This is the fourth in a series of review papers dealing with technological developments in exploration and with geophysical research at universities and industrial laboratories. Among the developments in exploration, the use of reproducible recording of seismic records continues to grow, with a trend toward digitizing reflection data for further computation. Refined digital methods have been developed for computation of synthetic seismograms. Well-logging developments have included the appearance of a resistivity logger capable of being pumped down the drill pipe; the availability of more tools for logging seismic velocity, accompanied by laboratory investigations of the manner in which seismic velocity is affected by porosity, fluid content, and other factors; commercial use of the scattered-gamma ray density tool; and further interest in gamma ray spectral logs. Remarkable advances have been made in the techniques of gravity measurement aboard surface vessels and aircraft, although the results are not directly applicable to prospecting. The proton precession magnetometer is being used in commercial air-borne surveys, but the rubidium vapor magnetometer is not available as an exploration tool. The development of a Doppler-positioned navigation method has greatly facilitated air-borne surveys. A ship-borne seep-detector has been outfitted for exploration in water-covered areas. A review is presented of research on all phases of geophysics at academic institutions in the United States, including laboratory experiments, field measurements, and theory. The review also gives partial coverage of geophysical research at European laboratories, including a discussion of Soviet research as gauged by recent visits to a number of research laboratories in the Soviet Union.

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