Why have the earthquakes in Turkey and Syria been so devastating? “The population has to prepare for months of aftershocks”

The devastation caused by the earthquakes suffered in Turkey and Syria once again shows the force that can be unleashed in these events and the risk associated with these hot spots on the planet.

But numerous doubts arise about this phenomenon, its origin and its consequences.

We answer them with the help of seismologists:

How did the earthquake occur?

The main earthquake, of magnitude 7.8, does not occur in a single point, although it is located that way on the maps.

"It is not instantaneous, nor is it at a point, it propagates throughout the entire fault and lasts 30 seconds," explains seismologist Itahiza Domínguez, from the National Geographic Institute (IGN).

“The size of the fault where the displacement occurs is 200 kilometers and the rupture moves along the entire fault.

The point where we located the epicenter is where the first seismic wave that reaches the seismographs has started”, details the expert, although the fracture and the earthquake occur in all those kilometers of fracture, as the map shows (below). .

More information

Earthquakes in Turkey and Syria, last minute live

The earthquake occurs on a long tearing fault: two tectonic plates rub horizontally, like the blocks of a puzzle.

The energy of the collision between the two plates has been concentrated at that point until it breaks and suddenly releases the energy.

The consequent aftershocks of the initial earthquake occur on that fault, the Eastern Anatolian fault, more than 500 kilometers long.

Is the second big earthquake of 7.5 an aftershock?

Nine hours after the first earthquake, another one hits to the north, measuring 7.5.

Some definitions of the word "aftershock" exclude earthquakes that are similar in size to the main one, or that occur far from the initial rupture.

In this case, it occurred on a different fault (the Sürgü and Çardak fault) and is almost the same magnitude.

It is a semantic or academic question, and specialists are divided between those who consider it a replica and those who suggest that it is a different seismic event, driven by the initial one.

"The first earthquake of 7.8 detonated a smaller one, a few minutes later, of 6.7: those are brothers," explains seismologist Gina Villalobos, from the Autonomous University of Tamaulipas.

“The 7.5 occurs further north and what I interpret is that the entire area was accumulating efforts and it was a matter of time before a fault broke.

The initial quake destabilized the entire region because it was an area charged with energy, ”she points out.

And she concludes: "It is not a replica, because it does not even occur in the same fault segment."

Domínguez agrees with this diagnosis: “The 7.8 triggers the 7.5, which would have released its energy independently after a while.

The initial earthquake affected the tectonics of the area: with a 200-kilometre fault, it affects everything around it, tensions that are released in a chain with new earthquakes”.

It appears to confirm that yesterday's massive M7.8 and M7.5 quakes were two separate events, not aftershocks.

One shot the other in a matter of hours.

https://t.co/atGKGnH5Bz

— IGEO (CSIC-UCM) (@IGeociencias) February 7, 2023

However, other specialists consider it a replica, such as Luis Cabañas, from the National Seismic Network: “It belongs to the same seismic series, although it is on another fault in another direction in that same extensive area.

It really is a break that has jumped from one side to the other, trigger the other: there is no simple line, but the region is full of fractures grouped one on top of the other.

The United States Geological Survey, the reference, speaks of "aftershock"

its communications.

And how long will the aftershocks last?

In any case, both the 7.8 earthquake and the following 7.5 earthquake generated significant aftershocks, making rescue tasks difficult and putting more affected buildings and infrastructure at risk.

In total, the two major earthquakes have been hit by some 135 major aftershocks, above magnitude 4, and hundreds of smaller ones.

“It cannot be said categorically how long it will last, but the rearrangement of the plates can last for months and even years.

The population has to be prepared for months of aftershocks,” warns Villalobos.

The experts consulted agree on this, such as Cabañas: “They can wait for more than six months.

The magnitudes of the aftershocks will decrease and the thrusts of the area will continue causing the plates to slide until another blockade occurs.

The stabilization of the seismic region takes a long time after such a brutal crustal rupture.

Domínguez summarizes it: “We can expect months of aftershocks, because there is a remnant seismicity for a while.

A few days minimum, but it all depends on the terrain, how the system rebalances, and other parameters.”

How do we measure the force of an earthquake?

