How Much Do You Really Know About Earthquakes?

How Much Do You Really Know About Earthquakes?

Do you think that the region of the country or world where you live in is immune from earthquake or seismic activity? Think again – Believe it or not earthquakes are very widespread and not just limited to certain geographical regions around the United States or around the world. Their frequency is also much more common than you may think. Earthquakes occur just about everywhere – or at least, it seems that way – Temblors happen on all continents and beneath the deep oceans. They shake the world’s highest mountains, the Himalayas, and the Earth’s deepest valley, the Dead Sea. Even from under the ice caps of both polar regions, seismometers regularly record rumblings in the Earth’s crust.

Seismic activity-prone areas of the world

Read on and discover some interesting facts and figures about those “helpless feeling” and “earth-shaking” phenomenons known as earthquakes. What you learn may surprise you. If any of this  sparks your interest any further, make sure to check out the links that follow for more  scientific and detailed information, charts and graphs.


Earthquake Facts

  • The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964.
  • The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960.
  • The earliest reported earthquake in California was felt in 1769 by the exploring expedition of Gaspar de Portola while the group was camping about 30 miles southeast of Los Angeles.
  • Before electronics allowed recordings of large earthquakes, scientists built large spring-pendulum seismometers in an attempt to record the long-period motion produced by such quakes. The largest one weighed about 15 tons. There is a medium-sized one three stories high in Mexico City that is still in operation.
  • The average rate of motion across the San Andreas Fault Zone during the past 3 million years is 2 inches per year. This is about the same rate at which your fingernails grow. Assuming this rate continues, scientists project that Los Angeles and San Francisco will be adjacent to one another in approximately 15 million years.
  • The East African Rift System is a 31-37 mile wide zone of active volcanic and faults that extends north-south in eastern Africa for 1864 miles from Ethiopia in the north to Zambezi in the south. It is a rare example of an active continental rift zone, where a continental plate is attempting to split into two plates which are moving away from one another.
  • The first “pendulum seismoscope” to measure the shaking of the ground during an earthquake was developed in 1751, and it wasn’t until 1855 that faults were recognized as the source of earthquakes.
  • Moonquakes (“earthquakes” on the moon) do occur, but they happen less frequently and have smaller magnitudes than earthquakes on the Earth. It appears they are related to the tidal stresses associated with the varying distance between the Earth and Moon. They also occur at great depth, about halfway between the surface and the center of the moon.
  • Although both are sea waves, a tsunami and a tidal wave are two different unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth. A tsunami is a sea wave caused by an underwater earthquake or landslide (usually triggered by an earthquake) displacing the ocean water.
  • The hypocenter of an earthquake is the location beneath the earth’s surface where the rupture of the fault begins. The epicenter of an earthquake is the location directly above the hypocenter on the surface of the earth.
  • The world’s greatest land mountain range is the Himalaya-Karakoram. It contains 96 of the world’s 109 peaks of over 24,000 feet. The longest range is the Andes of South America which is 4700 miles in length. Both were created by the movement of tectonic plates.
  • It is estimated that there are 500,000 detectable earthquakes in the world each year. About 100,000 of those can be felt, and approximately 100 of them cause damage.
  • It is thought that more damage was done by the resulting fire after the 1906 San Francisco earthquake than by the earthquake itself.
  • A seiche (pronounced SAYSH) is what happens in the swimming pools of Californians during and after an earthquake. It is “an internal wave oscillating in a body of water” or, in other words, it is the sloshing of the water in your swimming pool, or any body of water, caused by the ground shaking in an earthquake. It may continue for a few moments or a few hours, long after the generating force is gone. A seiche can also be caused by wind or tides.
  • Each year the southern California area has about 10,000 earthquakes. Most of them are so small that they are not felt. Only several hundred are greater than magnitude 3.0, and only about 15-20 are greater than magnitude 4.0. If there is a large earthquake, however, the aftershock sequence will produce many more earthquakes of all magnitudes for many months.
  • The magnitude of an earthquake is a measured value of the earthquake size. The magnitude is the same no matter where you are, or how strong or weak the shaking was in various locations. The intensity of an earthquake is a measure of the shaking created by the earthquake, and this value does vary with location.
