If you’ve ever experienced an earthquake, you might describe it as a sudden and violent shaking of the ground. The shaking comes from seismic waves, which are waves of energy that come from the earth’s crust and travel through its layers. According to the U.S. Geological Survey, the world experiences 500,000 earthquakes every year.
An earthquake occurs when two blocks of the earth slip past one another. The thin skin that forms the earth’s surface is actually composed of several pieces put together. These pieces, which are called tectonic plates, tend to move around slowly. This action causes a slipping or bumping effect at the plate edges, or plate boundaries. The pieces slip at a surface referred to as the fault, or fault plane. The edges, which are rough, get stuck while the rest of the plate continues to move. Thus the energy intended for moving the plate begins to accumulate. When the edges are freed, that accumulated energy in the form of seismic waves is released. This occurs at a place below the earth’s surface called the hypocenter. The seismic waves travel upward, shaking the earth as they move through it. Directly above the hypocenter is the epicenter, which is at the surface of the earth. When these waves arrive at the surface, the ground and everything on it or attached to it begins to shake.
In some cases, foreshocks can occur; these are smaller tremors that proceed the larger turbulence. The main tremors that people recognize as actual earthquakes are actually referred to as mainshocks. They are followed by aftershocks, which are smaller tremors that occur in the same location. The size of the aftershock depends on the size of the mainshock; it can continue to occur for weeks, months or even years after the main tremor.
Contrary to popular opinion, most earthquakes are not destructive. Out of the annual 500,000 earthquakes claimed by the USGS, only about 100,000 of them (20 percent) are felt. And out of that number, only about a hundred of them cause damage. However, the most serious earthquakes destroy property and claim lives. Much of the time, earthquakes are linked to subsequent storms, tsunamis, floods, and fires. In some cases, the effects cause more deaths and destruction than the earthquake itself.
Scientists who study earthquakes are called seismologists. They record earthquakes with instruments called seismometers. These instruments measure the motions of the ground when the earthquake occurs, and they produce recordings called seismograms. The diagrams that seismograms produce determine the size of the earthquake. A short wiggly line with few wiggles indicates a small earthquake, while a long wiggly line with a lot of wiggles signifies a large earthquake. Seismologists assign a number to each earthquake to denote its magnitude. For instance, an earthquake with a magnitude 3 is small and harmless, while an earthquake with a magnitude 9 is large and very dangerous.
Prediction and Preparedness
Over the years, seismologists have worked on earthquake warning systems to predict the time and place in which earthquakes will occur. These systems can provide notification of an earthquake already taking place, but before the ground begins to move. This helps people within the range of the tremor to go to a safer area. Unfortunately, earthquake warning systems cannot make predictions that pinpoint a specific day or month.
This article was written by Heather Johnson, a new writer who hopes to help you learn more about the world. She writes this on behalf of Allied Outdoor Solutions, your number one choice when looking for professionally-installed concrete. Check out their website today and see how they can help you!