formed at an underlapping restraining stepover between

the southern N060 and northern N045 segments of the

Carboneras Fault, whereas ridge SR is placed in an

overlapping restraining stepover. Both structures

(Ridges AR and SR) reveal a geometrical pattern in

agreement with a left-lateral strike-slip component on

the Carboneras Fault.

It is possible to find elongated hills along pure

strike-slip faults depending on the lateral displacement

of topographic features [44]. Nevertheless, in the case

of the Carboneras Fault, when the general slope of the

margin and the left-lateral movement along strike are

considered, it is not possible to attribute the blocking

and deflection of the Dalıas Tributary Valley System

drainage to pure sinistral strike-slip deformation. This

would bring deeper portions of the margin across the

fault, thereby locally increasing the slope, which would

be inconsistent with the observed drainage-blocking.

This is our explanation for suggesting that the Carbo-

neras Fault is also affected by a vertical slip component,

as has been pointed out for the onland segments by

[21,30].

Along the strike of the Carboneras Fault, we identify

changes in the dip direction of the fault escarpment,

which produces variations in the relative upthrown and

downthrown blocks (Figs. 5b and 6). Thus, along the

northern segment, the fault escarpment faces towards

the NW, opposite to the general gradient of the margin

but following the same arrangement of uplifted blocks

as the Carboneras Fault on land and on the continental

shelf (Fig. 7). In contrast, along ridge AR and the

southern segment, the main fault escarpment faces to

the SE, increasing the margin slope (Fig. 5b). This

arrangement suggests a bscissorsQ structure [44] illus-

trated in map view in Fig. 6. However, the distinction in

the sense of throw between normal and reverse vertical

components together with the detailed structure of the

Carboneras Fault at depth can only be resolved by using

deeper penetration seismic reflection systems.

5.3. The Carboneras Fault zone in the context of the

Eurasia-Africa plate convergence

Deformation associated with Eurasia-African plate

convergence in the Alboran Region is distributed over a

broad area encompassing the EBSZ, Betics, Alboran

Ridge, Moroccan Rif and Tell-Atlas in Northern

Algeria [4,12,13]. The convergence rate estimated by

[1,2] is about 4–5 mm/yr following a NW–SE direction.

Fig. 7. Interpretative structural map of the southeastern Iberian Margin based on the results from the HITS 2001 high-resolution acoustic data. Trace

of the Carboneras Fault on the shelf based on [32]. Faults are depicted as thick black lines, summarized from [11,17,20,25, and this work]. PF:

Palomares Fault; CAFZ: Corredor de las Alpujarras Fault Zone; CF: Carboneras Fault. Seismicity from the bInstituto Geografico NacionalQcatalogue for the period between 1970 and 2000 is depicted [8]. Smaller dots are epicentres of earthquakes for 2.5bmbb3.5, and larger dots are

epicentres of earthquakes for mbN3.5. The thick black outlined rectangle depicts the study area.


Recently published geodetic models based on GPS

velocities from the western Mediterranean [45,46] pre-

dicted a relatively slower (2.5 to 5 mm/yr) and more

oblique motion (208 counter-clockwise rotation in the

direction of convergence) of the present-day African

and Eurasian plates [45].

The new data presented show that the submarine

portion of the Carboneras Fault and associated faults

are active given that they affect all the sedimentary

sequences, cutting and folding the upper and recent

units, which according to [20,35] are of Late Holocene

age. Studies along the Carboneras Fault onland indicate

5–10 m of vertical offset across Tyrrhenian marine

terraces with no evidence of large lateral offset [30].

The central onland segment, known as La Serrata,

consists of two main parallel fault traces bounding a

1 km wide horst (Fig. 7), where stream-channels older

than 100 kyr are left-laterally offset by 80–100 m [30].

These authors suggest that the slip history of the onland

Carboneras Fault during the last 100 kyr appears to be

one of vertical uplift rather than strike-slip movement,

with maximum vertical slip rates in the order of 0.05–

0.1 mm/yr [30]. In contrast, based on neotectonic mod-

elling, the onland Carboneras Fault zone might accom-

modate about 0.7 mm/yr of sinistral strike-slip motion

[47,48]. Our findings on the submarine segments of the

Carboneras Fault do not disagree with the above sug-

gestions. However, the lack of reliable chronological

markers prevents us from estimating the vertical and

strike-slip rate components.

