Earthquakes are unique disasters because, unlike disasters directly related to weather and atmospheric conditions, such as tornadoes, hurricanes, and wildfires, earthquakes are entirely independent of the weather. This independence makes them almost impossible to predict, which is part of the reason they can be so dangerous.
The most powerful earthquake in the United States, as of 2025, was the 1964 Alaska earthquake, sometimes called the Good Friday earthquake because it occurred on Good Friday. More than 130 people died as the magnitude 9.2 quake rattled along more than 600 miles of the Aleutian Megathrust fault, causing more than $870 million (adjusted) in damages. Of those deaths, all but 15 were attributable to multiple tsunamis triggered by the quake in more than 20 countries, including one in Antarctica.
This article is the fourth in a series of charts providing information on tornadoes, hurricanes, wildfires, earthquakes, blizzards, and volcanoes.
Magnitude - How Big was the Earthquake?
Magnitude and intensity are two methods of measuring the impacts of an earthquake. The magnitude of an earthquake refers to the size of a quake at its source, sometimes referred to as the epicenter. This value is a single number and does not change based on location. An earthquake's magnitude used to be measured by the Richter scale. However, according to the United States Geological Survey (USGS), this scale fell out of favor due to its limited applicability outside the area of immediate impact; now, the Richter scale measures the local magnitude (ML) and is only used to describe smaller earthquakes where it is often one of the only magnitudes that can be measured by a seismic instrument.
Currently, the USGS uses the moment magnitude (Mw) to measure the size of an earthquake. First, geologists calculate the seismic moment, which is calculated as a product of the rigidity, or strength of the rock, the area of the fault that moved, and how far it "slipped." That seismic moment is then converted to a Richter-like scale, ranging from 1.0 to 10.0, for the final result. The magnitude may also be expressed in terms of the energy released by an earthquake, or the energy magnitude (Me). In the table below, the moment magnitude is listed next to the corresponding amount of energy released by an earthquake of that size. It is expressed in terms of the amount of trinitrotoluene (TNT) that would release the same amount of energy if detonated; for example, a magnitude 3.0 earthquake would release the same amount of energy as detonating 1,800 kg (almost 4,000 pounds) of TNT.
Intensity - How Hard did the Ground Shake?
The intensity of an earthquake, on the other hand, describes how the ground shakes during an earthquake. Unlike the (moment) magnitude of an earthquake, which is the same no matter where the quake is felt, the intensity of an earthquake varies based on multiple factors. The preferred measure of intensity, the Modified Mercalli (MM) scale, is based on specific descriptions of physical damage. These values, expressed as Roman numerals from I to X, are based on actual observations of the physical damages caused by an earthquake. Determining the MM rating of more powerful earthquakes—VIII and higher—may require the input of one or more structural engineers.
One of the key factors in the intensity of an earthquake is the depth of the epicenter. According to the USGS website, two earthquakes of roughly the same magnitude may have vastly different intensity values if one occurs deeper in the earth. The example given on that website compares the Northridge, CA earthquake (M6.7) to the Nisqually, WA earthquake (M6.8). Though the Nisqually earthquake had a slightly higher magnitude, and therefore released more energy, the Northridge quake was more intense because it occurred between three and eleven miles beneath the earth's surface, compared to the 30 to 36 mile depth of the Nisqually event.
| Season | Year-round |
| Areas at Most Risk | The greatest risk is to the areas of states that lie on a fault line. Listed beloware the key fault lines foundin the United States. San Andreas and Hayward Faults: California
Denali and Fairweather Faults, Alaska-Aleutian Megathrust: Alaska
New Madrid Fault: Missouri, Arkansas, Tennessee, Kentucky, Illinois
Cascadia Subduction Zone: California, Washington, Oregon
Wasatch Fault: Idaho to Utah
Rio Grande Rift: Colorado to Texas
Ramapo Fault Zone: New York, New Jersey, Pennsylvania |
| General Frequency | Average 440,000 per year worldwide Annual U.S. Earthquakes, 2020 to 2024:
2020 - 165,985 (5,536 M3.0 or above) 2021 - 135,294 (4,374 M3.0 or above) 2022 - 123,906 (4,028 M3.0 or above) 2023 - 122,299 (3,854 M3.0 or above) 2024 - 125,862 (4,241 M3.0 or above)
Note: The world's most active fault lines are in the United States. |
| Hazards | Falling objects, fires, collapsing structures, no advance warning, loss of utilities, inability to travel, ruptured gas and utility lines. |
| Magnitude | Moment (Mw) and Energy (Me) Magnitude, measured in energy released by TNT. 2.0 – 56 kg (123.5 lbs) - small to moderate lightning bolt 3.0 – 1,800 kg (3,968 lbs) - large lightning bolt 4.0 – 56,000 kg (123,459 lbs) 5.0 – 1.8 million kg (4 million lbs) - average tornado 6.0 – 56 million kg (123.5 million lbs) - Hiroshima atomic bomb 7.0 – 1.8 billion kg (4 billion lbs) 8.0 – 56 billion kg (1.2 trillion lbs) - Mount St. Helens eruption, 1980 9.0 – 1.8 trillion kg (4 trillion lbs) - Krakatoa eruption, 1883 10.0 – 56 trillion kg (1.2 quadrillion lbs) |
| Intensity and Damage | ModifiedMercalli(MM) Scale I-II. Very few people feel it, few on upper floors notice. No damage.
