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The tsunami generated by the offshore Samos Island earthquake (Mw = 7.0, 30 October 2020) is the largest in the Aegean Sea since 1956 CE. Our study was based on field surveys, video records, eyewitness accounts and far-field mareograms. Sea recession was the leading motion in most sites implying wave generation from seismic dislocation. At an epicentral distance of ~12 km (site K4, north Samos), sea recession, followed by extreme wave height (h~3.35 m), occurred 2′ and 4′ after the earthquake, respectively. In K4, the main wave moved obliquely to the coast. These features may reflect coupling of the broadside tsunami with landslide generated tsunami at offshore K4. The generation of an on-shelf edge-wave might be an alternative. A few kilometers from K4, a wave height of ~1 m was measured in several sites, except Vathy bay (east, h = 2 m) and Karlovasi port (west, h = 1.80 m) where the wave amplified. In Vathy bay, two inundations arrived with a time difference of ~19′, the second being the strongest. In Karlovasi, one inundation occurred. In both towns and in western Turkey, material damage was caused in sites with h > 1 m. In other islands, h ≤ 1 m was reported. The h > 0.5 m values follow power-law decay away from the source. We calculated a tsunami magnitude of Mt~7.0, a tsunami source area of 1960 km2 and a displacement amplitude of ~1 m in the tsunami source. A co-seismic 15–25 cm coastal uplift of Samos decreased the tsunami run-up. The early warning message perhaps contributed to decrease the tsunami impact.

The implementation of a new Tsunami Intensity Scale is proposed because a vast amount of data has been collected from the two megatsunamis that took place in the Indian Ocean in 2004 and northeast Japan in 2011. The newly proposed scale is 12-grade and is based on the assessment of a large number of objective criteria that are easily accessible and incorporated into six groups. As a result, it does not saturate as six-grade scales do. More specifically, the estimation of intensity values takes into account: (1) the quantities of the phenomena, (2) the direct impact on humans, (3) the impact on mobile objects, (4) the impact on coastal infrastructure, (5) the impact on the environment, and (6) the impact on structures. The new scale is compatible with the widely used EMS 1998 and ESI 2007 scales and has a reliable horizontal correspondence throughout the groups of criteria. It is easily and directly applicable to all environments, and particularly useful for the outlining of microzones of different intensities in any tsunami-affected area. It can be implemented for any land use/cover type, such as urban, rural, industrial, touristic, and so on, and at the same time, morphologic diversity of affected areas is not an obstacle to application.Online Material: Photos and satellite images of tsunami damage and associated intensity values.

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