Mallet–Milne lecture 2025: risk management and rehousing of people displaced by earthquake disasters

Major seismic events over the last century or more have led to large numbers of casualties and damage to buildings and infrastructure. The loss of homes and livelihoods have often led to either mass exodus from an affected region, or the rapid construction of makeshift houses that are often of a lower standard than that expected of newly built permanent dwellings. Often intended to be temporary or “transitional” accommodation, this rapid reconstruction can often remain for decades or centuries after. The primary objective of this study is to evaluate the effectiveness of public actions taken after major seismic events, specifically in managing large numbers of displaced people and mitigating the social impact and indirect losses caused by interruptions to various residential services. Several notable examples from around the world are presented and discussed. Having established that the response to this kind of emergency has generally been unsatisfactory and that a general approach to improving the situation is missing, the actions undertaken following the earthquake in L’Aquila, Italy, in 2009, are discussed, to investigate whether it is possible to derive approaches applicable in broader situations. This example shows that rapid construction of permanent housing was possible without compromising on the standards expected by modern building codes. This was achieved by using standardised designs for base-isolated platforms that effectively reduce the design seismic accelerations for multi-unit housing complexes built on top of them. Post-L’Aquila, this allowed effective quality control on the most critical component of the system – the base isolation system– while permitting multiple engineers and contractors to, in parallel, develop and implement the building designs, significantly expediting the post-earthquake recovery process. Encouraged by this example, the remainder of the paper discusses how this idea can be further developed before the next major earthquake occurs, to enable even more rapid implementation in an affected disaster zone. The application of performance-based design procedures at a regional scale is examined, to establish how extensive the problem could be, i.e. whether estimates of the potential number and location of displaced people lead to a sufficiently clear picture to allow the appropriate authority in a country (e.g. the national civil protection department) to deal with it, developing detailed plans in peace (i.e. non-emergency) time. If this is the case, national or regional emergency plans can focus on a limited number of locations, considering that population concentration, event magnitude and fault distance are limiting the cases in which the expected homeless people are greater than significant threshold values. A fundamental part of the study is devoted to the development of design approaches oriented towards rapid reconstruction, with the aim of completing high-tech alternative residential buildings. These buildings are characterized by a high level of seismic protection, continuity of use in case of strong earthquake, low levels of energy consumption, acceptable social and urban organization and potential for rational re-use following a reasonable emergency time, of the order of about ten years from past experiences. A key component of the solution is the application of seismic isolation. This approach aims to facilitate the use of different building construction technologies and the design and analysis of buildings by essentially eliminating the variability imposed by local input ground motion and soil conditions from the design process, and reducing the inertia force to a small fraction of gravity. Standardised base isolation solutions are developed, including technical details and a worked example to illustrate the feasibility and applicability of this approach.