CSIC scientists identify a new fault in the Alboran Sea

Scheme of the active structures that originated the seismic series of 2016-17 in the Alboran Sea. a, seismicity, main active structures, efforts and shortening. b, Diagram of the main tectonic structures. c, interpretative cross sections and seismicity orthogonal to the main seismic alignments. 1, fails sinistra. 2, normal failure. 3, recent normal failure. 4, epicenter of the main event (Mw = 6.3, January 25, 2016). 5, blind thrust. 6, 7, 8, fault segments related to the seismic crises of 2016, 1994 and 2004. 9, Displacement west of the deformation. 10, Convergence estimated with GPS data. 11, Convergence of plates. 12, Efforts. FP, underwater mount Francesc Pagès. MTD, mass transport depots./ CSIC
23 Juliol 2018

An international group of scientists led by the Spanish National Research Counci (CSIC) has identified a new fault in the Alboran Sea. The fracture produces little deformation in the seabed, although there are "relatively high magnitude earthquakes", such as the magnitude 6.3 on the Richter scale that affected the city of Melilla and several areas of Andalusia on January 25th on 2016. The results of this research, published in the journal Tectonics, allow establishing potential geological risks in the Alboran Sea.

The work, which is part of the INCRISIS geology and marine geophysics campaing carried out on the Hespérides in May 2016, places the new fault in the limits between the Eurasian and African tectonic plates in the Alboran Sea, at western Mediterranean Sea. So far, the best known fault in this area was the Al-Idrisi fault.

"After the earthquake on January 2016, which caused significant damage in Melilla and other Moroccan cities, we started mapping the seabed and studying the seismicity of the area, since this did not correspond to the position of the Al-Idrisi fault, which affects the central and southern area of ​​the Alboran Sea. Our research confirms that the initial seismicity is associated with a new fault, which has a Northeast-Southwest direction and produces little deformation on the seabed", says Jesús Galindo-Zaldívar, researcher at the Andalusian Institute of Earth Sciences (mixed center of the CSIC and the University of Granada) and principal author of the study.

Among the conclusions of the study, it is also noteworthy that the formation of the Gibraltar arch between Iberia and Africa continues with the migration of tectonic deformation towards the west. As for the seismicity, it also extends to the North, affecting the Campo de Dalias region, in Almería.


"High" seismic risk

The new localized fault zone, which extends to Morocco, was also the cause of two other earthquakes registered in 1994 and 2004. The latter, with a magnitude between 6.1 and 6.3 on the Richter scale, affected mainly the region of Alhucemas, in northern Morocco, and caused more than 600 deaths.

"In the 2004 earthquake, events of greater magnitude were not directly related to any known surface fault. That's why it was important for us to know the tectonics on land and sea. In addition, we studied both the area affected by the seismicity and the own fault of Al-Idrisi ", highlights Gemma Ercilla, researcher at the Institute of Marine Sciences. She adds: "The existence of underwater landslides and minor recent faults in the epicenter zone confirms the tectonic activity of this incipient fault zone with high seismic risk".

During the INCRISIS campaign, scientists delimited the area affected by the main earthquake and the subsequent seismicity until the Al-Idrisi fault. To know the morphology of the seafloor and the structure of the sub-fund, they used geophysical instruments, such as the multibeam probe, the parametric probe, the gravimeter and the magnetometer. They also used seismicity data from the National Geographic Institute to know the location of earthquakes and focal mechanisms. In addition, the ground investigations of the faults that produced the earthquakes of 1994 and 2004 were taken into account.

"Our work is the first step to focus future geological, seismic and geodetic studies in this main area of ​​deformation, from Alhucemas to the Campo de Dalias, which crosses the Alboran Sea" Galindo-Zaldívar points out.

This research is the result of the coordination and collaboration of the CSIC (Institute of Marine Sciences and Andalusian Institute of Earth Sciences), the University of Granada, the University of Jaén, the Royal Institute and Observatory of San Fernando's Navy, the Geological and Mining Institute of Spain, the Spanish Institute of Oceanography, the Navy Hydrographic Institute, Université Sorbonne de Paris, Université Mohammed Premier Oujda, Université Mohammed V-Agdal-Rabat and Université Abdelmalek Essaadi- Tetouan.




Article: J. Galindo‐Zaldivar, G. Ercilla, F. Estrada, M. Catalán, E. d’Acremont, O. Azzouz, D. Casas, M. Chourak, J. T. Vazquez, A. Chalouan, C. Sanz de Galdeano, M. Benmakhlouf, C. Gorini, B. Alonso, D. Palomino, J. A. Rengel y A. J. Gil. Imaging the growth of recent faults: the case of 2016‐17 seismic sequence sea bottom deformation in the Alboran Sea (Western Mediterranean). Tectonics. DOI: 10.1029/2017TC004941.



Press release CSIC