Imaging the Subsurface Plumbing Complex of Steamboat Geyser and Cistern
Spring with Hydrothermal Tremor Migration Using Seismic Interferometry
Abstract
Steamboat Geyser in Yellowstone National Park is the tallest active
geyser on Earth and is believed to have hydrologic connection to Cistern
Spring, a hydrothermal pool ~100 m southwest from the
geyser vent. Despite broad scientific interest, rare episodic Steamboat
eruptions have made it difficult to study its eruption dynamics and
underground plumbing architecture. In response to the recent
reactivation of Steamboat, which produced more than 115 eruptions since
March 2018 already, we deployed a dense seismic nodal array surrounding
the enigmatic geyser in summer 2019. The array recorded an abundant 1-5
Hz hydrothermal tremor originating from phase-transition events within
both Steamboat and Cistern. To constrain the spatiotemporal distribution
of the tremor sources, an interferometric-based polarization analysis
was developed. The observed tremor locations indicate that the conduit
beneath Steamboat is vertical and extends down to ~120 m
depth and the plumbing of Cistern includes a shallow vertical conduit
connecting with a deep, large, and laterally offset reservoir
~60 m southeast of the surface pool. No direct
connection between Steamboat and Cistern plumbing structures is found.
The temporal variation of the tremor combined with in situ temperature
and water depth measurements of Cistern, do reveal the interaction
between Steamboat and Cistern throughout the eruption/recharge cycles.
The observed delayed responses of Cistern in reaction to Steamboat
eruptions and recharges suggest the two plumbing structures might be
connected through a fractured/porous medium instead of a direct open
channel, consistent with our inferred plumbing structure.