On January 26, 2026, an M_S5.5 earthquake struck Diebu County, Gannan Tibetan Autonomous Prefecture, Gansu Province, with a focal depth of 10 km and an epicentral intensity of Ⅶ degree. It caused varying degrees of damage to buildings in the affected area. Based on post-earthquake damage assessments, this study analyzes the construction characteristics of local buildings and the seismic damage patterns across different structural types, revealing their failure mechanisms. The results indicate that rural buildings in the affected area are predominantly traditional timber-frame houses. The load-bearing timber frames mostly remained intact, but the rammed earth walls suffered severe damage, mainly cracking, partial collapse, and out-of-plane tilting. Brick-wood and brick-concrete structures are less common and primarily experienced varying degrees of wall cracking. Urban buildings are mostly brick-concrete or frame structures, with relatively minor damage, mostly wall cracking. The main causes of damage include high wall brittleness, weak connections between components, poor site selection, and unreasonable building layouts. Furthermore, most rural self-built houses lack seismic reinforcement measures. These findings can provide valuable references for post-earthquake reconstruction and seismic retrofitting of buildings, contributing to improving the overall disaster resilience of buildings in Northwest China.