123-2 A postglacial paleoseismic history of the Teton fault from a series of fault-proximal lakes in Grand Teton National Park, Wyoming

Session: Quaternary Research to Characterize Environmental and Geological Hazards

Presenting Author:

Authors:

Abstract:

The Teton normal fault in Grand Teton National Park, northwest Wyoming is recognized as one of the more active and hazardous faults in the Intermountain West. High fault activity during postglacial time (past ~15,000 years) is marked by 2 – 35 m fault scarps in Pinedale – age glacial sediments and landforms at the base of the precipitous eastern flank of the Teton Range. However, the fault currently occupies a seismic gap in the Intermountain Seismic Belt at the > M 3 level. Paleoseismic trench excavations and lake sediment studies along the fault have documented an irregular postglacial paleoseismic history and no evidence of large ground rupturing earthquakes in the past 5,000 years. To date, trench excavations have been performed at five locations and together, provide evidence for at least three major (e.g. up to magnitude Mw ∼ 7) earthquake events over the past ~10,000 years. In an effort to augment the direct evidence contained in trench exposures, sediments contained in a series of glacially-scoured lake basins positioned along the Teton fault have been targeted to construct indirect inventories of earthquake events since the lakes were formed ~15,000 years ago. Past earthquakes that generated slope failures in and around Teton lakes are expressed stratigraphically as coseismic turbidite deposits. These deposits can be readily identified, precisely dated, and securely correlated between sediment cores taken from multiple locations around the respective basins. Importantly, the ages of these diagnostic deposits can also be correlated between multiple lakes and to the timing of earthquakes identified in the fault trenches. In this study, we characterize the stratigraphic expression of earthquake deposits in Teton lakes and present paleoseismic datasets generated from five lake sites (Phelps Lake, Taggart Lake, Bradley Lake, Jenny Lake, and Leigh Lake). Results from the lake studies, combined with the multiple established trench datasets, provide high potential for constructing a remarkably detailed, cross-validated, and relatively complete postglacial paleoseismic history of the Teton fault.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10272

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