Abstract
The hard observational facts of seismology have been and are being used to test and to develop the hypotheses of continental drift, sea-floor spreading, plate tectonics, and related matters. Three kinds of evidence particularly important in such studies are (1) seismicity, (2) focal mechanisms, and (3) wave propagation and inferred earth structure. The quality and quantity of such evidence, especially types (1) and (2), increased rapidly in the 1960s as a result of new observational facilities, particularly the World-Wide Standardized Seismograph Network established, with the cooperation of many countries, by ESSA under the VELA Program of the federal government. In general, evidence from seismology strongly supports and contributes greatly to the new tectonics. Many major and previously unexplained observations, such as the spatial distribution of deep earthquakes and the worldwide pattern of seismicity and focal mechanisms, fall neatly into place. No serious obstacles to the new tectonics are found in seismology. Present research on this topic is directed toward development and refinement of the model to explain the seismologic observations in greater detail. Many major, challenging topics for investigation remain.
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