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| Titel |
Vertical coherency of heterogeneity in the Earth's mantle constrained from a comprehensive set of global seismic data. |
| VerfasserIn |
Lapo Boschi, Thorsten W. Becker, Goran Ekstrom, Hendrik-Jan van Heijst, Nathan A. Simmons, Jeannot Trampert |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044853
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| Zusammenfassung |
| We analyze a newly compiled, massive, and diverse set of global
seismic measurements to understand better the spatial and spectral
character of imaged mantle shear wave anomalies and their
uncertainties. Paying particular attention to the role of data
selection, regularization, and model parameterization, we strive to
explore a number of relevant concepts in mantle dynamics, including
the amount of vertical downward (slabs) and upward (plumes) mass
transport, and changes in spectral heterogeneity character with depth
below 660 km in the mid mantle. These issues and their geodynamic
implications have been debated vigorously, yet there are no firm
conclusions as to the robustness of seismological inferences.
To answer some of the related questions, we have compiled a new global
seismic database that combines a variety of seismic phases, measured
by independent authors with often profoundly different techniques:
various sets of (refracted and/or multiply reflected) shear-wave
traveltimes, three sets of Love- and Rayleigh-wave fundamental modes,
and two sets of Love- and Rayleigh-wave overtones. We have developed
new tomography software to invert such databases jointly, accounting
accurately for radial anisotropy throughout the mantle, and for the
nonlinear effects of crustal heterogeneity (based, at this stage, on a
global a-priori model).
We present the results of a suite of tomographic inversions, allowing
for more or less complicated structure in various regions of the
mantle. In particular, we explore the possibility of strong vertical
gradients (or discontinuities) in structure and spectra at various
depths, by iteratively modifying our vertical parameterization and
regularization in different depth ranges. Preliminary results indicate
that the data prefer a break in spectral character with an enhancement
of shorter wavelength anomalies below the upper mantle transition
zone, as suggested earlier. However, this break may in fact occur at
depths significantly below the 660 km phase change. Comparison of the
seismological power spectra maps with heterogeneity maps from recent
spherical convection computations shows that such changes in power
spectra with depth may, moreover, be compatible with whole mantle
convection. |
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