AbstractMixed multiple seismic systems (MMSSs) are ideally suited for sustainable seismic design (SSD). MMSSs are combinations of two or more different earthquake-resisting structures (ERSs) that provide lateral support for gravity frameworks. Same-system combinations have been demonstrated to not be suitable for SSD. Regardless of the carbon footprint reduction, unless a structure has been designed for seismic sustainability it would be disposable with greater harm to the environment. Here, design means planning for both seismic resistance as well as post-earthquake realignment and repair (PERR). Earthquakes are random, natural, and dynamic events, whereas PERR is a deliberate, manual, and static process. In SSD the practicality of PERR is as important as the relevance of the theoretical assumptions. In SSD the non-lateral-resisting items are designed not to partake in seismic resistance, nor hinder the realignment process. Additionally, efforts are made to mitigate the P-delta effects that undermine the global strength of the system and oppose the recentering effort. The purpose of this paper is to identify and remedy design flaws and physical issues that prevent MMSSs from achieving seismic sustainability as cost-effectively as possible. Two newly developed technologies, the ladder moment frame (LMF), and the fail-safe (FS) system, as well as a capacity distribution rule together with six simple axioms are introduced. Brief descriptions of LMF and FS are presented in the text.Practical ApplicationsAny structure designed to survive earthquakes is expected to either remain elastic and stable or be capable of post-earthquake realignment and repairs. Sustainable seismic design is a new field of research that promises improved environmental conditions and innovative developments in structural engineering. Regardless of the carbon footprint reduction, unless a structure has been designed for the purpose, it would be disposable with greater harm to the environment. Here, design implies planning for seismic resistance as well as post-earthquake realignment and repairs. The difference between conventional and sustainable seismic design is in the modes of behavior during and after the event. In conventional seismic design, the object is to satisfy code-specified requirements; in sustainable seismic design, the post-earthquake attributes of the system are as important as those during the event. The paper shows that seismic sustainability can be achieved without resorting to untenable costs and technologies. In light of current findings, it is suggested to include post-earthquake realignment and repairs in seismic design guidelines for new construction.