Dimitrios I. Papanikolaou

The steep northern slopes of Giona Mt in central continental Greece are the result of an E-W normal fault dipping 35–45° to the north, extending from the Mornos River in the west to the village of Gravia in the east. This fault creates a significant elevation difference of approximately 1500 m between the northern Giona footwall and the southern Iti hanging wall. The footwall comprises imbricated Mesozoic carbonates of the Parnassos unit, which exhibit large-scale drag folding near and parallel to the fault. The hanging wall comprises deformed sedimentary rocks of the Beotian unit and tectonic klippen of the Eastern Greece unit, forming a southward-tilted neotectonic block with subsidence near the Northern Giona Fault and uplift near the Ypati fault to the north. These two E-W faults represent younger structures disrupting the older NNW-trending tectonic framework. Fault scarps are observed all along the 14 km length of the Northern Giona fault accompanied by cataclastic zones, separating the carbonate formations of the Parnassos Unit from thick scree, slide blocks, boulders and olistholites. Inversion of fault-slip data has shown a mean slip vector of 45°, N004°E, which aligns with the current regional extensional deformation of the area, as confirmed by focal mechanism solutions. Based on the general asymmetry of the alpine units in the hanging wall, we interpret a listric fault geometry at depth using slip-line analysis and we forward modelled a disrupted fault-propagation fold using kinematic trishear algorithms, estimating a total displacement of 6500 m and a throw of approximately 2000 m. Seismic activity in the area of the Northern Giona Fault includes a magnitude 6.1 earthquake in 1852, which caused casualties, rockfalls and extensive damage, as well as a magnitude 5.1 event in 1983. The expected seismic magnitude is deterministically estimated between 6.2 and 6.7, depending on the potential westward continuation of the Northern Giona Fault beyond the Mornos River to the Northern Vardoussia saddle. The seismic hazard zone includes several villages located near the fault, particularly on the hanging wall, where intense landslide activity during seismic events could result in severe damage to regional infrastructure. The neotectonic development of the Northern Giona Fault highlights the importance of extending seismotectonic research into the mountainous regions of central Greece within the alpine formations, beyond the post-orogenic sedimentary basins.

Morphotectonic analysis of the offshore margins of the Aegean Islands in combination with onshore structures offers a rather complete image of the ongoing deformation within the Aegean micro-plate and especially along its eastern border zone with the Anatolian micro-plate. The swath data, off Lesvos and Samos islands, have been acquired by the hull-mounted RESON SeaBat 7160 on the oceanographic vessel NAFTILOS of the Hellenic Navy Hydrographic Service and gridded at 15m spatial resolution. Active tectonics affect both areas, as recorded by the intense seismic activity along with pronounced erosional and mass wasting processes.The southern margin of Lesvos Island is divided into three sub-basins. The main feature is the central elongated sub-basin extending nearly parallel to the coast, reaching 700m water depth. Its northern margin is bounded by an abrupt WNW-ESE normal fault with morphological slopes up to 41o, whereas its southern one is smoother with 5o of slope and the overall structure corresponds to a half-graben. At its eastern edge, the basin is interrupted by a narrow steep channel, trending NW-SE, and progressively becomes shallower. At the western part of the Lesvos margin, a shallow basin forms an assymetric tectonic graben. Along the northwestern margin, three E-W basins lying approximately at 300-400 m water depth, constitute pull-apart basins within the complex ENE-WSW shear zone of the southern strand of the North Anatolian Fault, bounded by the sub-parallel Skyros and Adramytion Faults. Seismic activity in 2017 comprised a 6.3 magnitude earthquake on the WSW-ESE normal fault of the Lesvos Basin and two major aftershocks of magnitude 5.2 and 5.0 at the NW-SE strike-slip faults of the channel. During 2020 and 2021 normal WNW-ESE faulting with magnitude 5.1 and ENE-WSW dextral strike-slip faulting with magnitudes 4.8, and 5.0 occurred at the western and northwestern basins. However, a magnitude 7.0 earthquake had occurred onshore at the NE-SW  Kalloni-Aghia Paraskevi strike-slip fault in 1867.The northern margin of Samos Island is bounded by a normal north dipping E-W fault that generated the strong earthquake of magnitude 7.0 on 30October 2020.The Samos Basin forms a half-graben of 690m water depth with morphological slopes of 31o along the fault zone. Several canyons trending N-S, carve the northern margin ending up between 100m and 600m water depth, and several mass wasting events can be identified alongside the Samos coastline. Westwards, the Ikaria Basin is significantly deeper, reaching 1100m water depth and is delineated by an abrupt zone of nearly 51⁰ slope values, corresponding to the NE-SW Samos active western margin, probably related to strike-slip faulting. Additionally, an impressive retrogressive erosional structure occupies the area between Samos and Ikaria islands, with two prominent meandering narrow canyons debouching at the Ikaria Basin.The combination of E-W to WNW-ESE normal faulting and NE-SW to ENE-WSW dextral strike-slip faulting with minor NW-SE sinistral strike-slip faulting is observed all over the North Aegean Sea, acommodating the southwestward motion of the Aegean micro-plate, relative to the Eurasian plate in the north and the Anatolian micro-plate in the East. 

