Impact of optical imagery and topography data resolution on the measurement of surface fault displacement using sub-pixel image correlation

Abstract

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.