  • The Wasatch Range, with its outstanding ski areas, runs North-South through Utah, and like all mountain ranges it was produced by a series of earthquakes. The 240-mile-long Wasatch Fault is made up of several segments, each capable of producing up to a magnitude 7.5 earthquake. During the past 6,000 years, there has been a magnitude 6.5+ about once every 350 years, and it has been about 350 years since the last powerful earthquake, which was on the Nephi segment.
  • There is no such thing as “earthquake weather”. Statistically, there is an equal distribution of earthquakes in cold weather, hot weather, rainy weather, etc. Furthermore, there is no physical way that the weather could affect the forces several miles beneath the surface of the earth. The changes in barometric pressure in the atmosphere are very small compared to the forces in the crust, and the effect of the barometric pressure does not reach beneath the soil.
  • From 1975-1995 there were only four states that did not have any earthquakes. They were: Florida, Iowa, North Dakota, and Wisconsin.
  • The core of the earth was the first internal structural element to be identified. In 1906 R.D. Oldham discovered it from his studies of earthquake records. The inner core is solid, and the outer core is liquid and so does not transmit the shear wave energy released during an earthquake.
  • The swimming pool at the University of Arizona in Tucson lost water from sloshing (seiche) caused by the 1985 magnitude 8.1 Michoacan, Mexico earthquake 1240 miles away.
  • Earthquakes occur in the central portion of the United States too! Some very powerful earthquakes occurred along the New Madrid Fault in the Mississippi Valley in 1811-1812. Because of the crustal structure in the Central US which efficiently propagates seismic energy, shaking from earthquakes in this part of the country are felt at a much greater distance from the epicenters than similar size quakes in the Western US.
  • Most earthquakes occur at depths of less than 50 miles from the Earth’s surface.
  • The San Andreas Fault is NOT a single, continuous fault, but rather is actually a fault zone made up of many segments. Movement may occur along any of the many fault segments along the zone at any time. The San Andreas fault system is more that 800 miles long, and in some spots is as much as 10 miles deep.
  • The world’s deadliest recorded earthquake occurred in 1556 in central China. It struck a region where most people lived in caves carved from soft rock. These dwellings collapsed during the earthquake, killing an estimated 830,000 people. In 1976 another deadly earthquake struck in Tangshan, China, where more than 250,000 people were killed.
  • Florida and North Dakota have the smallest number of earthquakes in the United States.
  • The deepest earthquakes typically occur at plate boundaries where the Earth”s crust is being subducted into the Earth’s mantle. These occur as deep as 400 miles below the surface.
  • Alaska is the most earthquake-prone state and one of the most seismically active regions in the world. Alaska experiences a magnitude 7 earthquake almost every year, and a magnitude 8 or greater earthquake on average every 14 years.
  • The majority of the earthquakes and volcanic eruptions occur along plate boundaries such as the boundary between the Pacific Plate and the North American plate. One of the most active plate boundaries where earthquakes and eruptions are frequent, for example, is around the massive Pacific Plate commonly referred to as the Pacific Ring of Fire.
  • The earliest recorded evidence of an earthquake has been traced back to 1831 BC in the Shandong province of China, but there is a fairly complete record starting in 780 BC during the Zhou Dynasty in China.
  • It was recognized as early as 350 BC by the Greek scientist Aristotle that soft ground shakes more than hard rock in an earthquake.
  • The cause of earthquakes was stated correctly in 1760 by British engineer John Michell, one of the first fathers of seismology, in a memoir where he wrote that earthquakes and the waves of energy that they make are caused by “shifting masses of rock miles below the surface”.
  • In 1663 the European settlers experienced their first earthquake in America.
  • Human beings can detect sounds in the frequency range 20-10,000 Hertz. If a P wave refracts out of the rock surface into the air, and it has a frequency in the audible range, it will be heard as a rumble. Most earthquake waves have a frequency of less than 20 Hz, so the waves themselves are usually not heard. Most of the rumbling noise heard during an earthquake is the building and its contents moving.
  • When the Chilean earthquake occurred in 1960, seismographs recorded seismic waves that traveled all around the Earth. These seismic waves shook the entire earth for many days! This phenomenon is called the free oscillation of the Earth.
  • The interior of Antarctica has “icequakes” which, although they are much smaller, are perhaps more frequent than earthquakes in Antarctica. The icequakes are similar to earthquakes, but occur within the ice sheet itself instead of the land underneath the ice. Some of our polar observers have told us they can hear the icequakes and see them on the South Pole seismograph station, but they are much too small to be seen on enough stations to obtain a location.


