Why was the Morocco quake so deadly?

The death toll from the 6.8 magnitude quake that struck in the High Atlas Mountains of Morocco late on Friday stood close to 3,000 on Tuesday, with more than 5,000 people injured.

Hopes of finding survivors under the rubble were fading, not least because many of the traditional mud brick houses that are common in the mountain villages crumbled to earthen rubble without leaving air pockets.

Here’s an explainer on the latest quake and why such temblors are so deadly.

What areas were most affected in the Moroccan earthquake?

The epicentre was high in the Atlas Mountains about 70km south of Marrakech in Al Haouz province. The region is largely rural, made up of red-rock mountains, picturesque gorges and glistening streams and lakes.

The earthquake shook most of Morocco and caused injury and death in other provinces, including Marrakech, Taroudant and Chichaoua.

Why is Marrakech historic?

The city is Morocco’s most widely visited destination, known for its palaces and spice markets amongst other attractions.

The earthquake cracked and crumbled parts of the walls that surround Marrakech’s old city, a UNESCO World Heritage site built in the 12th century. Videos showed dust emanating from parts of the Koutoubia Mosque, one of the city’s best known historic sites.

How does this quake compare to other ones?

Friday’s earthquake was Morocco’s strongest in over a century, but, though such powerful tremors are rare, it isn’t the country’s deadliest.

Just over 60 years ago, the country was rocked by a magnitude-5.8 quake that killed over 12,000 people on its western coast, where the city of Agadir crumbled.

That quake prompted changes in construction rules in Morocco, but many buildings, especially rural homes, are not built to withstand such tremors.

There had not been any earthquakes stronger than magnitude 6.0 within 500 kilometers of Friday’s tremor in at least a century, according to the US0 Geological Survey. Northern Morocco experiences earthquakes more often, including tremors of magnitude 6.4 in 2004 and magnitude 6.3 in 2016.

Elsewhere this year, a magnitude 7.8 temblor that shook Syria and Turkey killed more than 21,600 people.

Was the Morocco quake similar to the one in Turkey in February?

In Turkey, there was a horizontal sliding of the (tectonic) plates towards the West, namely Greece.

In Morocco, there is a convergence between Africa and Eurasia or Iberia, the Spanish part, and overlapping faults.

Why did the quake in Morocco kill so many people?

The magnitude of the quake - 6.8 - was quite strong.

This corresponds roughly to an average displacement on the fault line of around one metre in a few seconds, over several kilometres. This shakes the region enormously.

The depth was estimated to be at around 25-30 kilometres, but it seems to be going back up to 10 kilometres, increasing the effect of the rupture

This is what happened in France in 2019 in the Teil region in the (southern) Ardeche region. It was a low-intensity earthquake, but as it occurred at a depth of just one kilometre, it shook things up a lot.

Is it possible to predict this kind of event?

Unfortunately, these kind of events cannot be predicted.

Scientists try to estimate the recurrence periods according to the different magnitudes of the earthquakes, but then the behaviour can be chaotic, with two strong earthquakes over a short period and then nothing for a very long time.

What are earthquakes?

Earthquake, also known as earth tremor, is the abrupt shaking of the Earth’s surface. This phenomenon is caused primarily by a sudden burst of energy from within the Earth, mainly when two slabs of Earth brush against each other.

An earthquake can, in some cases, be preceded by a foreshock. The foreshock is a small-scale tremor that occurs before the earthquake. After an earthquake comes to pass, small aftershocks can take place. They can last for years, occurring at intervals. The bigger and more vehement the main quake, the larger and more frequent the aftershocks.

What causes earthquakes?

One of the main causes of an earthquake is the movement of tectonic plates below the Earth’s surface. Two plates brush against each other causing friction. This abrupt release of energy in the form of energy waves causes quaking on the surface of the Earth. Tremors caused by the plates are known as Tectonic Earthquakes and are the most dangerous in terms of intensity.

However, earthquakes can be caused by several other elements as well, including volcanic eruptions, underground explosions, and human activity.

Volcanic eruptions can force two tectonic plates to move unexpectedly against each other which produces small ripples of energy waves on the surface. Underground explosions occur much in the same way.

Human activity like mining, extensive construction, or the launch of a nuclear weapon, can sometimes cause seismic waves to form, resulting in a Collapsing or Explosion Earthquake.

Why are some areas more prone to earthquakes?

The gaps between tectonic plates are called faults or fault lines. Areas that fall directly above these faults, or even on the marginal edge of a plate, are more at risk of an earthquake. Northern Japan, South America and Eastern Africa are some of the most earthquake-prone areas as they are located on top of fault lines.

Morocco, especially the northern region of the country, is located right above the fault line between the African and Eurasian tectonic plates. Due to this precarious positioning, high magnitude earthquakes in Morocco are an unsurprising occurrence with devastating consequences.

What are the effects of an earthquake?

Surface-level devastation, loss of life, and cracks along the crust of the Earth are only some of the ruinous aftereffects of an earthquake. Though rare, earthquakes can also instigate tsunamis and landslides.

In Japan’s Sendai earthquake of 2011, the 9.0 magnitude quake was followed by a 15-metre tsunami.

The collapse of buildings, telephone towers, power plants, and other hazardous constructions can cause widespread fires and dangerous radiation leaks.

How are earthquakes recorded?

Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at that site.

Seismographs are instruments used to record the motion of the ground during an earthquake. They are installed in the ground throughout the world and operated as part of a seismographic network.

How are quake magnitudes measured?

The Richter magnitude scale (often shortened to Richter scale) is the most common standard of measurement for earthquakes. It was invented in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes.

What are the major tectonic plates?

There are 7 major tectonic plates:

1. The Pacific Plate (102,900,000 sq. km.) – This plate lies beneath the Pacific Ocean. It stretches across the western region North America to the eastern coast of Japan. This mammoth plate is the base for most of the Pacific Ring of Fire.

2. The North American Plate (75,900,000 sq. km.) – This plate lies below North America and some parts of the Atlantic. It stretches from the North Pole to the northern regions of Japan.

3. The Eurasian Plate (67,800,000 sq. km.) – Trapped between the African and North American plates, this tectonic plate has its reach under most of Europe, Russia and a pinch of Asia.

4. The African Plate (61,300,000 sq. km.) – Sharing a diverging border with the North American Plate, this tectonic plate encompasses the whole continent of Africa and most of the Atlantic Ocean’s edges.

5. The Antarctic Plate (60,900,000 sq. km.) – This tectonic plate is surrounded by the 4 major plates – African, Australian, South American and Pacific

6. The Indo-Australian Plate (58,900,000 sq. km.) – Although the name joins the two – India and Australia – it is more often considered that the two plates are separate entities. This plate stretches its boundaries from India to Australia. One side of this plate congregates with the Pacific Plate.

7. The South American Plate (43,600,000 sq. km.) – This plate encompasses South America and some parts of the Atlantic Ocean. The west zone of this plate converges with several smaller plates as well as the Antarctic Plate. Due to this several high-intensity earthquakes are known to occur along these fault lines.

Along with these major plates, there are approximately 10 minor plates.

- Sampurna Dutta is an intern at Gulf News / with inputs from agencies