This study investigates the progressive collapse behavior of a lightweight steel building with extensive glazing, representative of coastal structures, under sequential earthquake and tsunami loading. The research is situated in Yalova city, Turkey, a region at risk from seismic and tsunami hazards in the Sea of Marmara. The methodology involved a numerical simulation of a tsunami scenario triggered by a potential submarine landslide in the Çınarcık Basin. Bathymetric data were processed to simulate tsunami propagation and inundation, yielding hydrodynamic parameters at the study site. These parameters were used to calculate the tsunami drag force on a representative structure, which was then analyzed using a finite element model. Results demonstrate the high vulnerability of the glazed facades, with a calculated maximum tsunami drag force of 81 kN (for a flow depth of 1.55 m and current velocity of 1.92 m/s) leading to sequential glass failure. The failure initiated at the front glazing, propagated to the side and rear panels due to internal water pressure, and ultimately triggered a progressive collapse mechanism. The findings underscore that non-structural elements like glass facades are critical points of failure and emphasize the necessity for integrated design strategies that enhance collapse resistance against tsunami-induced loading in coastal seismic zones.