Crustal Structure of the High Lava Plains of Oregon: A Large Controlled-Source Experiment

Crustal Structure of the High Lava Plains of Oregon: A Large Controlled-Source Experiment Index map of the High Lava Plains controlled-source experiment. Yellow diamonds indicate shot points; black lines indicate the main instrument deployment. N-Newberry Volcano. H-Harney Basin. S-Steens Mountain. SRP-Snake River Plain.
The High Lava Plains (HLP) of eastern Oregon and adjacent parts of Idaho and Nevada were the target of a very large con- trolled-source seismic experiment in early September 2008. This survey was designed to image the crust and upper mantle with the purpose of understanding the tectonics and mechanisms that drive the intraplate volcanism of the High Lava Plains and how this volcanism is related to the Cascade subduction zone and the Basin and Range province. This was survey proved successful thanks to the 67 scientists, students, and volunteers deployed 2612 Texan short-period seismic recorders and 120 RT-130 recorders from the PASSCAL and EarthScope instrument pools, and fired 15 seismic sources spaced across the High Lava Plains (HLP) region. This was the largest number of instruments deployed in an on-land controlled-source seismic experiment on a crustal scale. This army of helpers included 42 students from 12 different universities, mainly the University of Oklahoma, Stanford, Oregon State, Arizona State, MIT, Miami-Ohio, University of Texas at Dallas, and Rhode Island, as well as a team from the Carnegie Institution of Washington. These deployers were ably assisted by 6 staff members from the PASSCAL/EarthScope Instrument Center. This deployment also took advantage of the >100 seismometers in the HLP broadband array whose deployment over the three years was led by Carnegie Institution of Washington and Arizona State University. The University of Oregon, Michigan Tech, and the U. S. Geological Survey also deployed an array in the Newberry volcano area to record earthquakes and the seismic sources. Together, these efforts are providing a deep and three-dimensional image of the structure of this region.
</p><p>New instrumentation built by the PASSCAL Instrument Center staff made it possible to carry out 3C recording using three Texan single-channel instruments at a site to study detailed crustal structure and anisotropy across the towering Steens Mountain region. The seismometers were located to provide high-resolution images of the mantle and crust directly beneath the path of volcanism that dotted the High Lava Plains during the past 16 Ma. In addition to the seismic component, the overarching project, funded by the National Science Foundation’s Continental Dynamics program, includes field geologists, petrologists, and geodynamicists interested in resolving the origin of the sudden massive outpouring of basalt volcanism 16 million years ago and the puzzling trend of age-progressive rhyolite domes that reaches west toward Newberry volcano, the youngest complex in the trend. Our results show that: 1) the crust thicken east of Steens Mountain near the 0.706 Sr isotope line; 2) Basin and Range structures extend well north of their physiographic expression; and 3) HLP lower crust has relatively high velocity suggesting underplating.
</p><p>Acknowledgements: This study was supported by the Continental Dynamics Program of the National Foundation (Award EAR-0641515)</p>


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