The earthquake in Chile on Saturday was one of the biggest the world has felt in the past century 鈥� so why was the tsunami that spread across the Pacific smaller than originally feared?
The magnitude-8.8 earthquake was devastating, claiming at least 700 lives. Large tsunami waves were reported along parts of Chile鈥檚 coastline: reports suggest the town of Constituci贸n was worst affected by the wave.
Yet locations further afield were more or less spared by the tsunami. Waves smaller than 1.5聽metres struck Hawaii and Japan, for example, causing very little damage. By contrast, a magnitude-9.5 earthquake in 1960 spawned a tsunami that claimed over 200 lives in Japan, Hawaii and the Philippines.
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of the National Oceanography Centre at the University of Southampton, UK, speculates that the reason might be that Saturday鈥檚 earthquake ruptured a relatively small segment of fault 鈥� around 350聽kilometres. The length of fault rupture determines the distance at which a tsunami begins to lose energy. By comparison, the magnitude-9.1 earthquake that generated the 2004 Indian ocean tsunami ruptured around 1600聽kilometres of fault.
Chile鈥檚 recent tsunami was also highly focused. 鈥淚t was quite a directed tsunami, rather than a 鈥榮tone in a pool鈥� type propagation,鈥� explains of the University of Wales, Newport. The tsunami was severe at the coast nearest the epicentre, and westward at the Juan Fernandez Islands, but the energy and height were lost quickly in other directions, he says.
Furthermore, the relatively deep origin of the earthquake 鈥� 35聽kilometres 鈥� may have minimised the uplift on the sea floor that displaced the water. 鈥淭he Chile quake was smaller and deeper than the Indian Ocean quake of 2004, so less energy was released and, most importantly, less of this reached the surface,鈥� says of University College London.
