Neither all earthquakes in the sea cause tsunamis, nor all tsunamis have their origin in an earthquake. One like this Wednesday occurs only when certain factors coincide that generate that massive movement of marine waters. In general, there must be an important earthquake whose epicenter (the projection on the surface of its underground origin) is in the seabed or not far from the coast. In addition, the earthquake mechanism must generally lead to that gigantic impulse of the waters, because there is a break of the seabed, with a sudden thrust from the oceanic background vertically. That is, the earthquake has to occur under the sea and releasing a lot of energy in a vertical movement, so that the cortex thrust up or down the water column that it has.
How do you know when you have to launch an alert?
Generate waves that spread at high speed through the ocean, up to 800 kilometers per hour in an open sea. But seismic waves travel much faster than tsunami, so, once there has been a great earthquake like this Wednesday in the Russian Peninsula of Kamchatka, alert systems can predict the behavior, direction and arrival of the phenomenon with sufficient margin of time to alert the population. Specifically, in the Pacific region there are many countries with great experience facing tsunamis, such as Japan, USA and Chile, which allows them to react very quickly. He has advanced his projections shortly after the earthquake, predicting waves on the Russian coasts, Ecuador and the Hawaii Islands. In the latter, the first waves have been measured above the meter high on the island of thread, after touring the tsunami about 5,000 kilometers since its origin.
What factors aggravate the risk?
There are several factors that can aggravate the risk that an earthquake derives in Tsunami, such as when it occurs under the sea or very close to the coast. The risk increases, above all, when the earthquake is of great magnitude (7 or more), it is shallow and causes a vertical displacement of the seabed, either raising or sinking the ground. This type of movements mobilizes huge volumes of water. In addition, earthquakes can also trigger ground landslides that push water and generate very large waves. Joanna Faure Walker, professor of earthquake geology and disaster risk reduction at the University College in London, explained in a statement of the Media Center science (SMC) that, in addition, also influences the displacement of the seabed, the depth and shape of the coastal line, and the existence of sea barriers or physical protection measures. As well as the obstacles on land, whether natural or built by the human being. “The extensive areas of low land are particularly vulnerable, since they can be largely devastated by a tsunami,” he said.
How long do you have to be alert?
The time between the earthquake and the arrival of the waves depends on the distance. If the epicenter is very close to the coast, the waves can arrive in a few minutes, sometimes in less than 10 or 20. If the epicenter is further, the waves take more, even hours, and the alert systems can warn in time, as happened in this case in Japan and the US It is the greatest.
What to do in case of a tsunami?
In case of Tsunami, the key is to act quickly and without waiting for official instructions when there are clear danger signs. In case of being on the coast and feeling that a strong and prolonged earthquake occurs, the most sensible thing is to assume that a tsunami can follow. It is also necessary to react if it is observed that the sea is removed suddenly, leaving the dry beach, or if a strange and strong noise from the sea begins to sound, similar to a roar, produced by the movement of the water.
Before any of these signs, the safest thing is to get away immediately from the coast and go to high areas or inland, at least two kilometers inwards or high places, such as hills or several -story buildings. It is important not to look at the sea or try to approach what happens.
During the evacuation, if there is traffic congestion, it is preferable to move on foot so as not to get caught. You should not return to the beach until the authorities indicate it, since several waves can occur over hours. After tsunami, you have to comply with the instructions of the Civil Guard, avoid entering flooded areas or touching fallen cables. Help to other people should be done whenever it does not imply putting personal safety at risk.
Is there danger in the high seas?
In the deep ocean, the tsunamis have lengths of hundreds of kilometers and heights of only a few meters, making them imperceptible. That is why it is often said that sailors on the high seas will not normally notice a tsunami when it passes below the helmets of their ships. However, when approaching the coast, the speed decreases and the height of the wave increases, being able to exceed 30 meters. Therefore, real danger is decided in the last kilometers, when the tsunami generated by an earthquake leaves the deep ocean and reaches the coast, where the coastal geomorphology is crucial to dissipate its strength or aggravate its intensity.
How strong was the earthquake?
Kamchatka’s 8.8 earthquake is registered in the world since 1900, according to the United States Geological Service. It is the worst since the tragic 9.0 earthquake that emerged in Tohoku (Japan) in 2011, which caused the Fukushima tsunami that swept its nuclear power plant.
Was such an earthquake expected?
This Wednesday is the last of a sequence of Seísmos started 10 days ago off the coast of the Kamchatka Peninsula. Before the earthquake on Wednesday, another 50 of magnitude were recorded greater than 5, including one of 7.4 on July 20, as highlighted by the United States Geological Service. This July 30, 24 replicas have been detected with a magnitude greater than 5, including a 6.9.
Why does Kamchatka move?
The outer layer of the earth is divided into huge tectonic plates that fit like the pieces of a puzzle. The earthquake has occurred in a very active region seismically, in which the Pacific plate slides below the North American plate. In the region of the Kamchatka Peninsula, the Pacific plaque moves northwest at a speed of about eight centimeters every year, which makes it one of the fastest convergent edges in the world, according to the United States geological service. In 1952 there was already an earthquake of magnitude 9, with an epicenter located just 30 kilometers from this Wednesday. Since then, the plate has moved almost six meters. In 1923, another great earthquake, of magnitude 8.4, shook the Russian peninsula. The American agency believes that the 8.8 earthquake on Wednesday has filled “any small emptiness” between the 1923 break and that of 1952.
