Liberty, and two co-authors, reported on June 3, 2021 that although the Wasatch fault is currently known to have a highâ€seismic hazard from motion along rangeâ€bounding faults, new seismic data reveal faulted and folded 13,000–30,000â€yrâ€old Lake Bonneville strata beneath Salt Lake City (SLC). Coupled with previous excavation trench, borehole, and other geologic and geophysical observations, we conclude that a zone of latest Pleistocene and/or Holocene faulting and folding kinematically links the East Bench and Warm Springs faults through a 3 km wide relay structure and transfer zone.
The authors characterized faults beneath downtown SLC as active, and these faults may displace or deform the ground surface during an earthquake. Through offset but linked faults, our observations support thoroughgoing ruptures across faults of the Wasatch fault zone (WFZ) and an elevated risk of earthquakeâ€induced building damage.
The authors concluded that Seismic imaging through SLC provides a catalog of faults, soil properties, and fluid distributions within a left step of two faults associated with the WFZ. They showed a strong relationship of VSVS to mapped geology and of VPVP to groundwater elevations. They placed our seismic results in the context of paleoseismic trench investigations, geologic maps, and other geophysical data to highlight structural controls needed to assess seismic hazard for the SLC area.
They identified a deformation zone and relay ramp that connects two active faults of the WFZ. These observations and models suggest that surface deformation within downtown SLC may accompany a large earthquake. In addition, they identified a broad zone of lateral spread deposits that lie above the transfer zone. The proximity of paleoliquefaction to the underlying faults suggests that M<5M<5 earthquakes may induce lateral spreading beneath downtown SLC. This fault connectivity model may also relate to other WFZ segments and could help refine the surfaceâ€rupture hazard and fault connectivity along other normal fault systems.
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