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

Abstract

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

Field survey of the 30 October 2020 Samos (Aegean Sea) tsunami in the Greek islands

“…If that is indeed the case, the origin of the submarine landslide may possibly lie just east of Ag. Nikolaos, in an area that features steep bathymetric inclines (Nomikou et al 2021 ).…”

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

“…The maximum earthquake magnitude of this fault from the rupture of the fault in its entirety is estimated at 6.7 [17]. (e) As regards offshore structures, a major offshore fault has been detected north of the island based on the linear coastline and the extremely steep seabed morphology north and northwest of Samos [3,6,10]. It is a 25-km-long WNW-ENE striking and NNW-ward dipping normal fault, separating Samos to the south (footwall) and the offshore northern Samos basin (hanging-wall) with a depth of more than 1000 m. The maximum earthquake magnitude expected from this fault has been estimated at 6.8 [8,9] or 6.9 [17].…”

“…As regards the northern part of Samos, local uplift has been detected based on uplifted beach rocks [27]. (g) A 15-km-wide asymmetric graben-like structure prevails in the area offshore northern Samos [3,6,10]. It is bounded by a major E-W-striking and northward-dipping fault zone comprising faults in an en echelon arrangement, which played a significant role during the formation of the structure and shaped the coastal morphology of northern Samos [3,6,10].…”

“…On 30 October 2020 (11:51:26 UTC), a very strong earthquake measuring moment magnitude Mw = 7.0 ruptured offshore to the north of Samos Island in the eastern Aegean Sea (Greece) (Figure 1) [1]. Fault plane solutions showed the activation of an E-W striking normal fault, which is likely dipping to the north [2,3] (Figure 1). Such a focal mechanism is consistent with the tectonic setting of the area [4][5][6][7][8][9][10].…”

“…The largest aftershock of 30 October 2020 and the aftershock of 20 January 2021 are also noted. Active faults onshore and offshore Samos are also presented based on [3,9,10,17]. NIB: North Ikaria Basin; KB: Kuşadası Bay; GR: Greece; TR: Turkey.…”