Coastal Dynamics 2013 Paper No. MODELING OF THE TOHOKU-OKI 2011 TSUNAMI GENERATION, FAR-FIELD AND COASTAL IMPACT: A MIXED CO-SEISMIC AND SMF SOURCE

Tsunami hazard assessment for future megathrust earthquakes requires that we understand the source mechanisms and tsunami generation processes for large historical events, such as the devastating Tohoku-oki tsunami of March 11th 2011. Although associated with a Magnitude 9 earthquake, simulations of the tsunami based solely on this co-seismic source do not reproduce the elevated runup heights of 40 m along the coast of northern Honshu, nor the wave timing and high frequency wave periods recorded at offshore GPS and DART buoys. Here, we show that an additional tsunami source associated with a large submarine mass failure (SMF), triggered North-East of the main source after a 2 min. delay, satisfies the necessary observations. To do so, we model the tsunami sourced from both earthquake and SMF. This dual source reproduces both the recorded onshore runups and the wave heights and wave frequencies recorded at offshore buoys. The significant contribution from an SMF to the Tohoku-oki tsunami has important implications for assessing coastal hazard from future megathrust earthquake events