The underwater area south and west of Lesvos was mapped for the first time, which caused large earthquakes.
The elaboration for the first time of a very detailed digital depth map and a corresponding one map of morphological slopes of the seabed south and west of it Lesvos, who has “given” major earthquakes in the past, is the result of the collaboration of the Laboratory of Natural Geography of the National and Kapodistrian University of Athens (EKPA) and the Hydrographic Service of the Navy (PN) using the depth data obtained on the Oceanographic Boat “Nautilus”.
The relevant scientific work was published in the prestigious international scientific journal “GeoHazards” entitled “Morphotectonic structures along the southwestern margin of the island of Lesvos and their correlation with the southern branch of the Northeast North Fault”. The study, led by Associate Professor Paraskevi (Evi) of Law at the University of Athens, is co-signed by Dimitris Papanikolaou and Danae Lampridou of EKPA. as well as Dimitris Evangelidis, Dimitris Litsa, Giannis Tsaparas, Elias Koliopano and Maria Petroulia of the Hydrographic Service of the Hellenic Navy.
As Mrs. Nomikou stated in APE-MPE, “the data collected by Y / G OK Naftilos, were processed for the construction of a high resolution depth map but also the creation of an underwater morphotectonic map, which presents all the geomorphological characteristics of the bottom south and west of Lesvos, in combination with the active tectonics of the area. “Such underwater morphotectonic maps are necessary for the entire Aegean and the Ionian Sea for the recording and assessment of underwater geo-hazards such as earthquakes, landslides and tsunamis, with the contribution of the Hydrographic Service to be important.”
Specifically, the zones of large discontinuities of the seabed relief with morphological slopes up to 45 degrees, corresponding to the underwater active faults in the area, were mapped. In addition, panoramic diagrams of the margin were constructed, where the active structures of the submarine faults were noted.
According to Professor D. Papanikolaou, “horizontal slip faults with NE-SW direction can give earthquakes of magnitude 7-7.5, while normal DBD-ANA direction faults can give earthquakes of magnitude 6-6.5. The seismic peculiarity of the area studied in the Eastern Aegean, is that it is located next to the intersection of the southern branch of the North Anatolian Fault with the tectonic shear zone of Western Anatolia, which delimits the Aegean microplate from the Anatolian microplate.
More specifically, three DBD-ANA management domains were distinguished. The main structure is an asymmetric basin with a tectonic structure of Lesvos with a length of 45 km, a width of 10 to 35 km and a depth of 704 meters (which gave in 2017 a large earthquake of magnitude 6.3), while there is also a shallower western basin with tectonic structure trench (which gave earthquakes of magnitude 5.1, 4.8 and 4.5 in 2021) and a third shallow eastern basin, which develops east of Plomari, separated by a deep trench-direction NW-SE (in which there were two major aftershocks in 2017). Morphotectonic analysis of three basins in the western margin of Lesvos was also carried out with direction A-D.
The submarine structures were associated with the land structures of Lesvos and thus a complete morphotectonic map was created, in which it seems that the main horizon-slip structure of Kalloni-Agia Paraskevi (which gave an earthquake of magnitude 7 in 1867) delimits the south south . Finally, the new depth data were combined with the previous data from the research of the Skyros Basin (which were published in 2019 by D. Papanikolaou and their collaborators in the journal of marine geology “Marine Geology”) and thus a single picture was given. of the structures of the southwestern margin of Lesvos with the eastern part of the Skyros Basin, which is the southern branch of the western extension of the large fault of Northern Anatolia in the Aegean Sea.
The analysis of the data also showed that the three western basins of Lesvos are internal tensile structures (Pull-apart basins) between the large faults of Skyros and Adramyti, which are characterized by a large clockwise horizontal slip. This is confirmed by the mechanisms of the generation of two earthquakes of magnitude 5 and 4.4 in 2019, which took place in the area.
Finally, the new data of Lesvos were compared by the researchers with the available data mainly from the Skyros and North Aegean basins and thus more general conclusions were drawn about the directions and characteristics of the active faults and the respective earthquakes. The main feature is the coexistence of earthquakes from horizontal sliding faults of NE-SW direction, which dominate, and earthquakes from normal faults of direction DBD-ANA.