First Results on the Mw=6.9 Samos Earthquake of 30 October 2020

Abstract

On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake struck the offshore region north of Samos Island, Greece, in the Gulf of Ephesos/Kuşadasi, causing two fatalities and 19 minor injuries at Samos Island, as well as 115 casualties and over 1,030 injuries in Western Turkey. Preliminary results indicate that the mainshock occurred on a north-dipping normal fault, with a focal mechanism of 270º/50º/-81º. The selection of the fault plane is supported by evidence of uplift at western Samos and over 10 cm of subsidence at the northernmost edge of the central part of the island. The distribution of relocated hypocenters shows clustering of events, east of the mainshock’s epicenter, where most major aftershocks have occurred. To the west, a smaller group of aftershocks is observed, separated by a spatial gap in seismicity. The latter is likely related to the region of the fault plane where most of the co-seismic slip occurred, with Coulomb stress-transfer towards the western and eastern margins of the rupture triggering aftershock activity. The apparent complexity of the mainshock’s source time function, supported by preliminary results, could indicate the rupture of more than one structures. This could explain the relatively weak magnitude of the largest aftershock (Mw=5.0). The mainshock caused damage mainly to non-engineered constructions, i.e. old residential buildings, churches and monuments in Samos Island, and minor damage to the majority of the building stock of the island built according to the National Seismic Code. On the other hand, it caused severe damage at Izmir, especially to high-rise buildings. The mainshock also triggered a small tsunami that reached heights of over 1 m, mainly affecting the Turkish coast.

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

“…Such a focal mechanism is consistent with the tectonic setting of the area [4][5][6][7][8][9][10]. The largest aftershock occurred a few hours after the main event (30 October 2020, 15:14:57 UTC) and its magnitude was calculated as Mw = 5.0 [1]. From the records of an SMG1 accelerometer installed in Vathy town, northeastern Samos, it was concluded that the peak ground acceleration (PGA) in the two horizontal components was 0.16 g and 0.23 g, respectively, while in the vertical component a PGA of 0.13 g was measured [11].…”

“…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).…”

On rapid multidisciplinary response aspects for Samos 2020 M7.0 earthquake

“…Concerning the rapid response, just a few hours after the event, thanks to the availability of synthetic aperture radar (SAR) data acquired from the Sentinel-1 mission of the European Union's Copernicus Programme, on the same day as the earthquake and less than 12 h apart, several scientific groups communicated their Differential Interferometric SAR (DInSAR) results on social media (Twitter, LinkedIn, Facebook, etc. ) or by preliminary reports (Chatzipetros et al 2020;Ganas et al 2020;Lekkas et al 2020;Papadimitriou et al 2020;Segou 2020). This information was available in addition to solutions obtained from regional GNSS networks covering the affected area (Ganas et al 2020).…”

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

“…It might be synchronous to the onshore Upper Miocene volcanic formations of Samos, observed along the Mytilini and Karlovassi basins (see Figure 2). [10] generally show E-W normal faulting (Figure 6a). The main shock (Magnitude 7.0) and most of the aftershocks (Magnitudes 5.2-3.9) occur in the central and eastern part of Samos Basin, forming a 20 km long seismic belt, which is smaller than expected for this magnitude (following the empirical relationships [45]).…”

“…The mainshock occurred on 30 October with magnitude 7.0 [10,11], and its focal mechanism indicated an E-W trending normal fault dipping to the north. Its epicenter is located about 8-10 km north of Samos Island to the north of Karlovassi, situated at the basinal area of the Samos Basin [12].…”