When an earthquake happens in the ocean and the size and magnitude are large enough, then a tsunami can be generated. That is what happened in Indonesia. See Indonesia earthquake and tsunami death toll surpasses 830. Most of the casualties counted so far are from the city of Palu. There are other cities and villages that border the island where Palu is located that have not been heard from yet.
There have been a number of significant earthquakes and tsunami events stretching back over 14 years. While the United States has done some work to improve our tsunami warning system here on the West Coast, not nearly enough has been done. In reality, there is little public education being done for our citizens. I expect we'll still have thousands of people rushing to the beaches to see a potential tsunami when a warning is given. Maybe it is a Darwinian moment of survival of the "smartest," but we could be doing more, much more.