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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 33 (1949)

Issue: 12. (December)

First Page: 2059

Last Page: 2060

Title: Offshore Seismic Problems Affecting Geologic Evaluation: ABSTRACT

Author(s): Curtis H. Johnson, Robert B. Galeski

Article Type: Meeting abstract


During 1948 and 1949 joint seismic operations were conducted offshore the coast of California by a group averaging 14 oil companies employing two crews for a total of 13 crew-months. This joint effort was required by the California Division of Fish and Game to minimize damage to fish. During this work a notable variety of problems were encountered.

It is concluded that geophysical methods other than seismic are not of sufficient resolving powers in the California offshore areas to detail structure.

Problems peculiar to marine work are: secondary energy bursts, circumvented by either firing charges shallow or jetting them into the bottom; multiple reflections from the ocean floor, which result in apparent reflections below basement for shallow water, unusable records in water around 500 feet deep and complete repetitions of section for very deep water; occurrence of high angle "erratics," interpreted in terms of faulting, buried stream channels, and bottom irregularities; constant velocity in deep water, handled by projecting shots and detectors to the ocean floor; surveying over vast expanses of water, accomplished by the use of shoran; and timing the programming of specific lines to best overcome bad Previous HitweatherNext Hit, ocean traffic Previous HithazardsTop, and damage to fish.

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Tactics designed to facilitate geological interpretation involve density of lines and shot points along lines and the use of L-spreads to obtain strike and dip. Factors in the interpretation of seismic results are diagnostic unconformities known in adjacent areas, submarine coring, regional submarine topography, and data from supplementary geophysical methods.

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Copyright 1997 American Association of Petroleum Geologists