@article{867a686460ce4ee4816af7a0dd1cecad,
title = "Local Source Vp and Vs Tomography in the Mount St. Helens Region With the iMUSH Broadband Array",
abstract = "We present new 3-D P wave and S wave velocity models of the upper 20 km of the Mount St. Helens (MSH) region. These were obtained using local-source arrival time tomography from earthquakes and explosions recorded at 70 broadband stations deployed as part of the imaging Magma Under St. Helens (iMUSH) project and augmented by several data sets. Principal features of our models include (1) low P wave and S wave velocities along the St. Helens seismic zone to depths of at least 20 km corresponding to high conductivity imaged by iMUSH magnetotelluric studies. This delineates a zone of weakness that magma can exploit at the location of MSH; (2) a 5- to 7-km diameter, 6–15 km deep, 3–6% negative P wave and S wave velocity anomaly beneath MSH, consistent with previous estimates of the source region for recent eruptions. We interpret this as a magma storage region containing up to 15–20 km3 of partial melt, which is about 5 times more than the largest documented eruption at MSH; (3) a broad region of low P wave velocity below 10-km depth extending between Mount Adams and Mount Rainier along and to the east of the main Cascade arc, which is likely due to high-temperature arc crust and possible presence of fluids or melt; (4) several anomalies associated with surface-mapped features, including high-velocity igneous units such as the Spud Mountain and Spirit Lake plutons and low velocities in the Chehalis sedimentary basin and the Indian Heaven volcanic field. Our results place further constraints on the geometry of these features at depth.",
keywords = "3-D velocity models, Mount St. Helens, local source tomography",
author = "Ulberg, {Carl W.} and Creager, {Kenneth C.} and Moran, {Seth C.} and Abers, {Geoffrey A.} and Thelen, {Weston A.} and Alan Levander and Eric Kiser and Brandon Schmandt and Hansen, {Steven M.} and Crosson, {Robert S.}",
note = "Funding Information: We thank all of the field work volunteers who contributed to the siting, installation, maintenance, and demobilization of the iMUSH broadband array, especially R. Denlinger, K. Hall, M. Thompson, J. Han, and A. Hotovec‐Ellis. We also thank O. Bachmann, P. Bedrosian, D. Blatter, E. Bowles‐Martinez, M. Clynne, K. Crosbie, M. Mann, S. Malone, V. Salters, A. Schultz, T. Sisson, and M. Wanke for valuable discussions throughout the project. We thank Editor M. Long as well as J. Pesicek, A. Trehu, and one anonymous reviewer for their thoughtful comments on the manuscript. L. Fisher, N. Sackman, and M. Williams helped pick arrival times, using Boulder Real Time Technologies Antelope seismic software ( http://www.brtt.com , last accessed March 2017). Broadband instruments and support were provided by the IRIS‐PASSCAL Instrument Center; data from the iMUSH, AltaRock, and Nodal array are stored at the IRIS Data Management Center, network codes XD (2014‐2016), YH (2016), and 1D (2014), respectively. The final 3‐D models will be available at the IRIS EMC ( http://ds.iris.edu/ds/products/emc/ ). Figures were plotted using the Generic Mapping Tool (GMT) software (Wessel et al., ). This work was funded by National Science Foundation Grant EAR‐1144568. Funding Information: We thank all of the field work volunteers who contributed to the siting, installation, maintenance, and demobilization of the iMUSH broadband array, especially R. Denlinger, K. Hall, M. Thompson, J. Han, and A. Hotovec-Ellis. We also thank O. Bachmann, P. Bedrosian, D. Blatter, E. Bowles-Martinez, M. Clynne, K. Crosbie, M. Mann, S. Malone, V. Salters, A. Schultz, T. Sisson, and M. Wanke for valuable discussions throughout the project. We thank Editor M. Long as well as J. Pesicek, A. Trehu, and one anonymous reviewer for their thoughtful comments on the manuscript. L. Fisher, N. Sackman, and M. Williams helped pick arrival times, using Boulder Real Time Technologies Antelope seismic software (http://www.brtt.com, last accessed March 2017). Broadband instruments and support were provided by the IRIS-PASSCAL Instrument Center; data from the iMUSH, AltaRock, and Nodal array are stored at the IRIS Data Management Center, network codes XD (2014-2016), YH (2016), and 1D (2014), respectively. The final 3-D models will be available at the IRIS EMC (http://ds.iris.edu/ds/products/emc/). Figures were plotted using the Generic Mapping Tool (GMT) software (Wessel et al.,). This work was funded by National Science Foundation Grant EAR-1144568. Publisher Copyright: {\textcopyright}2020. American Geophysical Union. All Rights Reserved.",
year = "2020",
month = mar,
day = "1",
doi = "10.1029/2019GC008888",
language = "English (US)",
volume = "21",
journal = "Geochemistry, Geophysics, Geosystems",
issn = "1525-2027",
publisher = "American Geophysical Union",
number = "3",
}