A team of scientists used artificial earthquakes generated by a truck with a vibrating hydraulic plate to better understand the depth and characteristics of the top of the magma chamber beneath Yellowstone caldera. The research, published in Nature, reveals that the boundary between the magma reservoir and the surrounding rock is very sharp, marking a transition at about 3.8 km depth.
Prior seismic imaging had provided estimates for the depth to the top of the reservoir ranging from 3 to 9 km, but these measurements were often blurry due to the edges of the reservoir being unclear. To sharpen this view, researchers created custom earthquakes by truck and measured their reflections with hundreds of seismometers. The data showed a two-part mixture of magma and solid mineral crystals would not fit the strength of the reflected signals, suggesting that bubbles are present at the top of the reservoir.
The concentration of bubbles was estimated to be around 14% in the cap layer of the reservoir, which is expected to rise efficiently toward the surface, preventing excessive build-up of pressure. This fits with gas measurements showing magmatic gases emitted at the surface in many areas of Yellowstone National Park.
The study provides new perspectives on the long-term view of a magmatic system that is mostly solid and currently stable. It also demonstrates that using Yellowstone as a natural laboratory can help better understand volcanoes and their eruptions elsewhere on Earth.
Source: https://www.usgs.gov/observatories/yvo/news/using-custom-earthquakes-define-top-yellowstones-magma-reservoir