A local shortening along an approximate NNW–SSE

axis is suggested by the regional stress field derived

from earthquake focal mechanisms inversions in the

Alboran Sea and southeast Spain [6,7]. This direction

also coincides with the most compressive horizontal

stress orientation and regime predicted by neotectonic


modelling based on thin-sheet finite element [47,48].

Considering the NNW–SSE shortening axis, we can

assume the strain regime of the newly identified struc-

tures: the Carboneras Fault may have a left-lateral

component, the N150 faults would move as right-later-

al, and the NS faults located to the west of the Chella

Bank would have a predominantly normal component

(Fig. 6). The geometrical relationship between the left-

lateral Carboneras Fault and the N150 to NS normal

faults identified in the area is compatible with the

model of block tectonics presented by [25] to explain

the neotectonic structures of the southern Almerıa prov-

ince. In their model, predominantly extensional struc-

tures (such as the NS and N150 faults) accommodate

the deformation produced by squeezing the wedge

located between the dextral strike-slip Corredor de las

Alpujarras and sinistral Carboneras fault zones (Fig. 7).

The combined movements of these large strike-slip

fault zones would induce a westward tectonic escape

[25].

Moment tensor solutions for small and moderate

earthquakes in the Alboran Sea show a predominant

left-lateral strike-slip motion. They mainly correspond

to the Alboran Ridge series of 2003, which follow a

N055 nodal plane [6,7] (Fig. 1). Focal mechanisms and

epicentre locations also indicate that the newly identi-

fied structures to the south of Adra and Campo de

Dalıas (i.e. N150, NS faults) are active and consistent

with the present-day extensional strain pattern of this

area [6,21,25,48] (Figs. 1 and 7).

The Carboneras Fault zone corresponds to the trans-

pressional southern end of the EBSZ. The new marine

geophysical data reveal that the morphological expres-

sion of the Carboneras Fault zone terminates against a

topographic high at 36817.3VN–3803.5VW on the

Alboran Sea (Figs. 5 and 6). This suggests that, in

contrast to previous works [e.g. 18], the Carboneras

Fault may not extend as a large continuous fault zone

connecting the Eastern Betics with the Jebha and

Nekor Faults in the North-African coast, calling into

question the bTrans-Alboran Shear ZoneQ. Instead, wepropose that strain along the offshore Carboneras Fault

zone is transferred to the parallel structure located

about 20 km to the south, which flanks the Alboran

Trough (Figs. 1 and 7).

5.4. Seismicity and active faulting offshore Almerıa

region: Implications for seismic hazard assessment in

the Southern Iberian Margin

Present day seismicity in the southeastern Iberian

Margin shows swarms of small to moderate magnitude

(Mwb5) shallow earthquakes [49] which are more con-

centrated to the north and east of the Chella Bank (Fig.

7). This seismicity seems to be associated with the

secondary N150 to NS faults, suggesting moderate

faulting in the region. Based on epicentre relocation,

these structures also seem to be the source of the

shallow (4.8 to 6.5 km) and moderate (Mw 4.8 to 5.1)

Adra earthquake swarms, the most intense earthquake

activity recorded recently in this region, which occurred

between December 1993 and January 1994 [25,49].

Slope instability features (landslide headscarps, de-

tached blocks, and debris flow deposits), which are

present on the bank flanks, could also be associated

with seismic and paleoseismic activity of this margin.

The unstable nature of the volcanic edifices together

with the moderate magnitude seismic activity recorded

in the area could account for the triggering of subma-

rine landslides observed on the banks, especially the

steep southern flanks of the Sabinar and Pollux Banks

(Figs. 5–7).

As regards the Carboneras Fault zone (onshore and

offshore), only few epicentres are placed along its trace.

