Abstract | Selecting (near) optimal intensity measures (IMs) for seismic fragility assessment is fundamental for the accurate and unbiased assessment of risk. While moderate/long-period structures benefit from a variety of well-established options, short-period structures and their non-structural components (NSCs) present a more ambiguous scenario. Mainly driven by nuclear power plant studies, it is the peak ground acceleration (PGA) that has long been the default choice. Challenging this notion, we test IM candidates ranging from single-period spectral acceleration (Sa) ordinates to geometric averages over a range of periods (AvgSa). Featuring both on-ground NSCs and on-structure ones, we encompass a spectrum of short-period structures and short-period components. Invariably, if one has the luxury of employing NSC-specific IMs, Sa at the fundamental period of the component tends to yield the best results. In the more general case, though, certain AvgSa options whose period range starts at 0.01–0.10s and ends at 0.40–0.50s, provide a consistently improved (or at worst equal performance) compared to PGA, for a wide variety of NSCs with periods ranging from 0.05 to 0.90s.