The amount and spatial distribution of surface displacement that occurs during an earthquake are critical information to our understanding of the earthquake source and rupture processes. However, the earthquake surface displacement generally occurs over wide regions, includes multiple components affecting the ground surface at different spatial scales, and is challenging to characterize. In this study, we assess the sensitivity of optical imagery and topography datasets of different resolutions to the earthquake surface displacement when using optical image cross-correlation (OIC) techniques. Results show that the average noise in the output displacement maps linearly increases with decreasing image resolution, leading to greater uncertainty in determining the geometry of the faults and the associated displacement. Fault displacements are, on average, under-estimated by a factor ~0.7-0.8 when using 10 m compared to 0.5 m resolution imagery. Our analysis suggests that an optical image resolution of ≤1 m is necessary to accurately capture the complexity of the ground displacement. We also demonstrate that sub-meter vertical accuracy of the digital surface/elevation model (DSM/DEM) is also required for accurate image orthorectification, and is better achieved using high-resolution stereo optical imagery than existing global baseline topography data. Together, these results highlight the measurement needs for improving the observation of earthquake surface displacement towards the development of future Earth surface topography and topography change observing systems.

Surface deformation associated with continental earthquake ruptures includes localized deformation on the faults, as well as deformation in the surrounding medium through distributed and/or diffuse processes. However, the role of the diffuse part of the surface deformation to the overall rupture process, as well as its underlying physical mechanisms are not yet well understood. In this study, we compute high-resolution near-fault displacement maps from optical image correlations for the 2021/05/21 Mw7.4 Maduo, Tibet, strike-slip earthquake, and measure the contributions of the different deformation components to the surface deformations for that event. Results show that surface slip along primary faults accommodates, on average, only ~25% of the total surface deformation. Majority of the surface coseismic deformation is in fact accommodated by diffuse deformation,especially in the epicentral area where no surface slip was observed. In fact, the contribution of the diffuse deformation increases as localized deformation on the fault decreases. Localized deformation also decreases with decreasing total surface displacement. These observations highlight a gradual localization of the surface coseismic deformation, from regions of diffuse low (0.1-0.3%) strain, to regions of highly localized (>1 %) strain, with increasing coseismic displacement. Using simple two-dimensional mechanical models we show that diffuse deformation may correspond to elastoplastic bulk yielding, accounting for the deficit in shallow fault slip in the regions of surface rupture gap.