Lake‐Bottom Seismograph Observations of Microseisms in Yellowstone Lake

Ambient‐noise records from a seismograph deployed in Yellowstone Lake during July–August 2016 contain high‐amplitude signals in the 0.4–1.1 Hz frequency band, which exhibit strong diurnal variations. These diurnal amplitude variations are highly coherent with wind‐speed data from a meteorological station on the lake’s northern shore, and as the wind builds over the course of a typical summer day, the amplitude and period of the microseism signal progressively increase, consistent with the evolution of a gravity‐wave amplitude spectrum. The peak spectral levels are at frequencies of ∼1.0  Hz, which is roughly twice the peak frequency of a fetch‐limited wavefield given the 10–19 km fetch to our lake‐floor station, suggesting the signals represent double‐frequency microseisms. The ∼3.4  hr lag observed between wind speed and seismic noise levels are consistent with this interpretation.