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Data Set #039

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About the Data

About the frequency of large earthquakes

    Earthquakes (ground shaking) are caused by relatively fast movement along breaks in the Earth's crust, known as faults. In general, the more movement or displacement along a fault during an event, the greater the amount of ground shaking. Ground shaking is also affected by the properties of the Earth materials through which the vibrations pass; weak soils or loose sediment can enhance ground shaking.

    There are several different methods of measuring the size of an earthquake; a popular measure of earthquake size is the Richter magnitude. The Richter magnitude is based upon the amplitude (height) of ground shaking as recorded on a machine (a seismometer). Earthquakes vary in size over many orders of magnitude, and therefore the Richter scale is logarithmic to accommodate this wide variation in earthquake sizes. On the logarithmic Richter scale, a magnitude 7 earthquake is 10 times bigger than a magnitude 6 earthquake. Earthquakes that are magnitude 7 or above are often (though not always) very damaging earthquakes.

    The United States Geological Survey has compiled information on the number of earthquakes around the globe that have equaled or exceeded magnitude 7. The data are expressed as the number of earthquakes per year for each year starting in 1900. Note that the older data in this table are somewhat suspect, because seismometers did not systematically record earthquakes in a standardized fashion with good spatial coverage until the 1930's or later.

    What is the recurrence interval for large earthquakes globally? How often do large earthquakes occur? These questions are fundamental to understanding the impact of earthquakes on the human population. We can better visualize the data using a histogram of the frequency of large earthquakes per year. This particular graph is a little challenging, as it shows the frequency of rates of earthquakes.

    The data are unimodal, with a mean around 20 large earthquakes per year on Earth. There is a wide variation in earthquake rate, from a low of 6 quakes per year in 1986 to a high of 41 quakes per year in 1943. The distribution of earthquake rates is skewed slightly to the right.

    Students could be queried also about the temporal variation in large earthquakes.  General information on earthquakes can be found at the US Geological Survey's website: http://www.usgs.gov/ .

Reference: United States Geological Survey, published in the New York Times. We haven't found the ultimate source yet.

     
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year

number of quakes >7.0

1900

13

1901

14

1902

8

1903

10

1904

16

1905

26

1906

32

1907

27

1908

18

1909

32

1910

36

1911

24

1912

22

1913

23

1914

22

1915

18

1916

25

1917

21

1918

21

1919

14

1920

8

1921

11

1922

14

1923

23

1924

18

1925

17

1926

19

1927

20

1928

22

1929

19

1930

13

1931

26

1932

13

1933

14

1934

22

1935

24

1936

21

1937

22

1938

26

1939

21

1940

23

1941

24

1942

27

1943

41

1944

31

1945

27

1946

35

1947

26

1948

28

1949

36

1950

29

1951

21

1952

17

1953

22

1954

17

1955

19

1956

15

1957

34

1958

10

1959

15

1960

22

1961

18

1962

15

1963

20

1964

15

1965

22

1966

19

1967

16

1968

30

1969

27

1970

29

1971

23

1972

20

1973

16

1974

21

1975

21

1976

25

1977

16

1978

18

1979

15

1980

18

1981

14

1982

10

1983

15

1984

8

1985

15

1986

6

1987

11

1988

8

1989

7

1990

13

1991

10

1992

23

1993

16

1994

15

1995

25

1996

22

1997

20

1998

16

1999

11

 

Bin

Frequency

5-10

6

10-15

16

15-20

27

20-25

28

25-30

14

30-35

5

35-40

3

40-45

1

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