What causes a super earthquake?


What causes a super earthquake?
© Tomohiro Ohsumi / Stringer Getty Images News

The devastating earthquake that hit central Japan at the beginning of 2024 brought to mind all the devastating earthquakes that have occurred on the planet in recent years. The most violent earthquakes are concentrated in specific areas of the planet, indicating the causes that underlie such a release of energy.

Almost all earthquakes that occur on the earth's surface are therefore concentrated in very specific areas of the planet, i.e. near the boundaries between one tectonic plate and another: these are in fact the most tectonically active areas, that is, where the plates move more or less slowly and suddenly than each other.

Japan earthquake© Tomohiro Ohsumi / Stringer Getty Images News

According to plate tectonics, the surface of the Earth is in fact composed of about a dozen large tectonic plates that move very slowly, due to the convection currents of the earth's mantle placed under the earth's crust.

Because they do not all move in the same direction, plates often collide directly by sliding sideways along the edge of one another. In general the movement of the plates is slow, imperceptible and constant. However, in some moments and in some areas, the movement stops and the area involved accumulates energy for decades or centuries until the so-called breaking load is reached, when due to internal forces, i.e.

the balance between pressures, tensions and frictions between the rocky masses, these movements occur suddenly and suddenly, releasing the accumulated energy and thus developing an earthquake.

The causes of teh super earthquake

It can be said that earthquakes are caused by sudden movements of rock masses within the earth's crust.

The earth's surface is in fact in slow but constant movement and earthquakes occur when the resulting tension accumulated by mechanical stress exceeds the capacity or resistance of the rock material to withstand it, i.e. it exceeds the so-called breaking load.

This condition occurs most often at tectonic plate boundaries. Seismic events that occur at the boundaries between plates are called tectonic earthquakes, while the less frequent ones that occur within the plates of the lithosphere are called intraplate earthquakes.

Japan earthquake© Buddhika Weerasinghe / Stringer Getty Images News

Earthquakes along the ridges are therefore the effect of the sudden failure of these welds upon reaching a certain level of mechanical stress.

In these areas, seismic phenomena are often also associated with volcanism due to the concomitance of the tectonic forces at play and for this reason volcanic eruptions are often preceded by earthquakes. The disposition of the seismic zones is mostly localized along the margins between the tectonic plates and in particular along the abyssal trenches, where the sinking of the oceanic crust beneath other portions of the earth's crust leads to the frictional melting of part of the rocky zone of contact, or along the oceanic ridges where the magma of the Earth's mantle rises to the surface through the fractures of the oceanic crust and, once solidified, joins the plates themselves.