Mushy Magma beneath Yellowstone

Mushy Magma beneath Yellowstone Recent GPS and InSAR studies show that the Yellowstone caldera is uplifting at a rate of 7 cm/year, which is apparently related to a magma recharge (Chang et al. 2007, Fig. A). In receiver functions recorded by EarthScope station H17A from 100 teleseismic earthquakes in 2008, two P-to-SV converted phases exist that are consistent with the top and bottom of a low velocity layer (LVL) at about 5 km depth beneath the Yellowstone caldera (Fig. B and C). Comparisons of synthetic waveforms and observed data for two velocity reductions are shown in Fig. D. Our preferred P- and S-wave velocities suggest at least 32% melt saturated with about 8% water plus CO2 by volume.
<p>
Recent GPS and InSAR studies show that the Yellowstone caldera is uplifting at a rate of 7 cm/year, which is apparently related to a magma recharge (Fig. A) [Chang et al., 2007]. Seismic tomographic studies, however, claim a high degree of crystallization of the underlying magma body based on velocities inferred from regional seismic data. In this research, we analyzed receiver functions recorded by EarthScope station H17A from 100 teleseismic earthquakes in 2008. Two P-to-SV converted phases that correspond to the top and bottom of a low velocity layer (LVL) are identified (Fig. B-C). After modeling these phases, we found the LVL at about 5 km depth beneath the caldera. P- and S-wave velocities are 2.3 km/sec and 1.1 km/sec, respectively. This shallow LVL beneath the Yellowstone Caldera is severe enough to cause difficulties with seismic tool applications. In particular, seismologists expect teleseismic P waves to arrive with motions up and away or down and back. Many of the observations recorded by the YISA PASSCAL array violate this assumption. Stations near the trailing edge have reversal radial-component motions, while stations near the leading edge do not (Fig. D). Synthetic wave propagation show that it is the edge of the LVL that are sharp enough for P wave to wrap around the ends to reach the receivers before the direct arrivals. If the velocity drop is not severe enough, radial and vertical components have the same polarities (Fig. D). The flipping of the radial component can be used to validate the low P velocity. We modeled the degree of magma melt by assuming a fluid-filled porous material consisting of granite and a mixture of rhyolite melt and supercritical water and CO2 at temperature of 800°C and pressure at 5 km. We found that this shallow magma body has a volume of over 4,300 km3 and is at least 32% melt saturated with about 8% water plus CO2 by volume.
</p><p>References
</p><p>Chang, W. L., R. B. Smith, C. Wicks, J. M. Farrell, and C. M. Puskas, Accelerated uplift and magmatic intrusion of the Yellowstone Caldera, 2004 to 2006, Science, 318, 952-956, 2007.
</p><p>Chu, R., D. V. Helmberger, D. Sun, J. M. Jackson, and L. Zhu, Mushy magma beneath Yellowstone, Geophys. Res. Lett., 37, L01306, 2010.
</p><p>Acknowledgements: 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 No. GPS.TO2-4.1-GRANT.MOORETO2. This is contribution 10035 of the Tectonics Observatory at Caltech.</p>

Comments

No comments yet.

  •  

Welcome

Welcome to the IRIS Image Gallery – a diverse collection of photographs and visuals that encompass the range and breadth of seismology and the seismological community.

Please browse through our albums. These low and medium-resolution images can be freely used for personal and educational/academic purposes, but we request you recognize the image contributor by including in your product or presentation the credit displayed with each image.

More information is available in the Image Use Agreement.

If you have any comments, questions, or suggestions related to the IRIS Image Gallery, you can send them to gallery@iris.edu.

Photo info

Popular tags