Geologic features altered by earthquakes provide striking evidence of the power of seismic events. It wasn't until the late 1970s, though, that their usefulness in helping to predict the timing of future earthquakes was considered. That's when geologist Kerry Sieh thought to use fractures in layers of sediment to determine the frequency of earthquake events. This video segment adapted from NOVA explores the method Dr. Sieh used to revolutionize earthquake prediction.