Geography Facts About Earthquakes

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An earthquake happens when two slabs of the ground abruptly move past one another.

The fault or fault plane is the surface where they slip. The hypocenter is the point beneath the earth’s surface where the earthquake begins, while the epicenter is the location directly above it on the earth’s surface.

Types of Earthquakes

Foreshocks are small earthquakes that happen before a larger earthquake. The main earthquake is called the mainshock. Earthquakes that happen after a large earthquake are called aftershocks. (Related: What is the Difference Between an Earthquake Swarm and Aftershocks)

Recording Earthquakes

Earthquakes are recorded using a machine called a seismograph. The seismograph measures the difference between the stationary and moving parts of the device to determine the duration, time, and magnitude of the earthquake. The vertical axis records ground displacement and the horizontal axis measures time.

The seismograph is securely fastened to the ground so that when the earth shakes, everything on the seismograph shakes except for the mass on the spring.

Drawing of a seismograph.
Drawing of a seismograph. Source: USGS, public domain.

Richter Scale

The size of an earthquake is recorded as a magnitude using the Richter Scale. The Richter Scale measures earthquakes on a logarithmic scale.

Global Earthquakes

Each year, there are about 14,000 recorded earthquakes that are magnitude 4 or higher.

Table: Worldwide Earthquakes 2000–2019

Magnitude:8.0+7–7.96–6.95–5.9Estimated
Deaths
Year:
20001141461344231
2001115121122421357
200201312712011685
2003114140120333819
20042141411515298101
2005110140169387992
20062914217126605
20074141782074708
2008012168176888708
200911614418961790
20101231502209226050
2011119185227621942
20122121081401689
201321712314531572
20141111431574756
201511812714199624
201601613015501297
20171610414551012
201811611716744535
2019191351492244
2020091121312not available
Source: USGS

Largest Recorded Earthquake in the World

The largest recorded earthquake in the world was a 9.5 magnitude earthquake in Chile on May 22, 1960.

Earthquakes in the United States

At Gillette Pass, a view to the north of the Denali fault trace in Alaska. The prior fault scarp is reoccupied by the surface rupture in this photo.
At Gillette Pass, a view to the north of the Denali fault trace in Alaska. The prior fault scarp is reoccupied by the surface rupture in this photo. Photo: Rod March, U.S. Geological Survey. Public domain.

Alask is the U.S. state that experiences the most earthquakes each year. A magnitude 7 earthquake occurs virtually every year in Alaska, and a magnitude 8 or higher earthquake occurs every 14 years on average.

California was the second most active state for number of earthquakes until 2014. An increase in seismicity in Oklahoma in 2014 has the state now ranked second for number of earthquakes. In Oklahoma, there were 585 earthquakes of magnitude 3 or larger in 2014, and roughly 200 in California.

Ground disturbance in southern California after the January 17, 1994 Northridge earthquake.
Ground disturbance in southern California after the January 17, 1994 Northridge earthquake. Photo: USGS, public domain.

Only four states experienced  no earthquakes between 1975 and 1995: Florida, Iowa, North Dakota, and Wisconsin.

Earthquake Counts by State 2010-2015 (M3+)

States201020112012201320142015
Alabama110026
Alaska224514091166132912961575
Arizona67433110
Arkansas15444410
California546195243240191130
Colorado42372137
Connecticut000001
Delaware000000
Florida000000
Georgia000000
Hawaii173440302653
Idaho744113138
Illinois102101
Indiana103000
Iowa000000
Kansas00024260
Kentucky002000
Louisiana100000
Maine101100
Maryland100000
Massachusetts000000
Michigan000002
Minnesota000010
Mississippi000003
Missouri232015
Montana7119142919
Nebraska201003
Nevada38862234161172
New Hampshire100000
New Jersey000000
New Mexico7736312
New York010002
North Carolina000010
North Dakota001000
Ohio130110
Oklahoma416334103585888
Oregon404243
Pennsylvania000000
Rhode Island000000
South Carolina000030
South Dakota031110
Tennessee104111
Texas9181116821
Utah1716166104
Vermont000000
Virginia174010
Washington514618611
West Virginia100100
Wisconsin000000
Wyoming436973179198
Source: USGS

Largest Earthquake in the United States

On Friday March 28, 1964 UTC, a magnitude 9.2 earthquake rocked Prince William Sound, Alaska, making it the greatest recorded earthquake in the United States.

