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Kansas Geological Survey, Public Information Circular (PIC) 3
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Where Earthquakes Occur

About 98 percent of all earthquakes occur in well-defined zones around the world, corresponding with the boundaries of the tectonic plates (Fig. 2). Seventy-five percent of the earthquakes occur in the zone around the Pacific Ocean. Twenty-three percent occur in a zone that ranges from the Mediterranean Sea through southern Asia and into China.

Figure 2--Principal earthquake zones of the earth (shaded in green). Over 90% of all earthquakes occur within these zones.

Zones ring the Pacific Ocean and bisect the Atlantic

The remaining two percent of earthquakes, which occur in the interiors of the major plates, can not be explained by plate tectonics. Notable examples of such earthquakes are the three very large New Madrid, Missouri, earthquakes that shook the eastern half of the United States in the winter of 1811-12. In terms of the amount of land shaken, these earthquakes were the largest in recorded U.S. history.

In a map published in 1971, seismologists classified regions of the U.S. according to the amount of earthquake damage they could expect to receive in any time period of several decades or more (Fig. 3). Large areas of California, Nevada, Utah, Idaho, and Yellowstone National Park are in the major damage zone, as are smaller areas in Missouri, South Carolina, and New England. Kansas, for the most part, is classified as a minor damage zone, although a zone of moderate damage runs across the state from Nebraska to Oklahoma. More recent research results have been incorporated nationwide into building codes that are used by architects and engineers.

Figure 3--Map of Earthquake risk.

Zones of high risk in California and Nevada, Utah and Idaho, and southeast Missouri

The amount of damage that occurs during an earthquake is closely related to the geology of an area. This relationship was first scientifically observed in the damage pattern of the 1906 San Francisco earthquake. The most severe damage occurred on "made land," where people used fill to raise land in areas that were formerly below sea level. Similarly, the major damage in San Francisco from the 1989 Loma Prieta earthquake was on made land, showing people's unfortunate tendency to ignore the lessons of history.

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Web version July 1996