EAGER: Spatio-temporal Imaging of Mount St. Helens Magmatic System using Efficient Waveform Inversion of Earthquake Records

Colorado School Of Mines, Golden CO

Investigators

Abstract

Mount St. Helens, in the Cascadia Subduction Zone, is an active volcano and is most well known for the devastating 1980 eruption which is widely regarded as the most disastrous volcanic eruption in the United States history in terms of loss of human life and damage to infrastructure. In fact, the United States Geological Survey (USGS) regards Mount St. Helens as a very high threat volcano. The work planned here will illuminate the Mount St. Helens magmatic plumbing system and help scientists better forecast impending volcanism and its possible duration. Such knowledge will be extremely useful for volcanic hazard mitigation and help save human lives. This project is a collaboration between a university (Colorado School of Mines) and a government institution (USGS) to extend the application of a cutting-edge technology, originally developed by a private enterprise (Seismic Science LLC) to image hydraulic fractures in oil & gas reservoirs, for monitoring volcanic systems for the betterment of the society. The investigators believe this collaboration will foster further cooperation, technology transfer, and exchange of ideas between the hydrocarbon industry and government entities. The processes and techniques developed under this project could potentially be extended to the other subduction zones in order to help image megathrust and volcanic systems all over the world. The architecture of the Mount St. Helens magmatic system and the spatio-temporal changes resulting from magma production, transport, and storage are poorly understood. To address these questions, extensive seismic data, in the form of active-seismic surveys and passive recordings, have been acquired over the past three decades and also as part of the EarthScope program. The investigators will use local earthquake recordings from both the active-seismic data (comprising of two nodal geophone arrays and PASSCAL Texan geophones) and broadband seismometers and the active-seismic waveform data to generate a high-resolution time-lapse 3-dimensional image of the Mount St. Helens magmatic system using waveform inversion. These images will extend from the shallow upper-crust all the way to the subducting slab underneath Mount St. Helens, thereby helping to shed light on the complete architecture of the magmatic system, the connections between different magma bodies, and the physical state of the rocks. Knowledge of the magmatic system at Mount St. Helens (in terms of its architecture and spatio-temporal changes) will provide valuable insight into a number of key scientific challenges including questions about crustal evolution, magma generation in the mantle, magma transport from the upper mantle to the shallow crust, the structure of magma reservoirs, and forecasting volcanism. The high-resolution spatio- temporal 3-dimensional images will be especially useful in understanding stress changes associated with magma emplacement/inflation and in deciphering the transport of melts in the crust and upper mantle. Also, the scale, extent, and connectivity of magma in the crust and mantle beneath Mount St. Helens is not fully established. High-resolution images of the deep crust and upper mantle, all the way to the slab, will help unravel the large-scale magmatic system in detail and will reveal intricate details of the subducting slab, the possibility of serpentinization of the mantle wedge, and the weak reflectivity of the Moho in the mantle fore- arc. The waveform processing and inversion technology employed in this project was originally developed at Seismic Science LLC for mapping fractures generated during hydraulic stimulation of low-permeability oil and gas formations. Under this project, Colorado School of Mines and United States Geological Survey (USGS) will collaborate to employ this technology to image the Mount St. Helens magmatic system at high resolution. 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.