The inside of the earth is a very hot burning mass of liquid matter. Due to some causes this heated matter in some part cools. It contracts. Its result is that the upper part of the earth at that particular place is drawn down. Then this produces cracks on the surface of the earth. The water of the ocean flows down through these cracks and comes in touch with the hot liquid. Sometimes the rain-water also finds its way down. It comes in contact with the heated matter. Steam is thus produced and it wants to rush out and the earth is violently shaken. Thus the earthquake is caused. There is an instrument called seismograph. It can show the force, place etc. of an earthquake. The point at which a earthquake breaks out is called the epicenter of the earthquake.