Why is it in the news?
A rare, powerful earthquake struck Morocco recently, killing hundreds of people and damaging buildings, including in the historic city of Marrakesh.
Morocco shares its borders with the following countries and regions
- North: Spain (with water border through the Strait of Gibraltar) and small Spanish-controlled exclaves, including Ceuta, Melilla, and Peñón de Vélez de la Gomera.
- East: Algeria.
- South: Western Sahara.
- De facto southern boundary with Mauritania due to Morocco’s control over most of Western Sahara.
Uncommon Earthquakes in North Africa
- Earthquakes are infrequent in North Africa, and seismicity rates are relatively low.
- Marrakesh, including the historic old city (UNESCO World Heritage Site), experienced building collapses and structural damage.
Shallow and dangerous Earthquake
- Magnitude of the earthquake: 6.8
- Followed by an aftershock of magnitude 4.9 just 19 minutes later.
- Epicentre located in the town of Ighil, approximately 70 km southwest of Marrakech.
- Epicentre depth: 18.5 km (shallow earthquake).
- Shallow earthquakes are more dangerous as they carry more energy than deeper ones.
- Deeper earthquakes spread seismic waves farther but lose energy while traveling greater distances.
Causes of the Morocco Earth quake
- While seismicity rates are indeed lower in the region, making earthquakes rarer, they are not completely unheard of.
- According to the US Geological Survey (USGS), large destructive earthquakes have been recorded and reported from Morocco in the western Mediterranean.
- 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 current quake, the USGS attributed it to “oblique-reverse faulting at shallow depth within the Moroccan High Atlas Mountain range”.
- The Atlas Mountains span about 2,300 kilometres across Morocco, Algeria and Tunisia.
- Known as fold mountains, they were created by the collision of tectonic masses: the Eurasian Plate to the north and the African Plate to the south.
About Fault Classification
- 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.
- Oblique-slip faults show characteristics of both dip-slip and strike-slip faults.
- The term ‘reverse’ refers to a situation that 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.