Earthquakes like the one that caused the tsunamis across south-east Asia yesterday cannot be predicted, but seismic monitoring systems can detect quakes and calculate their strength and location, allowing seismologists to predict where large sea waves may hit.

As seismic waves travel through the earth faster than tsunamis travel through the sea, such monitoring systems can give warnings of probable tsunamis several hours before they hit land, depending on the distance of the earthquake's centre from the shore.