InSAR permanent scatterer analysis reveals ups and downs in San Francisco Bay Area



Using new analysis techniques of spacebased radar data, surface deformation features caused by various tectonic, geomorphic, and hydrologic processes are imaged in the San Francisco Bay area of California. Uplift is due mainly to sub-mm/yr tectonic upheaval related to slip along and interaction of the complex array of San Andreas transform system faults, while seasonally recharging aquifers account for tens-of-millimeters rise. Observed downward motions are caused by seasonally depleting aquifers, active deep-seated landslides, and rapid settling of unconsolidated sediments and man-made fill alongside the San Francisco Bay.

Synthetic aperture radar interferometry (InSAR) from Earth-orbiting spacecraft has revolutionized the field of crustal deformation research since its first geophysical application about a decade ago [Massonnet et al., 1993]. During the last 10 years, InSAR has been used to study a wide range of surface displacements related to active faults, volcanoes, landslides, aquifers, oil fields, and glaciers, to name just a few, at a spatial resolution of less than 100 m and centimeter-level precision [see Massonnet and Feigl, 1998; and Burgmann et al., 2000a for reviews of the InSAR method and applications]. The temporal resolution is limited by the approximately monthly repeat time of satellite flyovers. Due to the viewing geometry of the radar satellite (the beam along which distance changes are measured is oriented at ∼23° off vertical), InSAR is particularly sensitive to vertical deformation, but cannot detect displacements parallel to the orbit track. Severe limitations to the InSAR method remain, especially decorrelation of surface scatterers due to vegetation or other surface change processes, incoherence caused by large satellite orbit separations between the two image acquisitions used to make an interferogram, and noise from signal delays in the Earth's atmosphere.