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Summary Glaciers are key components of the global climate system and sensitive indicators of environmental change. Their dynamics generate diverse seismic signals, whose source mechanisms offer valuable insights into their internal stress conditions. While moment tensor inversion has been applied to icequakes on a few alpine and polar glaciers, it had not yet been implemented on the Argentière Glacier (French Alps). In this study, we conduct a systematic characterization of icequake source mechanisms based on a dense dataset of 14 057 near-surface events recorded by 98 3-component sensors deployed at the surface of the glacier during the RESOLVE project. We apply a full waveform inversion method to jointly reconstruct the moment tensor and the source time wavelet for each event. The moment tensor Green’s functions used in the inversion are computed through numerical modeling of elastic wave propagation in a 3D medium, incorporating real surface topography. This approach allows us to exploit the full complexity of the recorded seismic signals and to move beyond previous analysis based on simplified models and single-component data. The results reveal a clear dominance of opening-type (tensile crack) mechanisms, consistent with extensional stress regimes at the crevasse locations, with principal stress direction almost perpendicular to the local crevasse orientations. The exceptional size of the catalog enables a detailed investigation of spatial patterns in source mechanisms, particularly highlighting structural complexity in the heavily crevassed downstream zone. The distribution of extensional and compressional mechanisms further indicates a highly heterogeneous stress field at the glacier surface, influenced by local crevasse geometry. Depth-dependent variations in the reconstructed moment tensors suggest that deeper events tend to involve more isotropic components, likely reflecting pressure-driven failure under overburden stress. These findings demonstrate the potential of full waveform inversion to characterize the source mechanisms associated with the icequakes on a glacier. This work represents a significant step toward integrating seismological modeling with glaciological interpretation in alpine environments.