Question: do you have an idea on how scientists would be able to predict earthquakes and tsunamis?

David Ingram answered on 13 Jun 2011:

Predicting earthquakes in advance is very difficult. I have some friends at the worlds most unsuccessful research institute. The Disaster Prevention Research Institute (DPRI) in Kyoto, Japan, was set up by imperial charter to predict earthquakes and they have shown it cannot be done – other than shortly before quakes associated with volcanic activity.

Tsunami come from undersea quakes and landslides so predicting when they will happen is practically impossible. Once an earthquake has been detected under the sea we can quickly calculate where the tsunami wave will go and when it will arrive and issue warnings. These calculations cannot be used to predict the wave height (or indeed if there is a tsunami) but can give evacuation warnings hours ahead of the arrival of the wave.

The predictions work because the wave travels at a fixed speed for any water depth [=sqrt(g*water depth)] so we can calculate arrival time from the quake location very quickly. Predictions of wave height are based on oceanic measuring devices which see the wave passing them. Wave height can be predicted from earthquake data but the geologists take serval days to produce the required data.

In the recent Japanese tsunami the earthquake was close to shore so the warning was only about 30 minutes. Hawaii got more than six hours warning of the same tsunami but when the wave reached them it was very very small.