Time-Resolved and Multimodal Observations of Rock Fracture: A Critical Review

Rock fracture develops through crack opening, frictional sliding, pore collapse and grain rearrangement, whose interactions govern the transition from local damage to macroscopic failure. Resolving these interactions requires measurements with different physical sensitivities, spatial supports and temporal resolutions. We critically synthesize time-resolved optical imaging, acoustic emission, X-ray tomography and electron microscopy, focusing on surface strain localization, internal crack connectivity and microstructural control of crack paths. We develop an evidence framework that links acquired signals to reconstructed quantities and mechanical interpretations through explicit spatial and temporal compatibility criteria. Within-experiment comparisons show why these distinctions matter. In one published sandstone experiment, the local fracture-energy estimate is 32% lower than the bulk estimate evaluated at the same tomographic observation times. Reanalysis of public three-dimensional strain fields quantifies how detection thresholds change the spatial overlap of incremental shear and dilation. These examples show that mechanical assumptions and reconstruction choices influence interpretation and that shared inputs limit the independence of apparently corroborating observations. The framework distinguishes correspondence among measurements from independent evidence for a fracture mechanism, and it defines priorities for spatial registration, uncertainty propagation and specimen-level replication in experiments on rock fracture.