Depth-dependent stochastic slip models governed by stress drop and rigidity variations in subduction zones: advancements in probabilistic tsunami hazard analysis.

The complexity of coseismic slip distributions plays a pivotal role in shaping tsunami hazards from both near and distant sources. Recent research underscores the significance of large shallow slips in tsunamigenic earthquakes, driven by dynamic amplification near the free surface and variable frictional conditions. Several novel methods are being proposed to incorporate depth-dependent features and shallow slip amplification in subduction earthquake models, possibly ensuring balanced long-term total slip across seismic cycles. This allows to incorporation of these slip models in Probabilistic Tsunami Hazard Assessment (PTHA). Applying this approach to the central and eastern Mediterranean using 3D subduction geometries, their findings revealed increased probabilities for larger tsunami inundation heights, underscoring the need for improved hazard assessments in global subduction zones. 

Depth-dependent rigidity variations also critically influence initial tsunami size estimates, highlighting the necessity of consistent rigidity models for accurate tsunami hazard analysis. Expanding previous models, our research incorporates both depth-dependent rigidity and stress drop into tsunami hazard modelling. This refinement aligns with common observations that shallow subduction earthquakes exhibit longer source durations than deeper events. By addressing inconsistencies arising from varying only rigidity, our enhanced methodology offers tsunami hazard curves grounded in a more physically robust seismic source model. 

Our study emphasizes the role of stress drop variability across three defined rigidity gradients with depth, ranging between the constant stress drop end-member model of Bilek & Lay (1999) and the Preliminary Reference Earth Model (PREM). We apply this approach to the Calabrian, Hellenic, and Cyprus subduction zones in the Mediterranean. Given a fixed seismic moment, rupture duration is influenced by rupture size and propagation velocity, in turn, related to the stress drop and rigidity, respectively. By adjusting rupture length and width along the dip, we calibrate our model to observed rupture durations, capturing the stress drop variation with depth. Differently from models imposing fixed stress drop values, ours prioritizes calibrating this gradient to achieve a physically more consistent representation of earthquake sources. 

This study explores the extent to which detailed modelling of stress drop variability, shallow slip amplification, and depth-dependent rigidity affect tsunami hazard curves within the Mediterranean basin, with a particular focus on the probabilities of larger inundation heights. The results contribute to refining earthquake source modelling for tsunami forecasting, benefiting both PTHA and early warning systems like Probabilistic Tsunami Forecasting. Parallelly, we are also testing the consistency of this model with tsunami observations of past Pacific events.