Strong earthquakes can cause fatalities on flat or gently sloping land through severe ground acceleration and liquefaction-induced ground failure, even without the presence of buildings or structures.
The claim is specific, empirical, and testable. The retrieved literature includes peer-reviewed studies documenting how strong ground motions and liquefaction on flat land or gentle alluvial plains can cause widespread ground failure, landslides, and fatalities independently of structural damage (e.g., papers 0 and 5). Therefore, the evidence strongly supports the claim.