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

Some of the larger earthquakes are preceded by foreshocks. Knowledge of past earthquake patterns allow scientists to estimate the odds that an earthquake striking today is a foreshock and will soon be followed by a larger main shock 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 main shock 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.” (McDonagh 121).

can only go as far as to declare that a temblor has a certain probability of occurring within a given time, but not that one will definitely strike.” (Ebel 28). 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 main shock, those before it are called foreshocks, and those occurring after are referred to as aftershocks.

will strike. I will discuss how earthquakes are formed and occur, and how scientists can more accurately predict the arrival of earthquakes.

The development of modern seismic monitoring networks and the knowledge gained from past shocks allowed earthquake forecasting and warnings to become

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