Geophysics

The word geophysics is composed of Latin roots, "geo" which means "earth", but the word "physics" which means "nature". Geophysics is the science that deals with the study of the earth in terms of physical principles; its objective includes the study and investigation of the phenomena that are related to the structure, the history of the evolution of the planet earth and its physical conditions; It covers the investigation of the interior of the Earth, its hydrosphere and its atmosphere, encompassing phenomena such as gravity, electricity and terrestrial magnetism. The Royal Academy summarizes the meaning of geophysics as part of the geology that is responsible for the study of terrestrial physics as such.

A Geophysics is a science that studies the physical phenomena that occur on our planet, highlighting among these, electromagnetism, the propagation of mechanical waves in the earth's crust and gravity. This science can be defined as the application of physics and geology to the study of the materials that make up the earth's crust and the fields of force that arise from it and exert their influence to the outside. Within the applied Geophysics, geophysical surveys or explorations stand out, through which this science investigates and defines particular geological formations and/or mineralized bodies of practical interest and suitable for industrial exploitation. The field of study of the prospections corresponds to the effects produced by rocks and metallic minerals in anomalous areas (deviated from the background), standing out among these: the gravitational attraction force, the radioactive disintegration, the spontaneous electric currents, the electrical resistance of the Soils, the speed of seismic waves.

A geophysicist is in charge of analyzing the different behaviors of the earth among them, seismology, oceanography, volcanology, tsunamis, climatic changes, soil characterization, renewable energies, and many other phenomena or behaviors of the earth.

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History

In ancient Greece are the first rigorous studies on the Earth and the sky, which also appear later in other civilizations (Chinese, Mayan), highlighting Eratosthenes of Cyrene who at the end of the third century BC calculated with little error the terrestrial radio, as the distance from the Earth to the Sun and the inclination of the planetary axis.

The knowledge of the Earth accelerated since the Renaissance. The term geophysics is initially used by Julius Fröbel in 1834 and other authors in following years, but it is published for the first time in Germany by Adolf Mühry in 1863: Beitraege zur Geophysik und Klimatographie, and then again in 1887 in the Handbuch der Geophysik de S. Günther.

Although there were some informal geophysical surveys since the early Middle Ages, the first specific apparatus of geophysical prospecting dates from 1879, the magnetometer of the Thalen and Tiberg Germans, with which they prospected iron successfully. And the first chair of geophysics is due to Emil Wiechert, in 1898 in Göttingen, Germany.

In Geophysics we can find two major parts that are its essence, internal geophysics and external geophysics.

Internal Geophysics

For its part, it deals with covering all that is involved in the interior of the earth, being its main topics of study: seismology (it studies earthquakes and everything related to them), geothermometry (it analyzes the extension of heat in the earth ), geodynamics (it is devoted to the study of the deformations and the efforts made by the earth and that generate movements in the mantle and in the lithosphere), geophysical prospecting (it is in charge of locating natural resources such as: water, oil, caves, and also archaeological remains), geophysical engineering (is responsible for the location of mineral and hydrocarbon deposits and also intervenes in public works or any construction in general), tectonophysics (addresses the tectonic processes that are those that end up distorting the lithosphere) and volcanology (responsible for the study of volcanoes and typical issues such as magma and lava).

External Geophysics

While External Geophysics focuses on the study of the physical properties of the earth's environment, its most important sub-branches are: geomagnetism (it studies the magnetic field generated by the same planet and the one that induces the earth and the solar wind in the ionosphere), paleomagnetism (it studies the magnetic field of the planet but in its beginnings), gravimetry (it is interested in the gravitational field of the planet), oceanography (its main subject of study are the oceans), meteorology (it studies the weather) , Aeronomy (it analyzes the upper layers of the atmosphere) and climatology (it studies the climate of today but also that of yesterday).

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Classification of geophysical methods

All the geophysical methods study the distribution in depth of some determined physical-chemical property of the subsoil layers, or of some characteristic related to said properties.

• 1.- Gravimetric method- It is based on the natural field of gravity and studies the variation of the vertical component of the gravity field.

The small variations or anomalies of the gravity due to these facts or other analogous ones can be detected with suitable instruments.

The gravimetric method is used as a method of general reconnaissance in petroleum prospecting, while in mining it is usually used, generally as a method of verification.

• 2.- Magnetic method- The earth is a natural magnet and gives rise to the earth's magnetic field. Small variations in this field may indicate the presence in depth of magnetic substances, which in some cases may be minerals of commercial interest such as magnetite, pyrrhotite, ilmenite, jacobsite, etc. Also, there are minerals of interest associated with magnetic substances, such as Cu, Pb and Zn sulfides, which frequently occur with pyrrhotine or other magnetic minerals.

The magnetic methods are used as methods of general recognition in oil prospecting and of recognition and detail in mining prospection.

• 3.- Seismic methods- By artificially producing a small earthquake and detecting the arrival times of the waves produced, once reflected or refracted in the different geological formations, we can arrive at a very approximate image of the seismic discontinuities. These discontinuities coincide, generally, with the stratigraphic discontinuities.

Seismic methods are divided into two classes: reflection and refraction.

The seismic method of reflection is the most used in oil prospecting and is a method of detail.

The seismic refraction method is a method of general recognition and detail, especially in oil prospecting, but its use is smaller.

• 4.- Electrical methods- They use the variations of the electrical properties, of the rocks, and minerals, in general their resistivity. Generally, except in the autopotential, telluric and AFMG methods that use natural electric fields, they use an artificial electric field created on the surface, by the passage of a current in the subsoil.

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Reference

https://britgeophysics.org/what-is-geophysics/

https://justkieranblog.wordpress.com/2015/12/14/difficulties-with-studying-geophysics/

https://www.tutorialspoint.com/physics_part2/physics_geophysics.htm