Large amplification of the 1906 Colombia–Ecuador earthquake tsunami in Hilo Bay induced by bay-scale resonance

Resumen

The megathrust earthquake that occurred along the Nazca Plate, near the coasts of Colombia and Ecuador in 1906, induced a large tsunami that propagated over the Pacific Ocean. The tsunami arrived in countries very far from the source region, including the United States and Japan. Part of the land covered by railroad tracks in Hilo Bay, Hawaii, United States, was inundated during the tsunami. The tsunami reached a height of several tens of centimetres in other regions of Hawaii, while residents in Hilo witnessed a height of 3.6 m in the bay. This study aimed to estimate the large amplification and inundation mechanisms of the 1906 Colombia–Ecuador tsunami in Hilo Bay, based on a detailed numerical simulation. First, available tsunami observation data were carefully examined and compared with the results of previous studies. The results indicate a maximum inundation height due to the tsunami in Hilo Bay ranging from 1.1 to 1.8 m. Next, a tsunami inundation simulation was performed under varying conditions, such as energy loss by bottom friction and tide level change, using an earthquake source model. The simulated results were consistent with the observation in terms of the inundation height and indicate that bay-scale resonance occurred in Hilo Bay. Furthermore, waves amplified by resonance were more significant than the primary wave. It can therefore be concluded that bay-scale resonance enhanced the tsunami inundation in Hilo Bay. These new results show that the tsunami magnitude of 8.7, estimated in a previous study, is an overestimation. Instead, the results suggest a lower tsunami magnitude of 8.4, which is consistent with the moment magnitude obtained from the earthquake source model.