are ground tremors that are principally caused by the
disturbance of the mechanical equilibrium of the Earth’s rocks.
It is today known that the Earth’s crust is made up of a
number of lithospheric plates, which are continuously moving,
resulting in the development of forces at their outer limits as
well as in their interiors.
When the exerted forces exceed the upper limit of elastic
deformation of the rocks, then these are ruptured and there is a
sudden and violent release of energy that is transmitted in all
directions in the form of a wave motion, which in effect
constitutes the earthquake. When this wave motion reaches the
Earth’s surface it can cause damage to buildings and other
structures, landslides, land subsidence and fracturing of the
ground as well as elevation and hydrographic changes. The point
or area of rupture of the rocks is called the focus or
hypocentre of the earthquake while the point on the Earth’s
surface above the focus is called the epicentre.
instruments, called seismographs, record the ground tremors of
earthquakes and provide seismologists with the necessary
information to study the causes, the genesis mechanisms, the
transmission of seismic waves, as well as their effect on
structures and on
Man and the environment.
The graduation of earthquakes is carried out by means of two parameters, the magnitude and the intensity. Magnitude is a measure of the quantity of energy that is released at the focus of an earthquake and is measured on a logarithmic scale that runs from 1 to 10 and is called Richter scale. Intensity is a measure of the fierceness with which an earthquake manifests itself at a particular place and is measured from I to XII on the modified Mercalli scale. Intensity I on this scale is defined as the intensity of an event felt by very few people, whereas intensity XII is that of a catastrophic event that causes total destruction.