Abstract

The subduction zone along the Tonga Trench has the highest convergence rate in the world, but limited records of its seismic and tsunamigenic activities. In 2009, a tsunami generated by an Mw 8.1 earthquake doublet caused severe impacts in the region including damage and loss of life on the south shores of Upolu and Savaii Islands, Samoa. Here we use numerical modeling aided by recorded data and eyewitness accounts to reconstruct the inundation of this event on southeast Upolu to study the characteristics and effects of the locally generated tsunami in the Tonga Trench region. We show that computed locations of large inundation are consistent with areas that were severely impacted. The distribution and intensity of inundation is dependent on local topographic and bathymetric features, configuration of coastal geomorphology, trapping of short-period waves over the reef flats and excitation of high frequency resonance modes. Sensitivity of the modelled inundation to rupture source indicates the initial intraplate normal fault rupture had a more dominant role in the east-northeastward propagation and inundation observed on southeast Upolu compared with the subsequent thrust fault sequence.