Measuring Earthquakes
The seismologists Beno Gutenberg and Charles Francis Richter introduced measurementoftheseismicen-ergy released by earthquakes on a magnitude scale in 1935. Each increase of one unit on the scale represents a 10-fold increase in the magnitude of an earthquake. Seismographs are designed to measure different components ofseismic waves, such as wave type, intensity, and duration. This table shows the typical effects of earthquakes in various magnitude ranges.
|
MAGNITUDE |
EARTHQUAKE EFFECTS |
|
Less than 3.5 |
Generally not felt, but recorded. |
|
3.5-5.4 |
Often felt, but rarely causes damage. |
|
Less than 6.0 |
At most, slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions. |
|
6.1-6.9 |
Can be destructive in areas up to about 100 km (61 mi) across where people live. |
|
7.0-7.9 |
Major earthquake. Can cause serious damage over larger areas. |
|
8 or greater |
Great earthquake. Can cause serious damage in areas several hundred km across. |
Magnitudes given for pre-20th-century events are generally estimations from intensity data. In cases where no magnitude was available, the earthquake’s maximum intensity, written as a Roman numeralfrom I to XII, is given.
|
YEAR |
MAGNITUDE OR |
|
YEAR |
MAGNITUDE OR |
|
||
|
(AD) |
AFFECTED AREA |
INTENSITY |
DEATHS |
(AD) |
AFFECTED AREA INTENSITY |
DEATHS |
|
|
365 |
Knossos, Crete, |
XI |
50,000 |
1950 |
China-India border, |
8.6 |
1,526 |
|
|
Greece |
|
|
|
near Myanmar (Burma) |
|
|
|
526 |
Antioch, Syria |
unknown |
250,000 |
1960 |
Puerto Montt, Chile |
9.5 |
1,655 |
|
844 |
Damascus, Syria |
VIII |
50,000 |
1960 |
Agadir, Morocco |
5.7 |
10,000- |
|
847 |
Damascus, Syria |
X |
70,000 |
|
|
|
15,000 |
|
847 |
Mosul, Iraq |
unknown |
50,000 |
1964 |
Prince William Sound, |
9.2 |
128 |
|
856 |
Damghan, Iran |
unknown |
200,000 |
|
Alaska |
|
|
|
893 |
Daipur, India |
unknown |
180,000 |
1968 |
Khorasan, Iran |
7.3 |
12,000 |
|
893 |
Ardabil, Iran |
unknown |
150,000 |
1970 |
northern Peru |
7.9 |
66,000 |
|
893 |
Caucasus |
unknown |
82,000 |
1970 |
Yunnan province, |
7.5 |
10,000 |
|
1042 |
Palmyra, Syria |
X |
50,000 |
|
China |
|
|
|
1138 |
Aleppo, Syria |
unknown |
230,000 |
1972 |
Fars, Iran |
7.1 |
5,054 |
|
1201 |
Upper Egypt or |
IX |
1,100,000 |
1972 |
Managua, Nicaragua |
6.2 |
5,000 |
|
|
Syria |
|
|
1974 |
Yunnan province, China |
6.8 |
20,000 |
|
1268 |
Cilicia, Anatolia, |
unknown |
60,000 |
1974 |
North-West Frontier |
6.2 |
5,300 |
|
|
Turkey |
|
|
|
Province, Pakistan |
|
|
|
1290 |
Chihli, China |
unknown |
100,000 |
1975 |
Liaoning province, China |
7.0 |
2,000 |
|
1556 |
Shaanxi province, |
8.0 |
830,000 |
1976 |
Mindanao, Philippines |
7.9 |
8,000 |
|
|
China |
|
|
1976 |
Tangshan, China |
7.5 |
255,000- |
|
1667 |
Shemakha, |
unknown |
80,000 |
|
|
|
655,000 |
|
|
Azerbaijan |
|
|
1976 |
Guatemala City, |
7.5 |
23,000 |
|
1668 |
Shandong province, |
XII |
50,000 |
|
Guatemala |
|
|
|
|
China |
|
|
1976 |
Turkey-Iran border |
7.3 |
5,000 |
|
1693 |
