Earthquake is one of the most disaster in recent world. Earthquake is not a recent disastrous event. It has a long history of occurrence. From the beginning of the earth formation earthquake is happening everyday in a small or big magnitude.
The ancient people did not know the actual cause of earthquake. The world is getting more knowledge and technology to explore the natural events. Uncivilised people think that earthquake is caused by God’s will. But recent technology prove that, this is a natural process as like as wind blows from east to west or west to east or north to south. This is so natural process happening throughout the world everyday. Scientist prove that the most occurrence of earthquake happened in the ring of fire. The ring of fire is the region where earth crust is subducting or moving far away from each other.
Plate tectonic is the main cause of happening earthquake. The theory of tectonic shows that earth is made up of some land mass called plate. These plates are moving continuously very slowly. The sources of plate tectonic movement is the energy from the hot magma inside the earth. The plate movement works like piece of paper moves on the boiling water in a glass.
The lifespan of human being is so tiny that people cannot realise the movement of plate. The plate moves 10 cm per year on average.
Modern human identify the location of the earthquake. Scientist developed some measuring technique called seismograph. The recorded seismic wave on a piece of paper is called seismogram. From the height of the seismic wave on a seismogram, we can identify the magnitude of the earthquake. Now the whole world is covered with earthquake measuring seismograph. For each location every seismograph detect some seismic wave from a specific earthquake. These seismic waves tells us the actual location of the seismic source. The actual source of seismic wave is called the epicenter of the earthquake. If earthquake happened then to get the actual location we need at least three seismograph data. From each seismograph data we can get a circle of approximate location of earthquake. Each circle then intersects in a specific point. The epicenter is that point of the actual location of the earthquake.
For details here is the picture to get the idea.