1 | A GLOBAL DIGITAL MAP OF SEDIMENT THICKNESS AT 1x1 deg |
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2 | |
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3 | SEDIMENT MAP (sedmap): |
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4 | ------------ |
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5 | This global sediment map is digitized on a 1x1 deg grid. |
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6 | In the oceans, published digital high-resolution maps were |
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7 | averaged (e.g. Pacific, Indian and South Atlantic oceans). |
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8 | In area for which such files are not available (e.g. Arctic |
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9 | and North Altantic ocean), the sediment thickness was hand- |
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10 | digitized using atlases and maps. The sediments in most of the |
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11 | continental areas (incl. shelves) were obtained by digitizing the |
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12 | Tectonic Map of the World provided by the EXXON rpoduction research |
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13 | group (1985). |
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14 | |
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15 | The file is sedmap.map and is specified the following way: |
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16 | the values corresponds to the cells with midpoints |
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17 | 89.5N 179.5W, 89.5 178.5W, 89.5 177.5W aso. |
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18 | The last value corresponds to 89.5S 179.5E. |
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19 | A postscript file of the map is sedmap.ps. |
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20 | Values are km. |
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21 | |
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22 | Preparing the map for input into GMT: |
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23 | ------------------------------------ |
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24 | A file which is more straight forward to be used as input |
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25 | for GMT (but is significantly larger!) is sedmap.gmt.gz. |
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26 | Ftp this file onto your UNIX machine, |
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27 | having the binary option switched on. Then type: |
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28 | gunzip sedmap.gmt. |
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29 | |
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30 | The uncompressed file will be about 2.5Mbyte large. |
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31 | This file will contain 64800 lines where each one |
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32 | specifies a cell with: longitude, latitude, value. |
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33 | To convert the file sedmap.map into GMT input format, |
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34 | use the fortran code map2gmt.f. |
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35 | On unix machines, simply type: |
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36 | f77 map2gmt.f -o map2gmt |
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37 | map2gmt |
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38 | |
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39 | this sequence reads in sedmap.map and |
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40 | creates the file sedmap.gmt. |
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41 | |
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42 | SEDIMENT MODEL (tarfile): |
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43 | -------------- |
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44 | We have also compiled elastic properties (rho, vp, vs) |
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45 | which are given in separate maps on the same 1x1 deg grid. |
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46 | Since these parameters change rapidly with depth, it became |
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47 | necessary to divide the sediment column into three layers, |
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48 | where the top layer is up to 2km thick, the second up to 5km. |
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49 | |
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50 | In the oceans, compressional velocities vp were calculated using |
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51 | published velocity functions, where available. On continents, we |
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52 | adopt the values given in global crustal model CRUST5.1 (2.1-2.5km/s |
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53 | in the first 2km, then 3.2-5.3km/s). |
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54 | |
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55 | Shear velocities and densities were calculated using the curves of |
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56 | Ludwig, Nafe and Drake. |
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57 | (Seismic Refraction, in "The Sea, Vol. 4, Ideas and Observations on |
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58 | Progress in the Study of the Seas", A.E. Maxwell (ed.), |
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59 | Wiley-Interscience, New York, 1970.) |
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60 | |
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61 | All 12 files (3 for each of thickness, vp, vs, rho) are assembled in |
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62 | the tarfile sedmod.tar. This file has been compressed using the |
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63 | UNIX compression gzip. Please use the binary option to ftp |
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64 | the tarfile, then type: gunzip sedmod.tar on your UNIX machine. |
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65 | You can extract all files by typing: tar -xvf sedmod.tar. |
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66 | |
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67 | The format is the same as for the sediment map: |
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68 | 360x180 numbers, where the first one is assigned to the cell |
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69 | with midpoint 89.5N 179.5W, then 89.5N 179.5W, aso. |
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70 | |
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71 | Please let us know if you have any problems. |
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72 | |
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73 | REFERENCE: |
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74 | --------- |
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75 | If you use this map or model, please use the following reference: |
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76 | G. Laske and G. Masters, A Global Digital Map of Sediment Thickness, |
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77 | EOS Trans. AGU, 78, F483, 1997. |
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78 | |
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79 | PLEASE PROVIDE FEEDBACK: |
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80 | ----------------------- |
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81 | Also, as this model is evolving, we depend on your feedback. |
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82 | We are curious to know what you use this map for, so |
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83 | please let us know and please send us |
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84 | suggestions and/or corrections for the model. |
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85 | (glaske@ucsd.edu or gmasters@ucsd.edu). |
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86 | |
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87 | WEB PAGE: |
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88 | -------- |
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89 | Please also check our Web page: |
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90 | http://mahi.ucsd.edu/Gabi/sediment.html |
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91 | |
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92 | Gabi Laske and Guy Masters |
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