7 October 18
The catastrophic tsunami on Sulawesi Island is a puzzle. As the emergency response gathers pace, scientists are scratching their heads to understand why it generated such big waves.
The magnitude 7.5 quake was certainly large - one of the biggest recorded anywhere on the globe this year.
But it was what geophysicists call a strike-slip event, where the ground breaks horizontally. In this instance, the rock to the east of the fault running up through the island moved northwards relative to the rock to the west.
Strike-slip quakes can cause tsunami events but the 6m-tall waves that crashed ashore at Palu city surprised everyone.
- AUTHOR: JONATHAN AMOS
- SOURCE: BBC