Do seismic intensity measures (IMs) measure up?

We show that, generally, Sa(T) and D are weakly dependent and conclude that fragilities defined as functions of Sa(T) have large uncertainties. The analysis considers linear/nonliear systems and single/multiple ordinates of Sa(T). Tools of random vibration, copula models, and multivariate extreme value theory are employed to quantify the dependence between Sa(T) and D.