morphological features and near surface sedimentary facies. Then, we look with
attention to recent sediment dynamics and tectonic activity using geological and
oceanographic approaches. In addition, we assess how the geomorphology of the
Alboran Sea offers us clues to determine the main potential geological hazards, as
well as how it can play an import role in the bionomy of the seafloor.
6.2 Setting
6.2.1 Geographical and Geological Settings
The Alboran Sea is the westernmost province of the Mediterranean Sea (Fig. 6.1). It
is east-west oriented and occupies an area of about 54,000 km
2 . It is 150 km wide
and 350 km long, presenting a maximum depth of 2294 m. It is partly land-locked,
bounded by the Strait of Gibraltar to the west. To the east, the Alboran Basin gives
way to the Algero-Balear Basin.
The origin and present-day setting of the Alboran Sea are controversial due to the
geological complexity of the region. It is a Neogene-Quaternary extensional basin
located within the Betic (Spain) and Rif (Morocco) alpine cordilleras, connected by
the Arc of Gibraltar (Andrieux et al. 1971) (Fig. 6.1b). The geodynamic evolution of
the Alboran Basin, still under debate, is determined by the relative motion between
Eurasia and Africa (Dewey et al. 1989). The westward displacement of the Betic-Rif
orogen during the development of the Arc of Gibraltar has been accommodated by
the major Trans-Alboran Shear zone (De Larouzière et al. 1988; Frasca et al. 2015).
Faults and folds have formed in the framework of recent NNW-SSE shortening and
regional Eurasian-African plate convergence (DeMets et al. 2015) (Fig. 6.1b). Seismicity in the Alboran Sea includes mostly shallow (<30 km depth), but also scarce
intermediate (30–120 km depth), and a few deep (600–640 km depth) events (Buforn
et al. 1991, 2011, 2017; www.ign.es) (Fig. 6.1b)
The shallow seismicity is characterised by low to moderate magnitude earthquakes (generally Mw < 5) and is heterogeneously distributed (www.ign.es; Buforn
et al. 2004) (Fig. 6.1b). GPS research shows that the Alboran Sea is undergoing a
heterogeneous ENE-WSW extension, increasing towards the Strait of Gibraltar, and
an orthogonal NNW-SSE shortening as high as 3.3 mm/year in its central part (Fadil
et al. 2006; Koulali et al. 2011; Palano et al. 2015; González-Castillo et al. 2015;
Galindo-Zaldívar et al. 2015).
The sedimentation in the Alboran Sea is mostly siliciclastic, primarily from
rivers, coastal erosion, and dust from the Sahara Desert (e.g. Moreno et al. 2002;
Jiménez-Espejo et al. 2008; Lobo et al. 2015). The Spanish and Moroccan margins
bordering the sea are quite similar from the point of view of sediment sources. Many
fluvial catchments in the Mediterranean region are characterised by small- to
medium-sized rivers and ephemeral streams with abrupt topographies, resulting
from the proximity of the mountain ranges and the adjacent coast (Liquete et al.
2009); these erode the Betic Mountains (>3000 m high) and the Rif Mountains
6 Seafloor Morphology and Processes in the Alboran Sea
159
attention to recent sediment dynamics and tectonic activity using geological and
oceanographic approaches. In addition, we assess how the geomorphology of the
Alboran Sea offers us clues to determine the main potential geological hazards, as
well as how it can play an import role in the bionomy of the seafloor.
6.2 Setting
6.2.1 Geographical and Geological Settings
The Alboran Sea is the westernmost province of the Mediterranean Sea (Fig. 6.1). It
is east-west oriented and occupies an area of about 54,000 km
2 . It is 150 km wide
and 350 km long, presenting a maximum depth of 2294 m. It is partly land-locked,
bounded by the Strait of Gibraltar to the west. To the east, the Alboran Basin gives
way to the Algero-Balear Basin.
The origin and present-day setting of the Alboran Sea are controversial due to the
geological complexity of the region. It is a Neogene-Quaternary extensional basin
located within the Betic (Spain) and Rif (Morocco) alpine cordilleras, connected by
the Arc of Gibraltar (Andrieux et al. 1971) (Fig. 6.1b). The geodynamic evolution of
the Alboran Basin, still under debate, is determined by the relative motion between
Eurasia and Africa (Dewey et al. 1989). The westward displacement of the Betic-Rif
orogen during the development of the Arc of Gibraltar has been accommodated by
the major Trans-Alboran Shear zone (De Larouzière et al. 1988; Frasca et al. 2015).
Faults and folds have formed in the framework of recent NNW-SSE shortening and
regional Eurasian-African plate convergence (DeMets et al. 2015) (Fig. 6.1b). Seismicity in the Alboran Sea includes mostly shallow (<30 km depth), but also scarce
intermediate (30–120 km depth), and a few deep (600–640 km depth) events (Buforn
et al. 1991, 2011, 2017; www.ign.es) (Fig. 6.1b)
The shallow seismicity is characterised by low to moderate magnitude earthquakes (generally Mw < 5) and is heterogeneously distributed (www.ign.es; Buforn
et al. 2004) (Fig. 6.1b). GPS research shows that the Alboran Sea is undergoing a
heterogeneous ENE-WSW extension, increasing towards the Strait of Gibraltar, and
an orthogonal NNW-SSE shortening as high as 3.3 mm/year in its central part (Fadil
et al. 2006; Koulali et al. 2011; Palano et al. 2015; González-Castillo et al. 2015;
Galindo-Zaldívar et al. 2015).
The sedimentation in the Alboran Sea is mostly siliciclastic, primarily from
rivers, coastal erosion, and dust from the Sahara Desert (e.g. Moreno et al. 2002;
Jiménez-Espejo et al. 2008; Lobo et al. 2015). The Spanish and Moroccan margins
bordering the sea are quite similar from the point of view of sediment sources. Many
fluvial catchments in the Mediterranean region are characterised by small- to
medium-sized rivers and ephemeral streams with abrupt topographies, resulting
from the proximity of the mountain ranges and the adjacent coast (Liquete et al.
2009); these erode the Betic Mountains (>3000 m high) and the Rif Mountains
6 Seafloor Morphology and Processes in the Alboran Sea
159