A seism of magnitude 8.8 occurred off the Kamchatka peninsula in Russia, causing a tsunami of almost 5 meters locally. Waves up to 3 meters are expected in Japan and the rest of East Asia remains on alert. But why does a Tsunami Seism are?
Seism as the main cause
According to the site of the Canadian government, tsunamis are “large waves or series of waves generated by the rapid displacement of large volumes of water due to seismic events, volcanic eruptions, landslides, glacial velves, impacts of meteorites and other disturbances”. Several potential causes therefore exist, the best known and recurrent being Seism. Its amplitude and its depth, here 20km, define the potential size of the tsunami: the more powerful a seism, the more powerful the tsunami.
When an earthquake of a minimum force of 7 and less than 50 km deep, the seabed can lift or lower in a brutal way, which will move a large quantity of water. This movement of water will form concentric waves which will propagate in the ocean in all directions, a bit as if we threw a pebble in the water. Nevertheless, in Haute-Mer, when the depth is very important, the wave does not exceed a few tens of centimeters high, but still moves to 800km/h.
As the coast approaches, the depth of the water decreases which will have the effect of straightening the wave since the energy of the earthquake it has not decreased. The earthquake was only in a way that “hidden” and can then reach several meters see tens of meters in height but in the process, nevertheless slows down.
The earthquakes have several causes, the main one (95%) being the motion of tectonic plates. But there is also volcanic activity, human activities, by deep mining (collapse of galleries), hydraulic fracture etc …
Other possible causes
As mentioned earlier, the earthquake is not the only cause: underwater volcanic eruptions can directly move water suddenly by collapsing an island or a crater.
In the same way, a spontaneous field (submarine or terrestrial) landslide can generate a large movement of water, like the 1958 Alaska tsunami, caused by the collapse of a mountain in a bay.
Another possibility, although much rarer, is an impact of meteorite. When for example 65 million years ago, a meteor of 10km in diameter crashed in the Mexico bay, creating a huge crater, and causing several tsunamis of 800 meters high.
