The Scripps 3D Mantle Models

This is the web site for the "Scripps mantle tomographic models". This page includes short summaries of the models, links to basic figures, and a list of references where to find more extensive descriptions. The link to SB4L18 includes a brief tutorial which summarizes the general features that are found in most current seismic tomographic models.

This site also provides links to our anonymous ftp area. The models are provided with README files, postscript plots of the models and Fortran 77 computer code to read the models. If you need assistance with the handling of our models, please don't hesitate to contact us.

Note that our models are strictly mantle models and stop at the Moho (the global average of the Moho depth is 22 km). Our data have been corrected for crustal effects (CRUST 5.1) prior to the inversions. Hence, the signal in the data resulting from variations in crustal structure has to be added to the predictions of the mantle models when comparing them to measured data.

SB4L18
SB10L18
S16B30
P16B30
Related sites
Publications
FTP section

SB4L18

This model is the latest Scripps "high-resolution" model. Our combined dataset to make the mantle models includes our surface wave phase velocity maps , free oscillation structure coefficients and long-period body wave absolute and differential travel times.

Our inversions employ the LSQR algorithm and we include first-difference smoothing both radially and laterally.

SB4L18 shows the typical features commonly found in mantle tomographic models:

large amplitude anomalies in the upper mantle
moderately large amplitude anomalies in the lowermost mantle
small-amplitude but significant anomalies in the mid-mantle
picture

strong anomalies in the upper mantle that correlate with surface tectonics (picture)
slab-like features in the mid-mantle (picture)
large harmonic degree 2 structure near the base of the mantle picture)

Go to ftp section for downloading this model.

This figure shows a slice through SB4L18 that goes through the center of the Earth. The cut of the slice is along the great circle that is marked by the blue circle in the center of the plot. One of the most prominent features is a seismically fast slab-like anomaly that extends from the surface beneath the Continental US well throughout the whole mantle. This is thought to be the image of the subducted Farallon plate.
Other marked features include two large slow anomalies under Africa and the central Pacific Ocean that originate at the CMB (core-mantle boundary) and extend well up into the lower mantle.
Also prominent are the seismically fast continental shields in the upper mantle: the South and West African Cratons, the southern extension of the Canadian Shield and the Australian Shield. Mid-ocean ridges are associated with slow anomalies in the upper mantle.
The black circle marks the 670km discontinuity between upper and lower mantle.

top

SB10L18

This model is our joint Vs/Vp model. Our combined dataset to make this model includes our surface wave phase velocity maps , free oscillation structure coefficients and long-period body wave absolute and differential travel times.

The model is parameterized by 18 layers of roughly 100km thickness in the upper mantle and transition zone and 200km thickness in the lower mantle. Each layer is devided into equal-area blocks of dimension 10 degrees at the equator. SB10L18 was obtained in a joint inversion for shear velocity, Vs, and bulk sound speed, Vc. See notes for retrieving Vp.

Our inversions employ the LSQR algorithm and we include first-difference smoothing both radially and laterally.

SB10L18 shows some interesting features that can be found in other joint models as well:

large amplitude anomalies in the upper mantle
moderately large amplitude anomalies in the lowermost mantle
small-amplitude but significant anomalies in the mid-mantle
the perturbations in Vs and Vp correlate throughout the mantle
perturbations in Vs are typically 3 times as large as those in Vc or Vp
the correlation of Vs and Vc decreases with depth
Vs and Vc are strongly negatively correlated in the lowermost mantle
picture

Point 7 implies that the anomalies in the lowermost mantle are most likely not caused by thermal effects (thermal effects make Vs and Vc correlate) but that chemical effects (composition) play a role. The strongest anti-correlation is found in the central Pacific.

Go to ftp section for downloading this model.

top

S16B30

This model is the 1996 Scripps model. Our combined dataset included our surface wave phase velocity maps , free oscillation structure coefficients and long-period body wave absolute and differential travel times.

The model is parameterized by 30 natural cubic B-splines radially and by spherical harmonics up to degree 16 laterally.

Our inversion was a direct matrix inversion using second-derivative smoothing both radially and laterally.

S16B30 is basically a smoothed version of SB4L18 as these models correlate very well, except in the transition zone (picture).

Go to ftp section for downloading this model.

top

P16B30

This model is the 1996 P velocity model of Bolton and Masters. The combined dataset included our Rayleigh wave phase velocity maps , free oscillation structure coefficients and long-period P wave absolute and differential travel times.

The model is parameterized by 30 natural cubic B-splines radially and by spherical harmonics up to degree 16 laterally.

Our inversion was a direct matrix inversion using second-derivative smoothing both radially and laterally.

The rms amplitudes in P16B30 vary very much like those of Vp in SB10L18 with depth though the correlation of these models is not quite as good as between S16B30 and SB4L18. (picture).

Go to ftp section for downloading this model.

top

Publications

Models SB4L18 and SB10L18 are described in:
Masters G., Laske, G., Bolton, H. and Dziewonski, A., 2000. "The Relative Behavior of Shear Velocity, Bulk Sound Speed, and Compressional Velocity in the Mantle: Implications for Chemical and Thermal Structure" in: S. Karato, A.M. Forte, R.C. Liebermann, G. Masters and L. Stixrude (eds.) "Earth's Deep Interior", AGU Monograph 117, AGU, Washington D.C.

Model S16B30 is described in:
Masters, G., Johnson, S., Laske, G. and Bolton H., A shear-velocity model of the mantle. Phil. Trans. R. Soc. Lond. A, 354, 1385-1411, 1996.

Model P16B30 is described in:
Bolton H., Long Period Travel Times and the Structure of the Mantle. PhD Thesis, La Jolla, 204 pages, 1996.

top