Theory of plates tectonics.

In our planet there are always new discoveries, each time much more surprising than the previous ones, but there are certain discoveries that cause restlessness in humans as is the case of climatic, environmental and supernatural phenomena.
The tectonic plates have always been a point of attention which demonstrate the uniqueness of the planet in which we live. To understand this discovery we must take a look at the past.
The theory of plate tectonics is divided into two parts: that of continental drift proposed by Alfred Wegener in the 1910s and that of the ocean floor expansion proposed by Harry Hammond Hess and accepted in the 1960s. The union of these theories was called plate tectonics theory in 1967 ...

Synopsis of Plate Tectonic Theory

But what does it consist of?

It is a geological theory that explains the way in which the lithosphere is structured, according to this theory the earth's crust is composed of at least a dozen rigid plates that move constantly, these blocks rest on a layer of hot and flexible rock called " Asthenosphere". This theory gives us an explanation to the tectonic plates that form the surface of the earth and to the displacements that are observed between them in their sliding on the fluid terrestrial mantle, their directions and interactions, also explains the formation of the mountain ranges. The evidence provided by Wegener on the displacement of the continents was added in the 60s to those obtained after the study of the ocean floor.

Important characters and their contributions.

To know how the conclusion was reached about the earthquakes we have today, we must know the geologists, geographers and researchers who made numerous contributions towards geography in the aspect we are dealing with.

• First of all we have Alfred Lothar Wegener who proposed the theory of continental drift.
  
  Alfred Wegener Biography

• Arhtur Holmes, was a British geologist who made two major contributions to the understanding of geology. He pioneered the use of radiometric dating of minerals and was the first earth scientist to grasp the mechanical and thermal implications of mantle convection, which led eventually to the acceptance of plate tectonics. Credits
  
  Arthur Holmes Biography

• William Maurice Ewing, has been described as the pioneer of geophysics, who worked in the investigation of the refraction and seismic reflection on oceanic platforms, ocean bottom photography, transmission of underwater sound including the Souffa channel, extraction of ocean floor samples in deep waters, the theory and observation of surface seismic waves, the fluidity of the earth's core, the generation and propagation of micro-organisms, submarine seismic explosions.
  
  William Ewing Biography

• Harry Hammond Hess, is considered one of the fathers of the unified theory of plate tectonics. He is best known for his theories on sea floor spreading. Credits
  
  Harry Hess Biography

• John Tuzo Wilson, Canadian geologist and geophysicist who achieved notoriety as one of the main authors of the final formulation of plate tectonics and the development of the theory of the supercontine cycle of Witts, thanks to his pioneering argument on the faults of transformation.
  
  John Wilson Biography

• Xavier Le Pichon, He is a French geophysicist, known for his integral model of tectonic plates, in addition to being the pioneer to propose a computational model in 1968.
  

  
  Xavier Le Pichon, Biography

Subduction zones.

The subduction zones refer to those areas where the plates collide with each other. They are located in the ocean trenches in the active continental margins.
Subduction is a mechanism consisting of the introduction of a plate under another in favor of a fault plane that is called Benioff plane. The subduction zones are presented in the following way:

• Zone of subduction between two oceanic plates, occurs when the plates converge or collide mutually. In this zone the destruction of the edges of the plates takes place, this encounter originates in the oceanic bottom that finishes diminishing the surface.

Two oceanic plates collide (similar density)

• Subduction between an oceanic plate and a continental plate, the oceanic plate is introduced below the continental plate originating in this a folding of the sedimentary crust, which gives rise to the mountains is the clash of the Nazca plate with the South American plate which in turn generates seismic movements.

Two plates of different density collide (a continental plate and an oceanic plate)

• Subduction between two continental plates, in this case because both plates are dense can not be dragged towards the mantle causing a shock between them. As a result of this collision, the mountain ranges and plateaus located behind the plates are formed. It is the case of the Indian plate with the Eurasian, the product of impact between them resulted in the formation of the Himalayas.

Two continental plates collide (similar density)

Seismic zones.

There are 7 major plates: the North American, the South American, the Eurasian, the African, the Indo-Australian, the Pacific plate and the Antarctic plate. There are also smaller plates that also have their own movements such as: Nazca, Cocos, Scottish, Caribbean, Arabian, Juan de Fuca and Filipino.

Plates tectonics

Earthquakes.

They are the movements of the earth's crust that vary in intensity and are generally of very short duration, caused by the displacement of tectonic plates or by volcanic activity. To classify the seismic activity, the seismicity index is used, which is the quantity of earthquakes produced in a determined place every 100 thousand kilometers of surface. According to this index, the earth is divided into 3 seismic zones.

• Seismic zone , is the zone where earthquakes are intense and frequent, generally coinciding with the limits of the plates.

• Penisísmic zone, it is where the earthquakes are intermittent without being frequent.

• Aseismic zone, it is the area where an earthquake is rarely located.

In conclusion there are several factors that modify the relief of the earth. Thanks to plate tectonics we know the surface of our world as it is.

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References

• http://thebritishgeographer.weebly.com/plate-tectonic-theory.html
• https://en.wikipedia.org/wiki/Plate_tectonics
• http://www.sepmstrata.org/page.aspx?pageid=628
• http://web.gccaz.edu/~lnewman/gph111/topic_units/plates/plates2.html