ABSTRACT We have demultiplexed and compressed data from a 3400-km-long seismic-reflection line collected between Cape Hatteras to the Mid-Atlantic Ridge in a continuing effort to reduce the amount of data loss due to old, deteriorating magnetic tapes. INTRODUCTION In 1974, Digicon Inc. recorded a 3400 km-long multichannel seismic-reflection profile extending from Cape Hatteras to the rift valley of the Mid-Atlantic Ridge. Jointly funded by the U.S. Geological Survey (USGS) and the National Science Foundation's Deep Sea Drilling Project (DSDP), the experiment was part of the International Phase of Ocean Drilling (IPOD). The data were recorded from the marine vessel Gulf Seal using a Texas Instruments DFS III recording system. A tuned airgun array totaling 1700 in.3 was used as the seismic source and a streamer with 48-non-linearly spaced hydrophone groups as the antenna. Shotpoint locations, generally spaced every 50 meters, are shown in figures 1 and 2. A summary of the shooting and recording parameters is shown in table 1. Segments of the data totalling approximately 1520 km were processed by Geophysical Services, Inc. (GSI) in the spring of 1975. Copies of the field tapes, and seismic sections can be accessed through the National Geophysical and Solar Terrrestial Data Center in Boulder, Colorado (Grow and Mark, 1977). The 631 original unprocessed field tapes were stored at the USGS seismic processing center in Denver, Colorado. DEMULTIPLEXING AND COMPRESSION Testing revealed that the data on the original field tapes were deteriorating. In order to prevent further loss of data, we demultiplexed the original field tapes and transfered the output to 183 new magnetic tapes at 6250 bpi in SEG-Y format, an industry accepted standard (Barry and others, 1975) As a result, our efforts yielded a data compression ratio of more than 3 to 1. Although there were segments on some of the field tapes where the oxide had actually fallen off the tapes, every effort was made to preserve as much of the data as possible. Close monitoring of the processing system during demultiplexing enabled the computer operators to prevent any further loss or misreading of data due to parity read errors. When exessive parity errors were found on input tapes, operators either ran the tapes through a tape cleaner or in more severe cases just did a tape copy. Shown in appendix I are the slot numbers, shotpoint and field file ranges of all the output tapes. Slot numbers refer to storage locations numbers within our tape library. Observer's notes are also archived at the Denver processing center and can be accessed through the Geophysics Group of the Branch of Petroleum Geology. REFERENCES Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats: