Relative Sea Level Changes and Morphotectonic Implications Triggered by the Samos Earthquake of 30th October 2020

Abstract

On 30th October 2020, the eastern Aegean Sea was shaken by a Mw = 7.0 earthquake. The epicenter was located near the northern coasts of Samos island. This tectonic event produced an uplift of the whole island as well as several cases of infrastructure damage, while a small tsunami followed the mainshock. Underwater and coastal geological, geomorphological, biological observations and measurements were performed at the entire coast revealing a complex character for the uplift. At the northwestern part of the island, maximum vertical displacements of +35 ± 5 cm were recorded at the northwestern tip, at Agios Isidoros. Conversely, the southeastern part was known for its subsidence through submerged archaeological remains and former sea level standstills. The 2020 underwater survey unveiled uplifted but still drowned sea level indicators. The vertical displacement at the south and southeastern part ranges between +23 ± 5 and +8 ± 5 cm suggesting a gradual fading of the uplift towards the east. The crucial value of tidal notches, as markers of co-seismic events, was validated from the outcome of this study. The co-seismic response of Samos coastal zone to the 30th October earthquake provides a basis for understanding the complex tectonics of this area.

Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

“…The activated fault was assumed to be running along the northern margin of Samos Island, which bounds from the south the Samos Basin as the aftershock distribution also indicated (see fault plane solutions on Figure 6a). A remarkable tsunami, reaching a height of 1-3 m, hit the coastal areas around the Samos Basin [13], and co-seismic uplift of shorelines at the western coastline of northern Samos was observed by 10-20 cm [14]. A tectonic uplift of 10 cm was also detected from coseismic interferometric analysis of SAR and GNSS on Samos Island [15].…”

Primary and Secondary Environmental Effects Triggered by the 30 October 2020, Mw = 7.0, Samos (Eastern Aegean Sea, Greece) Earthquake Based on Post-Event Field Surveys and InSAR Analysis

“…(a) The uplift detected in the field at the Asprochorti site in the northeastern part of Samos was 10 cm, while the InSAR analysis showed a small subsidence or relative stability (sections and profile graphs A1-A1 and B1-B1 in Figures 30 and 31). (b) The uplift detected in the field at the Kokkari site in the northeastern part of Samos was 22 cm [15], while the InSAR analysis showed a subsidence of 2 cm from the SARscape software and an uplift of 1.4 cm from the SNAP software (sections and profile graphs A2-A2 and B2-B2 in Figures 30 and 31). (c) The uplift detected in the field at the Karlovasi vessel shelter site was 24 cm, while the InSAR analysis showed a smaller uplift of 2.8 cm from the SARscape software and 6.3 cm from the SNAP software (sections and profile graphs A8-A8 and B8-B8 in Figures 30 and 31).…”

“…Neotectonic map illustrating the geological formations, the active faults onshore and offshore Samos, the major inactive faults, the main fault blocks of Samos Island based on onshore and offshore studies, the 2020 Samos earthquake epicenter, and its largest aftershocks. Data from onshore studies on the active tectonics of Samos [4,5,[7][8][9]15,17,23,24,27] and offshore studies based on continuous seismic reflection profiles [6] The geological structure of Samos also comprises Neogene (Miocene-Pliocene) formations and Quaternary deposits, which filled in the Karlovasi, Pyrgos, Mytilinii, and Paleokastro basins [4,5,7] (Figure 5). The Karlovasi and Mytilinii sedimentary basins, in the western and eastern part of Samos, respectively, are connected by a narrow passage, which corresponds to the Pyrgos Basin, while the Paleokastro basin is a second-order basin structure formed in the eastern part of Samos [4,5] (Figure 5).…”

“…According to preliminary reports, the earthquake also caused important effects on the natural environment of Samos, such as surface deformation and various types of ground failures [12]. Relative sea level changes [15] and a tsunami of moderate size [16] have also been reported. On 20 January 2021, a strong aftershock measuring magnitude Mw = 4.5 occurred closer to Samos Island with respect to the mainshock (Figure 1).…”

“…Rockfalls were observed along the fault scarp and the fragments fell into the sea (Figure 23c). It is significant to note that east of the rockfall site, [15] detected an uplift of +23 cm.…”