San Andreas Fault

The San Andreas fault is actually a fault zone made up of multiple segments, rather than a single continuous fault. At any time, movement may occur along any of the zone’s numerous fault segments.

The San Andreas fault system stretches for more than 1300 kilometers (800 miles) and is as deep as 16 kilometers (10 miles) in some places.

 The San Andreas fault has moved 0.59 inches per year (1.5 centimeters per year) over the last 23 million years. 

View of the San Andreas Fault looking southeast along the surface trace in the Carrizo Plain, north of Wallace Creek. Elkhorn Rd. meets the fault near the top of the photo. Photo: Scott Haefner, U.S. Geological Survey. Public domain.
View of the San Andreas Fault looking southeast along the surface trace in the Carrizo Plain, north of Wallace Creek. Elkhorn Rd. meets the fault near the top of the photo. Photo: Scott Haefner, U.S. Geological Survey. Public domain.

Most Seismically Active Areas on Earth

There are three major zones where earthquakes are more likely to happen: the Circum-Pacific belt, the Alpide Belt, and the mid-Atlantic Ridge belt.

The “Ring of Fire,” also known as the Circum-Pacific belt, is an earthquake-prone zone that surrounds the Pacific Ocean, accounting for over 90% of all earthquakes worldwide.

The belt runs along tectonic plate boundaries, where plates of predominantly oceanic crust descend (or subduct) beneath another plate. Slip between plates and rupture within plates produce earthquakes in these subduction zones.

The world’s largest earthquake, the 9.5 magnitude Chilean earthquake in 1960 occurred in this zone. The largest earthquake in the United States, the 1964 9.2 Alaskan tremor that occurred in the Prince William Sound region is also part of the Ring of Fire.

Map showing the Pacific Ring of Fire.
Map showing the Pacific Ring of Fire. Source: USGS, public domain.

The Alpide belt (which stretches from the Mediterranean region eastward to Turkey, Iran, and northern India) is the next most seismically active region (5-6 percent of earthquakes).

The submerged mid-Atlantic Ridge belt is the area that designates the separation of two tectonic plates (a divergent plate boundary). The majority of the mid-Atlantic Ridge is submerged and far from human settlement, although Iceland, which stands directly above the ridge, has seen earthquakes as strong as M6.9.

East African Rift System

The East African Rift System is a 50-60 km (31-37 mile) wide zone of active volcanics and faulting in eastern Africa that stretches north-south for more than 3000 km (1864 miles) from Ethiopia in the north to Zambezi in the south.

The East African Rift System is a rare example of an active continental rift zone, in which a continental plate attempts to split into two plates that are moving away from one another.

Earthquakes and Icequakes in Antarctica

Antarctica does experience earthquakes although not as frequently as other continents. Antarctica did experience an 8.1 magnitude earthquake in 1998 in the Balleny Islands region.

On Antarctica, the Global Seismographic Network (GSN) has only four stations. This means that smaller magnitude earthquakes may go unnoticed.

Antarctica more frequently experiences icequakes which is the movement within the ice sheet.

Tsunamis

A tsunami is a displaced sea wave created by an underwater earthquake or landslide (typically initiated by an earthquake). Tsunamis can be incredibly destructive and cause death.

Tsunami damage in Natori, Japan, 2011. Photo: Bruce Jaffe, USGS Pacific Coastal and Marine Science Center. Public domain.
Tsunami damage in Natori, Japan, 2011. Photo: Bruce Jaffe, USGS Pacific Coastal and Marine Science Center. Public domain.

The 1964 9.2 magnitude earthquake in Alaska triggered a tsunami that devastated many towns along the Gulf of Alaska. Waves reached a height of 67 meters at Valdez Inlet. 122 people lost their lives as a result of this tsunami.

Related: Debris from the 2011 Japanese Tsunami Carried Almost 300 Marine Species Across the Pacific Ocean

Is There Such a Thing as Earthquake Weather?

There is a statistically equal distribution of earthquakes in cold, hot, wet, and other weather conditions.

Moonquakes

The moon also experiences seismic activity. Known as moonquakes, they are less frequently and occur at smaller magnitudes than earthquakes.

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