Geophysics, v. 40, p. 344-352. Grow, J.A., and Markl, R.G., 1977, IPOD-USGS multichannel seismic reflection profile from Cape Hatteras to the Mid-Atlantic Ridge: Geology, v. 5, p. 625-630. [PB] [WS 8 in] *Figure 1 --- Shotpoint Map of Survey Area (Main IPOD line) [PB] [WS 4 in] *Figure 2 --- Shotpoint Map of IPOD close to Cape Hatteras showing lines A and B shot to tie the main IPOD line closer to wells (From Grow and Markl, 1977). DFS-III Instrument 346 m Offset Distance 50 m Spacing between center of traces 48 through 25 75 m Spacing between center of trace 25 and trace 24 100 m Spacing between center of traces 24 through 1 4 ms Sample Rate 10-12 s Recording length 36 Fold Coverage 9 m Gun Depth 1700 in.3 Displacement of Airgun Array *Table 1 --- Field parameters used in survey [PB] APPENDIX I SLOT PROJECT LINE REEL SPTS FILES TYPE 15054 GULF SEAL IPOD-A A-1 263-135 1-256 DEMUX 15055 GULF SEAL IPOD-A A-2 135-83 257-362 DEMUX 8372 GULF SEAL IPOD-B B-1 700-578 1-246 DEMUX 8373 GULF SEAL IPOD-B B-2 577-453 246-495 DEMUX 8374 GULF SEAL IPOD-B B-3 454-329 494-743 DEMUX 8375 GULF SEAL IPOD-B B-4 329-203 743-996 DEMUX 8376 GULF SEAL IPOD-B B-5 203-151 996-99 DEMUX 8377 GULF SEAL IPOD-B B-6 151-83 99-235 DEMUX 4567 GULF SEAL IPOD IPOD1A 101-228 1-256 DEMUX 4566 GULF SEAL IPOD IPOD1B 228-422 256-643 DEMUX 6453 GULF SEAL IPOD IPOD1C 422-549 643-897 DEMUX 4565 GULF SEAL IPOD IPOD1D 549-600 897-999 DEMUX 13244 GULF SEAL IPOD IPOD-1 600-727 999-254 DEMUX 13245 GULF SEAL IPOD IPOD-2 727-854 254-508 DEMUX 13246 GULF SEAL IPOD IPOD-3 854-984 508-768 DEMUX 13247 GULF SEAL IPOD IPOD-4 984-1102 768-4 DEMUX 13248 GULF SEAL IPOD IPOD-5 1102-1229 5-258 DEMUX 13249 GULF SEAL IPOD IPOD-6 1229-1356 258-512 DEMUX 13250 GULF SEAL IPOD IPOD-7 1356-1482 512-764 DEMUX 13251 GULF SEAL IPOD IPOD-8 1482-1575 764-950 DEMUX 13252 GULF SEAL IPOD IPOD-9 1539A-1668 1-260 DEMUX 13253 GULF SEAL IPOD IPOD-10 1668-1795 260-513 DEMUX 13254 GULF SEAL IPOD IPOD-11 1795-1921 513-766 DEMUX 13255 GULF SEAL IPOD IPOD-12 1921-2051 766-26 DEMUX 13256 GULF SEAL IPOD IPOD-13 2051-2067 26-58 DEMUX 13257 GULF SEAL IPOD IPOD-14 2068-2194 59-312 DEMUX 13258 GULF SEAL IPOD IPOD-15 2194-2321 312-566 DEMUX 13259 GULF SEAL IPOD IPOD-16 2321-2348A 566-98 DEMUX 13260 GULF SEAL IPOD IPOD-17 2348A-2478 98-357 DEMUX 13261 GULF SEAL IPOD IPOD-18 2478-2585 357-572 DEMUX 13262 GULF SEAL IPOD IPOD-19 2586-2740 573-882 DEMUX 13263 GULF SEAL IPOD IPOD-20 2740-2881 882-164 DEMUX 13264 GULF SEAL IPOD IPOD-21 2882-3057 165-516 DEMUX 13265 GULF SEAL IPOD IPOD-22 3057-3102 516-606 DEMUX 13267 GULF SEAL IPOD IPOD-24 3274-3407 950-336 DEMUX 13268 GULF SEAL IPOD IPOD-25 3407-3579 336-680 DEMUX 13269 GULF SEAL IPOD IPOD-26 3579-3753 680-28 DEMUX 13270 GULF