Seismology (Meaning and Explanation)

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

What is seismology?

Seismology or seismology It is a scientific discipline that is part of geophysics and that studies the propagation of seismic waves (movement waves) in the interior and surface of the planet, the result of the movements of the tectonic plates of the Earth's crust. In simpler terms, 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 types 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 tensions they cause and the impact that all this has or may 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 understanding the dynamics of the planet, and, on the other, allows you to anticipate catastrophic events and minimize their impact on society.

What is seismology used for?

Seismology objectives — Seismology provides key information on materials and techniques for construction.

The purposes of seismology are:

Study the propagation of seismic waves in the interior of the planet, which reveals information about how the Earth's interior 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 save lives and minimize the damage from earthquakes. This can occur, for example, by providing key information on materials and techniques for the construction industry, or by designing conduct manuals in the event of an earthquake.
Gather seismic information that can be useful to other disciplines and knowledge, to expand scientific knowledge.

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 going back at least 3,000 years in Ancient China and most 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 a natural origin for these terrestrial phenomena: individuals who can be considered today as the precursors of seismology. These include the Greeks 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 (78-139 AD) 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 doctor Martin 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 for a more 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 seismos (“earthquake”) and logos (“know” or “treated”).

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 (that is, ground) movements. In its modern version, it was created by the Scot James David Forbes (1809-1868) in 1842, and consists of a pendulum whose mass allows it to remain motionless by appealing to inertia, so that it can perceive and point on a 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?

Plate tectonic seismology — 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 its postulates, the Earth's crust is composed of tectonic plates or lithospheric plates, solid and around 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. On the East Pacific ridge plate near Easter Island, for example, movement occurs at a rate of 15 cm per year, while the Arctic ridge plate at the North Pole moves just 2.5 cm per year. anus. In all cases, When the plates move, they collide and rub other plates, which generates massive tension that, when released, precisely causes earthquakes and tremors.

What is the Richter scale?

Also known as Local Magnitude Scale (M_l), 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 shaking. 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 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 depth. For values greater than this scale, the seismological moment magnitude scale is used today (M_w), 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.