Plate tectonics can be visualized like large moving parts on the earth's crust. The constant movement of the plates causes major stresses, and, as a result, deformations or earthquakes occur on the plate boundaries. "Every year the Eurasian and African plates are moving 4-6 mm closer to each other. The boundary between the plates around the Atlantic Ocean and Algeria is very clear, whereas in the south of the Iberian Peninsula the boundary is much more blurred and complex," explained Asier Madarieta , a University of the Basque Country (EHU) researcher.
In the western Mediterranean the boundary between the Eurasia and Africa plates is totally determined by the Alboran domain. This field is moving westwards and is fostering the development of the active Gibraltar Arc by connecting the Betic Cordillera with the Rif Cordillera. "Until now we didn't know exactly what that boundary was like in that environment, and what geodynamic processes are taking place is under discussion," added Madarieta.
In a piece of research led by Madarieta, important dynamic processes taking place on that blurred boundary between the Eurasian and African plates were specified: "We saw how the crustal strain and the surface deformation in the Western Mediterranean are related on the boundary between the two plates located in the gap between the Iberian Peninsula and Northwest Africa," explained the researcher in the Water Environmental Processes Group ( HGI ). Indeed, the stress and deformation fields in that environment were calculated "by using deformation data obtained via satellite and data on earthquakes that have occurred in recent years".
Fresh data to advance research
Having compared these two aspects, the geodynamic and tectonic processes are now understood more comprehensively. In the research, they obtained a lot of new data on the boundary between the Eurasia and Africa plates, "we have specified it better". So, "we found out which sectors on the boundary are already under the dominance of the collision between Eurasia and Africa and which are still determined by the westward displacement of the Gibraltar Arc", Dr Madarieta explained.
He pointed out that the new data "confirm that the Iberian Peninsula is rotating clockwise". "The data indicate that the Gibraltar Arc is playing a significant role on the Eurasia-Africa boundary. To the east of the Straits of Gibraltar the crust of the Gibraltar Arc is absorbing the deformation caused by the Eurasia-Africa collision, thus preventing the stresses being transmitted to Iberia. On the other hand, to the west of the Straits of Gibraltar the direct collision between the Iberia (Eurasia) and Africa plates is taking place, and we believe that could affect the stresses being transmitted to the southwest of Iberia, by pushing Iberia from the southwest and making it rotate clockwise".
The stress fields provide information on the geodynamic processes, whereas the deformation field shows how the earth's surface is becoming deformed under the influence of these stresses. "But finding out which geological structure is causing the deformation is not at all easy," he said. With the new data it is possible to know, for example, where the faults (structures between the blocks that cause the earthquakes) are or where they could be. "As for Iberia, there are many places where there is a significant deformation or where earthquakes occur, but we don't know which tectonic structures are active there. These stress and deformation fields tell us where we have to go to look for these structures. And that way, we could find out what kind of folds and faults there may be, what their movement would be like, what kind of earthquakes they could cause and of what magnitude."
On the Iberian Peninsula, "we and many other research groups are producing a database of active Iberian faults ( QAFI -Quaternary Active Fault database of Iberia). Although we are working very hard, in some fields there is a lot to do, in the Western Pyrenees (Navarre) and in the west of the Gibraltar Arc (Cadiz-Seville), for example. So in these areas detailed geological and geophysical work has to be done to know which structures cause deformation, characterise them and specify their seismic potential", explained Madarieta.
A small window on geological evolution
Geodynamic changes are obviously terribly slow, and satellite data and precise earthquake data do not go back a long way. "These data only provide a small window on geological evolution. Most of the precise earthquake data only go back to 1980, and accurate satellite data back to 1999, whereas geodynamic changes are measured in millions of years. So it is important to conduct unified analyses of the different data," he said.
As the researcher pointed out, the database created in the research complements the databases used previously and that "increases the reliability of the results and conclusions". What is more, from now on "the data will increase exponentially: among other things we will be able to calculate the deformations in more detail, even in the places where we have little information available".
Additional information
Asier Madarieta-Txurruka is a researcher in the EHU's Department of Geology . This research was funded by the Basque Government as he received a Basque Government grant to conduct his post-PhD research. Thanks to this grant he is currently on a stay at the University of Palermo. Members of the University of Palermo and the University of Granada, among others, collaborated with Madarieta in this research.