SEAL IPOD IPOD-27 3753-3925 28-372 DEMUX 13271 GULF SEAL IPOD IPOD-28 3925-3940 372-402 DEMUX 13272 GULF SEAL IPOD IPOD-29 3940-4111 403-743 DEMUX 13273 GULF SEAL IPOD IPOD-30 4111-4281 743-83 DEMUX 13274 GULF SEAL IPOD IPOD-31 4281-4414A 83-10 DEMUX 13275 GULF SEAL IPOD IPOD-32 4414A-4583 10-348 DEMUX 13276 GULF SEAL IPOD IPOD-33 4583-4779 349-739 DEMUX 13277 GULF SEAL IPOD IPOD-34 4779-4972 739-125 DEMUX 13278 GULF SEAL IPOD IPOD-35 4972-5058 125-298 DEMUX 13279 GULF SEAL IPOD IPOD-36 5059-5256 299-694 DEMUX 13280 GULF SEAL IPOD IPOD-37 5256-5454 694-90 DEMUX 13281 GULF SEAL IPOD IPOD-38 5454-5652 90-485 DEMUX 13282 GULF SEAL IPOD IPOD-39 5652-5850 485-881 DEMUX 13283 GULF SEAL IPOD IPOD-40 5850-6047 881-275 DEMUX 13284 GULF SEAL IPOD IPOD-41 6047-6246 275-673 DEMUX 13285 GULF SEAL IPOD IPOD-42 6246-6422 673-26 DEMUX [PB] SLOT PROJECT LINE REEL SPTS FILES TYPE 13286 GULF SEAL IPOD IPOD-43 6422-6621 27-424 DEMUX 13287 GULF SEAL IPOD IPOD-44 6621-6748 424-677 DEMUX 13288 GULF SEAL IPOD IPOD-45 6748-6918 678-18 DEMUX 13289 GULF SEAL IPOD IPOD-46 6918-7100 18-401 DEMUX 13290 GULF SEAL IPOD IPOD-47 7100-7294 401-790 DEMUX 13291 GULF SEAL IPOD IPOD-48 7294-7483 790-168 DEMUX 13292 GULF SEAL IPOD IPOD-49 7483-7677 168-555 DEMUX 13293 GULF SEAL IPOD IPOD-50 7677-7681 555-564 DEMUX 16597 GULF SEAL IPOD IPOD-51 7682-7935 565-71 DEMUX 16598 GULF SEAL IPOD IPOD-52 7935-8188 71-577 DEMUX 16599 GULF SEAL IPOD IPOD-53 8188-8441 577-83 DEMUX 16600 GULF SEAL IPOD IPOD-54 8441-8695 83-592 DEMUX 16601 GULF SEAL IPOD IPOD-55 8695-8948 592-98 DEMUX 16602 GULF SEAL IPOD IPOD-56 8948-8967 98-135 DEMUX 16603 GULF SEAL IPOD IPOD-57 8967-9220 135-641 DEMUX 16604 GULF SEAL IPOD IPOD-58 9220-9295 641-812 DEMUX 16605 GULF SEAL IPOD IPOD-59 9296-9556 813-334 DEMUX 16606 GULF SEAL IPOD IPOD-60 9556-9810 334-841 DEMUX 16607 GULF SEAL IPOD IPOD-61 9810-10063 841-347 DEMUX 16608 GULF SEAL IPOD IPOD-62 10063-10316 347-853 DEMUX 16609 GULF SEAL IPOD IPOD-63 10316-10569 853-360 DEMUX 16610 GULF SEAL IPOD IPOD-64 10569-10823 360-867 DEMUX 16611 GULF SEAL IPOD IPOD-65 10823-10861 867-943 DEMUX 16612 GULF SEAL IPOD IPOD-66 10861-11108 943-438 DEMUX 16613 GULF SEAL IPOD IPOD-67 11108-11117 438-456 DEMUX 16614 GULF SEAL IPOD IPOD-68 11118-11328 457-417 DEMUX 16615 GULF SEAL IPOD IPOD-69 11328-11581 417-923 DEMUX 16616 GULF SEAL IPOD IPOD-70 11581-11827 923-416 DEMUX 16617 GULF SEAL IPOD IPOD-71 11827-12074 416-910 DEMUX 16618 GULF SEAL IPOD IPOD-72 12074-12320 910-402 DEMUX 16619 GULF SEAL IPOD IPOD-73 12320-12567 402-895 DEMUX 16620 GULF SEAL IPOD IPOD-74 12567-12820 895-402 DEMUX 16621 GULF SEAL IPOD IPOD-75 12820-12834 402-430 DEMUX 16622 GULF SEAL IPOD IPOD-76 12835-13057 431-876 DEMUX 16623 GULF SEAL IPOD IPOD-77 13057-13279 