"The two parameters used to measure earthquakes are magnitude and intensity," says the expert from the Autonomous University of Tamaulipas.

“Magnitude expresses the net energy that was released: a 9 releases 32 times more than an 8, regardless of where it is produced or who is affected,” she details.

Instead, the intensity measures the social and environmental impact: people affected, buildings hit, etc.

So even though the 7.8 released three times as much energy as the 7.5, the two are in the same category in terms of intensity: IX, very destructive.

Nine, in Roman numerals, on a scale —called Mercalli— that goes from I (very weak) to XII (catastrophic).

The two were very close to the towns and the second struck buildings that had been hit, thus equalizing their damage.

The one in Lorca in 2011 was intensity VII,

very strong, with nine fatalities and more than 300 injured.

In addition, as Domínguez explains, "the one in Lorca was similar, tearing, very close to the population", but only of magnitude 5.1, which means that it released 7,700 times less energy under the town.

That of Amatrice in Italy in 2016, of magnitude 6.2 and almost 300 deaths, was 38 times more energetic than that of Lorca, according to calculations by Itahiza Domínguez.

Could it be predicted?

Large earthquakes can be expected, because we know where the most conflictive points are, the areas with the greatest risk of active faults, such as the San Andreas fault in California, which, structurally, is very similar to the one that caused the catastrophe in Turkey and Syria.

But it is impossible to know when they will occur.

Although that did not prevent a group of Italian geologists from being sentenced to jail in Italy for assuring that "there is no danger" shortly before the L'Aquila earthquake.

“Earthquakes cannot be accurately forecast, so preventing consequences depends on preparedness (for example, through earthquake-resistant infrastructure) and efficient response.

Unfortunately, resilient infrastructure is patchy in southern Turkey and especially in Syria,

so saving lives now depends mainly on the response.

The next 24 hours are crucial to finding survivors;

after 48 hours, the number of survivors decreases enormously”, explains Carmen Solana, an expert in Volcanology and Risk Communication at the University of Portsmouth, to SMC.

Why has it caused so much devastation?

"In this case, it has been of great intensity because it has occurred in a highly populated area and in very shallow areas, close to the surface, with which there is no margin for the energy to dissipate," Villalobos points out.

And he adds: "The old constructions are added, without earthquake-resistant construction requirements, and with each earthquake they have been weakening."

Added to these structural conditions is the time the first earthquake occurred: early morning local time, which surprised people sleeping inside the buildings.

The Colombian expert compares it with what happened in Mexico City, where they suffered an earthquake in 1985 with "many thousands of deaths and they learned their lesson, they got their act together."

“Now, in the city, the building codes add scientific rigor and technical rigor.

In the rest of Mexico, other areas remain in absolute neglect.

In Chile, nothing happens with larger magnitude earthquakes because they know what they are facing and act accordingly,” she says.

"Maybe they fell asleep in Turkey," the expert muses, who regrets that in some risky regions there is what she calls "social myopia: neither I nor my parents experienced it, I don't think it will happen."

And she warns: "Decisions should be made thinking about the geological time frame, not the anthropological one."

Magnitude, scale, Richter, degrees...?

These quakes, according to the measurements available to us now, are magnitude 7.8 and 7.5.

There is no talk of degrees on that magnitude scale and they are not on the Richter scale either, but on a more precise one called "seismic moment magnitude".

“The Richter scale is more for local phenomena, for instruments from the time it was created [1935s], above magnitude 6.5 it saturates.

It works for moderate regional earthquakes, not for events that release so much energy;

for those, the magnitude of the seismic moment is used,” explains Cabañas, an expert from the National Seismic Network.

That is, above magnitude 6.5 the Richter scale is useless and it is better to use the "moment" scale.

But it is not necessary to add surnames to the data: it is worth saying "an earthquake of magnitude 7.8".

Why has it occurred in that area?

“Turkey is one of the most seismically active regions in the world because it is crossed by two major faults: the North Anatolian fault, which borders the Eurasian plate, and extends from the Armenian plateau to the Marmara Sea;

and the eastern Anatolian fault”, according to CSIC geologist Rosa María Mateos.

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