Tectonic Movements: How Earthquakes Happen

Earth cutaway schematic of the EarthFeeling the earth rumble under you has got to be one of the scariest moments you could experience. It may feel like the whole planet is moving and you are helpless to stop it or even run for safety. If you are one of those unlucky people who have experienced this, you are not alone, as thousands of others have also felt this unsettling thunder under their feet.

Fortunately, these movements, more commonly called – earthquakes, lasts less than a minute, but the damage it leaves behind in both human lives and property is incomprehensible.

So you ask yourself – why did this happen? What can be done about it? Let’s delve into what causes earthquakes and see if we can remove the mystery of why the earth moves.

The Tectonic Plates

Map of earthquakes across the world
Fault lines across the world. Red indicates heavy plate movement and black depicts the most intensive earthquakes.
At a level that is just under the earth’s service, within an area called the lithosphere are platforms called tectonic plates. According to scientific studies, these plates move about 0.6 inches per year. Well, that’s nothing to really get excited about, but it is when there is a heavy movement of these plates is when we need to worry.

The plates are broken up into 12 regions, like 12 pieces of a jigsaw puzzle that are connected to each other. When the plates move, they bump into each other at their connections, officially called boundaries, causing collisions, or conversely, break away from each other.

The image above is a historical account of previous earthquakes and depicts where these boundaries exist, which are called fault lines. The colors represent how intense the plate movements were; that is, how intense the earthquake was. It is also at these fault lines that when the plates move, volcanoes and tsunamis occur, and mountains can get created. As you can see, there is an abundance of fault lines across the entire west coast of the United States.

What lies directly under these plates is the source that causes the tectonic plates to move.

The Earth’s Mantle

Under the Earth graphic cut away
Under the tectonic plates is the mantle, which consists of magnesium and iron-bearing silicates. You can think of the tectonic plates as the ‘skin’ of the earth, analogous to the skin of an apple. So when there is movement in the mantle, the plates above it feel this movement and they will move accordingly. How much movement is dependent upon the intensity of the changes within the mantle.

How are the Plate Movements Quantified?

Earthquakes are caused by these collisions, as one plate moves over the other the earth shakes. The measurement of intensity is rated using a Richter Scale, which records the magnitude of the collisions, with ‘1’ being unnoticeable, up to ’10’, which can cause massive death and destruction. Fortunately, an earthquake of ’10’ is very rare.

What is the Current Theory of Plate Movement?

The reason why the plates move is still under conjecture, but one theory is that heat from radioactive processes within the planet’s interior is what causes the plates to move.

The latest theory is called slab pull, where areas of the lithosphere become less dense than the asthenosphere. This causes these areas above to sink further down into the mantle, pulling slabs of the lithosphere apart,  causing the plates to move in different directions. As a result, these regions are spreading or rifting,

Tetonic activity map over the Earth's history
Tectonic Activity Map Over the last One Million Years

The Latest Findings

As it turns out, such interactions between continental plates is not the only reason for these various geological processes. Research led by a joint team of the University of Toronto and the University of Aberdeen has achieved an enormous breakthrough!

According to the study that uses supercomputers to run a model of the Earth’s upper mantle and crust, prehistoric geological events could have left deep ‘scars’ that may play a significant role in earthquakes, tsunamis, formation of mountains or ocean trenches, and many other ongoing geological processes.

The models created by the researchers indicate that the previous plate boundaries could stay buried deep below the surface of the Earth. These structures, which are no less than many millions of years old, are located far from the current plate boundaries and may cause drastic changes in the surface properties and structure of the interior of the continents.

The researchers went a step further to propose a new map highlighting the ancient geology of the Earth. The ‘perennial plate tectonic map’ explains through illustrations how these prehistoric geological events could affect today’s geological processes. The map is based on the common tectonic map, which is taught in elementary school, but it has been modified to include the concealed, ancient plate boundaries that may be involved in plate tectonic activity in the past as well as the present.

Owing to this breakthrough, some major revisions are required to the fundamental idea of plate tectonics. The research paper titled, ‘Lasting mantle scars lead to perennial plate tectonics’ appeared in the Nature Communications issue of June 10, 2016.


So we see that plate movements below the Earth’s surface can cause these disturbances to occur, but how they occur is still a forum for debate. At least we know where it happens most (fault lines) and as best we can, precautions have been and will be taken for earthquakes to minimize damage.

The Fundamental Forces of Nature

Everything which happens around us is a result of the interaction of forces and we mean everything, from a fruit falling from a tree (remember Isaac Newton?) to Earth orbiting around the Sun, aa matter around us interacts with other bodies around it, This phenomenon is based on four fundamental forces

Gravity, the weakest of the four natural forces is present in our everyday lives. It determines how and why things around us stay at a certain height and why some objects fall down, while others take longer. 

Electromagnetic forces run our electric and digital machines and allow us to access the universe from the comfort of our homes. 