However, this does not mean that little seismological

hazard should be attributed to the Carboneras Fault. For

instance, the location of the Almerıa (MSK intensi-

tyN IX) and Adra (MSK intensityNVIII and Mw=6.1

[49]) historical events (Fig. 1) fall relatively close

(considering location uncertainties) to the submerged

trace of the Carboneras Fault as mapped in the present

study (Fig. 7). This suggests that the Carboneras Fault

is a possible source of these events, especially the 1522

Almerıa Earthquake and Tsunami (?). Considering that

tsunamis are not expected from pure strike-slip motion,

the occurrence of a tsunami in 1522 [8] may indicate a

large landslide, but possibly also, a dip-slip component

on the submarine portion of the Carboneras fault, in line

with our interpretations. Calculation of the relationship

between magnitude and intensity for the most important

historical earthquakes in the Ibero-Maghrebian region

assigns a magnitudemb 5.8–6.0 to the 1522 Almerıa

Earthquake [50].

In addition, a detailed macro- and micro-structural

analysis of clay-bearing fault-gouges in the northern

segment of the Carboneras Fault yields some insight

into its mechanical seismic behaviour [29,51]. It shows

a wide heterogeneous deformation zone with low per-

meability layers in the fault gouge, containing lenses of

fractured permeable rocks that may trigger large peri-

odic seismic events against a background of fault creep

in the surrounding materials [29]. The onland Carbo-

neras Fault has been suggested as an analogue for the

San Andreas Fault around Parkfield (California), where


geophysical observations of the fault suggest a large

zone (1–2 km) of deformation with fault creep and

Mw=6.0 recurrent earthquakes [29].

The Carboneras Fault zone is by far the longest,

continuous fault mapped in the southeastern Iberian

margin (50 km onshore, plus more than 100 km

offshore) (Fig. 7) and, therefore, it would be the

best candidate to generate large magnitude earth-

quakes. For instance, assuming a surface rupture

length of 70 km following a ~N045 trend (this

would include the assumed bnon-gougedQ southern

segment onshore, the shelf, and the northern offshore

segment of the Carboneras Fault, Fig. 7) and using the

empirical relationships of [52], a moment magnitude

of ~7.2 is obtained. The southeastern Iberian Margin

corresponds to the most seismically active and haz-

ardous Spanish region. It is considered to have a

moderate seismic hazard, between 0.8 and 1.6 m/s2

mean peak ground acceleration for a return period of

475 year, i.e., with 10% probability of exceedance in

50 years [53]. This correlates well with the values

obtained in a recent probabilistic seismic hazard as-

sessment in terms of Arias intensity for different soil

conditions in southeast Spain [54]. However, as these

models are mainly based on instrumental and histori-

cal earthquake catalogues, a reevaluation of the previ-

ously calculated seismic and tsunami hazard in the

region taking into account the offshore segments of

the Carboneras Fault could significantly increase the

suggested hazard.

Finally, a paleoseismic approach is required to pro-

vide an assessment of the seismic hazard associated

with the Carboneras Fault, especially when considering

high magnitude earthquakes and probably long recur-

rence intervals (104 years) [11,55]. Future work on the

Carboneras Fault will be devoted to the imaging of

deep structure and to the identification and dating of

geological markers of the fault offshore, and to geo-

physical surveying and trenching onshore. This will be

helpful in determining the past activity and seismic

parametres of the Carboneras Fault (geometry, slip

rate and recurrence interval).

6. Conclusions

1. New marine geophysical data (swath-bathymetry,

deep-towed sidescan sonar TOBI and high-resolu-

tion seismic data) from the Almerıa Margin show

that the superficial expression of the Carboneras

Fault consists of an upwarped 5–10 km wide defor-

mation zone. This is bounded by subvertical faults at

depth that trend N045 to N060 and extend for more

than 100 km. The drainage system of the margin is

deflected by the Carboneras Fault upwarp, and is

locally conditioned by secondary structures trending

N150.

2. The submarine Carboneras Fault displays geomor-

phic features and tectonic structures usually found

on strike-slip faults onland, such as deflected drain-

age, shutter ridges, water gaps, pressure ridges and

positive flower structures. A narrow underlapping

restraining stepover separates the 33 km long north-

ern segment trending N045 from the 26 km southern

segment trending N060. Obliquely trending folds

(N120–N130) and ben echelonQ pressure ridges sug-gest a left-lateral shear deformation along the Car-

boneras Fault. In addition, drainage blocking

produced by the northern segment of submarine

Carboneras Fault indicates a vertical slip component.

