Earth Day – why earthquakes happen
Plate tectonics
The 50th anniversary of Earth Day, which by coincidence comes exactly one month after the strong earthquake that struck Zagreb and its surroundings on 22 March 2020, is an opportunity to briefly summarise the theory of plate tectonics and in this way try to explain why our planet is so dynamic.
The theory of plate tectonics is a very important theory in geology, comparable in significance to Darwin’s theory of evolution in biology or Einstein’s theory of relativity in physics.
This theory changed the way we view the Earth, from static to dynamic, and provided a framework for explaining the composition, structure and internal processes of our planet.
The theory of plate tectonics combines two older ideas: the idea of the German geophysicist and meteorologist Alfred Wegener about continental drift, and the idea of the American geologist Harry H. Hess about sea-floor spreading, according to which mid-ocean ridges are formed and oceanic plates move horizontally.
Important evidence supporting the theory of continental drift includes the matching coastlines of continents, as well as fossil remains of the same animals and plants found today on continents that are very far apart.
According to the theory of plate tectonics, the Earth’s lithosphere is divided into plates that float on a layer of partially molten rock material called the asthenosphere, while the boundaries between lithospheric plates are actually zones of the greatest tectonic activity.
Lithospheric plates move away from each other, subduct beneath one another or slide past one another, and it is precisely in these areas that frequent earthquakes, volcanic activity, mountain uplift, metamorphism and deformation occur.
As a consequence of these processes, the arrangement of continents and oceans changed throughout the geological history of the Earth, and these processes continue today.