Perhaps Mother Nature offers no greater force than that of the earthquake. Across the span of time, earthquakes have been recorded for their incredible destructive forces, and their abilities to awe mankind with their unparalleled force. Earthquakes can often strike without any notice, leveling large cities and killing scores of innocent people. Not only can earthquakes bring harm to society through these methods of destruction, but they can also cause millions of dollars worth of damage to the areas they destroy, causing economic chaos. An earthquake is a natural phenomenon, occurring throughout the history of the world. Descriptions as old as recorded history show the significant effects earthquakes have had on people's lives. Long before there were scientific theories for the cause of earthquakes, people around the world created folklore to explain them. Until recent times, science has not had a complete understanding of how earthquakes are caused, and what can be done to predict when they will strike. This essay will discuss how earthquakes are formed and occur, how scientists can more accurately predict the arrival of earthquakes.
Before contemplating how earthquakes might possibly be prevented, it is essential that the process and formation of and earthquake be understood. Earthquakes are caused when the earth's crustal plates move, rub, or push against each other. The earth's crust (the outer layer of the earth) is made up of seven major plates and approximately thirteen smaller ones. The name plate is used to describe these portions of the earth's crust because they are literally "plates" or sections, composed of dirt and rock. These plates float on molten lava, called magma. Since the plates are floating on magma, they can slowly move. The place where friction occurs between plates is called a fault. A fault is a crack in a plate or a place where two or more plates meet. An example of a fault where two plates meet is the San Andrea's fault in California, where the Pacific and North American plates meet. The plates are about 30 miles thick under land and can be one to five miles thick beneath the ocean. The plates move because of convection currents. Magma has currents like the ocean does, that move in a circular motion beneath the plates. When two plates are pushing against each other, they are constantly building up tension on the fault. When two plates finally slip, they release a great amount of energy in the form of shock waves. These shock waves cause vibrations, which in turn cause the ground around the fault line to move and shake. This phenomenon is know as an earthquake.
Because of the incredible destructive capabilities of earthquakes, scientists are constantly trying to devise ways to ensure their early detection. Earth scientists have begun to forecast damaging earthquakes in California. Although quake forecasting is still maturing, it is now reliable enough to make official earthquake warnings possible. These warnings help government, industry, and private citizens prepare for large earthquakes and conduct rescue and recovery efforts in the aftermath of destructive shocks. In recent years, earthquake forecasting has advanced from a research frontier to an emerging science. This science is now being applied in quake-plagued California, where shocks are closely monitored and have been studied for many years. Earthquake forecasts declare that a temblor has a certain probability of occurring within a given time, not that one will definitely strike. In this way they are similar to weather forecasts. Scientists are able to make earthquake forecasts because quakes tend to occur in clusters that strike the same area within a limited time period. The largest quake in a cluster is called the mainshock, those before it are called foreshocks, and those after it are called aftershocks.
In any cluster, most quakes are aftershocks. Most aftershocks are too small to cause damage, but following a large mainshock one or more may be powerful. Such strong aftershocks can cause additional damage and casualties in areas already devastated by a mainshock, and also threaten the lives of rescuers searching for the injured. In the first few weeks after the 1994 magnitude 6.7 Northridge, California, earthquake, more than 3,000 aftershocks occurred. One magnitude 5.2 aftershock caused $7 million in damage just in electric utility equipment in the Los Angeles area alone. The U. S. Geological Survey (USGS) first began forecasting aftershocks following the 1989 magnitude 7.1 Loma Prieta, California, earthquake. By studying previous earthquakes, scientists had detected patterns in the way aftershocks decrease in number and magnitude with time. With such knowledge, scientists can estimate the daily odds for the occurrence of damaging aftershocks following large California temblors. These forecasts are relayed directly to the California Office of Emergency Services (OES) as well as to the public.
Some of the more larger earthquakes are preceded by foreshocks. Knowledge of past earthquake patterns allows scientists to estimate the odds that an earthquake striking today is a foreshock and will soon be followed by a larger mainshock in the same area. These odds depend on the earthquake's magnitude and the same seismic history of the fault on which it occurred. When a moderate earthquake hits California, scientists immediately estimate the probability that a damaging mainshcck will follow. If the threat is significant, a warning is issued. This warning process was put into action in June, 1988 when a magnitude 5.1 shock--one of the largest in the San Francisco Bay region since the great 1906 earthquake--struck 60 miles south of San Francisco. Alerted by the USGS that there was a 1 in 20 chance of a larger earthquake in the next five days, the California OES issued an advisory to warn the public. (The usual daily odds of a large earthquake in the Bay region are 1 in 15,000.) The warning period passed without further activity. In August, 1989, another earthquake hit the same area and a similar advisory was issued. Again nothing happened in the specified warning period. However, 69 days later, the area was rocked by the magnitude 7.1 Loma Prieta earthquake, which killed 63 people and caused $6 billion of damage in the San Francisco Bay region.
The lessons learned from these observations have already enabled earth scientists and emergency response officials to build a framework within which they communicate rapidly and effectively. Based on this experience, similar alert plans have been devised for geologic hazards in other areas of the United States. The development of modern seismic monitoring networks and the knowledge gained from past shocks, earthquake forecasts and warnings are now a reality. Continued effective communication of these forecasts to the public will help reduce the loss of life and property in future earthquakes.
In conclusion, earthquakes are a powerful force of nature. Although these destructive giants are indeed deadly, scientists are continually utilizing research data collected from previous earthquakes and observations, so that a more effective and efficient warning system may be put in place. Because of these scientist's work, society benefits from this advanced knowledge of when an earthquake will most probably strike. With the continued study of collected data, perhaps one day their will be a warning system that will be able to give enough advanced notice, so that casualties might be minimized even further.