3. The submarine portion of the Carboneras Fault and

associated faults cut and fold the most recent sedi-

mentary units of Late Holocene age, showing that

they are active structures. Considering the NNW-

SSE shortening axis, the Carboneras Fault may

have a left-lateral component, the N150 faults

would move as right-lateral, and the NS faults,

located to the west of the Chella Bank would have

a predominantly normal component. These struc-

tures are consistent with the model of block tectonics

suggested by [25]. The morphological expression of

the Carboneras Fault zone ends in a structural high

in the Alboran Sea, in contradiction to the alleged

continuous fault zone connecting South Spain with

North Africa, known as the bTrans-Alboran Shear

ZoneQ.4. Present-day seismicity in the Almerıa margin shows

swarms of small to moderate magnitude shallow

earthquakes [49], which are more concentrated to

the north and east of the Chella Bank and may be

associated with the secondary N150 to NS faults.

This moderate seismicity may have triggered the

submarine landslides observed on the flanks of the

banks. The submerged portion of the Carboneras

Fault is at least twice as long as its subaerial portion.

The onshore and offshore segments together consti-

tute one of the longest faults in the southeastern

Iberian Margin. Despite the low instrumental seis-

micity along its trace, the Carboneras Fault is a

potential source of large (up to moment magnitude

~7.2) events such as the 1522 Almerıa Earthquake.

Seismic and tsunami hazard assessment for southeast

Iberia and African margins would significantly in-

crease if the offshore segments of the Carboneras

Fault were considered.


Acknowledgements

The authors acknowledge the support of the MCYT

Accion Especial HITS (REN2000-2150-E), European

Commission European Access of Seafloor Survey Sys-

tems EASSS-III programme (HPRI-CT99-0047), Span-

ish national Project IMPULS (REN2003-05996MAR),

ESF EuroMargins WESTMED project (01-LEG-

EMA22F and Accion Especial REN2002-11230E-

MAR), and funding by Generalitat de Catalunya, re-

search group SGR2001-0081. We thank the captain,

crew and technical staff on board the R/V Hesperides

and the TOBI Team from the National Oceanography

Centre (Southampton, UK) for their assistance through-

out the data collection. We also thank Juan Acosta

(IEO, Madrid) for providing us with supplementary

bathymetric data from the program bFisheries Cartog-

raphy of the Alboran SeaQ. We are indebted to Miquel

Canals (Univ. Barcelona) for valuable suggestions dur-

ing the preparation of the cruise and Tim Le Bas (NOC,

UK) for assisting two of us (O.G. and J.G.) during the

processing of TOBI data. We benefited from fruitful

discussions during the revision of this article with Ana

Negredo (UC, Madrid) and Daniel Stich (INGV, Bolo-

gna). The latter is also acknowledged for providing

focal mechanisms for Fig. 1. We wish to thank Milene

Cormier (LDEO, USA) and three anonymous reviewers

whose constructive criticism enabled us to improve our

original manuscript.

References

[1] D.F. Argus, R.G. Gordon, C. DeMets, S. Stein, Closure of

the Africa-Eurasia-North America plate motion circuit and

tectonics of the Gloria Fault, J. Geophys. Res. 94 (1989)

5585–5602.

[2] C. DeMets, R.G. Gordon, D.F. Argus, S. Stein, Current plate

motions, Geophys. J. Int. 28 (1990) 2121–2124.

[3] D.T. Sandwell, W.H.F. Smith, Gravity anomaly from Geosat

and ERS1 satellite altimetry, J. Geophys. Res. 102 (1997)

10039–10054.

[4] E. Buforn, C. Sanz de Galdeano, A. Udıas, Seismotectonics of

Ibero–Maghrebian region, Tectonophysics 248 (1995) 247–261.

[5] J. Mezcua, J. Rueda, Seismological evidence for a delamina-

tion process under the Alboran Sea, Geophys. J. Int. 129

(1997) F1–F8.

[6] D. Stich, C.J. Ammon, J. Morales, Moment tensor solutions for

small and moderate earthquakes in the Ibero–Maghreb region, J.

Geophys. Res. 108 (2003) 2148–2168.

