Monitoring creep along the Hayward Fault using structure-from-motion photogrammetry of offset curbs

We present observations of sidewalk curbs that are offset by creep on the Hayward Fault in Fremont, CA. Using structure-from-motion photogrammetry techniques, we construct 3-D models from suites of 2-D photos taken from 2015 to 2018 at 20 sites along the fault. By aligning and comparing these models, we measure the 3-D displacements of each offset sidewalk through time at precisions of similar to 0.5 mm yr(-1). We find that on average individual offset curbs record <40 per cent of the overall creep rate measured at nearby alignment arrays (which span a fault-perpendicular distance of 100 m or more). The 'fault trace' can more accurately be considered a zone of deformation, narrower than an alignment array width but wider than one curb length (similar to 3-5 m). Sites for which we have multiple time intervals to compare show interannual temporal variability in creep rate and direction. Our methods offer a new, complementary approach to cheaply and efficiently document creep-related deformation in an urban setting, one that may be particularly useful for tracking deformation of engineered materials and their cohesion to the subsurface. Given the use of readily available equipment (consumer-grade camera, GPS, ruler), ease of data collection and accessibility of urban field sites, we believe that this style of monitoring would lend itself particularly well to citizen science efforts.