15 Groundbreaking Earthquake Facts

Nepal earthquake 2015
dutourdumonde / Getty Images

Earthquakes — Mother Nature's natural disasters that shake Earth’s surface whenever fractured pieces of its outer shell, known as tectonic plates, slide against, over, or under each other — remind us that we live on a dynamic planet.

The U.S. Geological Survey (USGS) estimates that as many as 20,000 temblors rattle the globe each year. But in spite of their fairly frequent occurrence, earthquakes are nothing to sneeze at. Here are 15 fascinating facts that illustrate just how extraordinary earthquakes can be.

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Earthquakes Can Move in Slow-Motion

Not all earthquakes are violent bursts of destruction that start and stop in mere seconds. Slow earthquakes, or “slow-slip” events as they’re called, release such tiny amounts of pent-up seismic energy at a time, that their quakes last anywhere from several days to several weeks.

Slow motion earthquakes remain somewhat of a mystery, but scientists believe their subdued, prolonged movement might be related to the myriad rock types found at their fault zones (the regions of Earth’s crust where tectonic plates meet). The presence of mushy and weak rocks alongside rigid and strong rocks could explain why some parts of slow-slip fault zones are close to failing (this would cause a typical earthquake), while other parts act to resist failure (this would cause sticking). 

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Earthquake "Shakiness" Isn't Measured by the Richter Scale

It’s a common misconception that the Richter Scale measures an earthquake’s overall strength. In reality, the Richter Scale only measures the magnitude, or physical size, of an earthquake. A quake’s intensity, or “shakiness,” is actually measured by a lesser-known scale called the Modified Mercalli Intensity Scale. Unlike magnitude, which is expressed in whole numbers and decimal fractions ranging from 1.0 to 9.9, earthquake intensities are expressed in Roman numerals ranging from I to X (one to ten).

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Earthquake Magnitude Isn't Measured by the Richter Scale Anymore

Speaking of the Richter Scale, did you know it is no longer used to measure earthquake magnitude? Today’s seismologists prefer the Moment Magnitude Scale (MMS) because it more accurately estimates magnitudes of global quakes. (Richter’s scale works well for calculating earthquakes in California, where he developed the concept, but it underestimates the size and energy emitted from global quakes whose seismic waves may travel at lower frequencies or from deeper within Earth’s crust.)

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Earthquakes Are Sensed by Animals Minutes to Days Before They Happen

Low angle view of birds flying against clear blue sky,New Jersey,United States,USA
Chloe Grinberg / 500px / Getty Images

According to the USGS, animals can’t predict earthquakes — that is, they can’t offer specifics about when a quake will occur, or where its epicenter will be. But thanks to their finely tuned senses, animals can detect a quake at its earliest stages. For example, it’s believed they can detect the arrival of primary waves (P-waves), which cause a parallel, back-and-forth motion and precede secondary waves (S-waves), which vibrate up and down. One study on animal behavior and earthquakes found that a colony of toads abandoned their mating site three days before a magnitude 6.3 earthquake struck L’Aquila, Italy in April 2009. The toads didn’t return until 10 days later after the last of the significant aftershocks had passed.

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Earthquakes Can Generate Lightning

On rare occasions, luminous phenomena, including balls of light, streamers, and steady glows have been linked to earthquakes. According to eyewitness reports, these so-called earthquake lights — like the blue light flashes captured on camera during the magnitude 8.0 quake that struck Peru on Aug. 15, 2007 — appear just before the fault rupture and also during the shaking period. Earthquake lights remain a mystery to scientists, although they continue to explore their causes.

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Earthquakes Can Uproot Crops

Following the magnitude 7.8 earthquake that hit Nepal in April 2015, scientists surveying the quake’s damage observed bushels of carrots scattered along the ground in various villages, as well as a multitude of villagers eating raw carrots. Apparently, the crops were uprooted from their fields by liquefaction — the fluid-like movement of loosely-packed or waterlogged soil as it gets vigorously shaken by earthquakes. 

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An Earthquake Moved Mt. Everest Over One Inch

Mount Everest with group of climbers
DanielPrudek / Getty Images

During the M7.8 Nepalese earthquake in 2015, the motion of the fault and of a series of related landslides actually moved Mt. Everest 1.2 inches to the southwest of where it previously stood! Due to geological goings-on, Everest naturally moves about 1.6 inches northwestward every year; so the Nepalese quake set the mountain back by one year's journey.

Originally, the Nepal quake was believed to have changed Mt. Everest's height, but after a years-long surveying and re-measuring project, Nepali and Chinese officials reported that this claim was untrue. (They did, however, announce in December 2020 that the mountain's official height was no longer 29,028 feet, but rather, 29,031 feet.)

