Seismology

We explain what seismology is, what it is for and what a seismograph is. Also, what is plate tectonics and the Richter scale.

Seismology
Seismology is the science that studies earthquakes and other similar phenomena.

What is seismology?

seismology or seismology It is a scientific discipline that is part of geophysics and that studies the propagation of seismic waves. (waves of movement) in the interior and on the surface of the planet, the result of the movements of the tectonic plates of the earth’s crust. Said in a simpler way, it is the science that studies earthquakes and other similar phenomena.

The interests of seismology are diverse, it is not only interested in tremors and earthquakes, but also in the tectonic dynamics that give rise to various kinds of relief on the earth’s surface, tidal waves, tsunamis, and the vibrations that accompany eruptions. volcanic. In general, it can be said that it is a discipline interested in the movements of the earth’s crust, the stresses that these cause and the impact that all this hasor can have, in life and especially in humanity.

It is a discipline in contact with other branches of geophysics, such as geology, and with other sciences such as geography, wave mechanics and chemistry. On the one hand, it provides knowledge for the understanding of the dynamics of the planet, and, on the other, allows anticipating catastrophic events and minimizing their impact on society.

See also: Geologic fault

What is seismology used for?

seismology objectives
Seismology provides key information on construction materials and techniques.

The purposes of seismology are:

  • Study the propagation of seismic waves inside the planet, which reveals information about how the interior of the Earth is made up: what materials, in what arrangement, according to what structures.
  • Answer the question about the origin of earthquakes and know the different types that exist: tremors, earthquakes, tidal waves, among others, as well as their associated phenomena: tsunamis, landslides, etc. This in order to understand them better.
  • Design strategies for earthquake prevention that allow to save lives and minimize the damage of tremors. This can occur, for example, by providing key information on materials and techniques for the construction industry, or the design of conduct manuals in the event of an earthquake.
  • Gather seismic information that may be useful to other disciplines and knowledge, to expand scientific knowledge.
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history of seismology

seismology history zhang chang heng
The first seismograph was invented by Zhang Heng in Ancient China.

Although earthquakes have existed since the beginning of humanity and have always been remembered as cataclysmic events, their scientific study is quite recent. There are records of earthquakes from at least 3,000 years ago in Ancient Chinaand most of them were interpreted as symptoms of the end of the world or divine punishment, according to the beliefs of each ancient civilization.

However, there were also philosophers and thinkers who wondered if there was not a natural origin of these terrestrial phenomena: individuals who can be considered today as the forerunners of seismology. Among them are the Greek Thales of Miletus (c. 624-c. 546 BC), Anaximenes of Miletus (c. 590-c. 528 BC), Aristotle of Stagira (384-22 BC). ) and Chinese Zhang Heng (AD 78-139) of the Han dynasty, inventor of the first seismograph.

Even so, The first scientific hypotheses about the origin of earthquakes arose between the 17th and 18th centuries.. The German scientist and Jesuit priest Athanasius Kircher (c. 1601-1680) proposed that they were the result of the fire that burned inside the Earth, while the English physician Martín Lister (1639-1712) and the French chemist Nicolás Lémery (1645 -1715) attributed them to “chemical explosions” that would take place in the core of the planet.

The first seismological experiments took place in the mid-19th century., and laid the foundations of a rather instrumental seismology. The Irish inventor Robert Mallet (1810-1881) played an important role in this, and it was he who coined the term “seismology”, from the Greek words seismós (“earthquake”) and logos (“know” or “treaty”).

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Already by the beginning of the 20th century, the first real advances in the understanding of earthquakes brought with them a greater knowledge of the interior of the Earth, and thus in 1960 the theory of plate tectonics arosewhich gave meaning to the knowledge gathered until then and allowed a unified comprehensive model of terrestrial seismic phenomena.

What is a seismograph?

seismology seismograph
In its modern version, the seismograph was created by James David Forbes in 1842.

A seismograph or seismometer It is a device designed to measure earthquakes and other minor telluric movements (that is, of the ground).. In its modern version, it was created by the Scotsman James David Forbes (1809-1868) in 1842, and consists of a pendulum whose mass allows it to remain motionless by appealing to inertia, so as to be able to perceive and aim on a piece of paper using a graphic implement, the vibrations of the earth’s crust.

Currently, seismographs are implements used continuously in monitoring the tectonic activity of the earth’s crust, in order to detect and classify earthquakes and volcanic eruptions that occur in different parts of the world. Some are used on the surface and others in the depths of the ocean floor, in order to capture as clearly as possible the P waves (primary) and S waves (secondary) that reverberate towards the surface.

What is plate tectonics?

seismology tectonic plates
The tectonic plates are solid and move on the mantle, which is semi-liquid.

Plate tectonics or global tectonics is the scientific theory that explains the structure and dynamics of movement of the earth’s lithosphere, that is, from the outermost and coldest layer of the planet. According to his postulates, the earth’s crust is composed of tectonic plates or lithospheric plates, solid and about 100 km thick, which move on the earth’s mantle, composed of molten rock in a semi-liquid state.

This tectonic shift is extremely slow and progressive., but varied depending on location and conditions. The East Pacific Ridge Plate near Easter Island, for example, moves at a rate of 15 cm per year, while the Arctic Ridge Plate at the North Pole moves just 2.5 cm per year. year. In all cases, The moving plates collide and rub against other plates, which generates a massive tension that, when released, precisely causes earthquakes. and tremors.

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This theory not only makes it possible to explain the origin of earthquakes, but also the depressions in the earth’s crust and orogenesis, that is, the appearance of mountains: when two plates meet head-on, the denser of the two can submerge under the other (generating a subduction or depression) or the lighter one can fold on itself (generating a mountain range). The topography of the Earth, in this way, is the result of millennia of tectonic displacements and shocks of this same nature.

What is the Richter scale?

Also known as the Local Magnitude Scale (mL), the Richter scale It is a logarithmic scale used in seismological studies worldwide to express the intensity of earthquakes., that is, the amount of energy that the earth’s crust releases when it shakes. Its name pays tribute to its creator, the American seismologist Charles Francis Richter (1900-1985), who together with the German Beno Gutenberg (1889-1960) designed the scale for the first time in 1935.

The Richter scale was a step forward in the standardization of seismology studies in the world, but it has a rather limited use. It is used to measure, on a scale from 2.0 to 6.9, the intensity of the earthquakes that have occurred, as long as they occur between 0 and 400 kilometers deep. For values ​​greater than this scale, the seismological scale of moment magnitude is used today (mw), capable of measuring extremely intense earthquakes with greater precision.

So, despite what is popularly said, there are no tremors “of 7 points on the Richter scale”, since the scale only goes up to 6.9.

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References

  • “Seismology” on Wikipedia.
  • “What is seismology?” at the National Geographic Institute (Spain).
  • “Notes on seismology” at the National University of Tucumán (Argentina).
  • “Plate tectonics” in the Mexican Geological Service.
  • “Seismology” in The Encyclopaedia Britannica.