Terremotos y Maremotos, ¿cómo se generan?


Although it seems incredible, earthquakes are very common and they happen constantly. If you look at the areas where earthquakes happen, they do not seem to be random. They delineate bands separating regions called lithospheric plates. These plates are the outermost part of our planet, formed by the crust and the uppermost part of the mantle, and move over a fluid layer called asthenosphere. It’s like cookies moving over custard. These cookies are in continuous movement with a ‘supersonic’ speed of… a few centimetres a year, similar to our nails growing. Yes, it is very slow, but this movement causes earthquakes, which are sudden ruptures of the interior of the Earth. With the motion, the plates move away, collide and rub against each other, and each movement generates a type of earthquakes. For example, at ocean ridges, which are long seafloor mountain ranges, the plates move away and produce shallow earthquakes of moderate size or magnitude, as occurs in the Atlantic ridge that crosses Iceland. Where the plates rub laterally, earthquakes also happen and often cause great damage because they occur near the surface, as in the San Francisco earthquake of 1906. And when two plates approach, the situation becomes more complicated: the plates collide, deform and overlap one over another. In these areas, the largest earthquakes of our planet happen, like in Japan in 2011, in Sumatra in 2004, and the biggest one, in Chile in 1960. And also the deepest earthquakes happen, up to 600 kilometres depth. An extreme case occurs when two continents collide; this generates a mountain range, like the Himalaya, created by the collision of India and Asia. This collision continues producing large earthquakes nowadays, such as the one in Nepal in 2015. If the earthquake is a sudden movement of the Earth, a tsunami is a sudden movement of water. A tsunami can be produced by the fall of a meteorite on the ocean, by avalanches and submarine volcanic eruptions, and also by an earthquake at the seafloor. The result is like throwing a stone into a pond: it generates a succession of waves that move away in all directions. Into the open sea, the waves of the tsunami travel at the speed of an airplane, but when they reach the coast, at shallower waters, they are slowed down by the seafloor and move more at the speed of a bicycle. On the contrary, the height of the waves increases when approaching the beach. The time between waves near the coast is usually about fifteen minutes. Earthquakes, tsunamis… sound exotic, but do they happen near us? Of course! The contact between the African and European plates produces earthquakes from the Alboran Sea to Saint Vincent Cape. And it was exactly there where one of the most destructive earthquakes of the Iberian Peninsula occurred. It generated a tsunami with 8 meters height waves in Cádiz, which also flooded Lisbon and reached England as well. This happened in 1755 and it could happen again. Today we know that the areas with largest seismic hazard of the country are the Pyrenees and the south and southeast of the Iberian Peninsula. The most recent destructive earthquake occurred just in the southeast, in 2011. It caused nine deaths and numerous damages in Lorca. And of course, we also have the Canary Islands, formed by volcanic activity that often produces earthquakes. About 700 earthquakes happen in the Canary Islands each year from the more than 3000 recorded annually in Spain. In the National Seismic Network, we are monitoring our territory continuously to keep us safer. Now you know that at the slow pace our nails grow, our planet moves generating tsunamis and earthquakes.

2 thoughts on “Terremotos y Maremotos, ¿cómo se generan?

  1. Enhorabuena!! Gran iniciativa poner la ciencia al alcance de todos!!

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