This map (incl. the postscript file) is available as part of a package including the whole 3-layer sediment model. Go to ftp section for details.
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Since the seismic velocity changes
rather rapidly with depth, it is necessary to subdivide the
sedimentary cover. We chose to specify the elastic parameters in a
3-layer model. While the top layer covers the first 2km of sediments, the second one (both shown here) covers the 5km underneath. For areas with sediments thicknesses larger than 7km, a third layer covers the rest (not shown here). |
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For much of the oceanic areas, detailed information of P-velocities
are available in form of regional velocity functions (v=v0
+Kt, where t is one-way vertical travel time to layer mid-points).
The plot shown here summarizes areas where velocity functions are
available
(areas of the same color do NOT have the same
velocity function).
The velocity functions will be summarized in a future
publication and are available upon request ( gmasters@ucsd.edu). |
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On continents, the velocities are less well known, as most refraction seismic profiles do not yield detailed information on the sedimentary cover. We therefore adopt the values given in CRUST 5.1 (2.1-2.5km/s in the first 2km, then 3.2-5.3km/s). The plot shown here summarizes Vp in the first two layers. Details on CRUST 5.1 can be found in the next section. |
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We average the new sediment map to 5x5° cells and compare the resulting map to the sedimentary cover of CRUST5.1 (layers 3 and 4, soft and hard sediments). |
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There is general agreement between the two maps and CRUST5.1 represents the actual thickness in most of the oceanic areas. Significant differences (up to 2.9km) can be found in some shelf regions and sedimentary basins (e.g. Arctic, north of Greenland). Sediments on continents appear slightly overpredicted by CRUST5.1, especially in Eurasia and the Western U.S.. |
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The Arctic and Antarctic Regions. |
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To illustrate this, we calculate phase velocity maps for Rayleigh wave at 35 seconds (28mHz) using our new sediment map and our global crustal model CRUST 5.1. In the top map, the sediments of CRUST 5.1 have been replaced with the new model, while the lower panel shows the predictions of CRUST 5.1 (with the CRUST 5.1 sediments). |
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In the difference plot, many blue areas correlate with red areas in the sediment difference map (e.g. Artic Ocean north of Greenland). A lack of sediments in CRUST 5.1 yields high phase velocities that are too high. Overestimation of the sediment thickness in large parts on the continents in CRUST 5.1 (e.g. Eurasia) leads to velocities which are too low. |
G. Laske and G. Masters, A Global Digital Map of Sediment Thickness,
EOS Trans. AGU, 78, F483, 1997.
Ludwig, W.F., J.E. Nafe and C.L. Drake, Seismic Refraction, in "The
Sea, Vol. 4, Ideas and Observations on Progress in the Study of the
Seas", A.E. Maxwell (ed.), Wiley-Interscience, New York, 1970.
Mooney, W.D., G. Laske and G. Masters, CRUST5.1: A global crustal
model at 5°x5°. J. Geophys. Res., 103, 727-747, 1998.
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References
| Reference | Region Covered |
| Tucholke, 1986 | North Atlantic (DNAG) |
| Tucholke and Uchupi, 1989a | North Atlantic (atlas) |
| Tucholke and Uchupi, 1989b | Mid Atlantic (atlas) |
| Divins and Rabinowitz, 1989 | South Atlantic |
| Salvador, 1986 | Gulf of Mexico (DNAG) |
| Jackson and Oakey, 1986 | Arctic Ocean (DNAG) |
| Hayes, 1991 | Antarctica, Southern Oceans |
| Ludwig and Houtz, 1979 | North and South Pacific Ocean |
| Renkin and Sclater, 1988 | North Pacific Ocean |
| Rabinowitz et al., 1988 | Indian Ocean |
| Exxon, 1985 | global sediment map (here, Continents) |
| Beloussov and Pavlenkova, 1984 | Eurasia |
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