This INSPIRE award is partially funded by the LIGO Research Support program in the Division of Physics in the Directorate for Mathematical and Physical Sciences and Geophysics program in the Division of Earth Sciences in the Directorate of Geosciences. Seismometer arrays are commonly used in geophysics, seismology, and engineering to study the propagation of seismic waves, detect and study their sources, and assess properties of the Earth's interior at various depths. The vast majority of seismometer arrays to date have been surface-based due to the ease of installation. This project will build and operate a dense, underground, three-dimensional array of 13 high-sensitivity broadband seismometers. The array will be located at the Homestake mine, SD, whose accessible depth of 4850 feet and vast horizontal span allow probing a 1-mile underground cube. Bringing together the existing techniques in gravitational physics and geophysics for analysis of transient and stochastic wave signals, this project is expected to give rise to qualitatively new seismic data analysis techniques. Importantly, results of these studies will also have a profound impact on the design of future underground experiments in gravitational physics, such as probes of the Equivalence Principle of Einstein's theory of relativity. Future underground gravitational-wave detectors that will observe otherwise inaccessible signatures of various astrophysical phenomena and of the Big Bang will also be designed based on the seismic noise studies conducted within this project.
This project will enable interactions between the geophysics and gravitational physics communities that would be of substantial mutual benefit. Since the future of gravity experiments is arguably underground, it is critical for the gravitational physics community to draw from the large body of knowledge in geophysics on seismic noise and seismic wave propagation. By allowing a team of physicists and geophysicists to work together on the analysis of this unique high-quality data in a mutually interesting environment, this project will lead to breakthroughs in seismic noise tomography. Such breakthroughs will have a broad range of applications and societal implications, ranging from nondestructive material testing to medical diagnosis, geophysical prospecting (detecting mineral deposits and oil), and homeland security (detecting underground cavities). The project will also educate several graduate and undergraduate students, exposing them to the frontiers of research at the intersection of the fields of geophysics and gravitational physics.
