Seismic behavior of the built environment is uncertain for a number of reasons, one of the most important of them is that surface ground motions are inherently variable. The aim of this book is to shed light on some of the variables that control much of this uncertainty, show a lower bound to this uncertainty by computing the statistics for sites (stations) that have recorded multiple earthquakes, and present the effects of plausible uncertainty reductions on the results of Probabilistic Seismic Hazard Analyses (PSHA). This book shows that single-site uncertainty is considerably lower than...