Postglacial Paleoseismicity of the Teton Normal Fault Recorded by Lake Sediments in Grand Teton National Park, WY

Date: 4/24/2019

Time: 09:00 AM

Room: Vashon

Records of past earthquake occurrence are important for developing accurate seismic hazard assessments and for understanding temporal changes in fault behavior. However, in many tectonically active environments, few reliable geologic archives exist, and the majority of paleoseismic records rely on trench excavations, which can be incomplete, discontinuous, and/or limited by dating uncertainties. The Teton fault, which cuts across Grand Teton National Park (GTNP), WY, has been identified by the USGS as one of the most hazardous faults in the western US. Past movement along this 70-km normal fault has created the iconic landscape of the Tetons, one of the youngest and most tectonically active mountain ranges in the Rockies. High seismicity in the surrounding region is associated with intraplate extension and modern activity of the nearby Yellowstone hotspot, but the Teton fault itself has been curiously quiescent during historic time, and little is known about its paleoseismic history. Here, we present a continuous 14,000-year reconstruction of past earthquake events at GTNP based on sediments preserved in prominent, glacially-excavated lake basins positioned directly along the Teton fault trace. Beginning immediately after deglaciation ~14 ka and until ~7.5 ka, a series of at least 7 major fault ruptures resulted in diagnostic turbidite deposits in the lakes at regular intervals of ~1000 years, followed by a period of prolonged inactivity. These observations are consistent with existing trench data and model simulations that suggest accelerated fault slip rates followed deglaciation of the Teton-Yellowstone region, as well as with geodetic monitoring data that indicate the Teton fault may be locked by ongoing Yellowstone hotspot dynamics. This presentation will place emphasis on lake sedimentary signatures of past seismic activity, methods of integrating geophysical tools with lake sediment core data, and the temporal relationship between regional deglaciation and fault activity.

Presenting Author: Darren J. Larsen

Authors