What is an Earthquake?
An earthquake is a natural hazard which occurs when the ground shakes or rocks violently. 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.
How Earthquakes Occur?
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.
How are earthquakes measured?
Scientists who study earthquakes (called seismologists) are NOT able to predict the exact time and location that an earthquake would strike. However, they are able to measure the magnitude of an earthquake or the amount of energy that is released from the earth when an earthquake takes place. Seismometers are used to record the seismic waves generated by an earthquake. Seismologists are then able to use these recordings to determine where the earthquake was located and how strong it was. Seismic waves may also be used to map the interior of the earth.
Magnitude is used to measure an earthquake’s size (usually on a Richter Scale) and is related to the amount of energy generated by the earthquake. The Mercalli Intensity Scale is used to categorize the levels of shaking observed during an earthquake.
A SEISMIC WAVE travels through the Earth, most often as the result of an earthquake, sometimes from an explosion. Seismic waves are also continually excited by the pounding of ocean waves and the wind.
INTENSITY describes the level of shaking during an earthquake.
MAGNITUDE is a measure of the strength of an earthquake and is related to the amount of energy released.
The HYPOCENTRE/FOCUS is the area within the crust where rocks ruptured and released their stored energy in an earthquake.
The EPICENTRE is the point on the earth’s surface that is directly above the hypocenter or focus. The epicenter is usually the location of greatest damage. Reference: http://odpm.gov.tt
PHIVOLCS EARTHQUAKE INTENSITY SCALE