Upper crustal structure of the Yellowstone Caldera from seismic delay time analyses and gravity correlations
The 1978 Yellowstone-Snake River Plain seismic experiment provided detailed refraction data that were recorded across a two-dimensional array of seismographs in Yellowstone National Park. A delay time analysis was applied to 173 crystalline basement P/sub g/ arrivals from these data to determine the three-dimensional distribution of velocities and the layer configuration of the upper crust beneath the Yellowstone caldera. The P wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows, averaging 2.8 km/s, that range in thickness from 1.5 to 2.0 km. Adjacent to the caldera, the crystalline upper crustal layer has a velocity of 6.05 +- 0.01 km/s, but this layer decreases by 6% to 5.70 km/s beneath the caldera and extends northeast 15 km beyond the caldera. Smaller zones of very low P velocity, 4.0 km/s, a 30% velocity reduction compared to the 6.05 km/s layer, occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the Upper and Midway Geyser basins. A three-dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of -60 mGal over the caldera correlates directly with (1) the surface layer of combined sediments and rhyolite flows, (2) the low-velocity, 5.7-km/s, upper crustal layer, and (3) the 4.0-km/s low-velocity zone beneath the northeastern caldera rim. An interpretation of the seismic velocities and densities, based on experimental data and theoretical models is made.
- Research Organization:
- Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112
- OSTI ID:
- 6771272
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:B4
- Country of Publication:
- United States
- Language:
- English
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