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Scientists are analysing recent earthquakes to establish the danger levels of eastern Andalusia's most active faults

Experts at the Instituto Andaluz de Ciencias de la Tierra (Granada University-CSIC), the Departamento de Geodinámica (UGR) and the Instituto Andaluz de Geofísica y Prevención de Desastres Sísmicos (UGR) are analysing the recent tectonic activity and the deformations in the Betica mountain chain in order to locate the most active faults in Eastern Andalusia and establish their danger levels.

One such case is the fault that runs through Granada capital. Following field analysis, mapping and study, the experts led by José Miguel Azañón have concluded that the movement in this fault could provoke earthquakes with a magnitude of 5-6 on the Richter scale, that is, similar to the one that occurred in Italy. However, the researchers also add that the fault can be considered moderately dangerous as the most recent sediments cut and displaced by the fault show that there have been no significant movements during the last 80,000 years. The scientists have just finalised a study on the tectonic control of the Sierra Nevada and surrounding areas' relief for the purposes of applying the conclusions to the assessment of geologic risk in this area. The experts have discovered that the most active seismic nuclei in the central sector of the Betica mountain chain correspond to the western border of the Sierra de Gador, between Berja and Adra, and the Granada Basin. According to the experts, the geometric characteristics of these faults (basically, the length of the active segments) could provoke earthquakes with a maximum magnitude of between 5.5 and 6 on the Richter scale. In this research, other members of the team have also discovered that the Baza fault continues active and that it has provoked recent earthquakes, such as the one that occurred in the Granada town of Benamaurel in 2003 or the one in the city in 1531. To reach these conclusions the experts analyse seismic series, that is, groups of earthquakes and, depending on their characteristics, they locate the most active faults, that is, the brusque breaks in the ground that generate earthquakes. Furthermore, the geologists have measured the length of the faults. This measurement is vital, as it indicates the maximum length of the terrain that could break up in an earthquake. In this way, the researchers calculate the maximum energy that the fault could produce should it move. Now the researchers seek to analyse the effects of the 1884 earthquake in Andalusia, which could have reached a magnitude of between 5.5 and 6, in order to understand the risk associated to these seismic movements, such as the mountainside instability they produce. Magnitude and intensity However, earthquakes are not measured solely in terms of their magnitude -the energy they release-, but also as regards the level of destruction they cause in the affected area, that is, their intensity. This latter variable can be affected by parameters such as the location of the hypocentre, that is, the area of breakage and release of energy and the point at which the earthquake commences, the design of the constructions, the topography, or the characteristics of the ground. Thus Azañón explains, "even though the earthquake in Italy had a magnitude of 5.8 (moderate from a geological perspective), the hypocentre was located very close to the surface, which, furthermore, was a populated area." Both parameters, he added, "affected the intensity and the earthquake's destructive capacity."

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