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INew Zealand is no stranger to destructive earthquakes and tsunamis, but what was surprising in the devastating 7.5-magnitude earthquake that swept the island of Sulawesi last Friday was its size. the tsunami that followed. About 30 minutes after the earthquake, waves six meters high swept the resort of Palu, destroying buildings and hundreds of deaths.
Most of the tsunami-generating earthquakes in this region result from a movement on the Sunda "Megathrust" fault, where the Indo-Australian plate dives under the Eurasian plate. The violent vertical movements caused by earthquakes can displace a huge amount of seawater and trigger a wave of tsunami at high speed.
However, the recent Sulawesi earthquake occurred on a "slipped" fault, which means that the plates have been shaking horizontally and should not have moved much water. So what caused the tsunami? One of the possibilities is that the earthquake triggered an underwater landslide, which would have displaced the water and created a wave of tsunami. Alternatively, if the break occurred on a strongly inclined seabed area, the horizontal movement could have pushed the seawater in front of the slope. And it is almost certain that the tsunami was magnified by the narrow shape of the bay, the energy of the waves concentrated by the coastline that was heading towards Palu.
