Offshore　seismic　motions　typically　undergo　remarkable　variation　at　different　locations　of　submarine　pipelines　due　to　the　spatial　effects　of　ground　motions.　Therefore,　this　paper　intends　to　contribute　to　an　insight　into　the　seismic　performance　of　FSSPs　subjected　to　offshore　spatial　earthquake　motions　and　identify　the　critical　impacts　of　seismic　excitation　type,　coherence　loss　effect　and　ground　motion　directionality.　In　view　of　this,　a　suite　of　underwater　shaking　table　tests　were　firstly　conducted　to　investigate　the　elastic　seismic　responses　of　the　FSSP　under　offshore　spatial　motions.　Subsequently,　a　response　difference　factor　(χR.ij)　is　defined　to　quantify　the　structural　response　discrepancies　caused　by　the　seismic　excitation　type　and　coherence　loss　effect.　Then,　a　numerical　modelling　scheme　for　FSSP　is　developed　and　its　excellent　response　prediction　capacities　are　verified　through　shaking　table　test　results.　Based　on　the　validated　numerical　model,　seismic　fragility　curves　of　the　FSSP　are　established　by　performing　the　probabilistic　seismic　demand　analyses.　Furthermore,　the　FSSP　fragilities　under　different　seismic　inputs　and　coherence　degrees　are　comprehensively　compared　and　discussed　in　terms　of　the　damage　probability　and　fragility　median　PGA.　Finally,　the　FSSP　fragilities　are　assessed　under　offshore　spatial　motions　with　various　horizontal　incidence　angles.　Both　experimental　and　numerical　results　consistently　highlight　the　significance　of　considering　the　seismic　excitation　type　and　coherence　loss　effect　in　seismic　performance　assessment　of　FSSPs.　Additionally,　as　the　seismic　incidence　angle　gradually　increases,　the　FSSP　fragilities　increases　first　and　then　decreases,　and　the　most　favorable　and　adverse　seismic　incident　angles　are　45°　and　90°,　respectively.　This　study　can　contribute　to　a　valuable　reference　for　realistically　evaluating　the　seismic　performance　of　FSSPs　subjected　to　offshore　spatial　earthquake　motions.　©　2025　Elsevier　Ltd