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Development of the plate tectonic theory
National defense, seismology, and earthquakes
Meanwhile, the U.S. military funded development of new, advanced seismometers to help monitor Soviet nuclear tests. By the late 1950s, the World Wide Standardized Seismographic Network had been deployed in over 40 countries.
The network operated 24 hours/day (because the Soviets didn't announce tests in advance).
The network recorded occasional nuclear tests, but also seismic waves from every moderate to strong earthquake anywhere in the world.
Data were made available to seismologists, permitting more accurate location of earthquakes.
By the early 1960s, scientists recognized that earthquakes occur mainly in narrow belts along oceanic trenches, ridges, and fracture zones, and also throughout Alpine-Himalayan belt.
By 1967, most of the theory of plate tectonics was in place: The outer shell of Earth, called its lithosphere, is broken up into numerous rigid plates. New plate material forms where plates spread apart, and is consumed where plates converge. Earthquakes (and active volcanoes) are concentrated at the boundaries of these plates.
updated January 28, 2002
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