About two full weeks after the two earthquakes that struck southern Turkey and northern Syria on the sixth of last February, a new earthquake struck the state of Hatay in southern Turkey in the early hours of yesterday evening, Monday, February 20, with a magnitude of 6.4 on the scale, which caused In the fall of some buildings, and the return of terror once again to the atmosphere, whether in Turkey or in other countries, as the impact of the earthquake also reached Lebanon, Syria and Palestine, and people felt it in Egypt and several other countries.
But what everyone does not realize is that this region may have been subjected to more than 6,000 aftershocks during that short period, some of which were actually greater than 5 and 6 degrees on the scale, but the recent earthquake in Hatay was large enough for people to feel and fear compared to previous tremors. It has over the past two weeks, and although if compared to the main earthquake of magnitude 7.8 on the scale it is twenty-five times smaller, it is still generally a moderate to strong earthquake that can cause damage.
Of course, the strong potential impact of this earthquake is mainly due to the fact that the buildings had already been damaged by the first earthquake, and accordingly would be fragile in the face of any new strikes, in addition to the risks of landslides, gas leaks, fires and rock falls that could also complicate efforts. Rescue, but the positive side of the matter is that the loss of life will most likely be limited, because people have already moved away from the damaged buildings, and the personnel of the rescue teams are already aware of the presence of these additional tremors and are taking precautions to deal with the matter.
aftershocks
In fact, from the first moment, this region was expected to witness a large number of earthquakes following the first earthquake, which are called in their entirety as "aftershocks", and it is a natural phenomenon that occurs in all earthquakes, but is more noticeable in major earthquakes (such as the Turkey earthquake ).
For example, after the 2004 Great Sumatra earthquake of magnitude 9.1, there were 14 aftershocks of magnitude 5.7-7.3 that occurred along an arc from Sumatra towards Nicobar and the Andaman Islands in the Bay of Bengal.
The same thing happened when Nepal was hit by an earthquake measuring 7.8 on the scale on April 25, 2015. In the thirteen months that followed this event, the country faced 459 aftershocks with magnitudes equal to or greater than 4 degrees. The largest aftershock of 7.3 occurred three years later. Weeks after the main earthquake, on 12 May, causing further damage to already damaged buildings and infrastructure.
But to understand how these aftershocks happen, let's start with the way earthquakes generally occur. The Earth's lithosphere (30 to 70 km thick on the continents and 6 to 12 km thick in the oceans) is made up of a number of pieces called tectonic plates. Which overlap with each other in a way that resembles paper puzzles, these plates move slowly, or say they swim for a distance of centimeters every year on another layer of the earth that lies below it and is called the mantle, and therefore we do not notice its impact.
Plate tectonics around the world (Wikipedia)
These tectonic plates are moving away from each other in places and approaching in others, and as the sides of two tectonic plates approach each other in one place, they rub against each other to create what scientists call the “fault”. The nature of the fault’s friction differs according to the nature of the rocks that rub against each other. And the direction of movement, the two sides of the cloud may slide in opposite directions, but at the same level, or one of them may move up or down.
In the normal case, the edges of the plates slide slowly and smoothly, but sometimes it is not like this, to understand that idea, imagine that there are two large marble pieces, each of which has a non-smooth face, we tied the top of them with a strong rope and began to pull it, at first it does not move We increase the tensile strength, and with the tension, the marble suddenly slips and moves for several centimeters, and during its movement, you notice that it vibrates severely.
This is exactly what happens in the case of an earthquake, but instead of the vertical position, the rocks of the ends of the two plates meet horizontally. Sometimes they rub against each other so they stand for a while, while each of them stores energy in this friction (this is the case in which you try to stretch but the piece of marble Don't move yet) and at some point that energy escapes, and those rocks move to an unusually large distance, and with their displacement, the energy starts to run everywhere in the planet, but it hits the closest points to it with the greatest force.
The borders of the three tectonic plates that form the features of the earth and natural phenomena (Al Jazeera and agencies)
Therefore, earthquakes are known as a measure of energy trapped between the rocks of the earth's crust, which emerges in the form of tremors on the surface, but this sudden release of energy resulting from the cracking of rocks in the first tremor causes friction on nearby rocks, which in turn stores a measure of energy as well, and with the accumulation of pressure these are destroyed. The rocks trigger a series of smaller tremors, which in turn give rise to smaller tremors.
For this reason, aftershocks usually occur near the epicenter of the main earthquake, but this does not prevent them from occurring in more distant areas in the country, and sometimes the main earthquake can cause other new, separate earthquakes related to the interaction of neighboring tectonic plates, whose movements are strained by The first earthquake, but in both cases things calm down with time and the tectonic plates settle again after emptying the stored energy.
The size of the tremors
Scientists are not always in agreement about the nature of aftershocks or prognostic tremors, and there is always debate about whether or not the aftershocks are related.
(Anatolia)
US Geological Survey scientists expect that there are at least one out of every 20 major earthquakes in the world usually followed by another major earthquake (but less than the first) during the first week, and these results are confirmed by a study conducted in 2002 on 117 earthquakes with a magnitude of 7.0 on the scale or higher , I found that only 13 of them were followed by nearby earthquakes that were at least of the same strength, and this seems to be what happened in the case of the Turkey earthquake, where the main tremor was followed by a large tremor of magnitude 7.5 after only nine hours and at a distance of about 90 km from the epicenter of the first tremor, which is rare case.
But in general, the greatest probability according to "Båth's Law" in geology is that aftershocks are usually of a value on the scale less than the main earthquake by a difference of about 1.2 degrees.
According to Omori's Law, the rates of aftershocks decrease with the passage of time, but they may continue for months or even years. This means that it is likely that Turkey and Syria will continue to experience tremors, but they will be smaller in scale, and at some point. You will reach a point that humans do not sense, but there is always a small chance of large aftershocks occurring even months after the first earthquake, and in very rare times the opposite may happen, where the first quake is less than the aftershock in strength, and here the first quake is redefined As a "foreshock", that is, a precursor to a greater shock.
Poor odds
One example of this case is the Sumatra earthquake on December 26, 2004, which we talked about a short while ago, as it was preceded by two full years of another earthquake of magnitude 7.3, on November 2, 2002. Some researchers believe that the first was a harbinger of the second largest. On the scale, it is considered one of the most powerful earthquakes to ever hit Earth.
In terms of damage and loss of life, the magnitude of the disaster caused by this earthquake and the tsunami that followed (the Boxing Day tsunami) was enormous, with about 230,000 people killed and missing, and about 1.7 million people displaced their homes.
Another example is the Great Chilean earthquake, which is the strongest earthquake recorded in history with a magnitude of 9.5 on the scale. It occurred on the afternoon of May 22, 1960, and the country had witnessed just one day before that another earthquake with a magnitude of 7.9. People thought it was the main earthquake, until the earthquake came. Bigger the next day.
In any case, scientists do not always agree on the nature of aftershocks or foreboding tremors, and there is always debate about whether the tremors are related or not, and it may appear that the second earthquake in Turkey or others like this earthquake were not aftershocks but rather a separate earthquake, especially Contrary to the usual, the new earthquake was larger in scale than the previous aftershocks.
But again, whether it is an aftershock or a new earthquake, the highest possibilities are that Turkey and its surroundings will continue to experience smaller tremors with time until the tectonic plates stabilize. These tremors reach at some point a level that people do not feel. This type of disturbance is known and occurs in All earthquakes, and what is happening now is no exception.