Abstract: The Longriba fault zone represents a major active structure within the Songpan-Ganzi block, demarcating pronounced contrasts in surface topography, crustal deformation, and deep crustal properties between the eastern and western parts of the block. Controversy persists regarding its deep geometry: magnetotelluric profiles typically image the fault terminating at the top of a mid-lower crustal conductive layer, whereas active-source seismic reflection profiles reveal it as a crustal-penetrating structure extending to the Moho. Teleseismic P-wave tomography suggests a southeast-dipping fault that extends at least into the mid-lower crust. Low-temperature thermochronology indicates that fault activity likely initiated around 38 Ma, driven by far-field stress propagation following the India-Eurasia collision. Tectonic analyzes link the fault to regional evolution, noting that the eastern margin of Qinghai-Xizang Plateau experienced significant denudation during the Late Cretaceous and Late Cenozoic, with the latter accounting for ~80% of total erosion, focused predominantly between the Longriba and Longmenshan fault zones. This spatial pattern suggests that the Longriba fault zone plausibly acts as a back-thrust to the Longmenshan fault zone, with both structures jointly accommodating crustal uplift and growth deformation in this region. Although current seismicity along the Longriba fault zone is low, its long evolutionary history, substantial surface trace, deep penetration, Late Pleistocene slip rate of ~5 mm/a, and evidence of paleoseismic events from trench studies collectively imply its considerable seismic potential risk. Given the ongoing India-Eurasia convergence, this fault zone warrants careful attention in regional seismic hazard assessment.