3D Dynamic Rupture Scenarios for the Hellenic Arc - Implications on Tsunami Generation

The Hellenic Arc is an active seismogenic zone in the Mediterranean Sea that hosted at least two historical M≥8 earthquakes, which both caused destructive tsunamis. Thick sediment covers in combination with a shallow low-angle subduction interface can provoke enhanced seafloor uplift above the fault.Long-term seismic-probabilistic tsunami hazard assessment (S-PTHA, e.g., Scala et al., 2020) and early warning systems typically rely on kinematic or stochastic source models. Their static displacement is then used to source tsunami models. However, the complex interaction of earthquake dynamics and tsunami genesis may not be fully captured.

We use the slab geometry from the European Database of Seismogenic Faults (EDSF, Basili et al., 2013) to create a range of 3D, high-resolution dynamic rupture earthquake scenarios. We vary hypocenter locations, which results in remarkable differences in spontaneous developing rupture speed, moment magnitude, and shallow fault slip dynamically penetrating into shallow velocity-strengthening regions, translating into strong variations of the final seafloor displacement across scenarios. The initial stress and fault strength conditions are constrained on the subduction zone scale (following Ulrich et al., 2021).

Our modeling suggests that margin-wide rupture would yield an Mw ~9 earthquake. In an additional model with unconsolidated sediments, we show that off-fault plastic yielding limits shallow fault slip but triples the horizontal seafloor uplift.

Smaller magnitude earthquake scenarios are obtained using an asperity approach following subduction earthquake scaling relations (Strasser et al., 2010). We choose a hypocenter location consistent with the 1303 Crete earthquake and lower the prestress outside a predefined circular asperity which leads to spontaneous rupture arrest.

Assigning observationally constrained along-arc varying initial stresses derived from source inversions (Kkallas et al., 2021), leads to spontaneous rupture arrest without prescribed asperities, limiting the fault slip to much smaller areas and resulting in earthquake magnitudes of Mw ~8.

We envision that mechanically consistent dynamic rupture models can provide building blocks toward combined, self-consistent, and physics-based Seismic and Tsunami Hazard Analysis.