Investigating the crust and uppermost mantle beneath volcanoes with new seismic analyses

Volcanic eruptions connect the Earth’s deep interior with its surface and atmosphere, and they have wide-ranging effects. As natural hazards, eruptions pose risks to human lives, infrastructure, and economies. Magma in the crust provides a favorable environment for development of geothermal energy systems.

Gases, like carbon dioxide, and tiny particles released into the atmosphere by volcanoes can affect weather and climate. Therefore, there is a need to understand how magma forms, ascends to the surface, and erupts. This project is studying how and where magma is currently being stored in the deep crust under three recently active volcanoes: Yellowstone and the Cascades Arc in North America, and the Altiplano-Puna Volcanic Complex in South America.

The project is measuring the speed of seismic waves, which were generated by distant earthquakes, as they travel beneath the volcanoes. The speed of seismic waves is sensitive to the abundance of magma and whether it is stored in flat horizontal layers or tall vertical columns. A key outcome of the project will be to advance knowledge of how the storage and migration of magma affect the eruptibility of volcanoes.

A second important outcome is the research training of one graduate student and two undergraduate students.

Mapping the distribution of melt in the crust and upper mantle is a long-standing goal in the Earth sciences that bears on a wide range of scientific and societal issues. One such issue is how the storage and migration of magma affect the eruptibility of volcanoes. There is emerging consensus that the magmatic system beneath active volcanoes spans the entire crust.

However, in volcanic settings, there are large error bars on crustal melt-fraction estimates, and the depth distribution of melt is challenging to resolve, especially in the lower crust. This project is studying the crustal architecture beneath active volcanoes with two types of seismic analyses that have thus far been rarely used in these settings.

One is radial anisotropy as estimated from intermediate-period (25-75 s) surface waves from teleseismic earthquakes, which provides constraints on the lower crust and uppermost mantle that complement the more commonly used ambient-noise studies. The other is Rayleigh wave amplification, which is sensitive to P-wave and S-wave speed in the lower crust and uppermost mantle.

The VP/VS ratio depends only weakly on temperature but is strongly sensitive to melt. These new data sets will be jointly inverted together with Rayleigh wave phase velocities from ambient noise and teleseismic earthquakes and Love wave phase velocities from ambient noise to produce depth-dependent models for VS, VP/VS, and radial anisotropy for three volcanic regions: Yellowstone and the Cascades Arc in North America, and the Altiplano-Puna Volcanic Complex in South America.

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.