HR: 16:00h
AN: V44B-01    [Abstracts]
TI: Seismic Tomography and Structure of the Transition Zone
AU: * Dziewonski, A M
EM: dziewons@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138, United States
AU: Kustowski, B
EM: kustowsk@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138, United States
AU: Lekic, V
EM: lekic@seismo.berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California at Berkeley, 209 McCone Hall, Berkeley, CA 94720, United States
AU: Romanowicz, B
EM: barbara@seismo.berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California at Berkeley, 209 McCone Hall, Berkeley, CA 94720, United States
AB: Most of the tomographic models employ data sets that had satisfactory resolution in a limited radial extent. For example, studies using teleseismic travel times do not have resolution in the upper mantle, even though using matrix conditioning methods it is possible to derive a "model" of the upper mantle. Similarly, some studies using surface waves presented detailed "models" at depths far exceeding resolution of the data used. A data set that fills in the gap created by the limitations of the surface wave dispersion and teleseismic travel times data consists of the higher modes. Only three modeling groups use the combination of all three data types and, therefore, can obtain the structure with a sufficient radial resolution to identify the properties just above, within and just below the transition zone. These three groups are Berkeley (non-linear asymptotic coupling theory; Li and Romanowicz, 1996) with the most recent model by Panning and Romanowicz (2006), Harvard (path average approximation; Woodhouse and Dziewonski, 1984) with the most recent model by Kustowski et al. (2007) and Caltech/Oxford (separation of overtones; van Heist and Woodhouse, 1997) as represented by a model of Ritsema et al. (1999). These global models have a nominal horizontal resolution of about 1,000 km and variable radial resolution, from about 50 km below the Moho, to 100-150 km in the asthenosphere and transition zone, and about 250 km in the middle and lowermost mantle. These models show that there are three boundary layers in the mantle. The one near the surface is dominated by spherical harmonics up to degree 8, with the peak at degree 5. It ends between 200 and 250 km depth, after which the power spectrum is low and tends to be white. The second boundary layer is in the transition zone, where overall power increases and is clearly dominated by degree 2. The spectrum changes abruptly at the top of lower mantle, where it decreases in amplitude and becomes white; this character of the spectrum continues to about 2000 km depth. The third boundary layer has the maximum power near the CMB, it is dominated by degrees 2 and 3. These great wavelength velocity anomalies are not limited to the lowermost mantle, but extend to about 1000 km above the CMB and, perhaps, with a significantly diminished amplitude all the way to the transition zone; this is further documented by consistently positive values of the radial correlation matrix in the lower mantle. The transition zone signature, both in wavenumber and space domains, implies impeded mass flux between the upper and lower mantle. There are three locations (Indonesia, Fiji-Tonga and South America) where spatially limited fast velocity anomalies underlie large scale fast velocity anomalies in the transition zone, thus indicating a possibility of some penetration of the subducted material into the lower mantle.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7270 Tomography (6982, 8180)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8180 Tomography (6982, 7270)
DE: 8410 Geochemical modeling (1009, 3610)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting