Act of nature.
The earthquake triggered the tsunami
An earthquake.
An earthquake happened, which triggered the tsunami.
It created the tsunami.
You can't predict earthquakes
An earthquake
It was triggered by an earthquake.
The tsunami was triggered by an earthquake.
Samoan crisis happened in 1887.
8.1 moment magnitude
The earthquake that caused the tsunami was on the same day, 29 September, 2009.
Samoan Clipper happened on 1938-01-11.