Why does the Earth Shake? - QS Study
QS Study

The study of seismic waves provides a comprehensive representation of the layered interior. An earthquake in simple words is shaking of the earth. It is a natural incident. It is caused due to discharge of energy, which generates waves that travel in all directions. Earthquakes are caused by the unexpected movement and fracturing of rock masses along preexisting faults.

A fault is a broken surface within the Earth’s crust. The point on the fault at which the displacement begins is called the “focus” of the earthquake. The discharge of energy occurs along a fault. A fault is a sharp fracture in the crustal rocks. Rocks along a fault are predisposed to move in opposite directions. As the overlying rock strata press them, the friction locks them together. However, their tendency to move apart at some point of time overcomes the friction. As a consequence, the blocks get collapsed and ultimately, they slide past one another unexpectedly. This causes a discharge of energy, and the energy waves travel in all directions. The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre. The energy waves travelling in dissimilar directions reach the surface. The point on the surface, adjacent to the focus, is called epicentre. It is the initial one to experience the waves. It is a point directly above the focus.

The seismic waves generated by an earthquake can be recorded and measured on a seismograph. The interpretation of the waves provides seismologists with a way of “seeing” into the inside of the Earth. The waves produced by earthquakes travel through the Earth and bounce off dissimilar features of the Earth’s interior. The patterns they form after bouncing off these features can be used to create images of the interior.