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SUMMARY On 2020 May 2, an Mw = 6.6 earthquake struck about 63 km south of Ierapetra in Crete, Greece. The earthquake generated a small tsunami which agitated local harbours. We studied this event in the context of earthquakes with seismic records in 1908, 1910, 1923, 1952, 2009 and 2013, all of similar magnitudes located south of Crete. Based on an energy-to-moment ratio, our analysis suggests that this event was neither slow nor fast, hence appropriate for using scaling laws to infer seafloor deformations. We also performed a field survey, three days after the event and present field observations from seven locations, including the island of Chrisi, where our highest measurement of 0.95 m was located. Runup along the coast of southern Crete ranged from 0.24 to 0.87 m. One tide gauge record is available for this event, and we did image analysis to obtain accurately timed water surface elevations from eyewitness videos and images. We undertook high-resolution hydrodynamic simulations using published moment tensor solutions to identify the source of the tsunami. Simulations were performed with two models, MOST (a nonlinear shallow water model) and COULWAVE (a Boussinesq-type model), to infer how different approximations of the parent equations of motion affect predictions for tsunamis of this size, which are fairly common in the Eastern Mediterranean and routinely trigger Tsunami Service Providers to issue warning messages. Based on the inter-model comparison, we conclude that the shallow-water equations are adequate in modelling this event at the distances considered, suggesting that such codes can be used to infer the tsunami source and to estimate tsunami impacts. Last, our field work revealed lack of knowledge of tsunami hazards, as most eyewitnesses remained near the waterfront, filming the associated unusual water motions instead of taking shelter on high ground. 

The time series of free surface elevation measured in and outside the shadow zone were compared and analyzed in the time-frequency domain by employing the continuous wavelet transform. Regardless of the conditions of the ERF wave in the shadow zone, an increase in magnitude of energy is noticeable not only in the peak frequency within a range of approximately 0.8 to 1 Hz but also in the low-frequency range of around 0.1 Hz corresponding to second up to third crest of the leading wave. To determine the effective frequency of ERF waves and evaluate their runup characteristics, we applied a new method of describing the ERF wave, which consists of linear superposition of two solitary waves. As a result, the ERF waves show the same trend in runup characteristics as for solitary waves. 

Tsunami generation from earthquake-induced seafloor deformations has long been recognized as a major hazard to coastal areas. Strike-slip faulting has generally been considered insufficient for triggering large tsunamis, except through the generation of submarine landslides. Herein, we demonstrate that ground motions due to strike-slip earthquakes can contribute to the generation of large tsunamis (>1 m), under rather generic conditions. To this end, we developed a computational framework that integrates models for earthquake rupture dynamics with models of tsunami generation and propagation. The three-dimensional time-dependent vertical and horizontal ground motions from spontaneous dynamic rupture models are used to drive boundary motions in the tsunami model. Our results suggest that supershear ruptures propagating along strike-slip faults, traversing narrow and shallow bays, are prime candidates for tsunami generation. We show that dynamic focusing and the large horizontal displacements, characteristic of strike-slip earthquakes on long faults, are critical drivers for the tsunami hazard. These findings point to intrinsic mechanisms for sizable tsunami generation by strike-slip faulting, which do not require complex seismic sources, landslides, or complicated bathymetry. Furthermore, our model identifies three distinct phases in the tsunamic motion, an instantaneous dynamic phase, a lagging coseismic phase, and a postseismic phase, each of which may affect coastal areas differently. We conclude that near-source tsunami hazards and risk from strike-slip faulting need to be re-evaluated.