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"Icequakes" Are a Real Thing

Glacier Calving into Alaskan Bay
GomezDavid / Getty Images

Icequakes are one type of cryoseism, or shaking event involving ice sheets and glaciers. Unlike traditional earthquakes, icequakes are caused when meltwater seeps down through glaciers, then refreezes and expands at their lower portions, resulting in cracking events whose vibrations can register on a seismograph. Eventually, these rifts may lead to the breaking-off of large chunks of glaciers in a process known as "ice calving." Antarctica and Greenland regularly experience icequakes, as does Europa, one of Jupiter’s icy moons.

Similarly, "frost quakes" can form in soil when saturated ground (like that after a soaking rainfall) freezes within a 48-hour period or less.

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According to Japanese Mythology, Earthquakes Were Caused by a Giant Catfish

Japanese art depicting villagers attacking a catfish.
Villagers blame catfish for an earthquake.

Tokyo University Library / Wikimedia Commons / Public Domain

The ancient Japanese believed that a great catfish, Namazu, living in the sea under the islands of Japan, was responsible for earthquakes. According to the myth, the creature was guarded by Kashima, a god of thunder, who held a heavy stone over Namazu to keep it from moving — but whenever Kashima got tired or was distracted from his duty, Namazu would wriggle his tail, causing an earthquake in the human world. 

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From Underground, Earthquakes Sound Like Thunder and Popcorn Popping

Following the historic 9.0 magnitude earthquake that struck Tohoku-Oki, Japan, in March 2011, researchers had the innovative idea to convert the disaster’s seismic wave data into audio. This allowed experts and the public to “hear” what the temblor sounded like as it moved through the earth. The sound of the 9.0 mainshock has been likened to low rumbling to thunder, while the aftershocks sound like the “pops” heard when popcorn popping or watching fireworks.

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Earthquakes Can Shorten Day Length

According to scientists at NASA’s Jet Propulsion Laboratory, the 9.0 magnitude earthquake that struck Japan in 2011 was so severe, it changed the distribution of Earth’s mass. As a result, the quake caused our planet to rotate a bit faster, which in turn shortened day length by 1.8 microseconds.

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Earth's Size Limits the Magnitude of Its Earthquakes

Planet Earth against black background
Frank Lee / Getty Images

The largest earthquake ever recorded on Earth is a magnitude 9.5. Given this, it’s natural to wonder if a magnitude 10 earthquake could ever occur. According to the USGS, while a M10 quake is possible, hypothetically speaking, it isn’t probable.

It all boils down to fault length; the longer the fault, the larger the quake. And as the USGS notes, no faults long enough to generate a so-called “mega quake” are known to exist. If they did exist, they’d be long enough to wrap around much of the planet. And as for the fault length needed to produce a magnitude 12 quake, it would need to be longer than the Earth itself — over 25,000 miles long!  

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Quakes Frequently Occur on Mars

NASA's InSight lander- Mars probe 3D Illustration
3D Illustration of NASA's InSight lander. FABIO BISPO / Getty Images

Thanks to observations from NASA’s InSight lander, we now know that Mars is a seismically active planet. During its first year on Mars, the spacecraft recorded nearly 500 “marsquakes.” Although Mars shakes frequently, the majority of its quakes seem to be minor in size — less than magnitude 4.

Mars doesn’t have active tectonic plates like Earth does. Instead, its quakes are triggered by the planet’s long-term cooling (it’s been cooling since it formed 4.6 billion years ago). As the Red Planet cools, it contracts, causing its brittle outer layers to fracture, and marsquakes to occur. 

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There's an Earthquake Memorial in Anchorage, Alaska

Anchorage, Alaska, is home to Earthquake Park — a 134-acre public green space commemorating the magnitude 9.2 earthquake that struck Southcentral Alaska on Good Friday in 1964. The park site marks the spot where a 1,200-foot by 8,000-foot strip of bluff slid into Cook Inlet, shifting the natural landscape sideways by as much as 500 feet. To this day, the Good Friday Earthquake remains the most powerful earthquake in recorded U.S. history and the second-largest worldwide behind the M9.5 quake that struck Chile four years earlier. 

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Earthquakes Can Be Triggered By Humans

Well for water injection into the reservoir. Maintaining reservoir pressure. Oil production. Well for maintenance of reservoir pressure
Water injection wells carry wastewater from oil refineries. Leonid Eremeychuk / Getty Images

People can actually trigger seismic activity by injecting industrial wastewater, such as that produced from oil and gas extraction, and fracking, into deep disposal wells. As explained by both the USGS and a study in the Journal of Geophysical Research: Solid Earth, pumping water deep into sedimentary formations increases pore pressure (pressure exerted by the fluid trapped in the cracks and pores of rocks). If this added pressure stresses an existing fault line, it can initiate "slip" along the fault and induce an earthquake.

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