The active tectonic structures along the southern margin of Lesvos Island, related to the seismic activity of July 2017, Aegean Sea, Greece

Hydrographic survey of the southeastern coastal margin of Lesvos Island (Greece) was conducted in January 2018 by R/V METEOR. The main morphological characteristic of the southern margin of Lesvos Island is a sub-parallel to the coast elongated basin, 30 km long, 5-10 km wide, and 700 m deep. It is interrupted by an oblique NW-SE narrow channel of 650 m depth, which separates the adjacent platform areas surrounding the longitudinal basin. The northern margin of the basin is abrupt with morphological slopes of more than 10 degrees, following the major WNW-ESE normal fault surface, running along the coastal zone, with an overall throw of more than 800 m. In contrast, the southern margin shows a gradual slope increase from 1 degrees to 5 degrees, where several shallow sub-bottom profiles across the basin have indicated the existence of some minor WNW-ESE normal faults and one reverse/strike-slip fault zone, with throws of a few up to 13 m. However, the NW-SE narrow channel intersecting the basin is bounded by two sub-vertical fault zones with sinistral strike-slip motion and throws of more than 150 m. The above structure was reflected in the mainshock of magnitude 6.3 (12/6/2017), corresponding to a WNW-ESE normal fault dipping to the SSW and the two major aftershocks of magnitude 5.2 and 5.0 corresponding to the two sub-parallel NW-SE sinistral strike-slip faults of the channel. This active deformation comprising WNW-ESE normal faults and NW-SE or NE-SW strike-slip faults is compatible with the area's overall tectonic frame at the eastern margin of the Aegean microplate.