Estimating a Tsunami Source by Sediment Transport Modeling: A Primary Attempt on a Historical/1867 Normal-Faulting Tsunami in Northern Taiwan

This study applies coupled tsunami hydrodynamic and sediment transport modeling to a historical earthquake-generated tsunami to estimate its source parameters for the first time. The Keelung Earthquake and Tsunami, which struck northern Taiwan in 1867, was investigated by comparing numerical simulations with geological records of the tsunami in the Jinshan Plain in addition to historical records of the tsunami's behavior, height, and coseismic subsidence. Onshore to offshore segments of the Shanchiao normal fault were examined as potential sources of the tsunami, and varying slips of 3.0, 4.5, and 6.0 m, which corresponded to an earthquake magnitude of Mw ~7, were tested individually. The tsunami hydrodynamic and sediment transport modeling strongly suggested a rupture in the cross-shore segment of the Shanchiao fault, which has not previously been considered as the source of the earthquake and tsunami. Unlike megathrust (subduction-zone) earthquakes, an intraplate earthquake on the Shanchiao fault has minimal potential to generate a large-scale tsunami that inundates extensive coastal areas and reworks and deposits tons of coastal sediment. However, local activity at a nearshore normal fault can generate damaging tsunamis even in a highly shallow bathymetry setting. The generation mechanism of the disastrous tsunami caused by near-shore normal faulting may provide useful implications for tsunami risk assessments in the tsunami-prone areas of the world.