Abstract: On August 10, 2026, an M_W7.4 intermediate-depth earthquake struck western Colombia, with a hypocentral depth ranging from approximately 96 to 107 km. This was an intraslab earthquake induced by the ongoing subduction of the Nazca Plate under the South American Plate. This earthquake exhibited an inverse spatial disaster distribution pattern: moderate damage in the mountainous epicentral region versus severe destruction in the far-field river valley urban agglomerations. This seismic event resulted in 241 fatalities and 3771 reported injuries. Numerous older masonry buildings lacking seismic detailing experienced progressive collapse, whereas lifeline infrastructure and historical and cultural heritage sites sustained varying degrees of damage. Based on source rupture characteristics and ground motion simulation results, this study analyzes the distinctive damage-generation mechanism of this intermediate-depth earthquake from four perspectives: large-scale uniform ground motion output from the seismic source, amplified horizontal effects caused by near-vertical incidence of seismic waves, approximately 30 s of strong ground motion induced by the coupling of rupture processes and site conditions, and cumulative damage of brittle masonry structures under cyclic loading. The study indicates that the seismic risk of intermediate-depth earthquakes depends not only on instantaneous peak ground acceleration but also on structural damage accumulation induced by long-duration cyclic loads. The Colombian government activated the highest level of national emergency response, conducted search and rescue operations and resettlement, repaired lifeline systems, mitigated secondary hazards, and accepted international humanitarian assistance, forming a domestically led and internationally coordinated emergency response model. This case study provides a reference for seismic design, seismic retrofitting of old buildings, and disaster risk management for river valley communities facing intermediate-depth earthquakes in global subduction zones.