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S-velocity model for the western US integrating body- and surface-wave constraints


Model highlights: The DNA10-S model integrates teleseismic body-wave traveltime and surface-wave phase velocity measurements into a single inversion to constrain the S-wave velocity structure beneath the western US (from the Pacific coast to ~100 deg W, from Mexico to Canada). By combining these datasets we can constrain both the lithospheric structure, with a horizontal resolution of ~100km and vertical resolution of ~10 km, and the mantle structure to 1000km depth with a resolution of ~250 km. This allows imaging of the process of mantle convection and its interaction with the lithosphere. The stable and old Colorado Plateau is imaged with two high-velocity and cylindrical anomalies extending into the mantle below. These are interpreted as lithospheric drips and can explain the Cenozoic uplift of the plateau. The low-velocity S-shaped plume conduit beneath Yellowstone extends from the lower mantle up to the active caldera and then spreads out beneath the Snake River Plain. For the first time we can image the parabola shape of the residual plume material that is aligned exactly with the surface tectonic parabola. Subduction has been ongoing beneath the Pacific Northwest for more than 150Ma. Today's high-velocity slab is imaged in the mantle, along with a series of similar features to the east of the current slab. These are interpreted as fossil slab fragments of the Farallon plate. The complex S-shape of the Yellowstone plume is a result of the plume weaving a path to the surface between these slab fragments.

NW-SE cross-section across the Colorado Plateau showing the two lithospheric drips. See Fig 13 Obrebski et al 2011

Section through the plume pancake at 50km depth showing the low-velocity plume material spreading out beneath the lithosphere. See Fig 12.

Vertical sections orientated perpendicular to the hotspot track. Beneath Yellowstone the plume conduite is observed. Below the Snake River Plain the shallowing and broadening plume head can be seen. See Fig 12.

Model specifications:

  • Parameters: DNA10-S is an S-velocity model
  • Coverage: Good resolution extends from the Pacific coast to the Great Plains (~100 deg W), from the Mexican boarder (31 deg N) to the Canadian boarder (49 deg N).
  • Data source: More than 1200 stations where used from the USArray transportable array, regional seismic networks, and temporary seismic deployments.
  • Data type: Relative traveltimes of teleseismic body waves (S and SKS) from about 162 earthquakes, and surface wave phase velocity measurements from 167 eartqhuakes were used to constrain the model.
  • Inversion: Finite frequency sensitivity kernels and phase velocity sensitivity kernels are used in a damped (but not smoothed) LSQR inversion.
  • Resolution: The model can resolve mantle structure to a depth of ~1000 km and with a lateral and vertical resolution of ~250km. In the upper ~200km where the surface waves provide additional constraints the lateral resolution is ~100km and the vertical resolution is ~10km.

Obrebski, M., R.M. Allen, F. Pollitz, S.-H. Hung. Lithosphere-Asthenosphere Interaction Beneath The Western US From the Joint Inversion of Body-wave Travel Times and Surface-waves Phase Velocities Geophys. J. Int. in press. download

The relation between the complex geologic history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geologic features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two datasets to image and study the link between the geology of the western US, the shallow structure of the Earth and the convective processes in mantle. Our multi- phase model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low density rocks isostatically sustain part of the high topography of the western US. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E-W extent of the USArray used in this study allows imaging the "slab graveyard", a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA09 velocity models are available for download and slicing at http://dna.berkeley.edu .


The following have contributed to the development of the DNA models: Richard Allen (UC Berkeley) Shu-Huei Hung (National Taiwan University) Mathias Obrebski (UC Berkeley) Robert Porritt (UC Berkeley) Fred Pollitz (USGS) Mei Xue (formerly UC Berkeley, now Tongji University)

Support for this project is provided by the Earthscope program of the National Science Foundation, and the University of California, Berkeley. The 3D visualization has been facilitated by the Keck Caves of the University of California, Davis.

This page is maintained by Richard Allen