GRE阅读：How to Forecast an Earthquake

　　Earthquakes are a common geological phenomenon; they happen all over the world every single day. However, most of the earthquakes are too weak for humans to feel. Since the dawn of time, man has sought to forecast earthquakes due to the possibility of their devastating effects. Even though earthquakes cannot be forecasted or predicted with 100 percent certainty, there are some things that you can do to help forecast earthquakes.

　　Look at geologic maps to find the locations of past earthquakes. Maps showing the locations of past earthquakes are available from the United States Geological Survey . By looking at these maps, you can see where earthquakes may be likely to occur again based on where they have occurred in the past.

　　Obtain information on when earthquakes have occurred in the past. In some locations that have experienced multiple earthquakes in the past, there may be some periodicity or pattern to when those earthquakes occurred. Knowing this periodicity can help you forecast when an earthquake may occur in the future. The USGS also has information on when earthquakes have occurred.