Space geodetic determination of spatial variability in relative sea level change, Los Angeles basin

We combine Synthetic Aperture Radar Interferometry (InSAR), tide gauge, and continuous GPS measurements to determine the spatial variation in vertical land motion (VLM) along the coast of the Los Angeles basin over the past decade, and to examine the impact of spatially variable VLM on relative sea level trends. By identifying radar scattering targets with long-term coherence we make height corrections which allow interferogram creation for nearly the entire ERS-1 catalog and permit estimation of average deformation rates with minimal temporal aliasing. Between Los Angeles Harbor and Newport Beach, mean VLM trends range from \~3.4 to -4.3 mm/yr, reflecting the high level of ground water and oil extraction activity in the region. West of Los Angeles Harbor, VLM rates and spatial variability are roughly half as large. The 8-year VLM trends exceed the long-term sea level trend (0.8 mm/yr) determined from the 80 year Los Angeles Harbor tide gauge. The high degree of observed VLM variability emphasizes the need for the spatially continuous measurements provided by InSAR; a single tide gauge assessment of regional RSL would otherwise have limited applicability.