Sicily, Italy |
7.5 |
60,000 |
1977 |
Bucharest, Romania |
7.2 |
1,500 |
|
1703 |
Jeddo, Japan |
unknown |
200,000 |
1978 |
Khorasan, Iran |
7.8 |
15,000 |
|
1727 |
Tabriz, Iran |
unknown |
77,000 |
1979 |
Colombia; Ecuador |
7.9 |
579 |
|
1730 |
Hokkaido, Japan |
unknown |
137,000 |
1980 |
Ech-Cheliff (El-Asnam), |
7.7 |
5,000 |
|
1731 |
Beijing, China |
unknown |
100,000 |
|
Algeria |
|
|
|
1739 |
China |
X |
50,000 |
1980 |
southern Italy |
6.5 |
3,114 |
|
1755 |
Lisbon, Portugal; |
8.7 |
70,000 |
1985 |
Michoacan, Mexico |
8.0 |
9,500- |
|
|
Spain; Morocco |
|
|
|
|
|
35,000 |
|
1755 |
Kashan, Iran |
unknown |
40,000 |
1988 |
Gyumri (Leninakan), |
6.8 |
25,000 |
|
1780 |
Tabriz, Iran |
unknown |
100,000 |
|
Armenia |
|
|
|
1783 |
Calabria, Italy |
unknown |
50,000 |
1990 |
Luzon, Philippines |
7.7 |
1,621 |
|
1811 |
New Madrid MO |
8.6 |
unknown |
1990 |
Rasht, Iran |
7.4 |
50,000 |
|
1812 |
Caracas, Venezuela |
7.7 |
26,000 |
1991 |
northern India |
6.8 |
2,000 |
|
1835 |
northern Japan |
7.6 |
28,300 |
1992 |
Flores Island, Indonesia |
7.5 |
2,500 |
|
1857 |
Tejon Pass, California |
7.9 |
1 |
1993 |
Latur, India |
6.2 |
9,748 |
|
1868 |
Arica, Chile |
9.0 |
25,000 |
1995 |
Sakhalin Island, Russia |
7.1 |
1,989 |
|
1868 |
Ecuador; Colombia |
7.7 |
70,000 |
1995 |
Kobe, Japan |
6.9 |
5,502 |
|
1883 |
Java, Indonesia |
unknown |
100,000 |
1997 |
eastern Iran |
7.3 |
1,567 |
|
1896 |
Sanriku, Japan |
8.5 |
27,000 |
1998 |
Feyzabad, Afghanistan |
6.6 |
4,000 |
|
1905 |
Calabria, Italy |
7.9 |
557 |
1999 |
Taiwan |
7.6 |
2,400 |
|
1905 |
Kangra, India |
7.5 |
19,000 |
1999 |
Golcuk, Turkey |
7.6 |
17,118 |
|
1906 |
off the coast of Ecuador 8.8 |
1,000 |
2001 |
El Salvador |
7.7 |
852 |
|
|
1906 |
Valparafso, Chile |
8.2 |
20,000 |
2001 |
Gujarat, India |
7.6 |
20,023 |
|
1906 |
San Francisco CA |
7.8 |
c. 3,000 |
2003 |
northern Algeria |
6.8 |
2,266 |
|
1907 |
southwestern Tajikistan 8.0 |
12,000 |
2003 |
Bam, Iran |
6.6 |
31,000 |
|
|
1908 |
Messina, Italy |
7.2 |
70,000 |
2004 |
off the western coast of |
9.1 |
227,898 |
|
1912 |
Sea of Marmara, Turkey 7.8 |
2,800 |
|
northern Sumatra, |
|
|
|
|
1915 |
Avezzano, Italy |
7.0 |
32,610 |
|
Indonesia |
|
|
|
1920 |
Ningxia province, China 7.8 |
200,000 |
2005 |
northern Sumatra, |
8.6 |
1,313 |
|
|
1923 |
Tokyo; Yokohama, Japan 7.9 |
143,000 |
|
Indonesia |
|
|
|
|
1927 |
Qinghai province, China 7.6 |
40,900 |
2005 |
Kashmir, Pakistan |
7.6 |
c. 86,000 |
|
|
1932 |
Gansu province, China |
7.6 |
unknown |
2006 |
Kuril Islands, Russia |
8.3 |
unknown |
|
1933 |
Sanriku, Japan |
8.4 |
2,990 |
2006 |
Tonga |
7.9 |
unknown |
|
1935 |
Quetta, Pakistan |
7.5 |
30,000 |
2006 |
Bantul, Indonesia |
6.3 |
5,749 |
|
1939 |
Erzincan, Turkey |
7.8 |
32,700 |
2007 |
southern Sumatra, |
8.5 |
25 |
|
1939 |
Chillan, Chile |
7.8 |
28,000 |
|
Indonesia |
\ |
\ |
|
1944 |
Tonankai, Japan |
8.1 |
998 |
2007 |
Solomon Islands |
8.1 |
54 |
|
1944 |
San Juan, Argentina |
7.4 |
c. 8,000 |
2007 |
off the coast of central |
