The Largest Earthquakes in the United States

Earthquakes are powerful forces of nature that can cause great damage and destruction. Over the years, there have been several very powerful quakes that have rocked different parts of the United States.

Many of the most powerful earthquakes have occurred in the same part of the country, although earthquakes can happen across the country at any given time.

As we look at U.S. earthquakes and the most powerful ones through the years, we’re also going to examine what states have the highest risk of significant earthquakes as well as some common causes. We’ll also share information on how an earthquake is measured.

U.S. Earthquakes

Different parts of the country are more prone to earthquakes because of their locations. This is not to say that a quake couldn’t happen anywhere. In fact, according to the U.S. Geological Survey's (USGS) Earthquake Information Center, every state in the U.S. has experienced some type of earthquake.

What Are the Most Common Causes of Earthquakes?

To understand what causes earthquakes to happen, it’s important to understand the fundamental characteristics of the earth.

The tectonic plates that make up the earth's crust are moving constantly. When these edges slide against each other in fault zones, friction can slow them down and pressure can build up over long periods of time. When the force of movement overcomes the friction, sections of the crust break or become displaced. This releases the pressure in the form of seismic waves. This is sometimes called a tectonic earthquake.

Besides tectonic earthquakes, there are also three other earthquake types:

• Volcanic earthquakes occur with volcanic activity.
• Collapse earthquakes are smaller earthquakes that result from the subterranean collapse of caverns or mines.
• Explosion earthquakes are caused by underground explosions of nuclear or chemical devices.

Although tectonic earthquakes can happen anywhere in the world, about 80% occur at the circum-Pacific seismic belt that is located along the Pacific Ocean’s rim — giving rise to the popular nickname, the "Ring of Fire".

The area below the earth’s surface where the earthquake starts is known as the hypocenter and the location directly above it on the earth’s surface is called the epicenter.

Some aftershocks can occur after an initial earthquake. An aftershock in the same area as the main shock is usually of a smaller magnitude. It forms as the crust around the displaced fault plane adjusts to the effects of the main shock. If the aftershock is larger than the main earthquake, it is redesignated as the main shock, and the first earthquake is then redesignated as a foreshock.

When talking about earthquakes it is also important to mention earthquake swarms. These are a sequence of earthquakes that strike in a specific area within a short amount of time. No single earthquake in the sequence has notably higher magnitudes than the others.

Earthquake Magnitude and the Richter Scale

A seismograph is the main instrument used to measure an earthquake. The seismograph produces a digital graphic recording of the ground motion that the seismic wave causes. This digital recording is called a seismogram.

An earthquake has one magnitude unit that does not depend on where the measurement is made. The Moment Magnitude Scale has been used since 1970 to measure magnitude because it supports earthquake detection all over the Earth. It measures the movement of the rock along the fault.

Any earthquake that measures above 7.0 is considered to be major and causes serious damage. Earthquakes 8.0 or higher can destroy areas near the epicenter. Any earthquake under 5.4 is often felt, but only minor damage is seen.

From 1935 until 1970, the Richter Scale was used to measure earthquake magnitude size. This was a mathematical formula seismologist Charles Richter invented to compare quake sizes. The Richter Scale was replaced because it only mainly worked for earthquakes in Southern California. It also was calculated to record only one type of earthquake wave. The Moment Magnitude Scale records all different seismic waves from an earthquake to seismographs around the world.

Richter's equations are still used for predicting future earthquakes and calculating earthquake hazards.

What 3 States in the U.S. Have the Highest Earthquake Risk?

The 3 states that have the highest earthquake risk in the United States are Alaska, California, and Hawaii.

Alaska

Seventy-five percent of all earthquakes in the United States with magnitudes larger than five occur in Alaska.

Alaska’s largest earthquakes are caused by the subduction of the Pacific plate beneath Alaska. This happens as the Pacific plate moves under the North American plate between 5-7 centimeters per year.

California

Scientists say that there is more than a 99 percent chance of one or more major earthquakes striking California in the next 30 years.

California earthquakes are caused by huge blocks of the earth’s crust moving, the Pacific and North American plates.

Hawaii

Earthquakes in Hawaii are caused by eruptive processes within active volcanoes or by deep structural adjustments. These are due to the islands’ weight on Earth’s underlying crust.

Researchers say that there is a 90% chance that people on the islands of Hawaii and Maui could experience damaging earthquakes during the next 100 years.

What Were the 5 Largest Earthquakes in the United States?

The U.S. has seen plenty of earthquakes, but there are five that stand out as the largest in this country’s history. Their damage and the carnage are proof that earthquakes are meant to be taken seriously.

1. Prince William Sound Alaska (March 28, 1964) — 9.2

The Great Alaska earthquake or the Good Friday Earthquake as it’s also called, is the most powerful earthquake to have occurred in the United States, and the second most powerful earthquake on record in the world. It hit March 27, 1964, at 5:36 local time (March 28 at 3:36 UTC).

The quake measured 9.2. and lasted just under 5 minutes. It triggered a tsunami and caused massive ground fissures. The quake destroyed several buildings and resulted in damage that was estimated to total $116 million. The quake was also responsible for 131 deaths.

2. Rat Islands, Alaska (February 4, 1965) — 8.7

The earthquake to hit the Rat Islands in 1965 triggered a 32-foot tsunami on Shemya Island. The quake was not just felt in Alaska but also in Japan, Ecuador, Mexico, and Russia. Because of its remote location, it did not cause any major damage, and no one was killed. The tsunami that it triggered did cause about $10,000 worth of damage.

3. Andreanof Islands (Alaska, March 9, 1957) — 8.6

When this 8.6 earthquake occurred in the Andreanof Islands. The earthquake happened close to Alaska at the Aleutian Trench. This is a plate boundary that divides the Pacific Plate from the North American Plate. The earthquake caused a major Pacific-wide tectonic tsunami.

The waves reached massive heights, but no casualties were reported. It did cause a great deal of damage that totaled some $5 million. The Seismic Sea Wave Warning System's warnings are credited with preventing more severe damage or fatalities.

4. East of Shumagin Islands (Alaska, November 10, 1938) — 8.3

The 1938 earthquake had a magnitude of 8.3 and caused limited damage to the relatively unpopulated region of the Alaska Peninsula. It was felt at False Pass, Unimark Island.

It did trigger an ocean-wide tsunami which was recorded at Dutch harbor, Seward, and Sitka, Alaska, and at Hilo and Honolulu, Hawaii. But it was unusually weak because the earthquake occurred at a depth of 35 km deep. There is no information regarding deaths or damage totals.

5. Lituya Bay, Alaska (July 10, 1958) — 8.3

This earthquake occurred on the Fairweather Fault in southeast Alaska. It led to a rockfall in Lituya Bay that generated a wave with a maximum height of 1,720 feet. this is the world’s largest recorded tsunami. It also triggered a rockslide of 30 million cubic meters and about 90 million tons into Lituya Bay. Five people were killed.

Largest Earthquakes in the U.S.

As you look at the largest earthquakes in North America, you’ll notice that no recent earthquakes make the list. Many of the earthquakes listed occurred years ago in places like Alaska, San Francisco, California, Nevada, and Hawaii. You’ll notice there is also one earthquake in Idaho that made the list due to its seismic activity. New Madrid, Missouri, and Hebgen Lake, Montana, are also on the list.

But if you are interested in viewing the biggest earthquakes that have happened around the world, you can explore our list of the Ten Largest Earthquakes Since 1900.

The following table lists the largest earthquakes in the United States on record, according to rank, magnitude, date, and location. For example, 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.

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