![]() Rivers flow downstream because of a topographic gradient and therefore a gravitational one: gravity never stops working. For analogous reasons, in the two hemispheres, the Coriolis force plays opposite and the linear velocity gradient induces clockwise or counterclockwise atmospheric circulation. Cyclones, tornadoes, rain and snow are controlled by those gradients. The greater the gradient, the faster the winds. What is the nature of these planetary gradients? How can we study them and how do they punctuate Earth dynamics? Each gust of wind is determined by atmospheric pressure gradient: areas where atmospheric pressure is greater push air toward areas of lower pressure. ![]() Earth hosts Life because of the mobility of its mantle, thermal gradients inducing volcanic eruptions and velocity differences among crustal volumes provoking faulting, mountain growth and ocean spreading. Lightning is the release of energy due to the breaking of materials when electric potential gradient overcomes their dielectric resistance. The gradient of electric potential between the two poles of a battery allows to start a car. A gradient generates forces producing or being the expression of a difference of a certain physical observable in time or space. Several gradients of parameters acting together with different times and rates on systems with a large number of degree of freedom can determine non-linearity, chaos and self-organization that can ultimately evolve into catastrophic collective behaviors. In the present article, a review is given of the most significant results of the last years in the field of geodynamics and earthquake geology following the common thread of gradients, which ultimately shape our planet.Ī gradient indicates a variation of any parameter, such as the degree of inclination of a plane in physics, the rate at which, for example, pressure or temperature vary in space or time in mathematics, a gradient is a vector having components the partial derivatives of a function with respect to its variables in chemistry, a gradient can be identified as the variation of electro-chemical potential differences between two bodies in biology, a gradient can be considered as the progressively increasing or decreasing differences in the growth rate, metabolism, physiological activity of a cell, organ or organism, in the distribution across membranes of ions with different concentrations and valences. In extensional regions, the dominant source of energy is given by gravitational potential, whereas in strike-slip faults and thrusts, earthquakes mainly dissipate elastic potential energy indeed. An even more wide-open debate rises for the occurrence of earthquakes, which should be framed within the different tectonic setting, which affects the spatial and temporal properties of seismicity. Moreover, several evidences indicate that tectonic plates follow a mainstream and how the lithosphere has a roughly westerly drift with respect to the asthenospheric mantle. While large part of the scientific community agreed that either bottom-up or top-down driven mantle convection is the cause of lithospheric displacements, geodetic observations and geodynamic models also support an astronomical contribution to plate motions. However, several counterarguments suggest that these mechanisms are insufficient to explain plate tectonics. Nowadays, slab-pull is considered the force with the greatest impact on plate motions, but also ridge-push, trench suction and physico-chemical heterogeneities are thought to play an important role. ![]() The lack of direct investigations still makes Earth interior poorly understood and prevents complete clarification of the mechanisms ruling geodynamics and tectonics. ![]() The surface of the Planet is featured by complex geological patterns produced by both endogenous and exogenous phenomena. The processes occurring on the Earth are controlled by several gradients.
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