The first major global tomographic study of the Earth
was made by Professor Adam M. Dziewonski
in the early 70's. The idea of this study was that the travel time anomalies
observed for many ray paths, criss-crossing the Earth between various points
near the Earth's surface and reaching different depths in its interior, could
be resolved formally into a three-dimensional (3-D) model.
This procedure is now called `seismic tomography', as it conceptually resembles the medical CAT-scan.
The early results were reported orally in 1974 and 1975 by Prof. Dziewonski and a full report
was published in January 1977 (Dziewonski et al., 1977). A more detailed description
can be found a
statement
written by Prof. Dziewonski.
The motivation for studying 3-D structure of the Earth's interior
is that it may offer the best information on the dynamic processes
in the deep interior of the Earth. As the seismic wave speeds
change with temperature, it is plausible to obtain 3-D snapshots
of the convection pattern in the Earth.
Active participants in this project are
Adam M. Dziewonski,
Göran Ekström,
Lapo Boschi,
Yu Gu,
and
Wei-jia Su.
Recently graduated:
Xian-feng Liu
- An anisotropic S-velocity model of the upper mantle,
S20A , showing the unique character of the anisotropy of the
Pacific upper mantle.
- Xian-Feng Liu's Ph.D thesis:
The Three-Dimensional Shear Wave Velocity Structure of the
Earth's Lower-Most Mantle
(Compressed postscript file, about 200 pages, 11 MB)
and a few pages best viewed in color: Pages
44,
65-66,
70-78,
83,
85-90,
106,
172,
175.
- Liu & Dziewonski (1997) have derived a degree 16 model S16U6L8
by including the travel times of ScS-S, SS-S, S-SKS, SKKS-SKS other absolute travel time data
and waveform data in the inversion. The model is parameterized separately for the upper
mantle and the lower mantle using B-spline basis functions. The paper has been
submitted to CMB monograph.
You can
download a hardcopy and
Figure 24 (color) here .
- MK12WM13 :
Simultaneous Inversion for 3-D Variations in Shear and Bulk Velocity
in the Mantle (Su & Dziewonski, 1997).
- Liu & Dziewonski (1994) have derived a global model SKS12_WM13 (in a format which is self-explained)
by including the travel times of ScS-S, SS-S, S-SKS, other absolute travel time data
and waveform data in the inversion.
- Su, Woodward & Dziewonski (1994) have derived a global model S12_WM13
by including the travel times of ScS-S, SS-S and other absolute travel time
data and waveform data in the inversion.
- Global travel time inversion using cubic B-splines parameterization, which makes an excellent compromise between the natural
smoothness of spherical harmonic and the reduction of free parameters
available by using cell-parameterized models for regional inversions.
- Topography of the 660 km discontinuity using long
period SS precursors (Gu, Dziewonski & Agee, 1997) .
- Topography of the 410 km discontinuity using long
period SS precursors (Gu, Dziewonski & Agee, 1997).
- Long and short wavelength images of Earth's mantle from ISC compressional wave delay time data, analyzing the properties of different modeling techniques (Boschi and Dziewonski, 1999).
- Whole Earth tomography: Mantle anisotropy or outer core heterogeneity from ISC compressional wave delay time data, looking for the solution in very different solution-spaces (Boschi and Dziewonski, 2000).
- Models of the mantle shear velocity and discontinuities in the pattern of lateral
heterogeneities (Gu, Dziewonski, Su, and Ekström, 2001).
- Preferential detection of the Lehmann discontinuity under continents (Gu, Dziewonski, and Ekström, 2001).
- Global variability of Transition Zone thickness (Gu, Dziewonski, in press, 2002).
How to use Harvard's 3-D Earth models?
Now, you can download Fortran and C++ source codes.
Contacting individual authors:
-
Adam M. Dziewonski,
-
Göran Ekström,
-
Lapo Boschi,
-
Yu Gu,
- Wei-jia Su,
-
Xian-feng Liu.
Last modified: Mon Aug 24 15:05:55 EST