U.S. DEPARTMENT OF THE INTERIOR / U.S. GEOLOGICAL SURVEY U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES DDS-13 International Phase of Ocean Drilling Seismic Line 1 Demultiplexed Data Cape Hatteras to Mid-Atlantic Ridge PROCESSING HISTORY ABSTRACT In an ongoing effort to reduce the amount of data loss due to old, deteriorating magnetic tapes, data from a 3400-km-long multichannel seismic-reflection line collected between Cape Hatteras and the Mid-Atlantic Ridge were demultiplexed, compressed, and output in an industry-standard SEG-Y format. INTRODUCTION A 3400-km-long multichannel seismic-reflection profile (Line 1) extending from Cape Hatteras to the rift valley of the Mid- Atlantic Ridge was recorded in 1974 by Digicon, Inc. Two small lines totaling 80 km (Lines A and B), connecting the main line to two coastal wells in North Carolina were simultaneously acquired. The experiment was part of the International Phase of Ocean Drilling (IPOD) and was jointly funded by the U.S. Geological Survey (USGS) and the National Science Foundation's Deep Sea Drilling Project (DSDP). The data were recorded from the marine vessel Gulf Seal using a Texas Instruments DFS III recording system. A tuned airgun array totaling 1,700 cubic inches was used to generate seismic source signals generally every 50 m, and a streamer with 48-nonlinearly spaced hydrophone groups was used to detect the returning seismic signals. A summary of the shooting and recording parameters is shown in table 1. Segments of the western half of the data totaling approximately 1,520 km, or slightly less than half of the line, were processed by Geophysical Services, Inc. (GSI), in the spring of 1975, and a geologic overview of this experiment can be found in Grow and Markl (1977). Copies of the demultiplexed field tapes are currently stored at the USGS seismic data processing center in Denver, Colorado. DEMULTIPLEXING AND COMPRESSION Testing revealed that the data on the original field tapes were deteriorating. To prevent any further loss of data, we demultiplexed the original 631 field tapes and transfered the output to 183 new magnetic tapes at 6250 bpi in an industry standard SEG-Y format (Barry and others, 1975). Our efforts 1 yielded a data compression ratio of more than 3 to 1. Although some of the field tapes had segments in which the magnetic oxide had actually fallen off, we preserved as much of the data as possible. Close monitoring of the processing system during demultiplexing enabled the computer operators to prevent any further data loss (or misreading of data) due to parity read errors. When excessive parity errors were found on input tapes, operators either passed the tapes through a tape cleaner or, in more severe cases, made a bit-for-bit tape copy. Less than 0.2 percent of the original data could not be recovered during demultiplexing. Shown in appendix I are the slot numbers, shotpoint ranges, and field file ranges of all the output tapes. Slot numbers refer to storage-location numbers within the Denver tape library, and reel numbers refer to the database reference number of our processing system. Observers' notes are also archived at the Denver processing center and can be obtained from the authors. 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. 