876-319 DEMUX 16624 GULF SEAL IPOD IPOD-78 13279-13501 319-764 DEMUX 16625 GULF SEAL IPOD IPOD-79 13501-13722 764-206 DEMUX 16626 GULF SEAL IPOD IPOD-80 13722-13944 206-650 DEMUX 16627 GULF SEAL IPOD IPOD-81 13944-14111 650-984 DEMUX 16628 GULF SEAL IPOD IPOD-82 14112-14363 985-487 DEMUX 16629 GULF SEAL IPOD IPOD-82B 14242-14258 246-277 DEMUX 16630 GULF SEAL IPOD IPOD-83 14363-14616 487-993 DEMUX 16631 GULF SEAL IPOD IPOD-84 14616-14867 993-496 DEMUX 16632 GULF SEAL IPOD IPOD-85 14867-15120 496-1 DEMUX 16633 GULF SEAL IPOD IPOD-86 15120-15371 1-504 DEMUX 16634 GULF SEAL IPOD IPOD-87 15371-15624 504-10 DEMUX 16635 GULF SEAL IPOD IPOD-88 15624-15875 10-512 DEMUX 16636 GULF SEAL IPOD IPOD-89 15875-16128 512-17 DEMUX 16637 GULF SEAL IPOD IPOD-90 16128-16249 17-259 DEMUX 16638 GULF SEAL IPOD IPOD-91 16250-16454 260-229 DEMUX 16639 GULF SEAL IPOD IPOD-92 16454-16706 229-733 DEMUX 16640 GULF SEAL IPOD IPOD-93 16706-16959 733-240 DEMUX 16641 GULF SEAL IPOD IPOD-94 16959-17212 240-746 DEMUX 16642 GULF SEAL IPOD IPOD-95 17212-17465 746-252 DEMUX 16643 GULF SEAL IPOD IPOD-96 17465-17717 252-755 DEMUX 16644 GULF SEAL IPOD IPOD-97 17717-17970 755-261 DEMUX 16645 GULF SEAL IPOD IPOD-98 17970-18222 261-765 DEMUX 16646 GULF SEAL IPOD IPOD-99 18222-18475 765-271 DEMUX 16647 GULF SEAL IPOD IPOD-100 18475-18726 271-773 DEMUX [PB] SLOT PROJECT LINE REEL SPTS FILES TYPE 16648 GULF SEAL IPOD IPOD-101 18726-18979 773-279 DEMUX 16649 GULF SEAL IPOD IPOD-102 18979-19197 279-716 DEMUX 16650 GULF SEAL IPOD IPOD-103 19198-19420 717-161 DEMUX 16651 GULF SEAL IPOD IPOD-104 19420-19643 161-607 DEMUX 16652 GULF SEAL IPOD IPOD-105 19643-19865 607-51 DEMUX 16653 GULF SEAL IPOD IPOD-106 19865-20087 51-496 DEMUX 16654 GULF SEAL IPOD IPOD-107 20087-20309 496-939 DEMUX 16655 GULF SEAL IPOD IPOD-108 20309-20531 939-383 DEMUX 16656 GULF SEAL IPOD IPOD-109 20531-20753 383-827 DEMUX 16657 GULF SEAL IPOD IPOD-110 20753-20970 827-262 DEMUX 16658 GULF SEAL IPOD IPOD-111 20970-21180 262-682 DEMUX 16659 GULF SEAL IPOD IPOD-112 21181-21403 683-128 DEMUX 16660 GULF SEAL IPOD IPOD-113 21403-21626 128-573 DEMUX 16661 GULF SEAL IPOD IPOD-114 21626-21847 573-16 DEMUX 16662 GULF SEAL IPOD IPOD-115 21848-22053 17-427 DEMUX 16663 GULF SEAL IPOD IPOD-116 22053-22276 427-874 DEMUX 16664 GULF SEAL IPOD IPOD-117 22276-22498 874-317 DEMUX 16665 GULF SEAL IPOD IPOD-118 22498-22719 317-759 DEMUX 16666 GULF SEAL IPOD IPOD-119 22719-22941 759-204 DEMUX 16667 GULF SEAL IPOD IPOD-120 22941-23128 204-257 DEMUX 16668 GULF SEAL IPOD IPOD-121 23128-23346 257-694 DEMUX 16669 GULF SEAL IPOD IPOD-122 23346-23567 694-135 DEMUX 16670 GULF SEAL IPOD IPOD-123 23567-23730 135-462 DEMUX 16671 GULF SEAL IPOD IPOD-124 23732-23954 465-910 DEMUX 16672 GULF SEAL IPOD IPOD-125 