[7] D. Stich, J. Morales, The IAG Regional Moment Tensor Project,

Instituto Andaluz de Geofısica, Granada (Spain), 2005, http://

www.ugr.es/iag/tensor.

[8] Instituto Geografico Nacional, Catalogo Sısmico Nacional

hasta el 2001, IGN, Madrid, Spain, 2001, http://www.geo.

ign.es/servidor/sismo/cnis/.

[9] D. Stich, J. Batllo, J. Morales, R. Macia, S. Dineva, Source

parameters of the Mw=6.1 1910 Adra earthquake (southern

Spain), Geophys. J. Int. 155 (2003) 539–546.

[10] C. Sanz de Galdeano, C. Lopez Casado, J. Delgado, M.A.

Peinado, Shallow seismicity and active faults in the Betic Cor-

dillera. A preliminary approach to seismic sources associated

with specific faults, Tectonophysics 248 (1995) 293–302.

[11] E. Masana, J.J. Martınez-Dıaz, J.L. Hernandez-Enrile, P. Santa-

nach, The Alhama de Murcia fault (SE Spain), a seismogenic

fault in a diffuse plate boundary: seismotectonic implications for

the Ibero–Magrebian region, J. Geophys. Res. 109 (2004) 1–17.

[12] N.L. Grimison, W.P. Chen, The Azores–Gibraltar plate bound-

ary: focal mechanisms, depths of earthquakes and their tectonic

implications, J. Geophys. Res. 91 (1986) 2029–2047.

[13] J.L. Morel, M. Meghraoui, Gorringe-Alboran-Tell tectonic zone:

a transpression system along the Africa-Eurasia plate boundary,

Geology 24 (1996) 755–758.

[14] C. Lopez Casado, C. Sanz de Galdeano, S. Molina Palacios, J.

Henares Romero, The structure of the Alboran Sea: an interpre-

tation from seismological and geological data, Tectonophysics

338 (2001) 79–95.

[15] J.C. Bousquet, Quaternary strike-slip faults in southeastern

Spain, Tectonophysics 52 (1979) 277–286.

[16] C. Sanz de Galdeano, Geologic evolution of the Betic Cordilleras

in the Western Mediterranean, Miocene to present, Tectonophy-

sics 172 (1990) 107–119.

[17] P.G. Silva, J.L. Goy, L. Somoza, C. Zazo, T. Bardajı, Landscape

response to strike-slip faulting linked to collisional settings:

Quaternary tectonics and basin formation in the Eastern Betics,

southeast Spain, Tectonophysics 224 (1993) 289–303.

[18] F. De Larouziere, J. deBolze, P. Bordet, J. Hernandez, C. Mon-

tenat, P. Ott d’Estevou, The Betic segment of the lithospheric

Trans Alboran shear zone during the late Miocene, Tectonophy-

sics 152 (1988) 41–52.

[19] M.C. Comas, J.P. Platt, J.I. Soto, A.B. Watts, The origin and

tectonic history of the Alboran Basin: insights from leg 161

results, in: R. Zahn, M.C. Comas, A. Klaus (Eds.), Proc. ODP,

Sci. Res., vol. 161, Ocean Drilling Program, College Station TX,

1999, pp. 555–580.

[20] J. Rodrıguez-Fernandez, A.J. Martın-Penela, Neogene evolution

of the Campo de Dalıas and the surrounding offshore areas

(Northeastern Alboran Sea), Geodin. Acta 6 (1993) 255–270.

[21] C. Marın-Lechado, J. Galindo-Zaldıvar, L.R. Rodrıguez-Fernan-

dez, I. Serrano, A. Pedrera, Active faults, seismicity and stresses

in an internal boundary of a tectonic arc (Campo de Dalıas and

Nıjar, southeastern Betic Cordilleras, Spain), Tectonophysics

396 (2005) 81–96.

[22] J. Andrieux, J.M. Fontbote, M. Mattauer, Sur un modele expli-

catif de l’Arc de Gibraltar, Earth Planet. Sci. Lett. 12 (1971)

191–198.

[23] C. Montenat, P. Ott D’Estevou, Late Neogene basins evolving in

the Eastern Betic transcurrent fault zone: an illustrated review,

in: P.F. Friend, C.J. Dabrıo (Eds.), Tertiary Basins of Spain,

Cambridge University Press, Cambridge, 1995, pp. 372–386.

