Fault-block patterns and local structural vulnerabilities associated with fatalities in the 2023 Jishishan earthquake

Background The 2023 Mw 6.2 Jishishan earthquake caused 151 fatalities despite its moderate magnitude. Field surveys documented 145 deaths at 100 fatality sites within 131 investigation sites. We combined these records with building information, terrain, strong-motion data, and fault-side position to examine why fatalities were concentrated in particular locations. Results Building damage accounted for 125 of the 145 field-verified deaths (86.2%). Most occurred in earthen-timber and masonry-timber dwellings. In several mixed-structure houses, unreinforced masonry washroom partitions near sleeping areas collapsed and caused fatalities even though the main structure remained largely intact. Relative to the mapped Lajishan North Margin Fault used as the analytical reference, 81 fatality sites and 111 deaths were on the hanging-wall side, compared with 19 sites and 34 deaths on the footwall side. The two sides also differed in lethality level and collapse direction. Machine-learning analysis showed that the ground-motion variables contributed mainly as a correlated group. Random five-fold cross-validation gave a mean R 2 of 0.618, but performance dropped markedly when entire villages were held out. Conclusions The observed mortality pattern reflected more than shaking intensity alone. Fatalities were concentrated where vulnerable rural buildings, hazardous indoor elements, and local ground-motion and environmental conditions occurred together. Combining field observations with local building and fault-side information can therefore help identify differences in fatality risk within the affected area. Because the analysis is based on a single earthquake, the framework needs to be tested with other events before broader use.