The 2020 Samos (Aegean Sea) M7 earthquake: a normal fault with rupture directivity and near surface slip explaining the tsunami generation and coastal uplift

Abstract

The 30 October 2020 M7 Samos earthquake occurred offshore the Greece-Turkey cross border region, and will be recalled as among the deadliest (118 fatalities) that affected both countries. It generated a strong tsunami and caused coseismic uplift of 20 to 35 cm of the NW part of the Samos Island. It ruptured a ~60 km long, north-dipping normal fault, related to the back-arc extension of the Aegean Sea area. Using picks from regional strong motion and broad-band waveforms we relocated the mainshock and the aftershocks, applying suitable velocity models. The closest strong-motion recordings, constrained the finite fault slip model, suggesting up-dip and westward propagation of the rupture. The westward rupture propagation is independently confirmed by the apparent source time functions inferred using the empirical Green's function method from nearregional broad-band and strong-motion waveforms. Static displacements measured by GNSS stations constrain near surface slip of ~1 m, explaining the tsunami and the island uplift. The 2020 Samos event showed that normal faults bounding the basins in the back-arc Aegean region can host M7 earthquakes and when combined with tsunami generation, constitute a constant threat for the nearby coastal areas of both Greece and Turkey.

Characteristics of Strong Ground Motions in the 30 October 2020, MW6.9 Aegean Sea Earthquake

“…On 30 October 2020 (11:51:27 UTC) a M W 6.9 normal-faulting earthquake occurred in the Aegean Sea ~10 km North of the Greek Island of Samos and ~35 km West of the coast of Turkey. Although multiple seismological agencies have reported slightly varying finite fault solutions for the earthquake (see Supplementary Table S1), we can deduce that the earthquake did occur in the shallow upper crust (depth of <12 km; Plicka et al, 2021), on the East-West trending Samos fault that dips steeply to the North. The previous geological surveys and field investigations of several researchers also strongly sustain the argument of North-dipping faulting for the region (Pınar, 2020) 1 .…”

“…The event was followed by thousands of aftershocks with a moment magnitude (M W ) up to 5.1. The event caused 15-35 cm of coseismic uplift along the coast of Samos (Plicka et al, 2021) and was accompanied by a tsunami that affected the northern coastline of Samos, as well as between Alaçatı and Gümüldür in Turkey with the water level reaching up to 1.9 m (Aktas et al, 2021). Because of the large magnitude and shallow nature of the earthquake on 30 October 2020, there were many coseismic surface ruptures reported (Lekkas et al, 2020;Aktas et al, 2021).…”