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Putting Geophysical Insights to Work |
Today, long-standing human concerns for public safety have benefited from an understanding of plate tectonics . For example, since the advent of plate tectonic theory in the late 1960s, scientists have recognized that the San Andreas fault in California is the boundary separating two plates that are slowly sliding past each other. The Pacific plate, the largest in the world, is moving in a northwesterly direction past North America, dragging the rim of the continent with it. Californians have long known that their land was earthquake-prone. The understanding that they are living on a major plate boundary clarifies that earthquakes are inevitable, that it is only a question of "when", not "if" they will occur.
Although scientists cannot yet predict when earthquakes will occur, understanding the rate of plate movement and the pattern of earthquakes associated with the San Andreas fault has prompted the California state government to take specific precautionary measures. In 1975, California established a Seismic Safety Commission, which, among other responsibilities, reviews and updates the state's earthquake hazard mitigation plan.
On a national level, the Earthquake Hazards Reduction Act in 1977 established the National Earthquake Hazards Reduction Program (NEHRP) to reduce earthquake hazards throughout the United States, something that earthquake specialists had been calling for since the great Alaskan earthquake of 1964. Research carried out by NEHRP participants influences not only programs of public education but also the development of seismic standards for the design and construction of buildings and other structures. One significant design change to the Uniform Building Code, for example, involves the principle of base isolation, in which a structure is supported by a number of bearing pads that are placed between the structure itself and its foundation, or base. As the ground moves in one direction, a structure on a fixed base lags behind, effectively going in the opposite direction; given the nature of earthquake ground waves, this means a structure actually vibrates back and forth, in many directions. If its base is isolated by intervening bearing pads, however, the pads themselves absorb the vibration and the building essentially remains stationary. Because of similar geologic hazards both Japanese and Californians are leaders in developing strengthened construction codes for, among other things, public schools, bridges, hospitals, and dams.
In addition to its relevance to public safety, the advent of plate tectonics theory has been a boon to essential economic activities such as mining and petroleum exploration. Since the 1970s, prospecting for oil and natural gas, for example, has been enhanced by the development and continued refinement of paleogeographic (literally "fossil" geography) maps that can help identify ancient environments that were conducive to the formation and preservation of petroleum sources.
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