The Facts

• Earthquakes occur when the stress between two opposing plates within the earth causes one or both plates to slip and the surrounding land to roll or shake. The San Andreas Fault in California is one of the more famous of these earthquake stress zones.
  
  

Earthquake Frequency

• Globally, between 70 and 75 earthquakes that cause damage occur annually. Thousands of smaller earthquakes happen each year, many of which are not even noticed or felt.
  
  

Reliability

• Even though scientists have been studying earthquakes for more than 40 years, most earthquakes cannot be predicted with reliable methods.
  
  

Parksfield

• Located south of the San Francisco Bay Area, the town of Parksfield is the site of California's San Andreas Fault Observatory at Depth (SAFOD) earthquake study. The project's intent is to find the geological key to earthquakes so that they can be better predicted.
  
  

ELARMS

• The Earthquake Alarms System, or ELARMS, is being tested in California and other earthquake-prone regions. Though it does not predict the initial quake, it can detect the quake quickly, measure the size and predict where the shock waves will travel, thus providing affected communities a moment's warning.
  
  

Precursors

• Earthquake precursors that have been observed in the natural world include sudden rises in water tables, unusual behavior in both wild and domestic animals, and unusual changes in temperature.