The other two natural forces, namely the strong and the weak nuclear forces, operate at the atomic level. They influence the fundamental particles of an atom including the proton and electrons. 

Each of the four fundamental forces of nature has unique properties and characteristics. Every single interaction which takes place in the universe can be explained through these forces. However, there are certain interactions that appear to be bizarre and are not explained by these four forces. This raises the question of the existence of a fifth, unknown and unexplained force of nature. Physicists are still struggling to find the answer.  


Photo of Woman Falling Down
Woman in Free Fall. Photo: Unsplash_011722_Bruce-Christianson-XyZxxJI8g30-unsplash1

If a pen slips out of your hand, it will immediately fall down and touch the ground. For humans, gravity appears to be the strongest and most obvious force of nature. In reality, gravity is actually the weakest of the four elements, at least on this planet. It’s a whole different animal in outer space. 

Simply defined, gravity is the attraction between any two objects which have a mass. The force depends upon the mass of the objects. According to the law of gravitation, the magnitude or intensity of the gravitational force can be calculated by multiplying the masses with the universal gravitational constant ‘G’. The resultant is then divided by the square of the distance between the centers of the masses. There is a different force of gravity constant for each object in the solar system and for that matter, the universe. The formula is F = G*m1*m2/r2 . One example would be the force of gravity on Earth is 9.8 meters per second squared or 9.8 m/s2

Gravity is very weak on the atomic level, but since most objects around us have so much mass, the force of gravity becomes stronger and more apparent. The force becomes stronger and more evident for universal objects with larger masses including the planets and stars. In this case, gravity is strong enough to keep them in an orbit. When it comes to galaxies, the mass further increases and gravity plays a crucial role in attracting galaxies even when they are far apart.  

The Weak Nuclear Force 

The weak nuclear force is much stronger than the gravitational force (1010 times). However, the force is only stronger within a certain range. It acts at a distance within the size of the proton. The particles which carry the weak nuclear force are called the weak vector bosons and have symbols w+, w-, and z0. The interaction between these particles causes one type of charged particle to turn into another type of charged particle. This interaction is responsible for phenomena such as beta and other radioactive decay

Electromagnetic Force 

Animated illustration of the electronmatic force's polority
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation. Photo: Wikimedia

The electromagnetic force, also known as magnetism is far stronger than the gravitational pull and has a much wider range than the weak nuclear force. It easily overrides gravity and it the third strongest force of nature is 1040 times stronger than the gravitational force.

An easy way to assess the strength of the electromagnetic force is to hold a magnet against a few paper clips. Gravity will attract the paper clips downwards but the electromagnetic force, which is stronger than gravity, will end up attracting the paper clips upwards. 

The electromagnetic force allows the interaction of particles with an electric charge. When the charged particles are at rest, they interact through electrostatic forces. When in motion, they mingle together through both electrical and magnetic forces. 

Though less powerful than the strong nuclear force, the electromagnetic force is by far the most prevalent force in the world. It can affect objects with a fair amount of power when they are at a reasonable distance. 

A military compass that was used during World War I
A military compass that was used during World War I

The Strong Nuclear Force

The strong nuclear force is the strongest fundamental force of nature. It is the biggest influence on the fundamental particles of the universe. It is this force that binds together the nuclei of the atom. However, the range of the strong nuclear force is only limited to subatomic particles. 

The nuclei of an atom are made up of a positively charged proton and a neutral charged neutron. Since like charges repel, each proton in the nuclei is working hard to get away from the other proton. This is where the strong nuclear force comes in. The strong force allows particles called gluons to stick together and create nucleons. These gluons can interact with other gluons and further strengthen the bond within the nuclei. The presence of a strong nuclear force is the reason why so much energy is released when the nuclei of an atom break down. 

The Fifth Force – Fact or Fiction 

Physicists around the world have unanimously agreed that the four fundamental forces explain every phenomenon (that we know of) in the universe. However, there are various mysteries of physics that cannot be explained by these four fundamental forces of nature.

One such mystery is the existence of dark matter. After immense research, physicists have agreed that dark matter is a form of a stable and huge particle that experiences gravity but no other known forces. Researchers have failed to identify the reason why dark matter does not experience any force other than gravity. 

There are many ideas about why other forces do not act on dark matter. One famous hypothesis is the presence of an unidentified fifth force. Physicists around the world are studying the possibilities of the existence of a fifth fundamental force of nature. But it is too early to claim its presence.  

How Mountains are Created

Mountains big and small have been the result of plate teconics.

The formation of the Himalayas was created when the Indian subplate burrowed under the European continent and formed the Appalachian Mountains.

When the North American and African plates collided, a large separation of earth materialized and the Atlantic Ocean opened up.

The volcanic and seismic activity of the West Coast of the US occurs as a result of grinding of the North American and Pacific plates.

The above are just a few examples of the effects of plate tectonics. The geological history of Earth is littered with such phenomena that have made the Earth what it is today.