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Unveiling Earth's Hidden Forces: Exploring Plate Tectonics and Earthquakes

Description: Journey into the dynamic world of Earth's tectonic plates and seismic events. This article discusses the tragic earthquake that struck Morocco, highlighting the intriguing collision of tectonic plates and the consequences of built-up stress. Gain insights into plate tectonics, where the Earth's outer layer is divided into mobile plates, and discover the types of plate boundaries, including divergent, convergent, and transform. Explore how the intensity and magnitude of earthquakes vary, shedding light on the science behind their destructive power. Dive deep into the Earth's geological mysteries with this informative piece.

Earthquake in Morocco

On 8 September, a deadly earthquake of magnitude of 6.8 struck Morocco, killing over 2,100 people and flattening homes and villages. The earthquake's epicentre was the Ighil area, about 70 km south of Marrakech (or Marrakesh).

There was a collision of the African and the Eurasian tectonic plates at a relatively shallow depth. The quake happened when a reverse fault – where the edge of the rock on one side of a fault slips under the other – occurred between the Morocco and Iberia microplates, which are both part of the larger African plate.

During the earthquake, the edge that lies towards the mountains slid over the other, pushing the mountainside up, a knock-on consequence of built-up tension between the African and Eurasia plates over time.

The faults can only hold the stress so much, and once in a while [thousands of years], an earthquake happens as a mechanism to release the [built-up] stress.

What is Plate Tectonics?

The outer layers of the Earth are divided into lithosphere and asthenosphere. This is based on differences in mechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily.

The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like (visco-elastic solid) asthenosphere. The plates are mobile, moving in constant, slow motion measured in rates of centimeters per year. The movements of plates over millions of years resulted in the opening and closure of oceans and the formation and disassembly of continents.

Intensity of Earthquake

According to the USGS, an earthquake's destructive power depends on three factors: strength, location, and distance from the epicentre.

The strength of shaking from an earthquake reduces with increasing distance from the earthquake's source. This explains why the strength of shaking at the surface from an earthquake that occurs at 500 km deep is considerably less than an earthquake which was to occur at, say, 20 km depth

While deeper quakes do indeed spread farther as seismic waves move radially upwards to the surface, they lose energy while travelling greater distances. Apart from the depth, the magnitude of an earthquake is also an indicator of how destructive a quake could be. Magnitude tells how big the seismic waves are, while strength refers to the energy they carry. “While each whole number increase in magnitude represents a tenfold increase in the measured amplitude, it represents 32 times more energy release

Types of Plate boundaries

There are three general types of plate boundaries: divergent, convergent, and transform.

1.  Divergent Plate boundary

Divergent boundaries occur where plates are moving apart. Hot mantle rock rises and partial melting occurs. New crust is created by the magma pushing up from the mantle.

•  New sea-floor at mid-ocean ridges 

Divergent boundaries are found in the ocean as mid-ocean ridges. A divergent boundary is the line between two plates where they are moving apart. This type of boundary is found over the rising plume of a mantle convection cell. The convection cell causes the two plates to move away from each other. As they move, melted rock fills the space created by their motion. The melted rock hardens and becomes new ocean floor.

•  Rift Valleys

Divergent boundaries can also be found on continents as rift valleys. When a rift valley forms on land, it may eventually split the landmass wide enough so that the sea flows into the valley. When this happens, the rift valley becomes a mid-ocean ridge. The East African Rift Valley is an example of rifting in progress.

2.  Convergent Plate boundary

In this crust is destroyed as two plates move towards each other. The heavier plate dives (subducts) beneath the more-bouyant plate.

•  Oceanic-oceanic convergence—When two oceanic plates converge, one subducts beneath the other, and in the process a trench is formed. (Example: The Marianas Trench, the Challenger Deep, at the southern end of the Marianas Trench, plunges deeper into the Earth’s interior (nearly 11,000 m) than Mount Everest, the world’s tallest mountain, rises above sea level (about 8,854 m).) 

•  Oceanic-Continental convergence—An oceanic plate converges on a continental plate and the denser crust of the oceanic plate sinks beneath the more-bouyant continental plate. In this type of convergence, trenches, strong, destructive earthquakes and the rapid uplift of mountain ranges are common. Water released from subducting slab facilitates melting. Rising melt builds volcanic arc. (Examples: Juan de Fuca plate subducting beneath the North American plate off shore in the Pacific Northwest.Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is being subducted beneath the South American Plate. In turn, the overriding South American Plate is being lifted up, creating the towering Andes mountains.)

•  Continental-continental convergence—When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. (Example: The Himalayan mountain range dramatically demonstrates one of the most visible and spectacular consequences of plate tectonics. The Himalayas, towering as high as 8,854 m above sea level, form the highest continental mountains in the world.)

3.  Transform Plate Boundaries

Under this plates slide past each other at transform boundaries; lithosphere is neither destroyed nor created. 

The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). Transform faults occur across a spreading center. Strong earthquakes can occur along a fault. The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion.

Here is a link to an article on Changes done to move from Colonial Past