III-IV. Noticeable to most people indoors, some outdoors. Often mistaken for a passing truck instead of an earthquake. Dishes and windows rattle, doors disturbed. Minimal to no damage.
V-VI. Most or all people feel it, many wake up, some dishes and windows broken, clocks may stop, objects overturned, plaster may fall, slight damage.
VII. Negligible damage in strong buildings, considerable damage in ordinary buildings, potential for partial collapse. Furniture overturns, chimneys and factory stacks fall.
VIII. Considerable damage to ordinary buildings, frame structures out of line, partial collapse, buildings shifted off foundations.
IX. Considerable damage to all buildings, buildings shifted off foundations, partial collapse.
X. Well-built wooden buildings destroyed, rails bent, masonry, frame structures and foundations destroyed.
XI. Rails heavily bent, few structures remain standing, bridges destroyed.
XII.Total or near total destruction, lines of sight and level distorted, objects thrown into air.
Note: XI and XII are part of the unabridged Mercalli scale and are not used universally. The USGS still uses the ten-level scale. According to the USGS, the criteria for determining earthquakes of this intensity refer to the presence of certain conditions that could or would cause spectacular failure during an intense earthquake. |
| General Safety | Secure objects that may fall or break. Latch cupboard doors; brace heavy furniture and appliances. Remove heavy items from walls, like pictures or memorabilia.
Respond to evacuation notices, and follow the directions of emergency personnel. Develop and follow a family emergency plan. |
| Home Safety | Drop. Cover. Hold On. – Get under a desk or table and hold on to the legs; it is safer than being in a doorway. Protect your head and neck with a large book, a pillow, or your arms. If thereisn'ta desk or table nearby, staydown and get next to an interior walland cover your head and neck. Stay away from windows, heavy appliances, furniture, andthe kitchen. If you are inside when a quake starts, stay inside. Do not go downstairs or outside while the building is shaking; objects may fall on you or you may fall.
Know where the water, gas, and electric shut-offs are and how to operate them.
If you turn off your gas, do not immediately turn it back on. Do not light matches, candles, stoves, grills, or other appliances until you are certain there are no gas leaks.
Have a plan to locate family members after an event–many social media networks have "mark me safe" features. |
| Auto Safety | Move out of traffic and carefully stop your car. Do not stop under or on a bridge or an overpass, or under trees, power lines, or large signs.
Stay inside your car until shaking stops; when you begin driving again watch for rocks, broken pavement, bumps in the road.
If you are in a mountainous area, watch out for falling rocks, landslides, and other debris. |
| In-the-Open Safety | If you are outside at the beginning of a quake, stay outside. Stay low, or crawl if you can, to minimize the risk of falling. Get into the open and stay away from buildings, power lines, light posts, or anything that could fall on you. |
| Coverage Issues - Homeowners | Falling object damageis excludedtopersonal propertyunless the roof or outside wall of the building is damaged first. Damage by falling objects to the interior ofbuilding,personal propertyin a building excluded unless the building itself was first damaged by a falling object. Earthquake exclusion applies to earthquakes caused by or related to a volcanic eruption. Earthquakes, shock waves and tremors before, during or after a volcanic eruption, are excluded for dwelling coverage, as are landslides, mudslides, subsidence, sinking, rising, sinkholes, and any other earth movement. Breakage of glass and safety glazing material part of building, windows, or doors is covered when damaged directly by earth movement. |
| Coverage Issues - Commercial Property | "Earth movement" excluded, including tremors and aftershocks; also includes mudslides andminesubsidence. Also applies to earth rising, sinking, or settling, including soil conditions that cause settling, cracking, or other disarranged foundations. Exclusion applies no matter what caused the quake. Includes earthquakes resulting from orrelatedto a volcanic eruption. However, if "earth movement," as described above, results in a fire or explosion, the damages from that fire or explosion are covered. |
| Sources | https://en.wikipedia.org/wiki/List_of_earthquakes_in_the_United_States https://en.wikipedia.org/wiki/1964_Alaska_earthquake# https://www.volcanodiscovery.com/earthquakes/global/stats.html https://sciencequery.com/fault-lines-of-the-united-states/ https://www.usgs.gov/programs/earthquake-hazards/modified-mercalli-intensity-scale https://dggs.alaska.gov/hazards/earthquakes.html https://www.cdc.gov/earthquakes/safety/stay-safe-during-an-earthquake.html |