Abstract | A novel scaling algorithm for ground motion accelerograms (GMs) is proposed in support of incremental dynamic analysis used to establish dependable statistical relationships between scalable intensity measures (IMs) and engineering demand parameters (EDPs) within a performance based earthquake engineering framework. Specifically, an iterative harmonic wavelet based scheme is employed to accomplish “surgical” changes to the spectral shape of suites of GMs to span various pre-defined levels of the spectral acceleration at the structural fundamental natural period, the most widely adopted IM. Since the target IM values may not be accomplished precisely by the local spectral modifications, a second step involving global uniform GM scaling is further considered. The proposed algorithm requires significantly smaller global (amplitude) scaling factors compared to the currently used scaling approach in which no initial local GM modification is undertaken. A numerical application of the proposed algorithm to elastoplastic structural systems shows the extent to which spectral shape may influence the displacement response of yielding structures and explains the conservative bias introduced by uniform global scaling.