Seismic land streamer data reveal complex tectonic structures beneath Salt Lake City

A seismic land streamer campaign reveals complex faulting and folding within late Quaternary Bonneville lake sediments and alluvial fan deposits beneath the downtown Salt Lake City urban corridor. From more than 15,000 shot gathers along 22 city streets, 35 km of two meter spaced seismic data provide detailed character of late Quaternary stratigraphy and tectonics within a step over region of the Wasatch fault system. We use first arrival tomography to obtain Vp distributions to 20-30 m depth, Rayleigh wave inversions to provide Vs profiles to about 30 m depth, and reflection imaging to 200-300 m depth to map the distribution of faults, fold, and lithologic boundaries. From these data, we provide 1) an updated city-wide Vs30 high frequency site response map, 2) stratigraphic mapping of transgressive and regressive paleolake Bonneville deposits, 3) distributions of tectonically induced lateral spread and colluvium deposits, 4) water table depths and zones of both confined and unconfined groundwater systems, and 5) distributions of active faults related to the Wasatch fault system. We find that complex near surface conditions highlighted in both Vp and Vs tomograms directly relate to changing hydrostratigraphy and active faulting. Complex near surface conditions can diminish reflection data quality. Lower Vp/Vs ratios in the upper 10 m and the presence of higher mode surface waves result in poorer reflection imaging capabilities at greater depths.