Deadliest Earthquakes on Record

(50,000 deaths or more)

The following table lists the deadliest earthquakes on record according to date, location, number of deaths, and magnitude. On Jan. 23, 1556, an 8.0 magnitude earthquake struck Shansi, China killing 830,000 people.

Date Location Deaths Magnitude
Jan. 23, 1556 Shansi, China 830,000 ~8
July 27, 1976 Tangshan, China 255,0001 7.5
Aug. 9, 1138 Aleppo, Syria 230,000 n.a.
Dec. 26, 2004 off west coast of northern Sumatra 225,000+ 9.0
Dec. 22, 8562 Damghan, Iran 200,000 n.a.
May 22, 1927 near Xining, Tsinghai, China 200,000 7.9
Dec. 16, 1920 Gansu, China 200,000 7.8
March 23, 8932 Ardabil, Iran 150,000 n.a.
Sept. 1, 1923 Kwanto, Japan 143,000 7.9
Oct. 5, 1948 Ashgabat, Turkmenistan, USSR 110,000 7.3
Dec. 28, 1908 Messina, Italy 70,000–
Sept. 1290 Chihli, China 100,000 n.a.
May 12, 2008 Eastern Sichuan, China 87,587 7.9
Oct. 8, 2005 Pakistan 80,361 7.6
Nov. 1667 Shemakha, Caucasia 80,000 n.a.
Nov. 18, 1727 Tabriz, Iran 77,000 n.a.
Dec. 25, 1932 Gansu, China 70,000 7.6
Nov. 1, 1755 Lisbon, Portugal 70,000 8.7
May 31, 1970 Peru 66,000 7.9
May 30, 1935 Quetta, Pakistan 30,000–
Jan. 11, 1693 Sicily, Italy 60,000 n.a.
12684 Silicia, Asia Minor 60,000 n.a.
June 20, 1990 Iran 50,000 7.7
Feb. 4, 1783 Calabria, Italy 50,000 n.a.
1. Official. Estimated death toll as high as 655,000.
2. Note that these dates are prior to A.D. 1000. No digit is missing.
3. Estimated.
4. No date available.
Source: National Earthquake Information Center, U.S. Geological Survey. Data compiled from several sources.



Recent Earthquake In Haiti

On Tuesday, January 12, 2010, a catastrophic earthquake, with a magnitude of 7.0 struck the island nation of Haiti. Its epicenter was near Léogâne, which is about 16 miles west of the capital city of Port-au-Prince, at a depth of 8.1 miles. A series of at least 33 aftershocks, with 14 of them ranging between 5.0 and 5.9 magnitudes were recorded by the United States Geological Survey. The International Red Cross estimated that about three million people were affected by the quake, and the Haitian Interior Minister, Paul Antoine Bien-Aimé, believes that 200,000 people or more may have died as a result of the disaster.

The earthquake caused major damage to Port-au-Prince. Most major landmarks were significantly damaged or destroyed, including the Presidential Palace, the National Assembly building, the Port-au-Prince Cathedral, as well as most area hospitals. The United Nations (UN) reported that the headquarters of the United Nations Stabilization Mission in Haiti (MINUSTAH), located in the capital, had collapsed and that the Mission’s Chief, Hédi Annabi, his deputy, Luiz Carlos da Costa, and the acting police commissioner were confirmed dead. Because the organizational structures in Haiti have been destroyed, this is considered the worst disaster that the UN has ever been confronted with.


The Ten Largest1 Earthquakes Since 1900

Location Date Magnitude2
1. Chile May 22, 1960 9.5
2. Prince William Sound, Alaska March 28, 19643 9.2
3. Andreanof Islands, Aleutian Islands March 9, 1957 9.1
4. Kamchatka Nov. 4, 1952 9.0
5. Off western coast of Sumatra, Indonesia Dec. 26, 2004 9.0
6. Off the coast of Ecuador Jan. 31, 1906 8.8
7. Rat Islands, Aleutian Islands Feb. 4, 1965 8.7
8. Northern Sumatra, Indonesia March 28, 2005 8.7
9. India-China border Aug. 15, 1950 8.6
10. Kamchatka Feb. 3, 1923 8.5
1. In terms of magnitude.
2. Moment magnitude.
3. March 28, 03:36:14 UT (March 27, 5:36 P.M. local time)
Source: National Earthquake Information Center, U.S. Geological Survey.



