Why the earthquake in Morocco has caused so much damage

Mustapha Baitas, the government’s official spokesperson, told Al Jazeera on Monday that search and rescue teams are “all working hard”, but some have yet to reach some remote villages and areas in Taroudant and Al-Haouz.

“The main challenges are rocks falling which lead to closures on roads, but there are helicopters to reach the remote areas and provide help and aid,” he said, adding that more than 1,000 doctors and more than 1,500 nurses have been mobilised, along with all hospitals.

Shallow and dangerous

The USGS reported that the epicentre of the Friday earthquake was roughly 18.5 km below the Earth’s surface, though Morocco’s own seismic agency pegged the depth at 11 km. Either way, it was a fairly shallow quake.

According to experts, such quakes are generally more dangerous as they carry more energy when they emerge to the surface when compared to quakes that occur deeper underneath the surface. While deeper quakes do indeed spread farther as seismic waves move radially upwards to the surface, they lose energy while travelling greater distances.

The epicentre of the quake (red dot) is roughly 70km south west of Marrakech. (Source: USGS)

For instance, the earthquakes that hammered Turkey and Syria in February this year also emerged from shallow depths — while the first earthquake, of magnitude 7.8, originated 17.9 km below the Earth’s surface, the subsequent ones emerged from even closer to the surface. They caused the death of more than 50,000 people and destroyed about 1,60,000 buildings containing 5,20,000 apartments.

Apart from the depth, the magnitude of an earthquake is also an indicator of how destructive a quake could be. Magnitude tells how big the seismic waves are, while strength refers to the energy they carry. “While each whole number increase in magnitude represents a tenfold increase in the measured amplitude, it represents 32 times more energy release,” the USGS said.

Simply put, the seismic waves produced by a magnitude 6 earthquake have 10 times higher amplitude than the ones produced by a magnitude 5 earthquake. The energy differential is even higher, 32 times for every change of 1 in magnitude.

A rare quake and no preparation

Also, earthquakes are not very common in North Africa, with seismicity — the occurrence or frequency of quakes in a region — rates comparatively low along the northern margin of the African continent, according to the USGS. Lahcen Mhanni, Head of the Seismic Monitoring and Warning Department at the National Institute of Geophysics, told 2M TV that the earthquake was the strongest ever recorded in the mountain region, The AP reported.

This means that unlike regions which frequently face such quakes, Morocco was not prepared for such a calamity. While a 1960 earthquake, which was a magnitude 5.8 quake and killed thousands, did bring about changes to construction rules, most Moroccan buildings, especially in rural areas and older cities, are not built to withstand such strong tremors.

In Marrakech, many houses in the tightly packed old city, a UNESCO World Heritage Site, had collapsed. Footage of the mediaeval city wall showed big cracks and sections that had simply fallen off. Rescue teams are currently working to find people underneath the rubble. Many people continue to stay outdoors in fear of another quake.

In villages near the epicentre, things were possibly even worse. “Our neighbours are under the rubble and people are working hard to rescue them using available means in the village,” Montasir Itri, a resident of the mountain village of Asni near the epicentre, told Reuters, adding that most of the houses in the village were damaged. Villages such as Asni lie on the Atlas mountains, making access a major issue for authorities and rescue teams.

Why the quake occurred

While seismicity rates are indeed lower in the region, making earthquakes rarer, they are not completely unheard of. The 1960 quake, known as the Agadir earthquake, took place in coastal western Morocco. Not only this, earthquakes in the magnitude 6 range are more common in the “northern part of Morocco near the Mediterranean Sea,” according to the USGS. For example, a magnitude 6.4 earthquake struck in February 2004 and a magnitude 6.3 in January 2016 rocked the region.

A map of the major tectonic plates on our planet. The quake occurred roughly 500 km away from the point where the African and Eurasian plates meet. (Wikimedia Commons)

Such quakes occur due to the “northward convergence of the African plate with respect to the Eurasian plate along a complex plate boundary.” With respect to Friday’s quake, the USGS attributed it to “oblique-reverse faulting at shallow depth within the Moroccan High Atlas Mountain range”.

A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other, causing earthquakes if the movement occurs rapidly. During a quake, the rock on one side of the fault suddenly slips with respect to the other.
Scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of the slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults, whereas faults which move horizontally are known as strike-slip faults.

Here the the movement occurs, in two directions. Horizontal movement along the slip plane and vertical movement along the dip plane. (Wikimedia Commons)

Oblique-slip faults show characteristics of both dip-slip and strike-slip faults. The term ‘reverse’ refers to a situation where the upper block, above the fault plane, moves up and over the lower block. This type of faulting is common in areas of compression — when one tectonic plate is converging into another.

Earthquake-prone areas in India

Western Himalayas are one of the most dangerous seismic zones in the world. Scientists say the Himalayan region, the 2500-km stretch from the Hindu Kush mountains to the end of Arunachal Pradesh, is due for a big earthquake, of a magnitude over 8 on the Richter scale, anytime. This is because of the huge amount of energy stored along the faultlines due to the continuous interaction of different tectonic plates. The energy can be released only in the form of massive earthquakes.

Why earthquakes can’t be predicted

An accurate prediction of an earthquake requires some sort of a precursory signal from within the Earth that indicates a big quake is on the way. Moreover, the signal must occur only before large earthquakes so that it doesn’t indicate every small movement within the earth’s surface. Currently, there is no equipment to find such precursors, even if they exist.