2 Table 1 -- Field parameters used in survey DATA ACQUISITION RECORDING PARAMETERS Instrument DFS III Near Offset Distance 346 m Spacing: traces 48 - 25 50 m Spacing: traces 25 - 24 75 m Spacing: traces 24 - 1 100 m Sample Rate 4 ms Recording length 10 - 12 s Fold Coverage 36 Gun Depth 9 m Airgun Array Displacement 1700 cu. in. Filter, 18dB/octave slope 6 - 12 Hz 3 NOTE: CD-ROM VOL numbers may change during production. APPENDIX I - USGS Tape Library Listing of IPOD Demultiplexed Tapes Library Slot Reel ID Shot Points Files CD-ROM VOL 4567 IPOD1A 101-228 1-256 1 4566 IPOD1B 228-422 256-643 1 6453 IPOD1C 422-549 643-897 1 4565 IPOD1D 549-600 897-999 1 13244 IPOD-1 600-727 999-254 2 13245 IPOD-2 727-854 254-508 2 13246 IPOD-3 854-984 508-768 2 13247 IPOD-4 984-1102 768-4 2 13248 IPOD-5 1102-1229 5-258 3 13249 IPOD-6 1229-1356 258-512 3 13250 IPOD-7 1356-1482 512-764 3 13251 IPOD-8 1482-1575 764-950 3 13252 IPOD-9 1539A-1668 1-260 4 13253 IPOD-10 1668-1795 260-513 4 13254 IPOD-11 1795-1921 513-766 4 13255 IPOD-12 1921-2051 766-26 4 13256 IPOD-13 2051-2067 26-58 5 13257 IPOD-14 2068-2194 59-312 5 13258 IPOD-15 2194-2321 312-566 5 13259 IPOD-16 2321-2348A 566-98 5 13260 IPOD-17 2348A-2478 98-357 6 13261 IPOD-18 2478-2585 357-572 6 13262 IPOD-19 2586-2740 573-882 6 13263 IPOD-20 2740-2881 882-164 6 13264 IPOD-21 2882-3057 165-516 7 13265 IPOD-22 3057-3102 516-606 7 13266 IPOD-23 3103-3274 607-950 7 13267 IPOD-24 3274-3407 950-336 7 13268 IPOD-25 3407-3579 336-680 7 13269 IPOD-26 3579-3753 680-28 8 13270 IPOD-27 3753-3925 28-372 8 13271 IPOD-28 3925-3940 372-402 8 13272 IPOD-29 3940-4111 403-743 8 13273 IPOD-30 4111-4281 743-83 8 13274 IPOD-31 4281-4414A 83-10 9 13275 IPOD-32 4414A-4583 10-348 9 13276 IPOD-33 4583-4779 349-739 9 13277 IPOD-34 4779-4972 739-125 9 13278 IPOD-35 4972-5058 125-298 9 13279 IPOD-36 5059-5256 299-694 10 13280 IPOD-37 5256-5454 694-90 10 13281 IPOD-38 5454-5652 90-485 10 13282 IPOD-39 5652-5850 485-881 10 13283 IPOD-40 5850-6047 881-275 11 13284 IPOD-41 6047-6246 275-673 11 13285 IPOD-42 6246-6422 673-26 11 13286 IPOD-43 6422-6621 27-424 11 13287 IPOD-44 6621-6748 424-677 11 13288 IPOD-45 6748-6918 678-18 12 4 NOTE: CD-ROM VOL numbers may change during production. APPENDIX I - USGS Tape Library Listing of IPOD Demultiplexed Tapes Library Slot Reel ID Shot Points Files CD-ROM VOL 13289 IPOD-46 6918-7100 18-401 12 13290 IPOD-47 7100-7294 401-790 12 13291 IPOD-48 7294-7483 790-168 12 13292 IPOD-49 7483-7677 168-555 12 13293 IPOD-50 7677-7681 555-564 12 16597 IPOD-51 7682-7935 565-71 13 16598 IPOD-52 7935-8188 71-577 13 16599 IPOD-53 8188-8441 577-83 13 16600 IPOD-54 8441-8695 83-592 13 16601 IPOD-55 8695-8948 592-98 14 16602 IPOD-56 8948-8967 98-135 14 16603 IPOD-57 8967-9220 135-641 14 16604 IPOD-58 9220-9295 641-812 14 16605 IPOD-59 9296-9556 813-334 14 16606 IPOD-60 9556-9810 334-841 14 16607 IPOD-61 9810-10063 841-347 15 16608 IPOD-62 10063-10316 347-853 15 16609 IPOD-63 10316-10569 853-360 15 16610 IPOD-64 10569-10823 360-867 15 16611 IPOD-65 10823-10861 867-943 15 16612 IPOD-66 10861-11108 943-438 16 16613 IPOD-67 11108-11117 438-456 16 16614 IPOD-68 11118-11328 457-417 16 16615 IPOD-69 11328-11581 417-923 16 16616 IPOD-70 11581-11827 923-416 16 16617 IPOD-71 11827-12074 416-910 16 16618 IPOD-72 12074-12320 910-402 17 16619 IPOD-73 12320-12567 402-895 17 16620 IPOD-74 12567-12820 895-402 17 16621 IPOD-75 12820-12834 402-430 17 16622 IPOD-76 12835-13057 431-876 17 16623 IPOD-77 13057-13279 876-319 18 16624 IPOD-78 13279-13501 319-764 18 16625 IPOD-79 13501-13722 764-206 18 16626 IPOD-80 13722-13944 206-650 18 16627 IPOD-81 13944-14111 650-984 18 16628 IPOD-82 14112-14363 985-487 19 16629 IPOD-82B 14242-14258 246-277 19 16630 IPOD-83 14363-14616 487-993 19 16631 IPOD-84 14616-14867 993-496 19 16632 IPOD-85 14867-15120 496-1 19 16633 IPOD-86 15120-15371 1-504 20 16634 IPOD-87 15371-15624 504-10 