Earthquake
An earthquake in simple words is the shaking of the earth.
It is a natural event.
It is caused due to release of energy, which generates waves that travel in all directions.
The vibrations called seismic waves are generated from earthquakes that travel through the Earth and are recorded on instruments called seismographs.
The location below the earth’s surface where the earthquake starts is called the hypocenter.
Location directly above it on the surface of the earth is called the epicenter.
Earthquake Causes
Fault Zones:
The release of energy occurs along a fault. A fault is a sharp break in the crustal rocks.
Rocks along a fault tend to move in opposite directions.
As the overlying rock strata press them, the friction locks them together.
However, their tendency to move apart at some point of time overcomes the friction.
As a result, the blocks get deformed and eventually, they slide past one another abruptly.
This causes earthquake in the form of release of energy, and the energy waves travel in all directions.
Types of Earthquake
Tectonic Earthquakes:
The most common ones are the tectonic earthquakes.
The Earth is made of three basic layers: a solid crust, a hot nearly solid mantle, a liquid outer core and a solid inner core.
Tectonic plates (Lithospheric plates) are constantly shifting as they drift around on the viscous, or slowly flowing, mantle layer below.
This non-stop movement causes stress on Earth’s crust.
When the stresses get too large, it leads to cracks called faults.
When tectonic plates move, it also causes movements at the faults.
Thus, the slipping of land along the faultline along convergent, divergent and transform boundaries cause earthquakes.
The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre.
The energy waves travelling in different directions reach the surface.
The point on the surface, nearest to the focus, is called epicentre. It is the first one to experience the waves. It is a point directly above the focus.
Volcanic Earthquake:
A special class of tectonic earthquake is sometimes recognised as volcanic earthquake. However, these are confined to areas of active volcanoes.
Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molten rock) are called volcano earthquakes.
These earthquakes can cause land to subside and can produce large ground cracks.
These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present.
Volcano-tectonic earthquakes don't indicate that the volcano will be erupting but can occur at any time.
Human Induced Earthquakes:
In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors. These are called collapse earthquakes.
Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.
The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes.
Distribution of Earthquakes
Earthquakes can strike any location at any time, but history shows they occur in the same general patterns year after year, principally in three large zones of the earth:
Circum-Pacific seismic belt:
World's greatest earthquake belt.
It is found along the rim of the Pacific Ocean, where about 81 percent of our planet's largest earthquakes occur.
Also known as "Ring of Fire".
The belt exists along boundaries of tectonic plates, where plates of mostly oceanic crust are sinking (or subducting) beneath another plate.
Earthquakes in these subduction zones are caused by slip between plates and rupture within plates.
Alpide earthquake belt (mid Continental belt):
It extends from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic.
This belt accounts for about 17 percent of the world's largest earthquakes, including some of the most destructive.
Mid-Atlantic Ridge:
The ridge marks where two tectonic plates are spreading apart (a divergent plate boundary).
Most of the mid-Atlantic Ridge is deep underwater and far from human development.
Earthquake in Morocco
Earthquake in Morocco
A powerful 6.8 magnitude earthquake struck Morocco near the ancient city of Marrakech.
This is the strongest quake to hit Morocco.
Causes of the Earthquake in Morocco
The earthquake resulted from the convergence of the African plate and the Eurasian plate along a complex plate boundary.
The earthquake's faulting mechanism was classified as "oblique-reverse," indicating movement along the fault plane where the upper block moves up and over the lower block within the Moroccan High Atlas Mountain range.
Faults are categorized by their dip (angle with respect to the surface) and slip direction.
Dip-slip faults include normal faults (upper block moves down lower block) and reverse faults (upper block moves up and over lower block), reverse faults are common in areas of tectonic compression.
Strike-slip faults involve horizontal movement along the fault plane.
Oblique-slip faults exhibit characteristics of both dip-slip and strike-slip faults.
Morocco
Morocco officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa.
It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to the east, and the disputed territory of Western Sahara to the south.
Its official and predominant religion is Islam and the official languages are Arabic and Berber.
Moroccan identity and culture is a mix of Arab, Berber, African and European cultures.
Its capital is Rabat.
Major Mountain Ranges: The Atlas and Rif Mountains.
Morocco is situated on the convergence plate of Africa and Eurasia, which are two of the major tectonic plates that make up the Earth’s crust.
These plates are constantly moving and colliding, creating mountains, volcanoes, earthquakes, and other geological features.
The Atlas Mountains in Morocco are a result of the collision between these plates, as they are squeezed and uplifted by the compressional forces.
Bhuj Earthquake
Bhuj Earthquake
The 2001 Gujarat earthquake, also known as the Bhuj earthquake, occurred on 26 January.
The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch District of Gujarat, India.
The intraplate earthquake measured 7.6 on the moment magnitude scale and occurred at 17.4 km depth.
It had a maximum felt intensity of X (Extreme) on the Mercalli intensity scale.
The earthquake killed 13,805 to 20,023 people.
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