This is the fifth of a series of review papers on the subject of research and progress in geophysical exploration.

In the three years since the last presentation of this

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nature the most salient trend in geophysical exploration has been one toward full utilization of the available data. Modern data processing equipment and techniques of analysis are being introduced while theoretical studies attack seismic stumbling blocks like multiple reflections, ghosts, diffractions, and scattering.

The vistas of innovation opened by digital recording and processing spurred several operators to intensive study of the possibilities and the cost picture of digital methods. The use of seismic energy sources other than conventional dynamite explosions is increasing, as are special shooting techniques aimed at ghost elimination. Synthetic seismograms from continuous velocity logs are being brought to bear increasingly on stratigraphic problems; inverse convolution techniques seek to reconstruct the CVL from better quality seismograms while research on synthetic seismograms continues at a high level.

Applications of the rubidium vapor magnetometer have been reported both in exploration for minerals and for oil. The accuracy of the airborne gravimeter has been improved, but is still insufficient for exploration purposes. The shipborne companion instrument is in use as an exploration tool.

Existing well logging methods have undergone further development with modern methods of electronic data processing being applied increasingly. A new logging technique, nuclear magnetism logging, promises to give an indication of porosity above a certain pore size. The attenuation of the signal in acoustic well logging is being used to locate fractures and to evaluate cement bondings.

There is a new interest in natural electromagnetic fields and the degree of coherence between electric and magnetic field components.

Several of the projects sponsored by Vela Uniform, the U. S. Government Project created to achieve adequate detection of underground nuclear blasts by the U. S. Atomic Energy Commission and other agencies, have exploration potential (e.g., long seismic and electrical profiles, theoretical studies, certain instrumental developments).

Academic research in all branches of geophysics is active, with major benefits deriving from modern data handling techniques, and the new defense interest in the earth sciences providing many opportunities.

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