Why was the Morocco earthquake so deadly?
The quake, which has killed thousands, was unusually large for Morocco and struck a region where most buildings are not earthquake-resilient
Morocco is dealing with the aftermath of its most devastating earthquake for decades. The tremor, which hit on 8 September in the High Atlas mountain range, around 70 kilometres southwest of Marrakesh, has killed more than 2,800 people, with thousands more injured. The death toll seems likely to rise as rescue and recovery efforts continue. Why was the quake so deadly?
Multiple factors have contributed, according to seismologists and disaster risk-reduction specialists.
The first was magnitude. At 6.8, the earthquake was not huge – the one that devastated parts of Turkey and Syria in February, for example, was magnitude 7.8. But it was unusually large for Morocco. “It’s exceptional for the region,” says Rémy Bossu, secretary-general of the Euro-Mediterranean Seismological Centre in Bruyères le Châtel, France.
Northern Africa is moderately seismically active. Tremors are caused by the ongoing collision of the African and Eurasian tectonic plates. “The collision explains the seismicity from Turkey to Gibraltar,” says Bossu.
Both are continental plates, adds Ziggy Lubkowski, associate director of seismic design at the engineering consultancy Arup in London. Consequently, the collision has forced rock upwards, creating the Atlas Mountains in the region where Friday’s quake happened. “It’s a rather complex, old collision.”
Maximum magnitude unknown
Because the region is only moderately active, really big earthquakes are rare, happening only once every few hundred years. Unfortunately, seismological records do not go back far enough to say how big earthquakes in this region can get, says Bossu. “It is challenging to evaluate the maximum magnitude, especially in moderate seismicity environments, because our observations are far too short.”
A further complication is the nature of the plate boundary. In some regions, like Turkey, there is a single clear boundary. But in northern Africa there is “a network of faults in a much larger area”, says Bossu. Instead of a localised region with a high risk of tremors, a large area has a low but still significant risk.
However, the biggest contributor to the disaster has been lack of preparedness, says disaster researcher Ilan Kelman at University College London in the UK. “Earthquakes don’t kill people, collapsing infrastructure does,” he says. “This was so devastating simply because people were not ready for it.”
Even moderate earthquakes can be lethal if societies are not prepared, says Kelman. He highlights the magnitude 5.9 quake that struck Agadir in Morocco on 29 February 1960. About one-third of the city’s population was killed and another third injured, mostly by collapsing buildings. Despite also not being a huge tremor, the USGS calls it “the most destructive ‘moderate’ quake (magnitude less than 6) in the 20th Century”.
Lack of preparation
Before the quake on 9 September, there was reason to believe Morocco could experience strong earthquakes. Kelman highlights a 2007 study that counted 1739 major earthquakes – defined as greater than magnitude 3 and not including aftershocks – in the country between 1045 and 2005, based largely on historical descriptions1.
And yet most buildings in the affected area were built of masonry and 'aggregate' — particulate matter such as gravel or sand — which is prone to collapse, says Kelman. Strengthening buildings with stronger materials such as reinforced concrete can help, but such measures might not have been practical for the area, which has high levels of poverty, he says.
Buildings in Morocco are often designed to control for extremes of temperature, which are an ever-present risk, whereas earthquake resilience has taken a back seat, in part because they are rarer, says Kelman. However, in some other regions traditional building materials like masonry or adobe have been successful adapted to be earthquake-resilient. “We know we can do it,” he says.
When attempting to make buildings more resilient to earthquakes, the most important thing is to talk to local people, says Kelman. “They know their architecture, they know what works for their needs,” he says.
Kelman says it is also crucial to think about earthquake resilience as part of sustainable development. People are often advised to have a “go bag” that contains essentials like bottled water, non-perishable food, medicines and a means of communication – but they need to have enough money to be able to afford to maintain it.
Consequently, he says building earthquake resilience means tackling broader societal problems like poverty and lack of education. “All aspects of disasters are political,” says Kelman. “All disaster risk reduction is about development.”
doi: https://doi.org/10.1038/d41586-023-02880-3
This story originally appeared on: Nature - Author:Michael Marshall
