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Deep Seismic Sounding database: 1956 Caspian Sea DSS experiment

(This is a topic from our old WWW site. Presently database is not on-line, but still exists on our network. For discussion please send e-mail to mike@synapse.ru)

DSS experiments on Caspian Sea where arranged in 1956 as preparation for the extensive DSS investigations planned by program ofInternational Geophysical Year in 1957-1958 on transition zone between Asia continent and Pacific ocean. This experiments were fulfilled successfully. Academician G.A.Gamburtsev and his school developed DSS method in preceeding years. Earth crust investigations were made on Pamyr, Tjan-Shan and in Turkmenia regions. The main aim of DSS Caspian experiments was to apply the DSS technics to sea conditions. Main features of DSS method for both land and sea studies are following. Line of investigations has to be covered by close spaced recording and shooting points to provide full set of reverse and overlap time distance curves for refraction waves from main layers in the earth crust. Amplitude and frequency parameters of waves had to be studied, and special attention for amplitude control had to be undertaken. The most reliable data on Earth crust structure were expected by precise interpretation offull and undistorted picture of seismic waves. The most distinctive feature of the marine DSS technics was the converted recording-shooting procedure, and seismic waves recording on depth by hydrophones or seismographs. The Caspian Sea

experiment was the first in the world example of large scale marine DSS investigations, and many features of DSS technics were tested and approved by this way. Similar experiments were followed later by scientists from USSR and another countries during many years, and continues up to now. DSS investigations on Caspian Sea were fulfilled in 1956 by Institute Physics of the Earth Academy of Sciences USSR in cooperation to Institute of Oceanology Academy of Sciences USSR, All-Union Geophysical Research Institute

Ministry of Geology of USSR and Oil Institute of Azerbaidjan Republic. A head of joint expedition was prof. E. J. Galperin, interpretation leader was prof. J. P. Kosminskaja. Four research ships took part in recording of seismic waves, owned by participating institute: Suvorov, Majakovsky, Morskoj Geolog, and Geophysik. Ships were anchored, and hydrophones were placed on sea bottom during seismic recordings. Shots were made by Navy trawler. Depth bombs were used 135 kilos TNT weight. The depth of explosion was taken 50 meter or less in shallowest sea. Land multichannel recording seismic stations were arranged on Zhiloy island (Central Caspian), near Krasnovodsk city on eastern shore, near Gamerat village (Lencoran city region, south-western shore).

Shot schedule was prepared before the observations on some profile. Exact timing was provided by marine contact chronometers checked by radio signals. Radionavigation systems were used for positioning the ships near the shores. Record of sound water waves were studied for location too.

Network of DSS lines consisted of 11 radial and ring profiles centered on recording stations Zhiloy island and Krasnovodsk city. On the main profiles 1, 2 and 3 shootings were made two or three times by new positions of marine recording stations. During 17 working days 367 shots were made along the profiles 2400 km total length.

The manual technics for seismic data proceedings was used, wide spread in seismic survey and DSS in 50s years. Tracing of some seismic waves was undertaking using separate records. Seismic sections were produced, used reverse and overlap time curves in the frame 2D permanent velocity model.

Content and form of presentation of original data in publications were not enough to estimate the reliability of tracing the seismic waves, and it did not allow to produce the independent interpretation. Some attempts of reinterpretation were undertaken in 90s, and were based on previous authors' versions of time distances curves. As a results, main features of the old sections were approved.

INTAS-94-1843 grant, devoted to studying of seismic structure of South Caspian Basin, mentioned as one of objectives to create anarchive and a data base of the DSS data, using new digitizing and processing technique.

Three kind of question had to be solved:

  1. Development od hardware and software solutions for old paperrecords digitizing, database structure development, and its adjustmentto DSS conditions.
  2. Studies of old paper records archives,search for numericaldata onexperiments parameters to fill the database relations. Preparationoforiginal materials and some results achieved before to be enteredinto a digital archive in a form of computer images (maps, record sections,paper records).
  3. Digitizingof DSSseismograms(wave forms) forms,providing binary compatibility for main research computer platforms:IBM PC and SUN, providing user interface to convert data for viewableformat (SAC, SEGY).

One can find more about a database in http://www.synapse.ru/eng/products/dss

Recently an access to an archive of Caspian DSS data is provided from Internet. CS56 (Caspian Sea, 1956) file system contains waveform data in binary format with CSS-2.8 .wfdisc file descriptors, scanned images of the original paper records (in .pcx and .jpg formats, ASCII files with parameter information and experiment description. File structure hierarchy (unlike to relation database structure) is:

  1. Experiment profile,
  2. Recording stations,
  3. Explosion,
  4. Waveforms.

Also, old scanned record sections are represented as well for each profile.

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