Fig. 1. Second invariant of the horizontal strain rates from GNSS models [Sandwell et al. , 2016a]. a) Average of 10 “best” models based on a spatial correlation analysis. b) Standard deviation of the 10 models. c) Radially-averaged cross spectra between all pairs of SCEC CGM-V1 strain rate models, performed in the area denoted by the white box in a). The mean and median of all the spectra have a 0.2 coherence at wavelengths of 30-40 km. Our objective for accurate strain-rate measurement is to maintain at least 0.2 coherence among the models, at a 10 km spacing, when integrated with InSAR.