EARTHQUAKE FAQ

UNITED STATES EARTHQUAKES

Q: Are there particular places in the United States where earthquakes are more likely to occur?

A: Although it is conceivable that a small earthquake could occur almost anywhere, earthquakes are much more common in some regions than others. Of the fifty United States, Alaska has the most earthquakes and the largest earthquakes; California probably has the second most, including some very large quakes.

Q: Are earthquakes in eastern North America different than earthquakes on the west coast?

A: In most ways, No. However, earthquakes are much less common in the interior of tectonic plates, as in the Eastern U. S., than at the edges, as in California, Oregon, and Washington. In addition, cold, high-density gneiss and granulite form the bedrock for most of the U. S. east coast. This type of rock transmits seismic waves very efficiently. Therefore, people as far south as Pennsylvania and Maryland may notice the occasional earthquake occurring in the Canadian province of Quebec, whereas an event of similar magnitude in Western California would go unnoticed in the closest states.

Q: Are the biggest earthquakes in the U. S. in California?

A: No. The biggest earthquakes in the U.S. occur in Alaska; in fact, the Alaskan earthquake of 27 March 1964, with a magnitude Mw of 9.2, was the second biggest earthquake to occur anywhere in the world in the 20th century. Alaska is also the U. S. state where earthquakes are the most common, i.e., earthquakes occur more frequently than in any other state.

Q: Are the biggest earthquakes in the contiguous U.S. in California?

A: No. Three huge earthquakes occurred between December 1811 and February 1812 near New Madrid, Missouri, which lies near where Missouri, Tennessee, and Arkansas meet. These earthquakes were large enough to change the course of the Mississippi River; they were felt as far away as Washington, D.C., and they rang church bells in Boston, Massachusetts. Although Charles Richter didn't invent the magnitude scale until 1935, the New Madrid earthquakes probably had magnitudes of about 8.5; larger than any historical earthquakes in California. It is true, however, that very large earthquakes (magnitude greater than 8) are more common in California than any other state in the continental U.S.
Saint Louis University Earthquake Center and more information on the New Madrid earthquakes.

Q: Considering the risk from earthquakes, is it safe to move to California?

A: Yes, but like any place you live, you need to exercise some common sense about where you live and work. Before finding a home in California you might want to find out where the known active faults are, and avoid living in poorly constructed, stone buildings, or in structures situated on steep slopes.

Q: When will the "Big One" occur in California?

A: First, what is the "Big One?" Research indicates that most areas of the world will experience earthquakes only up to a certain maximum size; this size depends on local stress levels, fault geometry, etc. Furthermore, earthquakes of the maximum size occur sporadically at some fixed interval; this interval is not so precise that you can predict the "big ones," but by analyzing the record of large earthquakes you can get some idea of how often they occur.

In California, the maximum size appears to be about magnitude 8; about the size of 1857 and 1906 quakes. Furthermore, careful studies of the effects of large quakes on rivers and creeks indicate that there have been numerous such maximum-size quakes over the past 1500 years or so, with a repeat interval of approximately 60 to 100 years. However, sometimes the interval between large quakes is greater than this; sometimes it is less. Since the last maximum-size California earthquake was in 1906, we are now "due" for another; but while it could happen tomorrow, it could hold off for another 100 years.

Q: What other states have earthquakes?

A: All 50 states occasionally have earthquakes. However, like Texas, many states never have experienced very large, very damaging earthquakes in historical times. The states which have had earthquakes with magnitudes of 7 or above are Alaska, California (largest were 1857 and 1906), Hawaii (1868, 1975), Idaho (1983), Missouri-Tennessee (1811-1812), Montana (1959), Nevada (1915, 1932, 1954), South Carolina (1886), and Washington (1949).

Q: What was the most destructive earthquake in U. S. history?

A: In terms of lives lost, U.S. earthquakes have not been nearly as serious as quakes elsewhere in the world. Only four U.S. earthquakes killed more than 100 people; these were the 1906 San Francisco earthquake (700 deaths), the 1933 Long Beach, California earthquake (115 deaths), the 1946 Alaska earthquake (131 deaths), and the 1964 Alaska earthquake (131 deaths).

As to property damage, the two most serious U.S. earthquakes were the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake. In terms of current dollars, each did about six billion dollars damage.

U.S. Earthquakes
Where Damage Exceeded 100 Million 1990 Dollars

Date	Damage (millions of $)	Damage Adjusted to 1990 (millions of $)	Location
1906 April 18	400	5,800	San Francisco, CA
1933 March 11	40	402	Long Beach, CA
1935 October 19	19	181	Helena, MT
1946 April 1	25	168	Alaska
1949 April 13	25	137	Seattle, WA
1964 March 28	540	2,276	Alaska
1971 February 9	553	1,784	San Fernando, CA
1987 October 1	358	412	Whittier, CA
1989 October 18	5,600	5,902	Loma Prieta

Source: Catalog of Significant Earthquakes 2150 B. C. - 1991 A. D., National Geophysical Data Center A, U. S. Dept. of Commerce, Boulder, Colorado, 1992.

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Last modified: 26 Jul 2001 13:34
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EARTHQUAKE FAQ

UNITED STATES EARTHQUAKES

U.S. EarthquakesWhere Damage Exceeded 100 Million 1990 Dollars

U.S. Earthquakes
Where Damage Exceeded 100 Million 1990 Dollars