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Plate Tectronics

Cut Away of Earth's Crust
Cut away schematic of the Earth, By derivative work: Anasofiapaixao Earth_internal_structure.png: USGS (Earth_internal_structure.png) [Public domain], via Wikimedia Commons
According to the theory of plate tectonics, the earth’s lithosphere contains plates that move gradually over the asthenosphere. The major geological processes, such as earthquakes and the formation of volcanoes and mountain belts occur at the places of the interaction of these plates. As a result, the following changes have been witnessed in the earth’s geology:

The formation of the Himalayas – when the Indian subplate burrowed under the Eurasian plate, or the formation of the Appalachian Mountains, when the North American and African plates collided. The separation of North America from Europe by the opening of the Atlantic.

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 mentioned are just a few examples of the effects of plate tectonics. The geological history of earth is littered with such phenomena and processes that have made the Earth how it is today.

The Latest Findings

But as it turns out, such interactions between continental plates is not the only reason for various geological processes. Research led by a joint team of the University of Toronto and University of Aberdeen researchers has achieved an enormous breakthrough! According to the research that uses supercomputers to run a model of the Earth’s upper mantle and crust, the 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 the 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 recent 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 Nature Communications issue of June 10, 2016.

The Science Behind Earthquakes

We’re all familiar, or at least come across time and again, with the terms tectonic plates, fault lines and seismic zones. But there are quite a few of us who cannot make up the connection between these and basically answer the simple question of what causes earthquakes? How and why the tectonic plates move and what is it beneath the surface of the earth that makes all these hazardous movements to happen’ are two of the most pressing questions related to earthquakes.

Keep reading to get the aforementioned questions answered and get your hands on some essential knowledge about the basics of earthquakes.

Tectonic plates and fault lines

The planet Earth is composed of four layers, inner and outer core, mantle and the crust which is the outermost core. The outer/top-most part of the plastic-like mantle and crust make up a thin layer over the surface of the earth. In order to understand tectonic plates, it is essential to know that this thin outer layer is not a single piece; rather it is a number of pieces joined together. These pieces of crust, called tectonic plates, together with the block of the earth right beneath them, are not static; they move and slide at their boundaries against each other.  These boundaries are referred to as ‘plate boundaries’. When we say the word fault line, we are basically referring to these boundaries collectively. It is here that the blocks of earth slide past each other causing the earthquake.

So, how does an earthquake happen?

As mentioned above, tectonic plates are not static. As their boundaries are joined or stuck with each other, it is easier for the plate itself to move than the respective boundary to move at the same pace because of higher friction. As plates move, pressure builds up on the plate boundaries causing energy to be increasingly stored in them. It is only when the pressure build-up from the plates’ movement overcomes the friction between the jagged plate boundaries that they are unstuck and slide past each other. This releases the energy being stored for far too long. The radiation of this released energy across the tectonic plate is what is scientifically called ‘Seismic Waves’. As these waves move past the earth, they shake the earth. Upon reaching the surface, they shake the surface of the earth.

The area below the surface of the earth, the origin of the earthquake, is called the hypocenter. Its corresponding area right on the surface of the earth is called epicenter. The path that the seismic waves travel from the hypocenter and epicenter is basically the fault plane, the movement of which against the neighboring plane causes the earthquake.

Breaking misconceptions

One major misconception about earthquakes is that the tectonic plates move only before/during the earthquake. This is not true. It is totally natural for the tectonic plates to keep having slight movements at all times, which do not escalate into an earthquake. As established above, it is only when the movement of tectonic plates is significant enough to overpower the friction holding the boundaries together that earthquake happens.