A new and defective regulation in California for protecting critical buildings from earthquakes

The California Geological Survey issued a new regulatory directive specifying that critical buildings be designed for 50- and 100-year earthquakes obtained by probabilistic seismic hazard analysis (PSHA). PSHA incorporates serious uncertainties. Chiefly, they are: (1) PSHA smears earthquakes together to produce motions that are unrealistic for any specific earthquake-generating fault source, (2) PSHA assumes there is an essentially log–linear predictability through time for both the sizes of earthquakes and their motions, although earthquake experiences deny this assumption, and (3) PSHA derives design values from an almost total lack of data on the recurrences that it claims to represent. Error bands for probabilistic motions, if honestly applied, would be so enormously broad that probabilistic values would be seen to be too uncertain as a rational basis for critical designs. Worse yet, the directive of the California Geological Survey has forced a de facto elimination of deterministic seismic hazard analysis (DSHA) from consideration. Yet, DSHA provides more logical, more transparent, more peer reviewable, and more dependable solutions than does PSHA. In summary, the new regulatory directive fails to provide the public in California with a necessary level of seismic safety. [Copyright &y& Elsevier]