Inversion of the Slip Distribution of an Earthquake From InSAR Phase Gradients: Examples Using Izmit Case Study

This letter investigates the estimation of the slip distribution of a seismic event using the information provided by interferometric phase gradients. Even if the technique is expected to be suboptimal when compared with an estimation using the unwrapped interferometric phase, such an approach would permit to avoid the solution of phase ambiguities also including the parts of the interferogram that could not be reached by the phase unwrapping otherwise. This specifically addresses the cases where the motion gradients are so strong that particular areas have to be masked out due to unwrapping errors. Aim of this letter is to propose a possible way to include such areas modeling the motion with phase gradients. The rationale of this letter relies on the description of the coseismic motion given by the Okada model that provides both the 3-D surface displacement and the gradient tensor information. Based on the latter, this letter defines an inversion strategy that uses the information extracted by the phase gradients, hence avoiding phase unwrapping. This technique is tested on real test sites and compared with the results obtained using the absolute phase.