Engineering Lessons from September 28, 2018 Indonesian Tsunami: Scouring Mechanisms and Effects on Infrastructure

The September 28, 2018 earthquake and tsunami, which occurred north of Palu City, Indonesia, attracted widespread interest from the scientific community due to the unusually large tsunami that occurred after a strike-slip earthquake with a relatively small moment magnitude (MW = 7.5). To understand the structural performance of buildings and infrastructure under hydrodynamic loads and their associated effects, the authors conducted field surveys in Palu City. Light wooden frame constructions and masonry infill walls were common in the area, some of which were severely damaged by the earthquake and tsunami. Reinforced concrete structures remained predominantly intact, although they suffered soil-related issues such as scour around rigid building members. Local structural failures caused by the loss of supporting soil were also observed during the field survey, resulting in an overall reduction in the stability of the inspected structures. Based on the observations made, knowledge gaps and research needs concerning coastal and structural scouring are discussed. These are tied into the latest community research activities and put in the context of a published ASCE standard chapter that discusses tsunami design.