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The Great Salt Lake as a Recorder of Sublacustrine Surface Rupture and Strong Shaking in the Wasatch Front Region, Utah

Description: 

The Great Salt Lake (GSL) is a broad (30-km-wide), shallow (≤15-m-deep), and low-relief saline endorheic lake adjacent to the Wasatch Front region of Utah. Here, we explore the GSL as a potential recorder of Wasatch Front earthquakes and attempt to disentangle evidence of strong shaking and sublacustrine surface rupture. We focus on the western margin of Antelope Island, where sublacustrine scarps along the Great Salt Lake fault (GSLF) span the eastern lake margin, and previous subbottom Chirp data and piston cores suggest Holocene surface ruptures as young as ~0.6 ka. In our study, Chirp data show GSLF hanging-wall deformation, growth faulting, and stratal onlap in support of multiple Holocene ruptures, with the youngest within ~1 m (~1.2 ms) of the lake bottom. We also interpret 14 <2-m-long gravity cores arranged in three fault-normal transects. Photo logs, X-ray computed tomography, multi-sensor data, and grain-size measurements show lacustrine sediments characterized by light to dark gray, flat to wavy laminated, brine-shrimp-fecal-pellet-derived silt and fine sand. These background sediments are punctuated by massive ≤41-cm-thick disturbance horizons, which range from homogenites to normally graded silt and sand beds with evidence of sediment resuspension and transport. After evaluating possible mechanisms of sediment disturbance, we are most confident in a tectonic interpretation. We describe and correlate these disturbance horizons among the cores and constrain their timing using radiocarbon ages of terrestrial plant remains and charcoal included in Bayesian models. Preliminary results suggest that GSL sediments record strong shaking from large-magnitude (likely surface rupturing) Wasatch fault earthquakes as well as the most recent GSLF rupture. We plan to refine the GSL disturbance horizon chronology, compare to compilations of terrestrial Wasatch fault paleoearthquakes, and evaluate whether the GSL acts as a reliable Wasatch Front lacustrine seismograph.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - II

Type: Oral

Date: 5/1/2024

Presentation Time: 11:00 AM (local time)

Presenting Author: Christopher

Student Presenter: No

Invited Presentation: 

Authors