8.0 |
514 |
|
1945 |
off the coast of Pakistan 8.0 |
4,000 |
|
Peru |
|
|
|
|
1946 |
Nankaido, Japan |
8.1 |
1,362 |
2008 |
eastern Sichuan |
7.9 |
69,000 |
|
1948 |
Ashgabat, Turkmenistan 7.3 |
110,000 |
|
province, China |
|
|
|
A tsunami is a catastrophic ocean wave, usually caused by a submarine earthquake occurring less than 30 mi (50 km) beneath the seafloor, with a magnitude greater than 6.5. Underwater or coastal landslides or volcanic eruptions also may cause a tsunami. The often-used term tidal wave is a misnomer: the wave has no connection with the tides. After the earthquake or other generating impulse, a train of simple, progressive oscillatory waves is propagated great distances at the ocean surface in ever-widening circles, much like the waves produced by a pebble falling into a shallow pool. In deep water, the wavelengths are enormous, about 60 to 125 mi (100 to 200 km), and the wave heights are very small, only 1 to 2 ft (0.3 to 0.6 m). The resulting wave steepness is extremely low; coupled with the waves’ long periods that vary from five minutes to an hour, this enables normal wind waves and swell to completely obscure the waves in deep water. Thus, a ship in the open ocean experiences the passage of a tsunami as an insignificant rise and fall. As the waves approach the continental coasts, friction with the increasingly shallow bottom reduces the velocity of the waves. The period must remain constant; consequently, as the velocity lessens, the wavelengths become shortened and the wave amplitudes increase, coastal waters rising as high as 100 feet (30 m) in 10 to 15 minutes. By a poorly understood process, the continental shelf waters begin to oscillate after the rise in sea level. Between three and five major oscillations generate most of the damage; the oscillations cease, however, only several days after they begin. Occasionally, the first arrival of a tsunami at a coast may be a trough, the water receding and exposing the shallow seafloor.
Deadly Volcano Eruptions
Casualty figures are approximate.
|
VOLCANO (LOCATION) |
YEAR |
CASUALTIES |
|
Tambora (Indonesia) |
1815 |
92,0001 |
|
Krakatoa (Indonesia) |
1883 |
36,0001 |
|
Pelee (Martinique) |
1902 |
30,000 |
|
Ruiz (Colombia) |
1985 |
25,0002 |
|
Etna (Italy) |
1669 |
20,000 |
|
Unzen (Japan) |
1792 |
15,000 |
|
Kelud (Indonesia) |
1586 |
10,000 |
|
Laki (Iceland) |
1783 |
9,000 |
|
Kelud (Indonesia) |
1919 |
5,000 |
|
Vesuvius (Italy) |
79 |
3,360 |
|
Awu (Indonesia) |
1711 |
3,200 |
|
Raung (Indonesia) |
1638 |
3,000 |
|
VOLCANO (LOCATION) |
YEAR |
CASUALTIES |
|
Raung (Indonesia) |
1730 |
3,000 |
|
Lamington (Papua New Guinea) |
1951 |
3,000 |
|
Awu (Indonesia) |
1856 |
2,800 |
|
Taal (Philippines) |
1906 |
1,500 |
|
Taal (Philippines) |
1911 |
1,300 |
|
Etna (Italy) |
1536 |
1,000 |
|
Paricutfn (Mexico) |
1949 |
1,000 |
|
Purace (Colombia) |
1949 |
1,000 |
|
Pinatubo (Philippines) |
1991 |
350 |
|
El Chichon (Mexico) |
1982 |
100 |
|
St. Helens (Washington) |
1980 |
57 |
