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.