Verticle Slice Through A
Subduction Zone
| Between Earthquakes [ slow distortion ] |
During An Earthquake [ quake starts tsunami ] |
Minutes Later [ tsunami waves spread ] |
|
| One of the many tectonic plates that make up the Earth's outer shell descends, or "subducts," under an adjacent plate. This kind of boundary between plates is called a "subduction zone." When the plates move suddenly in an area where they are usualy stuck, an earthquake happens. |
Stuck to the subducting plate, the overriding plate gets squeezed. Its leading edge is dragged down, while an area behind it bulges upward. This movement goes on for decades or centuries, slowly building up stress. |
An earthquake along a subduction zone happens when the leading edge of the overriding plate breaks free and springs seaward, raising the sea floor and the water above it. This uplift starts a tsunami. Meanwhile, the bulge behind the leading edge collapses, thinning the plate and lowering coastal areas. |
Part of the tsunami races toward nearby land, growing taller as it comes close to shore. Another part heads accross the ocean toward distant shores. This explains how a tsunami may occure many hundreds of miles from where it originates. |
______________________________________________________________