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What is an Earthquake?

An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth’s surface.

For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that form the Earth’s surface move slowly over, under, and past each other. Sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free causing the ground to shake. Most earthquakes occur at the boundaries where the plates meet; however, some earthquakes occur in the middle of plates.

The earth is made up of four major layers: the inner core, outer core, mantle and crust. The crust is the outermost and thinnest layer of the earth made out of rock. This layer of rock is not one smooth continuous layer, in fact the rock is broken into several large pieces that can fit together like a jigsaw puzzle. These pieces are known as tectonic plates. These tectonic plates are able to move around and interact with one another; sliding and bumping into each other. When two or more of these plates meet, they can lock or stick together, similar to when your fingers interlock with each other. The plates continue to move about trying to get themselves unstuck from one another and this causes energy to build up below the plates. When the plates are able to break free from each other, the built up energy is released moving through the Earth resulting in the shaking of the ground or what we call an earthquake. The region where two or more plates meet is known as a plate boundary.

An earthquake typically lasts under one (1) minute or sixty (60) seconds, but the shaking could be so violent at times to cause irreparable damage. When an earthquake first takes place, it is known as the main event. However, there may be a series of smaller earthquakes that could occur after the main one. These smaller earthquakes are known as the aftershocks and are capable of inflicting further damage. The aftershock is just as unpredictable as the main one.

An earthquake can take place at any time, day or night, without any forewarning at all and is capable of inflicting the same type of damage as a major hurricane. This makes it the most unpredictable and feared of all natural disasters.

Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at the site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake in a wave.

There are many different ways to measure different aspects of an earthquake. Magnitude is the most common measure of an earthquake’s size. It is a measure of the size of the earthquake source and is the same number no matter where you are or what the shaking feels like. The Richter scale measures the largest wiggle on the recording, but other magnitude scales measure different parts of the earthquake.