20 16635 IPOD-88 15624-15875 10-512 20 16636 IPOD-89 15875-16128 512-17 20 16637 IPOD-90 16128-16249 17-259 20 16638 IPOD-91 16250-16454 260-229 21 16639 IPOD-92 16454-16706 229-733 21 16640 IPOD-93 16706-16959 733-240 21 5 NOTE: CD-ROM VOL numbers may change during production. APPENDIX I - USGS Tape Library Listing of IPOD Demultiplexed Tapes Library Slot Reel ID Shot Points Files CD-ROM VOL 16641 IPOD-94 16959-17212 240-746 21 16642 IPOD-95 17212-17465 746-252 21 16643 IPOD-96 17465-17717 252-755 22 16644 IPOD-97 17717-17970 755-261 22 16645 IPOD-98 17970-18222 261-765 22 16646 IPOD-99 18222-18475 765-271 22 16647 IPOD-100 18475-18726 271-773 22 16648 IPOD-101 18726-18979 773-279 23 16649 IPOD-102 18979-19197 279-716 23 16650 IPOD-103 19198-19420 717-161 23 16651 IPOD-104 19420-19643 161-607 23 16652 IPOD-105 19643-19865 607-51 23 16653 IPOD-106 19865-20087 51-496 24 16654 IPOD-107 20087-20309 496-939 24 16655 IPOD-108 20309-20531 939-383 24 16656 IPOD-109 20531-20753 383-827 24 16657 IPOD-110 20753-20970 827-262 25 16658 IPOD-111 20970-21180 262-682 25 16659 IPOD-112 21181-21403 683-128 25 16660 IPOD-113 21403-21626 128-573 25 16661 IPOD-114 21626-21847 573-16 26 16662 IPOD-115 21848-22053 17-427 26 16663 IPOD-116 22053-22276 427-874 26 16664 IPOD-117 22276-22498 874-317 26 16665 IPOD-118 22498-22719 317-759 27 16666 IPOD-119 22719-22941 759-204 27 16667 IPOD-120 22941-23128 204-257 27 16668 IPOD-121 23128-23346 257-694 27 16669 IPOD-122 23346-23567 694-135 28 16670 IPOD-123 23567-23730 135-462 28 16671 IPOD-124 23732-23954 465-910 28 16672 IPOD-125 23954-24173 911-347 28 16673 IPOD-126 24173-24391 348-784 28 16674 IPOD-127 24392-24614 785-229 29 16675 IPOD-128 24614-24836 229-673 29 16676 IPOD-129 24836-25057 673-115 29 16677 IPOD-130 25057-25101 115-204 29 16678 IPOD-131 25102-25325 205-651 29 16679 IPOD-132 25325-25544 651-90 30 16680 IPOD-133 25544-25767 90-535 30 16885 IPOD-134 25767-25989 535-979 30 16886 IPOD-135 25989-26210 979-422 30 16887 IPOD-136 26210-26432 422-866 31 16888 IPOD-137 26432-26647 866-296 31 16889 IPOD-138 26647-26870 296-741 31 16890 IPOD-139 26870-27091 741-184 31 16891 IPOD-140 27091-27314 184-630 32 16892 IPOD-141 27314-27536 630-74 32 16893 IPOD-142 27536-27759 74-520 32 6 NOTE: CD-ROM VOL numbers may change during production. APPENDIX I - USGS Tape Library Listing of IPOD Demultiplexed Tapes Library Slot Reel ID Shot Points Files CD-ROM VOL 16894 IPOD-143 27759-27766 520-533 32 16895 IPOD-144 27766-27988 533-977 32 16896 IPOD-145 27988-28211 977-423 33 16897 IPOD-146 28211-28433 423-867 33 16898 IPOD-147 28433-28655 867-311 33 16899 IPOD-148 28655-28878 311-757 33 16900 IPOD-149 28878-29100 757-201 34 16901 IPOD-150 29100-29322 201-646 34 16902 IPOD-151 29322-29544 646-90 34 16903 IPOD-152 29544-29768 90-537 34 16904 IPOD-153 29768-29886 537-774 35 16905 IPOD-154 29886-29911 774-824 35 16906 IPOD-155 29912-30133 825-269 35 16907 IPOD-156 30134-30356 269-713 35 16908 IPOD-157 30356-30580 713-162 35 16909 IPOD-158 30580-30803 162-608 36 16910 IPOD-159 30803-31026 608-53 36 16911 IPOD-160 31026-31244 53-490 36 16912 IPOD-161 31244-31467 490-936 36 16913 IPOD-162 31467-31688 936-378 36 16914 IPOD-163 31688-31912 378-825 37 16915 IPOD-164 31912-32133 825-268 37 16916 IPOD-165 32133-32355 268-711 37 16917 IPOD-166 32355-32576 711-153 37 16918 IPOD-167 32576-32798 153-598 38 16919 IPOD-168 32798-33019 598-40 38 16920 IPOD-169 33019-33241 40-484 38 16921 IPOD-170 33241-33463 484-927 38 16922 IPOD-171 33463-33686 927-374 39 16923 IPOD-172 33686-33909 374-819 39 16924 IPOD-173 33909-34110 819-222 39 7