Tsunami Hazard Assessment and Recent Mega-Thrust Earthquakes

Recent mega-thrust earthquakes and tsunamis like the Sumatra-Andaman 2004 and Tohoku 2011, among several others in the last decade, caused immense damage and casualties and revealed some limitations in our previous knowledge of tectonic processes. How does this understanding affects our ability to designing countermeasures for tsunami risk mitigation? To start answering this question, I will review some studies about the tsunami causative sources of the Maule 2010 and Tohoku 2011 mega-thrust events. In both cases, coseismic ruptures were different from what was generally expected in terms of slip amplitude and distribution over the fault plane, and therefore about the way the accumulated tectonic strain was released. However, exceptional monitoring efforts were performed in advance in these two subduction zones and these events ended up being the best recorded ever of their kind. The geophysical datasets made available to the scientific community fostered studies about the source by means of inversion techniques that were already refined in the last decades, and especially after the Sumatra-Andaman 2004 earthquake and tsunami. This unprecedented amount of high quality research significantly improved our general knowledge of mega-thrust events while opening several new questions. Based on the ongoing scientific discussion, I will illustrate some of the learned lessons to be taken into account for making tsunami hazard assessment more effective, which cannot be considered a straightforward extension of common seismic hazard assessment, especially if considering the trade off between 1) the feasibility of the computational effort needed if the full expected source variability is included, and 2) the sensitivity of tsunami hazard results to simplifying assumptions about the seismic source characterization.