Probabilistic liquefaction hazard assessment in urban centres with a non-liquefiable surface layer overlying a liquefiable stratum

Understanding the interaction between multiple earthquake-related hazards is essential for improving risk assessments in urban areas. This study presents a multi-hazard framework to integrate earthquake motion and liquefaction within a probabilistic liquefaction hazard assessment in an urban area. The novel contribution of this work is the development of a probabilistic liquefaction framework designed for sites with a non-liquefiable upper layer overlying a liquefiable layer, conditions common in many urban environments but rarely addressed. This approach is particularly useful for regions with limited data, as it makes effective use of available local seismic and geotechnical information. The methodology involves: (i) selecting and applying an appropriate probabilistic liquefaction manifestation severity model based on local geotechnical conditions; and (ii) integrating probabilistic seismic hazard assessment outputs with simplified geotechnical profiles that reflect the potential liquefaction impact, which are then incorporated into the liquefaction manifestation severity assessment. The case study focuses on the Aguablanca District in Cali, Colombia, an area with moderate to high liquefaction susceptibility. Liquefaction manifestation probabilities were computed using two indices: the Liquefaction Potential Index (LPI) and an Ishihara-inspired LPI (LPI_ISH). Results for a 50-year exposure period indicate moderate surface manifestation, aligning with regional studies. The study also explores the implications for an earthquake scenario with a return period of 475 years, for which the analysis indicates surface liquefaction manifestations ranging from moderate to severe. The detailed liquefaction assessment for given urban area in Colombia provides a solid basis for risk reduction and urban planning strategies in liquefaction-prone areas.