The tsunami that ricocheted around the world following the Indian Ocean earthquake last year left a puzzling pattern of waves in its wake. Beaches in Peru and Mexico, nearly 20,000 kilometres from the earthquake, received waves that were three times larger than those hitting the shores of the Cocos Islands, just 1700 km away. Now it turns out that the waves were funnelled along underwater structures, such as mid-ocean ridges and continental shelves.Researchers find that there were two main factors affecting the manner in which the tsunami wave spread – focusing from the source, and guidance from the topography of the sea floor. Close to the epicentre the waves were controlled mostly by the shape of the earthquake fault and the long-thin rectangle of water it violently displaced. “Cocos Island lies to one side, so it didn’t receive much direct energy,” explains Titov. Meanwhile, waves further afield were shaped more by sea floor topography. The energy shot along mid-ocean ridges and continental shelves, to reach far-field locations like Peru and Mexico. The simulation also explains why some nearby islands, like Nias, did not suffer much initially, but were hit by a large wave many hours later. New scientist has compiled tons of data and a lot of analysis – excellent read for those interested.
Category : Tsunami
|
