Geophysics Science, also called terrestrial physics, which studies the various physical phenomena (thermodynamic, optical, electrical etc.) that take place in the atmosphere, on the surface and inside the Earth. It is traditionally divided into three fundamental branches, corresponding to the three aggregation states (solid, liquid, gaseous) of the matter that makes up the Earth: physics of the solid Earth, physics of surface and deep waters, physics of the atmosphere. However, it is an established belief that, beyond the conventional division into separate disciplines, the object of study, the Earth, must be seen as unique and indivisible. For example, phenomena such as large earthquakes, the periodic movements of atmospheric air masses and the melting of the ice caps, producing a mass displacement, affect the rotation axis of the Earth and the length of the day; the large volcanic eruptions, introducing large quantities of aerosols into the stratosphere, produce a decrease in the average temperature at the earth’s surface, with sensitive effects on the global climate. We are still looking for an explanation of the mechanisms that determine the functioning of the Earth system as a whole and, in particular, for the evident dynamism of its evolution, of which the current arrangement of continents and oceans and the distribution of earthquakes and volcanoes.
- Continents and oceans
Terrestrial geography provides only a current, static image of a dynamic process in which continents drift on the Earth’s surface, ‘floating’ on a softer layer from the rheological point of view, transported by a process associated with a continuous generation and consumption of the oceanic crust. The geophysical investigation helps to clarify and deepen the interpretative scheme of plate tectonics. Seismological investigations allow, with the epicentral location of earthquakes, the definition of the margins of the plates as well as the determination of the crustal thickness. Gravimetric surveys confirm these results, framing them in a general isostatic balance in all geologically stable areas. The study of the Earth’s magnetic field and the magnetic properties of the rocks has made it possible to identify the periodic alternations of polarity of the field itself, of which traces remain in the residual magnetization relating to the genesis and positioning of many rock formations. From the study of ocean magnetic anomalies, in particular, it is possible to obtain a detailed reconstruction of the processes of opening the ocean bottoms and therefore of the kinematics of the tectonic plates.
- The internal structure of the Earth
Knowledge of the internal structure of the Earth is certainly one of the most important objectives of geophysics. From the study of seismic waves produced by earthquakes and used as a diagnostic tool, it was possible to refine the radial model (which provided for speed variations only with depth) of the propagation of seismic waves. Regardless of seismology, other geophysical disciplines have placed constraints on the identification of the internal subdivisions of the Earth (crust, mantle, nucleus, etc.). The nucleus, divided into a fluid external part and a solid internal part, is the source of the Earth’s magnetic field whose existence is explained by magnetofluidodynamic processes (➔ magnetism). The inner core certainly remains the least known part of the Earth; some analyzes of the seismic waves that pass through it would lead us to hypothesize a more complex structure than previously believed, with a possible internal anisotropy and, according to some, a super-rotation.
- Fluid dynamics and the Earth system
The processes that regulate the dynamics of the fluids constituting the Earth system, and therefore of the ocean and the atmosphere, are highly developed themes of research in g. and have acquired great political and social relevance. Just think of climate change and its possible consequences on health, agriculture, infrastructure and economy. In this context, the increase in the greenhouse effect in the troposphere, mainly attributable to the combustion of natural fossil resources since the era of industrial development, and the destruction of stratospheric ozone, highlighted during each southern spring by the so-called ‘hole ozone ‘inAntarctica, are the subjects of greatest impact. Also in the complex mechanism of atmospheric circulation and ocean waters, issues of great interest emerge, such as, for example, the alarm raised by the awareness of the extension on a planetary scale of the effects associated with the phenomenon ofEl Niño: the rise in the surface temperature of the ocean which generally takes place in December along the western coast of Peru and is the cause of torrential rains in normally arid regions, with serious consequences for human life and particularly serious damage to the environment and territory. Despite the enormous progress made in the study of these phenomena, many uncertainties and many problems still remain to be solved.
- Interactions between Earth and Sun
The Earth is naturally also an open system towards the Universe and therefore is subject to the actions of the other celestial bodies; among non-gravitational interactions, those with the Sun are particularly significant. The analysis of the available data of solar, spatial and terrestrial observations, mainly of the electromagnetic type, constitutes the phenomenological framework for studying these interactions. This study is part of a discipline called, similarly to the meteorological case, climatology (or meteorology) space, as it mainly tends to provide information on the dynamic evolution of the phenomena in question. This theme is of great interest also for the effects that these phenomena have on human life and on society. Solar perturbations, with their consequences on the magnetosphere, in fact affect telecommunication systems via cable or over the air and even artificial satellites.
- Earth as a complex system
The development of technologies and their insertion in the environment in which we live will require in the future a greater integration of the complex system of knowledge in which the g. plays an essential role. As is evident from the variability of the observables necessary to define terrestrial phenomena, the Earth is a clear example of a complex system. In g., In many cases, the fundamental laws of physics are complicated or impossible to apply because of the difficulty in univocally defining all the factors that can influence the phenomena that you want to study. It is therefore natural that, precisely in this field, the science of complexity is starting to play a role of fundamental importance, also in the description of catastrophic events.
Gutenberg-Richter’s law, according to which the logarithm of the total number of events is proportional to their magnitude, represents a law of scaleaccording to fractal geometry models of the seismic source. This law is clearly inserted in the explanation necessary to understand the phenomena that characterize systems far from equilibrium. In equilibrium systems, a small stress corresponds to a response proportional to it or, more concisely, the system responds in a linear way. On the other hand, when the system is brought very far from equilibrium by a great stress, as happens in an earthquake, the response no longer depends linearly on the stress and it is in fact impossible to make reliable predictions on the behavior of the system. This appears clearly when predictions are prepared on the development of the dynamics of a given geophysical phenomenon; it is one of the most evident examples, perhaps, the difficulty of quantitatively predicting the extent of global warming on Earth, a problem on which the development of the more complex research programs in the g is focusing. of fluids.