A hydrographic survey of the southwestern coastal margin of Lesvos Island (Greece) was conducted by the Naftilos vessel of the Hellenic Hydrographic Service. The results have been included in a bathymetric map and morphological slope map of the area. Based on the neotectonic and seismotectonic data of the broader area, a morphotectonic map of Lesvos Island has been compiled. The main feature is the basin sub-parallel to the coast elongated Lesvos Basin, 45 km long, 10–35 km wide, and 700 m deep. The northern margin of the basin is abrupt, with morphological slopes towards the south between 35° and 45° corresponding to a WNW-ESE normal fault, in contrast with the southern margin that shows a gradual slope increase from 1° to 5° towards the north. Thus, the main Lesvos Basin represents a half-graben structure. The geometry of the main basin is interrupted at its eastern segment by an oblique NW-SE narrow channel of 650 m depth and 8 km length. East of the channel, the main basin continues as a shallow Eastern Basin. At the western part of the Lesvos margin, the shallow Western Basin forms an asymmetric tectonic graben. Thus, the Lesvos southern margin is segmented in three basins with different morphotectonic characteristics. At the northwestern margin of Lesvos, three shallow basins of 300–400 m depth are observed with WNW-ESE trending high slope margins, probably controlled by normal faults. Shallow water marine terraces representing the last low stands of the glacial periods are observed at 140 m and 200 m depth at the two edges of the Lesvos margin. A secondary E-W fault disrupts the two terraces at the eastern part of the southern Lesvos margin. The NE-SW strike-slip fault zone of Kalloni-Aghia Paraskevi, activated in 1867, borders the west of the Lesvos Basin from the shallow Western Basin. The Lesvos bathymetric data were combined with those of the eastern Skyros Basin, representing the southern strand of the North Anatolian Fault in the North Aegean Sea, and the resulted tectonic map indicates that the three Lesvos western basins are pull-aparts of the strike-slip fault zone between the Skyros Fault and the Adramytion (Edremit) Fault. The seismic activity since 2017 has shown the co-existence of normal faulting and strike-slip faulting throughout the 90 km long Lesvos southern margin.

The active Kos-Nisyros-Tilos volcanic field is located in the eastern sector of the Aegean Volcanic Arc resulting from the subduction of the African plate beneath the Aegean plate. The volcanic activity is developed since Middle Pleistocene and it occurs within a tectonic graben with several volcanic outcrops both onshore and offshore. Data obtained from previous offshore geophysical surveys and ROV exploration, combined with geospatial techniques have been used to construct synthetic maps of the broader submarine area. The volcanic relief is analyzed from the base of the volcanic structures offshore to their summits onshore reaching 1373 m of height and their volumes have been computed with 24.26 km³ for Nisyros Island and a total volume of 54.42 km³ for the entire volcanic area. The volcanic structures are distinguished in: (1) volcanic cones at the islands of Nisyros (older strato-volcano), Pergousa, Yali and Strongyli, (2) volcanic domes at the islands of Pachia, East Kondeliousa and Nisyros (younger Prophitis Ilias domes), (3) submarine volcanic calderas (Avyssos and Kefalos). Submarine volcanic debris avalanches have been also described south of Nisyros and undulating features at the eastern Kefalos bay. Submarine canyons and channels are developed along the Kos southern margin contrary to the Tilos margin. Ground truth campaigns with submarine vessels and ROVs have verified the previous analysis in several submarine volcanic sites. The geohazards of the area comprise: (1) seismic hazard, both due to the activation of major marginal faults and minor intra-volcanic faults, (2) volcanic hazard, related to the recent volcanic structures and long term iconic eruptions related to the deep submarine calderas, (3) tsunami hazard, related to the seismic hazard as well as to the numerous unstable submarine slopes with potential of gravity sliding.