Long and short wavelength images of the Earth's mantle
The large amount of seismic travel time data available today has encouraged
a number of tomographic studies of the Earth's global structure, making
it possible to generate very high resolution images of the mantle. Such
images are characterized by short wavelength features that did not appear
in previous lower resolution spherical harmonics models. Seismic inverse
problems do not have a single solution; a great deal of arbitrarity is
involved when a tomographic model is to be determined, and this is why
images of the same physical observable are often appreciably different
from each other. Moreover, even though an encouraging agreement exists
between different high resolution models, the reliability of the low-order
ones has been confirmed by their compatibility with the observed geoid
and the normal mode splitting functions. For these reasons, we still believe
that it is worthwhile to investigate the discrepancies between different
approaches to seismic global tomography. We present tomographic models
of different wavelength and resolution; we address the existing discrepancies
between them, and attempt to explain them by means of a careful analysis
of both the theory associated with the regularized inversion procedure,
and the geophysical implications involved.
The figure above is an example of the models that we are trying to compare. A is the degree 12 spherical harmonic model MK12WM13 (expressed in terms of P velocity anomalies) of Su and Dziewonski (PEPI, 1997); B is the new BDP98 P block model of Boschi and Dziewonski; C is the P model of van der Hilst et al. (Nature, 1997), with a block parametrization finer than the one of BDP98. A discussion of the discrepancies and similarities between these models is attempted in Boschi and Dziewonski (JGR, 1999).
THE MODEL BDP98 (model B above) IS AVAILABLE VIA ANONYMOUS FTP at
ftp.seismology.harvard.edu.
Once you are connected type ``cd users/boschi/BDP98''; the ``read.me'' file in
that directory will provide informations as to the contents of the various
files. Email Lapo Boschi for further questions.
Harvard seismology: 3-D Earth Structure
Lapo Boschi,
Department of Earth and Planetary Science, Harvard University
Last
modified: Tue Jul 25 17:02:34 EST 2000