The earthquake struck about 75km southwest of Marrakech. Source: The Conversation / OpenStreetMap
At a relatively shallow depth of about 20km, “severe” ground-shaking intensities were reported around the quake’s epicentre, where several remote villages are located.
The ground shaking associated with the earthquake resulted in the total collapse of many dwellings near its epicentre, a great number of which were traditional mud brick constructions. Rockfalls and landslides have buried villages in the remote, mountainous region.
Sadly these numbers will probably increase. Significant aftershocks are possible in the weeks and months following an earthquake of this magnitude. These may result in the collapse of buildings that were damaged – but remained standing – during the main shock.
Brittle buildings crumbled from the impact
Sobering photos and videos have emerged from Morocco, showing a level of structural damage and destruction that’s hard to comprehend. Close to the epicentre in the mountains, villages with rural dwellings, largely constructed from mud brick and stone, seem to have been pulverised. These types of structures are extremely brittle and essentially provide little, if any, seismic resistance.
Although it’s too early to gauge the full extent of the impact, initial reports suggest some of the city’s historical treasures, including the 12th-century Koutoubia Mosque and the renowned red walls, may have suffered some damage.
Destroyed houses and buildings in the city of Amizmiz, southwest of Marrakesh. Source: ABACA / Lafargue Raphael
Much of the damage observed to new construction appears to be attributed to reinforced concrete frame buildings filled with brittle, hollow red clay bricks. The mortar holding the bricks together quickly cracks, which greatly reduces the stiffness of the overall structure.
To compensate, the reinforced concrete frame will attempt to resist the large horizontal loads. But without an abundance of carefully placed reinforcing steel embedded in the concrete (particularly where the beams meet the columns), it’s unlikely such a structure will survive a large earthquake. Other lateral load-resisting systems could be employed, such as walls, but these also require careful steel reinforcements – which increases the cost of construction.
A lack of building codes and regulations
Areas that have more stringent building codes and regulations, and that enforce the use of appropriate building materials, generally weather seismic events better. This is particularly true for regions that also apply simple design philosophies, such as the “capacity design” approach.
Damaged buildings in Asni, south of Marrakesh, Morocco. Source: EPA / Yoan Valat
In essence, this approach compels engineers to carefully consider how and where damage will occur, enabling certain components of a building to absorb and dissipate energy, while ensuring the structure doesn’t collapse. It was this simple design philosophy that can be credited for the impressive performance of most reinforced concrete buildings constructed after the 1980s in Christchurch, New Zealand, during and after the 2010-2011 Canterbury earthquake.
Dr Ryan Hoult is a research fellow at the Université catholique de Louvain (UCLouvain), Belgium. He is a recent recipient of a Marie Curie Postdoctoral Fellowship to investigate new reinforcement materials for improved seismic performance of concrete structures.