The wavelength of a tsunami can be up to 800km long. They travel at speeds of 800kph. Which means you might have to wait an hour for a second seismic shift. If you are on the beach and the sea suddenly withdraws, it can only mean one thing. Head for the hills – and stay there.
However it is distinctly possible you may not have enough time to evacuate like the poor buggers who lived in Lisbon in 1755. The town was reduced to rubble in six minutes thanks to a sea earthquake that generated waves of 17m (or 55 feet high in the old money).
So why does the earth behave so badly at times? Why does it need to belch on occasion? According to the Modified Mercalli Scale (which measures intensity at a particular location based on observed effects unlike the Richter scale which measures magnitude), a force 9 will cause significant damage to well designed buildings though it is not certain how the sea affects this observation.
Its probably safe to say you don’t want to be on the beach when it happens. The cause is when two parts of the earth move suddenly in relation to each other along a fault line.
The epicentre is a point upon the land (or bottom of the sea) directly above the focal point of the collision. When stretched rocks snap, there is a sudden release of energy and it spreads out in waves. Shock waves travel out from the focus speeding up depending on the density of the material around them.
It is happening all the time at fault lines that mark off the boundary between the continental plates but usually the battle takes the path of least resistance which results in boring old friction. Occasionally a tendon stretched too far will snap and will release massive amounts of energy which vibrates back and forth. Rising lava under a volcano can do the same thing but is only a minor culprit compared to earthquakes. Science still has no idea why deep earthquakes (700km or lower) occur.
The whiteness of those waves crashing through the western hotels of Phuket in the December 2004 tsunami was visually awesome and will share with 9/11 iconology the ability of news bite pictures to define a new kind of terrorism.
Nature’s own remedy shuddering through the rocks by blasting 8.9 Eichter’s of earthquake and then let the sea do the dirty work for us.
Every so often the banality of time is interfered with by a swift kick to the tectonic plates. America’s coasts will be paranoid. What if this happened off Japan or Iceland (both having equally lively geology)? This would be Jerry Bruckheimer’s ultimate fantasy realised, waves tumbling over the statue of liberty for once without the aid of a computer graphic interface.