Imaging the Deep Subsurface Plumbing of Old Faithful Geyser From Low-Frequency Hydrothermal Tremor Migration

Abstract

Old Faithful Geyser in Yellowstone is one of the most well-known hydrothermal features in the world. Despite abundant geophysical studies, the structure of Old Faithful's plumbing system beneath ~20-m depth remained largely elusive. By deploying a temporary dense three-component geophone array, we observe 1–5 Hz low-frequency hydrothermal tremor originating from Old Faithful's deeper conduit. By applying seismic interferometry and polarization analyses, we track seismic tremor source migration throughout the eruption/recharge cycle. The tremor source drops rapidly to ~80-m depth right after the eruption and gradually ascends vertically back to ~20-m depth, coinciding with the previously inferred bubble trap location. Likely excited by the liquid/steam phase transition, the observed tremor source migration can provide new constraints on the recharge process and deeper conduit geometry. Combined with the shallow conduit structure from previous studies, these results provide constraints on the major fluid pathway down to 80-m depth.