Analysis of building seismic damage characteristics and topographic amplification effects of the 2026 Diebu Ms5.5 earthquake
Abstract
On January 26, 2026, an Ms5.5 shallow-focus earthquake occurred in Diebu County, Gannan Tibetan Autonomous Prefecture, Gansu Province. The affected area lies within the alpine gorge of the Bailong River on the eastern margin of the Tibetan Plateau, a region characterized by rugged topography and complex geological conditions that are typically prone to topographic amplification of ground motion. To address how topographic and site conditions control ground-motion amplification and the resulting spatial distribution of seismic damage, this study selected Dianga Town in Diebu County—the area covered by the earthquake damage survey—as the study area. Field damage surveys, seismic station monitoring data, and FLAC3D three-dimensional numerical simulations were integrated to systematically reveal the relationships among ground-motion amplification, building damage, and slope deformation. Results indicate that the seismic intensity in the study area reached VI–VII on the Chinese seismic intensity scale. Ground-motion amplification was closely associated with the spatially non-uniform distribution of seismic damage: at steep cliffs, slope shoulders, and high-elevation sites, peak ground acceleration (PGA) amplification factors approached 2.0, and buildings at these locations experienced significantly more severe damage than those at other sites. Seismic loading also altered the shear strain distribution pattern of the slope, causing the zone of concentrated shear strain to redistribute and extend toward the residential area. Topographic relief, excavation-induced free faces, and elevation differences were identified as the primary factors contributing to topographic amplification in the studied alpine gorge; in particular, an elevation difference of only about 100 m produced pronounced differences in seismic damage. These findings qualitatively reveal the mechanism of ground-motion amplification and provide a scientific basis for seismic fortification and geological hazard mitigation in villages and towns within alpine gorge areas on the eastern margin of the Tibetan Plateau.