Integrated Sentinel‐1 InSAR and GNSS Time‐Series Along the San Andreas Fault System

Measuring crustal strain and seismic moment accumulation, is crucial for understanding the growth and distribution of seismic hazards along major fault systems. Here, we develop a methodology to integrate 4.5 years (2015–2019.5) of Sentinel‐1 Interferometric Synthetic Aperture Radar (InSAR) and continuous Global Navigation Satellite System (GNSS) time series to achieve 6 to 12‐day sampling of surface displacements at ∼500 m spatial resolution over the entire San Andreas fault system. Numerous interesting deformation signals are identified with this product (video link: https://www.youtube.com/watch?v=SxNLQKmHWpY). We decompose the line‐of‐sight InSAR displacements into three dimensions by combining the deformation azimuth from a GNSS‐derived interseismic fault model. We then construct strain rate maps using a smoothing interpolator with constraints from elasticity. The resulting deformation field reveals a wide array of crustal deformation processes including, on‐ and off‐fault secular and transient tectonic deformation, creep rates on all the major faults, and vertical signals associated with hydrological processes. The strain rate maps show significant off‐fault components that were not captured by GNSS‐only models. These results are important in assessing the seismic hazard in the region. Seismic hazard models rely on accurate measurements of small motion over large areas on the Earth's crust. Traditional geodetic models based on Global Navigation Satellite System (GNSS) data cannot resolve small scale deformation patterns, mainly due to expensive and limited station deployment. Interferometric Synthetic Aperture Radar (InSAR) has become the emerging tool for mapping surface deformation, with its advantages of low‐cost and full‐coverage. Yet InSAR measurements, compared to GNSS, come with larger biases from the atmospheric noise, especially over length scales greater than 80 km. Here, we combined the two methods to resolve fine spatial scales and achieve high accuracy. Our results are presented as deformation time‐series over the entire San Andreas fault system (video link: https://www.youtube.com/watch?v=SxNLQKmHWpY). From these deformation time series, we have estimated fault creep rates and strain accumulation. One important finding is that there is significant off‐fault strain, though we suspect this is mainly due to hydrological processes. These results will advance our knowledge of the earthquake cycle, strain/moment accumulation, and the associated seismic hazards. A practical approach is developed to integrate Sentinel‐1 Interferometric Synthetic Aperture Radar and Global Navigation Satellite System time‐series over the entire San Andreas fault systemThe product is used to estimate fault creep and three components of horizontal crustal strain which shows notable off‐fault portionChallenges remain in separating tectonic and hydrologic sources and whether hydrologic strain will increase seismic hazards A practical approach is developed to integrate Sentinel‐1 Interferometric Synthetic Aperture Radar and Global Navigation Satellite System time‐series over the entire San Andreas fault system The product is used to estimate fault creep and three components of horizontal crustal strain which shows notable off‐fault portion Challenges remain in separating tectonic and hydrologic sources and whether hydrologic strain will increase seismic hazards