The plate boundary region in Morocco is very complex, as there are multiple areas of active faults instead of one well-defined fault, and since the relative movements are slow, it is difficult to use geodesy tools to determine which faults are active and how fast they are moving
About 399 years after the earthquake of May 11, 1624 – which struck the city of Fez, which a study published in 2017 described as “one of the worst natural disasters in the history of Morocco” – the country was exposed on the evening of Friday, September 9, 2023, to a similar earthquake.
A magnitude 6.8 earthquake struck about 70 kilometers southwest of Marrakesh at 11:11 p.m. local time. It was felt in large areas in the north and northeast of Morocco, and was felt in areas of Algeria, Spain and Portugal.
According to earthquake strength standards, an earthquake with a magnitude of 6.8 is considered a strong earthquake, but even moderate-strength earthquakes are capable of causing serious damage to this region. About 140 kilometers to the southwest of the last earthquake area, an earthquake with a magnitude of 5.8 in 1960 killed Between 12 thousand and 15 thousand people.
Compared to the 1960 earthquake
A 5.8 magnitude quake releases about 10 times less energy than a 6.8 earthquake like the one that occurred Friday evening (a correct one on seismometers means a 10-fold increase), yet the catastrophic damage in the 1960 quake was due in part to buildings built with compressed clay. Sand and gravel were rammed to form walls and structures, and these buildings collapsed completely, as inadequate construction is usually the largest contributor to earthquake disasters.
Although the 1960 earthquake led to changes in building rules in Morocco, many buildings – especially rural homes – did not comply with these rules, which Bill McGuire, professor of geophysical and climate risks at University College London, attributes to the rare occurrence of large earthquakes in Morocco.
McGuire says in a report published by the American Associated Press, “The problem is that when devastating earthquakes are rare, buildings are simply not built with sufficient strength to deal with strong earthquakes, which leads to many of them collapsing and causing a large number of victims.”
Based on the strength of the earthquake and the weakness of local buildings, the US Geological Survey’s Prompt Global Earthquake Evaluation System (BAGER) predicted that there would be major deaths, but the US Geological Survey confirmed that these estimates were uncertain, as similar earthquakes had not occurred in this part of Morocco to the extent Enough to train their AI system to make an accurate prediction.
The infrequency of earthquakes also affected the ability of the Global Earthquake Assessment System to provide reliable estimates of losses and limited the ability of researchers to accurately conceptualize the causes that led to the ground moving with a magnitude of 6.8 in a different area than the earthquake of May 11, 1624.
According to the US Geological Survey, earthquakes with a magnitude of 6 or stronger are not common in this region. Since 1900, no earthquake with a magnitude of 6 or stronger has occurred within 500 kilometers of this earthquake, and only 9 earthquakes with a magnitude of 5 or stronger have occurred, and most These tremors occurred to the east of the September 8, 2023 earthquake.
So, what happened?
Zakaria Hamimi, Vice President of the International Federation for Geoscience Ethics, told Al Jazeera Net, “There is great difficulty in understanding what happened in Morocco. In addition to the scarcity of large-scale earthquakes in the past, which helps us understand what happened on September 8, 2023, the location of Morocco is very complex.” “.
He explains, “Morocco is located along the border of an unknown and slow-moving tectonic plate that separates North Africa (the Nubian plate, or what is called the African plate) and Europe (the Eurasian plate), and the Eurasian plate moves south and east relative to the Nubian plate at a rate of only 4 millimeters per year.”
Tectonic plates are rock blocks that move very slowly relative to each other, usually a few centimeters per year. This movement, even if it is slow, causes a huge amount of faults at the plate boundaries, which in turn causes earthquakes.
Hamimi adds, “The plate boundary region in Morocco is very complex, as there are multiple areas of active faults instead of one well-defined fault, and because the relative movements are slow, it is difficult to use the tools of geodesy (a science that investigates topics related to the Earth’s size, shape, dimensions, interior, and magnetic field.” And the temperature of its interior) to determine active faults and how quickly they are actually moving.”
Eljazeera