[24] S. Duggen, K. Hoernle, H. van der Bogaard, Magmatic evolu-

tion of the Alboran region: the role of subduction in forming the

western Mediterranean and causing the Messinian Salinity Cri-

sis, Earth Planet. Sci. Lett. 218 (2004) 91–108.

[25] J.J. Martınez-Dıaz, J.L. Hernandez-Enrile, Neotectonics andmor-

photectonics of the southern Almerıa region (Betic Cordillera-

Spain) kinematics implications, Int. J. Earth Sci. 93 (2004)

189–206.

http://www.ugr.es/iag/tensor

http://www.geo.ign.es/servidor/sismo/cnis/


[26] J. Alvarez-Marron, Pliocene to Holocene structure of the

eastern Alboran Sea (Western Mediterranean), in: R. Zahn,

M.C. Comas, A. Klaus (Eds.), Proc. ODP, Sci. Res., vol.

161, Ocean Drilling Program, College Station TX, 1999,

pp. 345–355.

[27] J.V.A. Keller, S.H. Hall, C.J. Dart, K.R. McClay, The geometry

and evolution of a transpressional strike-slip system: the Car-

boneras fault, SE Spain, J. Geol. Soc. (Lond.) 152 (1995)

339–351.

[28] K.R. Reicherter, S. Reiss, The Carboneras Fault Zone (south-

eastern Spain) revisited with Groud Penetrating Radar–Quater-

nary structural styles from high-resolution images, Neth. J.

Geosci. 80 (2001) 129–138.

[29] D.R. Faulkner, A.C. Lewis, E.H. Rutter, On the internal structure

and mechanics of large strike-slip fault zones: field observations

of the Carboneras fault in southeastern Spain, Tectonophysics

367 (2003) 235–251.

[30] J.W. Bell, F. Amelung, G.C.P. King, Preliminary late Quaternary

slip history of the Carboneras Fault, southeastern Spain, J.

Geodyn. 24 (1997) 51–66.

[31] P. Huibregtse, H. van Alebeek, M. Zaal, C. Biermann, Palaeos-

tress analysis of the northern Nijar and southern Vera basins:

constraints for the Neogene displacement history of major strike-

slip faults in the Betic Cordilleras, SE Spain, Tectonophysics

300 (1998) 79–101.

[32] J.L. Sanz, et al., Estudio de la Plataforma Continental Espanola,

Mapa hoja MC051-Almerıa-Serie C. Ministerio de Agricultura,

Pesca y Alimentacion, Secretarıa General de Pesca Marıtima,

Instituto Espanol de Oceanografıa, 2003.

[33] M. Garcıa, B. Alonso, G. Ercilla, E. Gracia, The Tributary

Valley Systems of the Almerıa Canyon (Alboran Sea, SW

Mediterranean): Sedimentary architecture, Mar. Geol., in press.

[34] B. Alonso, A. Maldonado, Plio-Quaternary margin growth pat-

tern in a complex tectonic setting: northeastern Alboran Sea,

Geo Mar. Lett. 12 (1992) 137–143.

[35] F. Estrada, G. Ercilla, G. Alonso, Pliocene-Quaternary tectonic-

sedimentary evolution of the NE Alboran Sea (SW Mediterra-

nean Sea), Tectonophysics 282 (1997) 423–442.

[36] B.T. Cronin, N.H. Kenyon, J. Woodside, T. den Bezemer, A. van

der Wal, M.K. Ivanov, A. Limonov, The Almerıa Canyon: a

meandering channel system on an active margin, Alboran Sea,

Western Mediterranean, in: K.T. Pickering, R.N. Hiscott, N.H.

Kenyon, F. Ricci Lucchi, R.D.A. Smith (Eds.), Atlas of Deep

Water Environments: Architectural Style in Turbidite Systems,

Chapman and Hall, London, 1995, pp. 84–88.

[37] M.C. Comas, V. Garcıa-Duenas, M.J. Jurado, Neogene tectonic

evolution of the Alboran Sea from MCS Data, Geo Mar. Lett. 12

(1992) 157–164.

