IndexWhat is an earthquake?What causes earthquakes and where do they occur?Why does the earth shake when there is an earthquake?How are earthquakes recorded?How do scientists measure their size? How can scientists know where the earthquake occurred? Can scientists predict earthquakes? What is an earthquake? An earthquake is what happens when two blocks of earth suddenly slide past each other. The surface on which they slide is called a fault or fault plane. The location below the Earth's surface where the earthquake begins is called the hypocenter, while the location directly above it on the Earth's surface is called the epicenter. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Sometimes an earthquake has warning shocks. These are smaller earthquakes that occur in the same location as the larger earthquake that follows. Scientists cannot say that an earthquake is a foreshock until the larger earthquake occurs. The largest major earthquake is called a mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur later in the same location as the main shock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock! What causes earthquakes and where do they occur? The earth has four main layers: the inner core, the outer core, the mantle and the crust. The crust and upper mantle form a thin skin on the surface of our planet. But this skin is not whole: it is made up of many pieces, like a puzzle that covers the surface of the earth. Not only that, these puzzle pieces continue to move slowly, sliding past each other and colliding with each other. We call these pieces of the puzzle tectonic plates, and the edges of the plates are called plate boundaries. Plate boundaries are made up of numerous faults, and most earthquakes in the world occur on these faults. Because the edges of the plates are rough, they get stuck while the rest of the plate continues to move. Eventually, when the plate has moved far enough, the edges of one of the faults break away and an earthquake occurs. Why does the earth shake when there is an earthquake? As the edges of the faults are stuck together and the rest of the block moves, the energy that would normally cause the blocks to slide past each other is stored. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it breaks away, all the stored energy is released. Energy radiates from the fault in all directions in the form of seismic waves like ripples on a pond. Seismic waves shake the earth as they move across it, and when the waves reach the earth's surface, they shake the ground and everything on it, like us and our homes! (see P&S Wave box)How are earthquakes recorded?Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. The seismograph has a base that attaches securely to the ground and a heavy weight that hangs freely. When an earthquake causes the ground to shake, the base of the seismograph also shakes, but the suspended weight does not. Instead the spring or the rope on which it is hanging absorbs all the movement. The difference in position between the trembling part of the seismograph and the immobile part is recorded. How do scientists measure the size of earthquakes? The size of an earthquake depends on the size of the fault and the amount of slip on the fault,.