October 12, 2021 Tsunami: Crete, Greece

Reference #13066:

The mini tsunami that occurred after the 6.3 R earthquake was insignificant.

Reference #13067:

Sea level readings indicate that no tsunami was generated. The tsunami alert is cancelled. However, earthquakes of this size can generate small tsunami that cause locally changes in currents and resonance in harbours authorities should be aware of this possibility and take appropriate action.

Reference #13956:

The Kasos island tide gauge record analysis shows a small signal after the earthquake, but it can hardly demonstrate the existence of tsunami waves due to the low signal-to-noise ratio.

NOA’s tide gauge in Kasos, which supports the operations of the Hellenic National Tsunami Warning Center (HL-NTWC, one of the three Tsunami Service Providers operating in the Eastern Mediterranean), picked up what appears to be a very small tsunami. No other tide gauge in the region showed any sea level excitation after the earthquake. Given the noise-level wave amplitudes of the Kasos tide gauge record, tsunami-ongoing messages were not issued by the Tsunami Service Providers, and the authors are not aware of sightings of tsunami waves or currents being reported.

Whilst the ratio values are evenly distributed across the frequency range of the plot, which is further evidence that if any tsunami signal exists it is close to background level, the peaks at 6.6 and 9.8 min period stand out in that the rise in energy is not narrow-peaked.\

From the analysis of the Kasos tide gauge record, it cannot be concluded with certainty whether a (small) tsunami was recorded or not since the signal after the earthquake remains close to the background noise level. The oscillation energy marginally increased after the earthquake, but this alone does not prove the presence of tsunami waves, since storm waves could also have contributed. If tsunami waves were indeed recorded, the sign of first-wave arrival is the generation of spectral energy in the 6–10 min period range starting at ∼ 18 min after the earthquake, and peaking at the arrival of the first distinguishable drawdown of the water level at∼39 min after the earthquake. The wavelet and periodogram analyses thus suggest that any tsunami spectral energy from the source would lie primarily in the 6–10 min period range.