Mushy magma beneath Yellowstone
A recent prospective on the Yellowstone Caldera discounts its explosive potential based on inferences from tomographic studies which suggests a high degree of crystallization of the underlying magma body. In this study, we show that many of the first teleseismic P-wave arrivals observed at seismic stations on the edge of the caldera did not travel through the magma body but have taken longer but faster paths around the edge. After applying a number of waveform modeling tools, we obtain much lower seismic velocities than previous studies, 2.3 km/sec (V_p) and 1.1 km/sec (V_s). We estimate the physical state of the magma body by assuming a fluid-saturated porous material consisting of granite and a mixture of rhyolite melt and water and CO_2 at a temperature of 800°C and pressure at 5 km (0.1 GPa). We found that this relatively shallow magma body has a volume of over 4,300 km^3 and is about 32% melt saturated with about 8% water plus CO_2 by volume.
Additional Information© 2010 American Geophysical Union. Received 3 November 2009; accepted 15 December 2009; published 15 January 2010. We are grateful to two GRL reviewers for their careful reviews. We thank Robert W. Clayton for the constructive discussions. The 2D finite difference modeling code was provided by Zhimei Yan. All waveform data used in this study were obtained from IRIS Data Management Center. This work is funded by the Tectonics Observatory at California Institute of Technology under grant GPS.TO2-4.1-GRANT. MOORETO2. This is contribution 10035 of the Tectonics Observatory at Caltech.
Published - Chu2010p7039Geophys_Res_Lett.pdf