Abstract
The Yellowstone hot spot has recently been shown to be a plume that extends into the transition zone. At roughly 60–120 km depth, the plume material rising beneath Yellowstone Park is sheared SW by North America Plate motion, producing a profound low velocity layer emplaced beneath the thin lithosphere. To constrain the absolute seismic velocity of the plate‐sheared plume layer, fundamental mode Rayleigh wave observations have been inverted for phase velocity using the two plane wave technique. The resulting phase velocity models are inverted with Moho‐converted P to S arrival times to better constrain crustal thickness and absolute S wave velocity structure to ∼120 km depth. A regionalized S wave velocity model has an extremely low velocity minimum of 3.8 ± 0.1 km/s at 80 km depth beneath the hot spot track. Nonregionalized 3‐D velocity models find a velocity minimum of 3.9 km/s beneath the hot spot track. Below 120 km depth, our resolution diminishes such that the lateral spreading of the plume track is not resolved. The volume of the low velocity plume layer is small and the estimated buoyancy flux for the Yellowstone plume is <0.1 Mg/s which contrasts with the ∼9 Mg/s value for Hawaii. In addition, a notable region of thick crust and high lower crustal velocities is found around Billings, Montana, consistent with previous refraction and receiver function studies that interpret this as evidence for a massive Precambrian underplating event.
Highlights
[2] Over the last $17 Ma, the Yellowstone hot spot has produced a series of progressively younger silicic eruptions that extend from the Oregon-Nevada border NE to Yellowstone National Park [Christiansen and Yeats, 1992]
P and S wave tomography studies [Yuan and Dueker, 2005; Waite et al, 2006] have found a low velocity conduit extending from Yellowstone Park and inclined 15° from vertical toward the NW
[6] To estimate phase velocity, we used a technique developed by Forsyth and Li [2005] which accounts for simple multipathing effects, allowing shorter period Rayleigh waves to be reliably measured
Summary
[2] Over the last $17 Ma, the Yellowstone hot spot has produced a series of progressively younger silicic eruptions that extend from the Oregon-Nevada border NE to Yellowstone National Park [Christiansen and Yeats, 1992]. We measure the velocity of fundamental mode Rayleigh waves in the region These data are combined with measurements of the relative arrival time difference between receiver function direct P. and Pms arrivals to produce models of absolute S wave velocity and crustal thickness variations. Band-pass filtered traces without a relatively simple fundamental mode Rayleigh wave envelope were rejected. This data culling produced 81 events to be analyzed, for any given event, measurable Rayleigh wave energy was not generally observed at all periods. 22 43 46 56 60 63 64 59 51 68 69 64 53 38 28 18 associated with periods with one real and one imaginary component at each band-pass period
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