Examine seismograms, tracings or recordings of seismic activity at a particular location. If you see an increase in seismic activity on a seismogram, a large earthquake may soon follow.
Observe rocks in various areas. Sometimes, rocks will contain layers of disturbed sediments that indicate ancient, severe earthquakes. Knowing the locations of these past severe earthquakes can indicate that future severe earthquakes may occur in these same areas.
Take note of foreshocks. Sometimes large earthquakes are preceeded by smaller earthquakes known as foreshocks. If small earthquakes are occuring in a particular area over a particular period of time, then a larger, more severe earthquake may be forecasted for that area.
Look at the behavior of animals. Although highly controversial, some animals, such as dogs and cats, may change their behavior patterns prior to an earthquake.
Think about tidal forces. Tidal forces as predictors of future earthquakes is an uNPRoven theory. The phenomenon, known as syzygy, says that tidal patterns can be used to forecast earthquakes, especially those involving oceanic crust.