23954-24173 911-347 DEMUX 16673 GULF SEAL IPOD IPOD-126 24173-24391 348-784 DEMUX 16674 GULF SEAL IPOD IPOD-127 24392-24614 785-229 DEMUX 16675 GULF SEAL IPOD IPOD-128 24614-24836 229-673 DEMUX 16676 GULF SEAL IPOD IPOD-129 24836-25057 673-115 DEMUX 16677 GULF SEAL IPOD IPOD-130 25057-25101 115-204 DEMUX 16678 GULF SEAL IPOD IPOD-131 25102-25325 205-651 DEMUX 16679 GULF SEAL IPOD IPOD-132 25325-25544 651-90 DEMUX 16680 GULF SEAL IPOD IPOD-133 25544-25767 90-535 DEMUX 16885 GULF SEAL IPOD IPOD-134 25767-25989 535-979 DEMUX 16886 GULF SEAL IPOD IPOD-135 25989-26210 979-422 DEMUX 16887 GULF SEAL IPOD IPOD-136 26210-26432 422-866 DEMUX 16888 GULF SEAL IPOD IPOD-137 26432-26647 866-296 DEMUX 16889 GULF SEAL IPOD IPOD-138 26647-26870 296-741 DEMUX 16890 GULF SEAL IPOD IPOD-139 26870-27091 741-184 DEMUX 16891 GULF SEAL IPOD IPOD-140 27091-27314 184-630 DEMUX 16892 GULF SEAL IPOD IPOD-141 27314-27536 630-74 DEMUX 16893 GULF SEAL IPOD IPOD-142 27536-27759 74-520 DEMUX 16894 GULF SEAL IPOD IPOD-143 27759-27766 520-533 DEMUX 16895 GULF SEAL IPOD IPOD-144 27766-27988 533-977 DEMUX 16896 GULF SEAL IPOD IPOD-145 27988-28211 977-423 DEMUX 16897 GULF SEAL IPOD IPOD-146 28211-28433 423-867 DEMUX 16898 GULF SEAL IPOD IPOD-147 28433-28655 867-311 DEMUX 16899 GULF SEAL IPOD IPOD-148 28655-28878 311-757 DEMUX 16900 GULF SEAL IPOD IPOD-149 28878-29100 757-201 DEMUX 16901 GULF SEAL IPOD IPOD-150 29100-29322 201-646 DEMUX 16902 GULF SEAL IPOD IPOD-151 29322-29544 646-90 DEMUX 16903 GULF SEAL IPOD IPOD-152 29544-29768 90-537 DEMUX 16904 GULF SEAL IPOD IPOD-153 29768-29886 537-774 DEMUX 16905 GULF SEAL IPOD IPOD-154 29886-29911 774-824 DEMUX 16906 GULF SEAL IPOD IPOD-155 29912-30133 825-269 DEMUX 16907 GULF SEAL IPOD IPOD-156 30134-30356 269-713 DEMUX 16908 GULF SEAL IPOD IPOD-157 30356-30580 713-162 DEMUX 16909 GULF SEAL IPOD IPOD-158 30580-30803 162-608 DEMUX 16910 GULF SEAL IPOD IPOD-159 30803-31026 608-53 DEMUX [PB] SLOT PROJECT LINE REEL SPTS FILES TYPE 16911 GULF SEAL IPOD IPOD-160 31026-31244 53-490 DEMUX 16912 GULF SEAL IPOD IPOD-161 31244-31467 490-936 DEMUX 16913 GULF SEAL IPOD IPOD-162 31467-31688 936-378 DEMUX 16914 GULF SEAL IPOD IPOD-163 31688-31912 378-825 DEMUX 16915 GULF SEAL IPOD IPOD-164 31912-32133 825-268 DEMUX 16916 GULF SEAL IPOD IPOD-165 32133-32355 268-711 DEMUX 16917 GULF SEAL IPOD IPOD-166 32355-32576 711-153 DEMUX 16918 GULF SEAL IPOD IPOD-167 32576-32798 153-598 DEMUX 16919 GULF SEAL IPOD IPOD-168 32798-33019 598-40 DEMUX 16920 GULF SEAL IPOD IPOD-169 33019-33241 40-484 DEMUX 16921 GULF SEAL IPOD IPOD-170 33241-33463 484-927 DEMUX 16922 GULF SEAL IPOD IPOD-171 33463-33686 927-374 DEMUX 16923 GULF SEAL IPOD IPOD-172 33686-33909 374-819 DEMUX 16924 GULF SEAL IPOD IPOD-173 33909-34110 819-222 DEMUX