Seismic waves are still a main source of information when it comes to understanding both the composition of, and the dynamic processes ongoing in, the Earth’s interior, including earthquakes. For example, so-called seismic “coda” waves, because of their large number of scattering interactions with the medium, can be indicative of slight changes in stress fields before catastrophic fracturing that might provide pre-cursory signs of earthquakes. To study such phenomena in the laboratory, current approaches employ experimentation at frequencies (and scales) that are at least 4 orders of magnitude higher (and smaller) than the frequencies at which the phenomena occur in the real-world. This is so, because reflections from the boundaries of the experimental domain would otherwise disturb and invalidate the experiments by virtue of masking the signal of interests. Because of the long wavelengths involved, it is also impractical to build the vast experimental facilities that would be required to otherwise avoid such boundary reflections. However, it is often not known if the physics governing the phenomena stays the same over those 4 orders of magnitude or more. Thus, there is a need for a radically new laboratory experimental approach for studying the interaction of seismic waves with the real complex media of the Earth’s subsurface.
The MATRIX (Machine for Time-Revesal and Immersive eXperimentation) project, aims to establish a fundamentally new approach to seismic wave experimentation that involves fully immersing a physical seismic experiment within a virtual numerical environment. This enormously challenging endeavour, which is relevant to many outstanding issues in seismology, has not been previously attempted. By continuously varying the output of numerous transponders closely spaced around the physical domain using a control algorithm that takes advantage of measurements made by a scanning Laser-Doppler Vibrometer and a novel theory of immersive boundary conditions, waves travelling between the physical and numerical domains will seamlessly propagate back and forth between the two domains without being affected by reflections at the boundaries between the two domains. This will allow us to investigate diverse types of Earth materials using frequencies that are much closer to those of seismic waves propagating through the Earth than previously possible. The novel laboratory enables experimentation under highly controlled conditions.
