Abstract
<jats:p>Great megathrust earthquakes produce deformation over a wide range of spatial scales, yet how near‑trench, near‑field, and far‑field static displacements collectively constrain the same rupture remains poorly understood. Here we analyze the 29 July 2025 Mw 8.8 Kamchatka earthquake using spatially multi-scale observations: tsunami-derived initial uplift models for near-trench offshore deformation, Sentinel-1 InSAR and local GNSS offsets for near-field onshore deformation, and regional-to-far-field GNSS offsets extending to ~4000 km. These data are interpreted with a spherical 3D finite-element model that includes trench bathymetry, slab geometry, and first-order elastic heterogeneity. Land-based geodesy constrains the onshore and long-wavelength deformation field but does not uniquely resolve shallow offshore slip. Incorporating two alternative tsunami-derived uplift models produces distinct shallow-rupture scenarios: one with slip mainly at 20–40 km depth and limited trench slip, and another with extensive slip shallower than 20 km. Despite these differences, acceptable slip models predict nearly identical far-field horizontal displacements beyond ~1000 km, showing that far-field GNSS offsets provide little direct constraint on detailed slip. Earth-structure tests show that a first-order heterogeneous spherical model reproduces the far-field response of a more detailed LITHO1.0-PREM model to within ~5%, whereas a homogeneous elastic model overpredicts regional deformation. Together, these results provide a mechanically consistent, spatially multi-scale analyses of the 2025 Kamchatka rupture, linking near-trench tsunami constraints, near-field geodesy, and far-field static deformation in a heterogeneous spherical Earth.</jats:p>