[38] A. Mauffret, A. Maldonado, A.C. Campillo, Tectonic framework

of the Eastern Alboran and Western Algerian Basins, Western

Mediterranean, Geo Mar. Lett. 12 (1992) 104–110.

[39] A.B. Watts, J.P. Platt, P. Buhl, Tectonic evolution of the Alboran

Sea, Basin Res. 5 (1993) 153–177.

[40] C. Flewellen, N. Millard, I. Rouse, TOBI, a vehicle for deep

ocean survey, Electr. Comm. Eng. J. 5 (1993) 85–93.

[41] A. Polonia, L. Gasperini, A. Amorosi, E. Bonatti, G. Bortoluzzi,

N. Cagatay, L. Capotondi, M.-H. Cormier, N. Gorur, C.

McHugh, L. Seeber, Holocene slip rate of the North Anatolian

Fault beneath the Sea of Marmara, Earth Planet. Sci. Lett. 227

(2004) 411–426.

[42] E. Gracia, J.J. Danobeitia, J. Verges, PARSIFAL team, Mapping

active faults offshore Portugal (368 N–388 N): implications for

seismic hazard assessment along the southwest Iberian margin,

Geology 31 (2003) 83–86.

[43] J. Holbrook, S.A. Schumm, Geomorphic and sedimentary re-

sponse of rivers to tectonic deformation: a brief review and

critique of a tool for recognizing subtle epeirogenic deformation

in modern and ancient settings, Tectonophysics 305 (1999)

287–306.

[44] A.G. Sylvester, Strike-slip faults, Geol. Soc. Amer. Bull. 100

(1988) 1666–1703.

[45] E. Calais, C. DeMets, J.M. Nocquet, Evidence for a post-3.16-

Ma change in Nubia-Eurasia-North America plate motions?

Earth Planet. Sci. Lett. 216 (2003) 81–92.

[46] J.M. Nocquet, E. Calais, Geodetic measurements of crustal

deformation in the Western Mediterranean and Europe, Pure

Appl. Geophys. 161 (2004) 661–681.

[47] I. Jimenez-Munt, A.M. Negredo, Neotectonic modelling of the

western part of the Africa-Eurasia plate boundary: from the Mid-

Atlantic ridge to Algeria, Earth Planet. Sci. Lett. 205 (2003)

257–271.

[48] A.M. Negredo, P. Bird, C. Sanz de Galdeano, E. Buforn, Neo-

tectonic modeling of the Ibero–Maghrebian region, J. Geophys.

Res. 107 (B11) (2002) 2292–2307.

[49] D. Stich, G. Alguacil, J. Morales, The relative locations of

multiplets in the vicinity of the Western Almerıa (southern

Spain) earthquake series of 1993–1994, Geophys. J. Int. 146

(2001) 801–812.

[50] C. Lopez Casado, S. Molina, J.J. Giner, J. Delgado, Magnitude-

intensity relationships in the Ibero–Magrebhian Region, Nat.

Hazards 22 (2000) 721-297.

[51] E.H. Rutter, R.H. Maddock, S.H. Hall, S.H. White, Comparative

microstructures of natural fault gouges and experimentally pro-

duced clay-bearing fault gouges, Pure Appl. Geophys. 124

(1986) 3–30.

[52] D.L. Wells, K.J. Coppersmith, New empirical relationships

among magnitude, rupture length, rupture width, rupture area,

and surface displacement, Bull. Seismol. Soc. Am. 84 (1994)

974–1002.

[53] J.A. Pelaez, C. Lopez Casado, Seismic hazard estimate at the

Iberian Peninsula, Pure Appl. Geophys. 159 (2002) 2699–2713.

[54] J.A. Pelaez, J. Delgado, C. Lopez Casado, A preliminary prob-

abilistic seismic hazard assessment in terms of Arias intensity in

southeastern Spain, Eng. Geol. 77 (2005) 139–151.

[55] E. Masana, J.A. Villamarın, J.G. Sanchez-Cabanero, J. Plaza, P.

Santanach, Seismogenic faulting in an area of low seismic

activity: paleoseismicity of the El Camp fault (Northeast

Spain), Netherlands, J. Geosci./Geol. Mijnbouw 80 (2001)

229–241.

new active faulting offshore se spain (alboran sea): implications...

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