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Understanding plate tectonics helps to explain the cause of submarine earthquakes. The Earth's surface or lithosphere comprises tectonic plates which average approximately 80 km (50 mi) in thickness, and are continuously moving very slowly upon a bed of magma in the asthenosphere and inner mantle.
Normal tsunamis result from displacement of the sea floor due to movements in the Earth's crust (plate tectonics). Powerful earthquakes may cause the sea floor to displace vertically on the order of tens of metres, which in turn displaces the water column above and leads to the formation of a tsunami.
A 1996 study published by seismologist Kenji Satake supplemented the research by Atwater et al. with tsunami evidence across the Pacific. [4] Japanese annals, which have recorded natural disasters since approximately 600 CE, [2] had reports of a sixteen-foot tsunami that struck the coast of Honshu Island during the Genroku era.
Large tsunamis have occurred in the US and will again. A magnitude 9.2 earthquake in the Gulf of Alaska caused damage and loss of life along the West Coast in 1964. More than 150 tsunamis have ...
The US West Coast is the confluence of a number of the Earth's tectonic plates, and tremors are not uncommon. But a strong 7 magnitude quake isn't typically seen in the region.
As early as 426 BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause. [12] [13] The oldest human record of a tsunami dates back to 479 BC, in the Greek colony of Potidaea, thought to be triggered by an earthquake.
The epicentre was close to the Santa Cruz Islands within Temotu Province at the boundaries of the Indo-Australian and Pacific tectonic plates, causing local evacuations, a tsunami of 11 m (36 ft) and killing at least ten people.
The most important clue linking the tsunami in Japan and the earthquake in the Pacific Northwest comes from studies of tree rings (dendrochronology), which show that several "ghost forests" of red cedar trees in Oregon and Washington, killed by lowering of coastal forests into the tidal zone by the earthquake, have outermost growth rings that formed in 1699, the last growing season before the ...