Evaluating earthquake impacts in Oslo, Norway: a multi-method approach

Abstract In this study, we conducted a comprehensive seismic risk assessment for Oslo (capital of Norway), integrating both deterministic and probabilistic approaches to capture a holistic view of potential earthquake impacts. Based on the field data from exposed major faults in the Oslo rift margin and historical earthquakes in this region, the deterministic analysis examined three scenarios: (i) an Mw 5.4 earthquake that occurred in 1904 in the Oslo rift zone; (ii) a hypothetical Mw 6.0 event on the east side of the rift zone (Østmarka event), and (iii) a hypothetical Mw 6.0 event along an exposed fault zone in the central rift zone (Nesodden event). Among the three scenarios, the Østmarka event resulted in the highest losses, while the 1904 scenario showed negligible impact. In both the Østmarka and the 475-year return period probabilistic scenarios, Sentrum and Frogner neighbourhoods consistently emerged as the most affected areas. This is primarily due to a combination of local soil conditions and the prevalence of unreinforced masonry buildings, highlighting the critical interplay between physical hazard and locally specific vulnerability associated with the neighbourhood’s particular characteristics. The combination of deterministic and probabilistic approaches offers a detailed and nuanced understanding of seismic risks in Oslo. The findings underscore the need for targeted mitigation efforts and preparedness strategies, particularly in neighbourhoods that are more susceptible to seismic risks. By integrating these comprehensive risk assessments, the study provides valuable insights into the uneven distribution of seismic risk across Oslo. The results aim to inform local authorities and policymakers, aiding in the development of effective strategies to enhance the resilience of the city’s infrastructure and population against future seismic events.