The long-term topographic growth and frequent seismicity in the eastern Tibetan Plateau during the India-Asia collision, remain poorly understood. End-member models of lower crustal flow and brittle crustal shortening reflect contrasting deformation controlled by different rheological structures within the lithosphere. Our physical analog models reveal that the contrast rheology between the Sichuan Basin and Songpan- Garze terrane sculpts the steepest plateau margin and demonstrates how crustal heterogeneity governs mountain elevation, strain accumulation, and seismicity. Seismogenic faults, associated with brittle deformation, develop on a weak detachment, decoupling upper and lower crustal deformation and facilitating strain propagation toward the plateau margin. The Longriba and Longmenshan fault belts, of equivalent along-strike length, operate as a single, coherent pop-up system. Particle Image Velocimetry analysis shows simultaneous activity on these NE-trending faults, driving northeastward oblique thrust propagation, consistent with the 2008 Mw7.9 Wenchuan earthquake rupture process. Despite significant strain accumulation on both NS-trending and NE-trending faults, the seismically quiescent Longriba fault, defining the Yangtze-Yellow River divide, could host a Wenchuan-class earthquake, threatening critical infrastructure and Asia’s major river headwaters. Our rheological stratified physical experiments provide a quantitative, scale-bridging framework that links long-term tectonic kinematics, strain partitioning and topographic growth to short- term seismic hazard assessment, highlighting rheology as the fundamental control for physically-based mountain-building models worldwide.