Madrid (EFE).- Magnitude, intensity or measurement scales are some of the concepts related to earthquakes, phenomena that occur constantly in the world although often negligible, with few exceptions, which make them catastrophic because they exceed a series of thresholds , like those of Turkey and several surrounding countries this morning.
Some of the keys to understanding the severity of earthquakes, according to the National Geographic Institute (IGN) of Spain, are the following:
How are they produced?
The areas in which earthquakes occur do not seem random, they delineate strips that separate regions.
These plates are the outermost part of the planet and move on a fluid layer. This movement causes earthquakes, that is, sudden ruptures of the interior of the earth. As the plates move away, they collide and rub laterally, and each movement generates a type of earthquake.
What are the most dangerous earthquakes?
When two plates get closer, the situation becomes more complicated. Plates collide, warp, and overlap one on top of the other. This is how the largest earthquakes occur, such as the one in Japan in 2011, or the one in Sumatra in 2004, or the one in Chile in 1960. The deepest earthquakes also occur in this way, up to 600 kilometers underground.
Extreme cases occur when two continents collide, creating a range of mountains like the Himalayas, created by the collision of India and Asia. That collision continues to produce large earthquakes like the one in Nepal in 2015.
How are they different from tidal waves?
The earthquake is a sudden movement of the earth, while the tsunami is a sudden movement of the water. The tsunami can be generated by the fall of a meteorite in the ocean, by avalanches and submarine volcanic eruptions, and also by an earthquake at the bottom of the sea.
The result is like throwing a stone into a pond, which generates a succession of waves that recede in all directions on the high seas. Tsunami waves travel at the speed of an airplane, but when they reach the shallow shore they slow down against the bottom and move more slowly even though the height of the waves increases as they approach the beach.
What is the seismic magnitude?
The magnitude of an earthquake measures, with the help of instruments, the energy released by the earthquake. It is a unique and objective value for each earthquake that does not depend on where you are.
How are earthquakes measured?
On various scales depending on the type of earthquake, the measurement system, etc. The best known is Richter’s (1935), but others are currently used, preferably the moment magnitude scale (Mw), which coincides with Richter’s only in earthquakes of magnitude less than 6.9.
Magnitude scales do not have a stop for their measurement. For example, the 1960 Valdivia (Chile) earthquake registered a magnitude of 9.5 and the 2004 earthquake in the Indian Ocean off the island of Sumatra was 9.3.
What is intensity?
The intensity of an earthquake indicates how its effect has been felt in a place. How people have suffered from it, its impact on objects and damage to buildings. Its value differs depending on the distance from each place where it has been felt to the epicenter. The seismological institutes usually give the data of maximum intensity, that is, how it has felt in the most affected place.
What are the intensity scales?
There are several scales for measuring intensity: the two main ones are the Mercalli scale and the European Macroseismic Scale (EMS). Both have twelve degrees expressed in Roman numerals from I (very weak or barely felt) to XII (catastrophic or completely devastating).