A proverb of Confucius states “Study the past if you would divine the future.” If we could learn about the past history of earthquakes on a specific fault, then we could serve society well by better forecasting the future earthquake behavior of that fault.For most of the world, the period of historical records is short: about 200 years in California and less than that in New Zealand, Oregon, and other parts of the world. And even where the historical record is thousands of years long, such as in north central China or the eastern Mediterranean region, it is commonly difficult to correlate a major historical earthquake with a specific active fault. Even if this correlation could be made without ambiguity, the recurrence intervals for many faults are longer than even a historical record of several thousand years. For these reasons, the history of large earthquakes on faults must, for the most part, be learned from the geological record.