Yellowstone is one of the world’s largest volcanic systems. In the last 2.1 Ma it has had 3 major eruptions (2.1, 1.3, and 0.64 Ma) releasing an estimated 2500 km^3, 280 km^3 and 1000 km^3 of material, respectively. Yellowstone also features widespread seismicity and ground deformation rates of up to 7 cm/yr. Recently, Farrell et al. compiled an earthquake data set from 1984 to 2011 which they used to construct a 3D P-wave velocity structure of the Yellowstone system. The low P-wave velocity zone is taken to be the volcanic reservoir which is 2.5 times larger than suggested by a previous study. The goal of this study was to provide a better estimate of magmatic volume, melt distribution, and fluid state, all which influence the volcanic and earthquake hazard in the area.

This study looked at over 48,000 P-wave arrivals from more than 4,500 earthquakes. They only used events where at least 8 P-wave observations were available with uncertainties less than 0.12 s. Farrell et al. used an automatic picking method to ensure consistency in the selection of their first P-wave arrivals. They inverted the data to find the hypocenter, origin time, and 3D P-wave velocity structure. Sensitivity tests showed that they had adequate resolution to identify low-velocity bodies to depths of ~17km.

Based upon their inversion, they estimated the volume of melt in the Yellowstone system to be between 200 km^3 and 600 km^3. This suggests that there is enough material available for an eruption of similar size to the 1.3 Ma event.

For more details, check out the paper here.