A GLOBAL DIGITAL MAP OF SEDIMENT THICKNESS AT 1x1 deg

SEDIMENT MAP (sedmap):
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This global sediment map is digitized on a 1x1 deg grid. 
In the oceans, published digital high-resolution maps were
averaged (e.g. Pacific, Indian and South Atlantic oceans). 
In area for which such files are not available (e.g. Arctic
and North Altantic ocean), the sediment thickness was hand-
digitized using atlases and maps. The sediments in most of the
continental areas (incl. shelves) were obtained by digitizing the
Tectonic Map of the World provided by the EXXON rpoduction research
group (1985).

The file is sedmap.map and is specified the following way: 
the values corresponds to the cells with midpoints
 89.5N 179.5W, 89.5 178.5W, 89.5 177.5W aso.
The last value corresponds to 89.5S 179.5E.
A postscript file of the map is sedmap.ps.
Values are km.

Preparing the map for input into GMT:
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A file which is more straight forward to be used as input
for GMT (but is significantly larger!) is sedmap.gmt.gz. 
Ftp this file onto your UNIX machine,
having the binary option switched on. Then type:
gunzip sedmap.gmt.

The uncompressed file will be about 2.5Mbyte large.
This file will contain 64800 lines where each one
specifies a cell with: longitude, latitude, value.
To convert the file sedmap.map into GMT input format,
use the fortran code map2gmt.f.
On unix machines, simply type:
f77 map2gmt.f -o map2gmt
map2gmt

this sequence reads in sedmap.map and
creates the file sedmap.gmt.

SEDIMENT MODEL (tarfile):
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We have also compiled elastic properties (rho, vp, vs) 
which are given in separate maps on the same 1x1 deg grid.
Since these parameters change rapidly with depth, it became
necessary to divide the sediment column into three layers,
where the top layer is up to 2km thick, the second up to 5km.

In the oceans, compressional velocities vp were calculated using 
published velocity functions, where available. On continents, we 
adopt the values given in global crustal model CRUST5.1 (2.1-2.5km/s 
in the first 2km, then 3.2-5.3km/s).

Shear velocities and densities were calculated using the curves of 
Ludwig, Nafe and 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.)

All 12 files (3 for each of thickness, vp, vs, rho) are assembled in
the tarfile sedmaps.tar. This file has been compressed using the
UNIX compression gzip. Please use the binary option to ftp
the tarfile, then type: gunzip sedmaps.tar on your UNIX machine.
You can extract all files by typing: tar -xvf sedmaps.tar.

The format is the same as for the sediment map:
360x180 numbers, where the first one is assigned to the cell
with midpoint 89.5N 179.5W, then 89.5N 179.5W, aso.

Please let us know if you have any problems.

REFERENCE:
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If you use this map or model, please use the following reference:
G. Laske and G. Masters, A Global Digital Map of Sediment Thickness,
EOS Trans. AGU, 78, F483, 1997.

PLEASE PROVIDE FEEDBACK:
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Also, as this model is evolving, we depend on your feedback. 
We are curious to know what you use this map for, so
please let us know and please send us
suggestions and/or corrections for the model. 
(glaske@ucsd.edu or gmasters@ucsd.edu).

WEB PAGE:
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Please also check our Web page:
http://mahi.ucsd.edu/Gabi/sediment.html 

Gabi Laske and Guy Masters

update:
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30 Apr., 2010
sedmap.grd: grd file to be read by gmt
sedmap.xyz: the map file, one value in each line, together with longitude and latitude