Climate change and seismic resilience: Key considerations for Alaska’s infrastructure and built environment

Alaska from 2001 to 2015 suggest that this layer ranges from 0 cm in the North Slope to 300 cm in Coastal and Southern Alaska [53]. As a result of climate change, the thickness of the active layer is expected to increase by 20–30% across most of the permafrost area in the North- ern Hemisphere throughout the 21st century [54]. Fluctuations in active layer depth can influ- ence other natural surface subsystems such as vegetation distribution and forest leaf cover [55, 56]. Overall changes in permafrost distributions will result in the discontinuous zone shifting further north, with reductions in the size of the continuous zone. Changes in the mechanical properties of soils due to warming permafrost will alter the strength of soil layers. Most of the strength of frozen, fine-grained soil is generated by ice bonding, which creates a cohesive bond between soil particles [51]. Therefore, the extent of strength deterioration during thaw depends on the ice content of the permafrost. Permafrost with low ice content is generally considered thaw stable. When this permafrost melts, a layer of talik (perennially thawed soil) is generated between the upper, active layer, and the lower per- manently frozen permafrost. In contrast, ice-rich permafrost is considered thaw unstable. As ice-rich permafrost warms, the presence of melted water reduces the strength and stiffness of these soils [10] leading to ground surface subsidence and thermokarst formation. Past research has shown that the seismic response of soil-foundation-structure systems is influenced by

changes to the stiffness and strength of underlying soil layers [57–62]. Fig 4 shows the concep- tual impact of permafrost thaw on the seismic response of a building, suggesting seismic motions propagating through once frozen soil will further deteriorate the soil strength due to changes in the stress and strain experienced by the material. Buildings and other structures resting on previously frozen but now saturated or near-saturated soil deposits that are sub- jected to intense ground motions may experience a sudden reduction in support. This loss in bearing capacity results in foundation settlements and rotations [61, 62], which in turn may damage underground utilities (Fig 4B). Therefore, it is prudent for practitioners to account for the variation and effect of permafrost thickness due to climate change over the design life of infrastructure systems (i.e., considering foundations depths and load transfer mechanisms). Permafrost in the southern sections of Alaska has temperatures near the freezing point [51]. Soils in these locations are at the greatest risk of experiencing complete permafrost disappear- ance. According to Fig 3B, these regions also have the greatest seismic hazard, which means Fig 4. Conceptual impact of permafrost thaw on the seismic response of building-foundation systems showing (a) typical Arctic soil profile and (b) climate-induced permafrost thaw. https://doi.org/10.1371/journal.pone.0292320.g004 PLOS ONE Climate change and seismic resilience: Key considerations for Alaska’s infrastructure and built environment

PLOS ONE | https://doi.org/10.1371/journal.pone.0292320 October 18, 2023 7 / 17