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In September 2018, Sulawesi in Indonesia was hit first by an earthquake, and then, without warning, by a tsunami. 2000 people were killed.

But why, when Indonesia has a tsunami early warning system, was there no warning? Brunel's Assistant Professor of Civil Engineering, Dr Mohammad Heidarzadeh, explains...

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To trigger a tsunami early-warning system for a specific earthquake we need to ask three questions. The first questions is – was the location of the earthquake on the land or in the water? For a tsunami early warning system to trigger a tsunami warning, we need it to be in the water.

The second question we ask is – is the magnitude of the earthquake above eight or less than eight? If it’s a more than eight, we’re obviously concerned about a potential tsunami. If it’s less than eight, there’s less potential for a tsunami.

And the third question is – what type of earthquake is it? Is it a thrust (verticle) earthquake or a strike-slip (horizontal) earthquake? Only a thrust earthquake is able to generate a tsunami.

In the case of the tsunami is Sulawesi in Indonesia in September 2018, the answer to the first question was yes, but the answers to the second and third questions were no. The magnitude of the Sulawesi earthquake was 7.5, which is a moderate earthquake in terms of tsunami genesis, and the type of earthquake was a strike-slip earthquake, not a thrust earthquake.

That’s why the tsunami early warning system was not triggered.

But the Sulawesi tsunami was generated and 2000 people were killed. The reason for that was that, because of the shaking of the earthquake, and the instability brought about by the earthquake, some of the seafloor slopes failed. Because of the failure of the seafloor slopes, a large amount of mass was moved downward, and because of this moving, sliding mass, a large wave was generated.

Reported by:

Tim Pilgrim, Media Relations
+44 (0)1895 268965
tim.pilgrim@brunel.ac.uk