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Main active faults during the Quaternary extracted from the QAFI database (García-Mayordomo et al., 2015; IGME, 2015) Data source: ©Instituto Geológico y Minero de España (IGME) FCR:Crevillente fault, FBS:Bajo Segura fault, FP=Palomares fault, FC:Carboneras fault, FAL:Alhama-Lorca fault.

Seismicity in the east Baetic System

The south-eastern area is characterized by earthquakes of moderate magnitude, although some have occurred occasionally with intensities of VIII (Orihuela in 1048, 1482 and 1673; Almeria in 1487 and 1658; and Lorca in 1674), VIII-IX (Almeria in 1522 -fall of houses- and Vera in 1518 -fall of houses and 165 victims-) and intensity IX-X in 1829 in Torrevieja. Recently, earthquakes with magnitudes close to 5 have occurred in 1999 M4.7 Mula; 2002 M5.2 Bullas; 2005 M4.8 La Paca; and 2011 M5.1 Lorca, the latter causing 9 fatalities. In the northeast zone, recent seismicity is low. However, significant historical events have occurred in this area with intensities of VIII or IX, such as 1396 in Tabernes de la Valldigna, 1644 in Alcoy (22 victims) and 1748 in Estubeny, which destroyed Montesa, Sellent and Estubeny and caused 38 deaths.

Geology and tectonics of the east Baetic System

The upper third comprises the eastern lands of the Betic mountain range. Units from the external areas, to the north, emerge with the Pre-Baetic represented in the eastern half of the mountain range, with parautochthonous or moderately allochthonous units of sedimentary rocks from the Triassic to the Miocene, with a very low metamorphic degree. It is a deformed cover and detached from the varicose base. The Sub-Baetic rides on the Pre-Baetic, and has very deformed and allochthonous units. All the external units are detached from the substrate in favour of the plastic materials of the upper Triassic, which generate kilometre-long blocks that move by means of subhorizontal dipping faults. The region is full of saline diapirs that locally disrupt the stratigraphy.

In the central and southern part, the three complexes of the Internal areas emerge. The Maláguide Complex outcrops in Sª Espuña and in Vélez Rubio with Jurassic limestones. The Paleocene is calcareous and margoarenous. In the upper Miocene the main phase of the Alpine orogeny takes place and the Betic mountain range rises. In Sª Espuña, the upper Miocene is discordant with all units and is affected by the great active fault of Alhama de Murcia. The Alpujarre Complex has the most important outcrops in the sierras of Las Estancias, Alhamilla, Cabrera and the coastal strip from Cabo de Palos to the north of Carboneras. The rocks have a low metamorphic degree. The units are separated by normal take-off faults generated in an extensional regime. The contact of the Complejo Nevadofilabre. with the Alpujarride is of an extensional type. They are isolated outcrops of schist, quartzite, gneiss and marble (Macael). They stand out in the nuclei of the Filabres, Alhamilla and Almagrera mountain ranges and the coastal line of Cartagena. All the units have medium-high alpine metamorphism and a late-post alpine metamorphism structure. The dominant deformation is the posterior extensional to the anterior compressive ones. In the base of the Alpujarride and Nevado-Filabride complexes there are important remains of magmatism, metamorphism and pre-alpine orogeny.

Over the last 25 Ma, synorogenic sedimentary basins have developed that formed within the orogen and were initially filled with marine deposits. Later, in the upper Quaternary Miocene, they changed to a continental regime and have little deformation. They are polygonal basins, strongly subsident and sometimes connected to each other. In this area, the basins of Alcoy, Tibi and the Vinalopo valley stand out above the Crevillente fault. To the south of the fault, the Bajo Segura basin is very important. In the area of Almeria are the Almeria-Nijar, Vera, Cartagena and Sorbas basins.

Throughout the eastern sector of this area there are frequent sightings of volcanic rocks related to the region's Neogene volcanism, whose best representative is the area extending from Cabo de Gata to the Mar Menor.

The southern sector of this area is known as the Eastern Betica shear zone. It is a corridor, about 250 km long, of passing faults that extend towards the sea at its NE and SW ends. Its seismic activity is related to different active faults with predominantly NE-SW direction and sinestral and inverse movement such as those of Crevillente, Bajo Segura, Carrascoy, Los Tollos, Alhama de Murcia, Palomares and Carboneras. Among these, the Alhama de Murcia fault stands out, being about 87 km long and made up of four segments, associated with the 2011 earthquake M5.1 in Lorca and the Carboneras fault with about 50 km on land and 90 km continuing along the sea towards the southwest. To the north of the Crevillente fault, on what would be the Pre-Baetic, the terrain is much more stable, with the passing faults of Socovos, in a NW-SW direction, and Jumilla, in a NE-SW direction, being the most important.

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