Shallow Active-Source Seismic Imaging of Old Faithful Geyser in the Upper Geyser Basin of Yellowstone National Park.

The Upper Geyser Basin of Yellowstone National Park consists of active geysers which erupt groundwater from a subsurface reservoir, the most famous of which is Old Faithful. To image the Old Faithful hydrothermal system, we process 2-D and 3-D active-source seismic data recorded in November 2016. Our 3-D array consists of 521 receivers and 343 shots while our 2-D line trends SW-NE, centered on Old Faithful Geyser, with 39 receivers and 39 shots. Both arrays have a station spacing of ~25m, but there is a ~100m gap in any direction from the Old Faithful Geyser orifice. The source in this experiment was a sledgehammer striking a metal plate, and we typically stacked 5 hammer strikes per shot location. Our receivers are 3-component, 5-Hz Magseis Fairfield Z-Land seismometers. We pick refracted first arrivals and invert the arrivals to create a velocity model and tomographic profiles. We aim to visualize changes in lithology around Old Faithful geyser and its subsurface plumbing system. Preliminary results from the 2-D profile show slight differences from previous studies, with the P-wave refraction images allowing for more detailed interpretation. Creating tomographic profiles and depth-migrated shot gathers will contribute to scientific understanding of the Old Faithful hydrothermal reservoir beneath Old Faithful by allowing us to visualize in 2-D and 3-D the geometry and structure of the shallow hydrothermal conduits feeding the geyser.