Geophysical imaging of shallow degassing in a Yellowstone hydrothermal system

Abstract

The Yellowstone Plateau Volcanic Field, which hosts over 10,000 thermal features, is the world's largest active continental hydrothermal system, yet very little is known about the shallow “plumbing” system connecting hydrothermal reservoirs to surface features. Here we present the results of geophysical investigations of shallow hydrothermal degassing in Yellowstone. We measured electrical resistivity, compressional‐wave velocity from refraction data, and shear wave velocity from surface‐wave analysis to image shallow hydrothermal degassing to depths of 15–30 m. We find that resistivity helps identify fluid pathways and that Poisson's ratio shows good sensitivity to saturation variations, highlighting gas‐saturated areas and the local water table. Porosity and saturation predicted from rock physics modeling provide critical insight to estimate the fluid phase separation depth and understand the structure of hydrothermal systems. Finally, our results show that Poisson's ratio can effectively discriminate gas‐ from water‐saturated zones in hydrothermal systems.

Heat and Mass Transport in a Vapor‐Dominated Hydrothermal Area in Yellowstone National Park, USA: Inferences From Magnetic, Electrical, Electromagnetic, Subsurface Temperature, and Diffuse CO2 Flux Measurements

“…Our study builds upon previous geophysical studies that imaged subsurface structures, fluid flow pathways, and hydrothermal alteration in volcano‐hydrothermal systems (e.g., Aizawa et al, ; Bouligand et al, ; Byrdina et al, ; Finn et al, ; Finn & Morgan, ; Gresse et al, , ; Hase et al, ; Pasquet et al, ; Revil et al, ; Rosas‐Carbajal et al, ; Soengkono, ). In contrast to many of these studies that used a single geophysical method and often resulted in a nonunique interpretation, we combine several different geophysical methods and quantify the spatial relationships among the diverse data sets.…”

Identifying recharge under subtle ephemeral features in flat-lying semi-arid region using a combined geophysical approach

“…Poisson's ratio increases as fluid saturation increases (Bachrach et al, 2000;Dvorkin and Nur, 1996;Nur and Simmons, 1969;Salem, 2000). Furthermore, Poisson's ratio is an indicator for determining the difference between gas and fluid saturated materials (Gregory, 1976;Pasquet et al, 2016) and has been shown to be useful to track pressure changes (Prasad, 2002), map the water table depth (Bachrach et al, 2000;Pasquet et al, 2015b;Salem, 2000;Uyanık, 2011), and differentiate gas and fluid in hydrothermal systems (Pasquet et al, 2016). To image the water table with Poisson's ratio, the conceptual model of the geology must be simplified (i.e.…”

Time-Lapse Seismic and Electrical Monitoring of the Vadose Zone during a Controlled Infiltration Experiment at the Ploemeur Hydrological Observatory, France

“…For applications to characterize the critical zone, it is possible to combine Pand S-wave refraction tomography [18,19] or to use surface-wave profiling methods [20,21]. These approaches have been tested in further studies [22,23] and applied for quantitative estimations of hydrological parameters in hydrothermal contexts [24]. Nevertheless, there are inherent incompatibilities between P-wave tomography and surface-wave analysis as they involve distinct wavefield examinations and different assumptions about the medium and, as a result, V P and V S models have contrasting resolutions, investigation depths, and posterior uncertainties.…”