How does earthquakes cause tsunamis

For example, the Great Chilean tsunami was generated by a magnitude 9. Its waves were destructive not only in Chile, but also as far away as Hawaii, Japan and elsewhere in the Pacific. It should be noted that not all earthquakes generate tsunamis. Usually, it takes an earthquake with a Richter magnitude exceeding 7. Most tsunamis are generated by shallow, great earthquakes at subductions zones. A devastating 8. National Weather Service to issue a warning for at least 50 countries or territories around the Pacific.

The tsunami waves have already reached Hawaii, where officials have ordered an evacuation of Hawaii's coastal areas. A few factors come into play: the strength of the quake , the direction of the temblor's motion and the topography of the seafloor. First, magnitude of the quake, which is a measure of the amplitude of the largest seismic wave recorded for the earthquake, must exceed a certain threshold.

The 8. Magnitudes are measured on a logarithmic scale, so a magnitude-5 temblor would have seismic waves that are 10 times greater in amplitude than a magnitude-4 earthquake. They move relative to each other at rates of up to several inches per year. A plate boundary is the area where two plates come into contact. The way one plate moves relative to another determines the type of boundary: spreading, where the two plates move away from each other; subduction, where the two plates move toward each other, with one sliding beneath the other; and transform, where the two plates slide horizontally past each other.

Subduction is the main cause of major tsunami events. There are subduction zones with associated deep-sea trenches off Chile, Alaska, Japan, and Indonesia, for example, that have produced large earthquakes and devastating tsunamis, many of which caused damage and loss of life in the Hawaiian Islands. Part of the seafloor snaps upward as the tension is released.

The entire column of seawater is pushed toward the surface, creating an enormous bulge. As the water flattens out, giant ripples race outward.