The InSAR lookbook: an illustrated guide to earthquake interferograms

Interferometric Synthetic Aperture Radar (InSAR) is the prevalent method for mapping earthquake deformation and is seeing ever-increasing popularity through a new generation of satellite missions. Nowadays, following any large onshore earthquake, InSAR images (interferograms) are quickly disseminated across the community and media, but outside of InSAR specialists there remains a lack of general understanding of how to interpret them. We begin our study by describing how InSAR fringe patterns are determined by the combination of horizontal and vertical ground motions and ascending or descending satellite viewing geometries. In our "lookbook", we synthesize interferograms for a comprehensive suite of faulting styles, including strike-slip, reverse, normal, low-angle thrust, low-angle normal, and oblique-slip faults. This highlights the most common InSAR fringe patterns and demonstrates how strike-slip, dip-slip, and oblique-slip earthquakes produce distinct fringe patterns controlled primarily by their strike angles. We offer guidelines for utilizing the lookbook to assess earthquake mechanisms visually and to pick the causative fault plane from two nodal planes. Lastly, by comparing modelled interferograms and real-world earthquakes, we showcase the broad applicability of the lookbook, even for complex multiple segment ruptures.