a seismologist explains what happened

A very large earthquake has occurred in the south-east of Turkey, near the border with Syria. Data from seismometers that measure ground shaking caused by earthquake waves indicate that this event was a magnitude 7.8 out of 10 on the moment magnitude scale. Seismic waves were picked up by sensors around the world (you can watch them ripple through Europe) including places as far away United Kingdom.

This was a really big one.

The quake has already had dire consequences for people living nearby due to energy traveling away from the source or epicenter. Many buildings have collapsed, at least 2,000 people are estimated to have died across the two countries, and there are reports of gas pipelines being damaged leading to fires.

Why did this happen here

There are earthquakes in this area of ​​Turkey because it is located at the intersection of three of the tectonic plates in the Earth’s crust: the Anatolian, Arabian and African plates. Arabia is moving north into Europe, causing the Anatolian plate (on which Turkey sits) to be pushed out to the west.

Map of tectonic plate movements around Turkey

Map of tectonic plate movements around Turkey

The movement of tectonic plates increases pressure on fault zones at their boundaries. Earthquakes and earthquakes are caused by the sudden release of this pressure.

This latest earthquake probably occurred on one of the major faults that mark the boundaries between the Anatolian and Arabian plates: either the East Anatolian fault or the Dead Sea Transform fault. These are “strike-slip faults”, which means they accommodate some motion of plates moving over each other.

‘More significant’ than previous earthquakes

Although there are many earthquakes in this area every year due to the constant motion of the tectonic plates, today’s earthquake is particularly large and devastating because so much energy was released. The United States Geological Survey (USGS) says only three earthquakes greater than magnitude 6 have occurred within 250km of this location since 1970. At magnitude 7.8, the February 6 event is far larger than previous ones in the area , releasing more than twice. as much energy as the largest earthquake previously recorded in the region (size 7.4).

Modern seismologists use the minute magnitude scale, which represents the amount of energy released by an earthquake (the Richter scale is outdated, although it is sometimes misquoted in the news). This scale is non-linear: each step up represents 32 times more energy released. That means a magnitude 7.8 releases about 6,000 times more energy than the more moderate magnitude 5 earthquakes that might normally occur in the region.

We tend to think of earthquake energy as coming from a single location, or epicenter, but they are actually caused by movement along a fault area. The bigger the earthquake, the more area the fault will have moved. For something as large as this magnitude 7.8 there was probably movement over an area about 190km long and 25km wide. This means that the shaking will be felt over a very large area.

An estimated 610,000 people in the surrounding area felt violently intense shaking (enough to cause significant property damage) up to about 80km to the northeast along the tectonic plate boundary. Light tremors were felt as far away as the Turkish capital Istanbul (about 815km away), as well as Baghdad in Iraq (800km) and Cairo in Egypt (950km).

What about aftershocks?

Large earthquakes are followed by many smaller earthquakes called aftershocks as the crust adjusts to the changes in stress. These can continue for days to years after the initial event. In the first 12 hours after the initial earthquake in southeastern Turkey there were already three other earthquakes above magnitude 6.0. The first one was 6.7 which happened only 11 minutes after the first shock, and there were hundreds of smaller aftershocks.

Later this morning another very large magnitude 7.5 occurred further north on a different but adjacent fault system: the Sürgü Fault. Technically, this one was powerful enough to count as a separate earthquake in its own right, although it was probably triggered by the first earthquake, and will create its own series of aftershocks.

Although usually much smaller than the main shock, they can have equally devastating consequences, further damaging the infrastructure damaged by the first earthquake and hampering rescue efforts.

As the people living in this region feel the aftermath of this major earthquake, we can only hope that Turkey and Syria receive international assistance as soon as possible to help with ongoing rescue efforts, among the continuous action.

This article from The Conversation is republished under a Creative Commons license. Read the original article.

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Jenny Jenkins does not work for, consult with, or own shares in, or receive funding from, any company or organization that would benefit from this article, and she has disclosed no relevant relationships beyond her academic appointment.

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