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We present a source solution for the tsunami generated by the Mw 6.6 earthquake that occurred on 2 May 2020, about 80 km offshore south of Crete, in the Cretan Passage, on the shallow portion of the Hellenic Arc subduction zone (HASZ). The tide gauges recorded this local tsunami on the southern coast of Crete and Kasos island. We used Crete tsunami observations to constrain the geometry and orientation of the causative fault, the rupture mechanism, and the slip amount. We first modelled an ensemble of synthetic tsunami waveforms at the tide gauge locations, produced for a range of earthquake parameter values as constrained by some of the available moment tensor solutions. We allow for both a splay and a back-thrust fault, corresponding to the two nodal planes of the moment tensor solution. We then measured the misfit between the synthetic and the Ierapetra observed marigram for each source parameter set. Our results identify the shallow, steeply dipping back-thrust fault as the one producing the lowest misfit to the tsunami data. However, a rupture on a lower angle fault, possibly a splay fault, with a sinistral component due to the oblique convergence on this segment of the HASZ, cannot be completely ruled out. This earthquake reminds us that the uncertainty regarding potential earthquake mechanisms at a specific location remains quite significant. In this case, for example, it is not possible to anticipate if the next event will be one occurring on the subduction interface, on a splay fault, or on a back-thrust, which seems the most likely for the event under investigation. This circumstance bears important consequences because back-thrust and splay faults might enhance the tsunamigenic potential with respect to the subduction interface due to their steeper dip. Then, these results are relevant for tsunami forecasting in the framework of both the long-term hazard assessment and the early warning systems. [ABSTRACT FROM AUTHOR]

We present a source solution for the tsunami generated by the Mw 6.6 earthquake that occurred on May 2, 2020, about 807 km offshore south of Crete, in the Cretan Passage, on the shallow portion of the Hellenic Arc Subduction Zone (HASZ). The tide-gauges recorded this local tsunami on the southern coast of Crete island and Kasos island. We used these tsunami observations to constrain the geometry and orientation of the causative fault, the rupture mechanism and the slip amount. We first modelled an ensemble of synthetic tsunami waveforms at the tide-gauge locations, produced for a range of earthquake parameter values as constrained by some of the available moment tensor solutions. We allow for both a splay and a back-thrust fault, corresponding to the two nodal planes of the moment tensor solution. We then measured the misfit between the synthetic and the observed marigrams for each source parameter set. Our results identify the shallow steeply-dipping back-thrust fault as the one producing the lowest misfit to the tsunami data. However, a rupture on a lower angle fault, possibly a splay fault, with a sinistral component due to the oblique convergence on this segment of the HASZ, cannot be completely ruled out. This earthquake reminds us that the uncertainty regarding potential earthquake mechanisms at a specific location remains quite significant. In this case, for example, it is not possible to anticipate if the next event will be one occurring on the subduction interface, on a splay fault, or on a back-thrust which seems the most likely for the event under investigation. This circumstance bears important consequences because back-thrust and splay faults might enhance the tsunamigenic potential with respect to the subduction interface due to their steeper dip. Then, these results are relevant for tsunami forecasting both in the framework of the long-term hazard assessment and of the early warning systems. [ABSTRACT FROM AUTHOR]

The Italian Tsunami Warning Centre situated at Istituto Nazionale di Geofisica e Vulcanologia (CAT-INGV) is 24/7 operational since the 1st January 2017 and is governed in the frame of the Italian Tsunami Warning System (SiAM), constituted by the Italian Civil Protection Department (DPC), the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Italian Institute for Environmental Protection and Research (ISPRA). The CAT-INGV is committed to deliver tsunami alert messages. At present state, the CAT-INGV operations adopt a Decision Matrix (DM) that considers the available earthquake's parameters (hypocentre and magnitude) and the distance of the epicentre from the nearest coast and from the target forecast points to be alerted. The two defined alert levels (advisory/orange and watch/red) are then associated to each target forecast point and to the corresponding coastal areas in front of them. Moreover, along the coasts are defined evacuation maps which, ideally, need to include all the areas subject to inundation for a given level of acceptable risk. Numerical modelling is by far the most accredited tool to model tsunami propagation and inundation but a massive use of tsunami inundation simulations on high-resolution numerical grids of coastal areas still represents a challenge in some practical applications. As an alternative, empirical or analytical simplified methods based on amplification factors and/or coastal dissipation models can provide rapid approximated estimates of inundation. In the frame of SiAM, inundation distances associated to the alert levels are defined using a GIS-based approach that convert reference maximum run-up values into inundation lines considering the inundation dissipation obtained with empirical methods. While for the advisory/orange is set by convention based on the definition of the alert level and the uncertainty on DEM model, the reference maximum run-up value for the watch/red is derived from the results of the regional Seismic Probabilistic Tsunami Hazard Analysis (S-PTHA) developed in the TSUMAPS-NEAM project (http://www.tsumaps-neam.eu/), by selecting the tsunami intensity relative to the 2500 yr average return period at the 84th percentile of the epistemic uncertainty distribution. The TSUMAPS-NEAM model evaluated the inshore tsunami intensity from off-shore (50 m depth) maximum waive height through amplification factors and accounting for uncertainty.The aim of the present work is to evaluate the performances of the adopted simplified procedure by comparing the results of the proposed method with the inundation maps obtained using high resolution tsunami numerical inundation simulations for a set of sources placed offshore in front of the target area and having different magnitudes and focal mechanisms. The selected target area is the coastal segment placed in the South-Eastern Sicily, Italy, between Catania and Siracusa, two touristic and commercial urban areas, comprising harbour infrastructures and a petrochemical complex. This area has experienced destructive tsunamis in the past and the coast presents very different terrain morphological features. Tsunami scenarios are modelled with Tsunami-HySEA, a non-linear hydrostatic shallow-water multi-GPU code.The work is funded by the TSUMAPS-NEAM (Grant agreement ECHO/SUB/2015/718568/PREV26) project and the Agreement between Istituto Nazionale di Geofisica e Vulcanologia (INGV) and Italian Civil Protection Department (DPC). [ABSTRACT FROM AUTHOR]