Recent Earthquake In Chile

On Saturday, February 27, 1010, a powerful 8.8 magnitude occurred just off the coast of Chile at 03:34 local time (06:34 UTC), and lasting for about three minutes. Cities experiencing the strongest shaking included Concepcion (just 71 miles away and Chile’s 2nd largest city with a population of about 670,000), Temuco with extensive damage as well as the capital and largest city of Santiago (197 miles northeast, population of over 6 million in the metro area). Tsunami warnings were issued in 53 countries, and a tsunami was recorded, with amplitude of up to 8 ft 6 inches high, on the coast at Valparaíso, Chile. Chilean President ,Michelle Bachelet, declared a “state of catastrophe”. She also confirmed the deaths of at least 708 people – 723 at last update – which is sure to still climb higher over the next few days as more debris is removed. Many more people have not been accounted for or have been reported missing. More than half a million homes were destroyed in an event in which scientists declared was 500 times stronger than the earthquake in Haiti just six weeks earlier. The epicenter of the earthquake was offshore in the Maule Region, which is about 5 miles west of Curanipe and 71 miles northeast of Chile’s second largest city, Concepción. The earthquake also caused seiches to occur in Lake Pontchartrain to the north of New Orleans, United States, located nearly 4,700 miles from the epicenter of the quake. The Virgin Islands, Guam, American Somoa as well as Hawaii were all on high alert for the potential of a Tsunami. Alerts were issued and many local beaches were closed up and down the Pacific Coast region of Baja California, California, Oregon, Washington and British Columbia.


The Largest Earthquakes in the United States

The following table lists the largest earthquakes in the United States on record, according to rank, magnitude, date, and location. The largest earthquake to hit the U.S. was on March 28, 1964, when a 9.2 magnitude quake struck Prince William Sound in Alaska.

Rank Magnitude Date Location
1. 9.2 March 28, 1964 Prince William Sound, Alaska1
2. 8.8 March 9, 1957 Andreanof Islands, Alaska
3. 8.7 Feb. 4, 1965 Rat Islands, Alaska
4. 8.3 Nov. 10, 1938 East of Shumagin Islands, Alaska
8.3 July 10, 1958 Lituya Bay, Alaska
6. 8.2 Sept. 10, 1899 Yakutat Bay, Alaska
8.2 Sept. 4, 1899 Near Cape Yakataga, Alaska
8. 8.0 May 7, 1986 Andreanof Islands, Alaska
9. 7.9 Feb. 7, 1812 New Madrid, Missouri
7.9 Jan. 9, 1857 Fort Tejon, California
7.9 April 3, 1868 Ka’u District, Island of Hawaii
7.9 Oct. 9, 1900 Kodiak Island, Alaska
7.9 Nov. 30, 1987 Gulf of Alaska
7.9 Nov. 3, 2002 Central Alaska
15. 7.8 March 26, 1872 Owens Valley, California
7.8 Feb. 24, 1892 Imperial Valley, California
7.8 Nov. 17, 2003 Rat Island, Alaska
17. 7.7 Dec. 16, 1811 New Madrid, Missouri area
7.7 April 18, 1906 San Francisco, California
7.7 Oct. 3, 1915 Pleasant Valley, Nevada
20. 7.6 Jan. 23, 1812 New Madrid, Missouri
7.6 June 28, 1992 Landers, California
22. 7.5 July 21, 1952 Kern County, California
23. 7.3 Nov. 4, 1927 West of Lompoc, California
7.3 Dec. 16, 1954 Dixie Valley, Nevada
7.3 Aug. 18, 1959 Hebgen Lake, Montana
7.3 Oct. 28, 1983 Borah Peak, Idaho

1. March 28, 03:36:14 UT (March 27, 5:36 P.M. local time)
Source: National Earthquake Information Center, U.S. Geological Survey


* This article was originally posted on this site 12/5/2009

* Revised, updated and re-posted on 1/18/2010

* Updated once again on 3/1/2010


Links for additional information, maps and recent seismic activity: