Collaborative Research: Controlled source seismic investigation of the top of the Yellowstone magmatic system

University Of Utah, Salt Lake City UT

Investigators

Abstract

Among the most important mysteries regarding the Yellowstone volcanic system is whether it currently contains upper crustal magma with high enough melt fractions to be eruptible over human time scales. Prior imaging of the structure beneath Yellowstone caldera offers potentially conflicting evidence with some studies indicating magma that is unlikely to be eruptible and others indicating magma that is near the eruptible range but only present in isolated locations. These studies relied on relatively long wavelength sampling from natural seismic sources such as earthquakes. This project will use a controlled seismic source, a high-frequency vibrator truck, and hundreds of densely spaced seismic instruments to scrutinize the top of the Yellowstone magma reservoir, estimated to be about 4-8 km below the surface. This experiment will provide a new level on constraint on the melts at the top of the magma reservoir. Additionally, the project will gain insights on the distribution of hydrothermal fluids above the magma reservoir including their depth extent and the degree of subsurface connectivity among distinct geothermal basins at the surface. This project increases the involvement of younger generations of scientists in controlled source research projects, providing training in methods that are relevant to natural resource exploration industries. Two graduate students will be trained in applied seismic imaging. The investigators will engage with National Park personnel to advance informal education for Yellowstone’s approximately 4 million annual visitors. The project primarily seeks to test whether seismic velocities near the top of the Yellowstone magma reservoir are consistent with concentrations of magma approaching eruptible melt fractions. Additionally, it will investigate reservoirs and pathways for magmatic volatiles that influence upper crustal seismicity and the locations of distinct geothermal basins within the caldera. A new ability to address these questions will be provided by controlled source data collection with an array of 3-component receivers along two densely sampled transects whose locations are guided by prior passive source imaging studies. Controlled source reflection imaging and amplitude versus offset analysis are rarely possible above silicic magma reservoirs, because most are too small or lack road access directly above the reservoirs. In this case, favorable road transects exist above the magma reservoir inferred from passive source imaging with sparser arrays and lower frequencies. Prior estimates of melt fractions in the upper crustal reservoir vary widely, and the new survey will help clarify the potential presence and volume of eruptible magma using reflected wave amplitudes from controlled source P-to-P and P-to-S reflections. The combination of Vp and Vs constraints also has the potential to map subsurface accumulations of magmatic volatiles, which may provide new insights into the physical properties of the source regions of seismicity and deep underpinnings of distinct geothermal basins. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.