Major offshore areas widely developed around the Korean Peninsula are in the Yellow Sea off the west coast, East China Sea off the south coast, and in narrow belts in the Japan Sea off the east coast. Geologic and geophysical surveys in these Korean offshore areas have been carried out since 1966 by the Geological and Mineral Institute of Korea (GMIK) and since 1969 by oil companies who obtained concessions on seven blocks from the Korean government.

The GMIK has conducted reconnaissance seismic and magnetic surveys for general study of submarine geology. Oil companies have conducted preliminary and detail seismic, magnetic, and gravimetric surveys. Wildcat drilling was started in 1972 and four holes were drilled by three oil companies.

Submarine geology of the offshore area can be summarized as follows. The Yellow Sea area has Tertiary sedimentary rocks with thicknesses of more than 1,000 m with several basin structures separated by uplifted basement or intrusive igneous rocks.

The East China Sea and southern part of Japan Sea have Tertiary sedimentary rocks with thicknesses of more than 2,000 m with northeast-southwest zonal structure and folded and faulted structures in Tertiary beds.

In the Japan Sea area Tertiary sedimentary rock in Pohang offshore area is less than 1,000 m thick and extends northward almost 100 km. Sedimentary rocks, more than 3,000 m thick and of probable Cenozoic age, are present on the continental slope.

Petroleum potentials in offshore Tertiary strata must be studied further before final conclusions can be reached. Even so, rocks with high-organic content occur in the Yellow Sea area, and in the East China Sea and the Japan Sea areas good reservoir rock and potential structures for hydrocarbon accumulation have been detected. Further drilling work is recommended to discover hydrocarbons and to reevaluate the submarine geology and structure.

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