Abstract
Abstract Although the Wasatch fault is currently known to have a high-seismic hazard from motion along range-bounding faults, new seismic data reveal faulted and folded 13,000–30,000-yr-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. We characterize 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 throughgoing ruptures across faults of the Wasatch fault zone (WFZ) and an elevated risk of earthquake-induced building damage.
Highlights
The active, 350 km long Wasatch fault zone (WFZ) defines the eastern boundary of the Basin and Range Province in northern Utah (Fig. 1)
The downtown Salt Lake City (SLC) area lies within a left step between the East Bench fault (EBF) and Warm Springs fault (WSF) of the SLC segment (Personius and Scott, 1992; Fig. 2)
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
Summary
The active, 350 km long Wasatch fault zone (WFZ) defines the eastern boundary of the Basin and Range Province in northern Utah (Fig. 1). Centered near 250 m distance, we identify the crest of a ∼250 m wide fold, that lies slightly east of a wide fold noted with a CPT transect located about 200 m to the north (Leeflang, 2008), and west of a similar fold identified on 700 south and 800 south seismic profiles (described subsequently) This fold is bounded by faults that offset and tilt late Quaternary strata. Unlike our 500 south VS result, we find no seismic evidence consistent with lateral spreading along either profile
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