Comparison with Predicted Ground Motions

Future ground motions are predicted by a probabilistic seismic hazard analysis probabilistic seismic hazard analysis. In this chapter, the predicted ground motions are compared with the strongest recorded ground motions. The 10,000-year mean return period (MRP) predicted ground motions at two sites in the United States are much stronger than any ground motions in 200,000 instrument-years of recorded data. The energy demand of 20,000-year MRP ground motions is completely unrealistic, even though 20,000-year ground motion also has nearly a 100% chance of exceeding 200,000 years of recorded data. Overprediction of hazards (and risks) is harmful because it increases the cost of insurance, results in inefficient allocation of resources; deprives the public of the benefits of projects that are deemed “too risky” or “too costly” because of overprediction; and causes others to doubt the predictions and not take them seriously.