People and Planet - Predicting Earthquakes

What would make a good prediction? Knowing where, when, and the magnitude of the quake would make it possible for people to evacuate.

A GOOD PREDICTION
Scientists are a long way from being able to predict earthquakes. A good prediction must be detailed and accurate. Where will the earthquake occur? When will it occur? What will be the magnitude of the quake? With a good prediction authorities could get people to evacuate. An unnecessary evacuation is expensive and causes people not to believe authorities the next time an evacuation is ordered. 

Currently scientists cannot predict exactly when or where an earthquake will occur.  However they can, with accuracy, predict general areas where earthquakes will occur. Scientists know that earthquakes take place at plate boundaries and tend to happen where they’ve occurred before.  Fault segments behave consistently. A segment with frequent small earthquakes or one with infrequent huge earthquakes will likely do the same thing in the future.

When an earthquake will occur is much more difficult to predict. Since stress on a fault builds up at the same rate over time, earthquakes should occur at regular intervals But so far scientists cannot predict when quakes will occur even to within a few years.    For example, around Parkfield, California, an earthquake of magnitude 6.0 or higher occurs about every 22 years. So seismologists predicted that one would strike in 1993, but that quake came in 2004 - 11 years late.

EARTHQUAKE SIGNS
Scientists’ use of technology has helped improve earthquake prediction.  Earthquake prediction is very difficult and not very successful, but scientists are looking for a variety of clues in a variety of locations and to try to advance the field.

It's been twenty years since the Loma Prieta Earthquake ravaged downtown Santa Cruz and damaged San Francisco's Marina District and the Bay Bridge. QUEST looks at the dramatic improvements in earthquake prediction technology since 1989.