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Variations of the 1959 m7.3 Hebgen Lake Earthquake Record in Four Proximal Lacustrine Systems, West Yellowstone Region, USA

Description: 

The M7.3 1959 Hebgen Lake earthquake in southwestern Montana is one of the largest earthquakes recorded within the Intermountain West, United States. Ground-shaking and hanging-wall subsidence caused an approximately 6-meter-high seiche in Hebgen Lake, liquefaction features in adjacent valleys, a massive landslide that dammed the Madison River to form Earthquake Lake, and increased activity in hydrothermal systems of the Yellowstone caldera. Accordingly, lakes within the southern Madison and eastern Centennial Valleys, ≤25 km from the epicenter, experienced shaking of Modified Mercalli Intensity VI-VII. We characterize how the 1959 earthquake signature is recorded in the stratigraphic record of four lakes in this area that have varying morphometric and hydrologic properties such as depth, shape, surface area, and catchment area. We present data from 24 sediment cores along transects of Wade Lake (9 cores), Cliff Lake (5 cores), Hebgen Lake reservoir (3 cores), and Henry’s Lake (7 cores). Each lake records background sediment consisting of laminated to thinly bedded silt and sand with distinct sedimentary disturbances such as 1) normally graded sand beds, 2) massive, poorly sorted deposits, and 3) macro floral debris, all likely indicators of the 1959 Hebgen earthquake. To test this hypothesis, we use fallout radionuclide ¹³⁷Cs, where concentrations become measurable after 1954 CE and the maximum value indicates 1963 CE. Preliminary ¹³⁷Cs concentrations and their locations in the Henry’s Lake core support the interpretation of the disturbance horizons being formed by the 1959 earthquake. Fallout ¹³⁷Cs data are pending to constrain the timing of disturbance horizons for the remaining three lakes. Comparing characteristics of the 1959 event deposit in these four lakes will illuminate how differences in lake morphometry or setting may impact lacustrine records of strong ground shaking. Ultimately these observations will help calibrate how Intermountain West lakes record strong shaking and facilitate comparisons to both terrestrial and lacustrine paleoseismic data globally.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Sylvia

Student Presenter: No

Invited Presentation: 

Authors