Violent Supershear Earthquakes Are Much More Common Than Previously Thought

A picture of a building following an earthquake.

According to a study led by the University of California, Los Angeles geophysicists powerful supershear earthquakes, previously thought to be rare, are significantly more common than previously believed. The study was recently published in the journal Nature Geoscience.

The researchers examined all 6.7-or-greater magnitude strike-slip earthquakes globally since 2000, identifying 12 of the supershear type, or around 14%. (Four of the earthquakes had previously gone unreported.)

This figure is more than twice what experts expected; before, fewer than 6% of strike-slip earthquakes were classified as supershear.

Strike-slip earthquakes occur when the edges of two tectonic plates push sideways against one other. Supershear quakes are a subtype of that group that occurs when faults under the surface rupture faster than shear waves — seismic waves that shake the earth — can travel through rock. Similar to a sonic boom, the effect corrals energy that is subsequently violently released.

As a consequence, compared to other earthquakes of the same size, supershear earthquakes tend to generate greater shaking and can be more destructive.

“When an airplane flies faster than sound can travel through air, a cone of pent-up sound waves forms in front of the plane and when it catches up, we hear it all at once,” said Lingsen Meng, UCLA’s Leon and Joanne V.C. Knopoff Professor of Physics and Geophysics, and the paper’s corresponding author. “Supershear earthquakes are potentially more destructive than other kinds of earthquakes because they are more effective at generating seismic waves, with more shaking, which could cause more damage.”

The research also found that supershear earthquakes occur as commonly beneath the oceans as they do on land and that they are most likely to occur along strike-slip faults, such as California’s San Andreas Fault.

The findings suggest that disaster planning efforts should take into consideration whether nearby faults are capable of producing supershear earthquakes and if so, take measures to prepare for a higher level of shaking and potential damage than could be caused by non-supershear earthquakes.

Meng said the reason relatively few supershear earthquakes have been found is that researchers mainly study earthquakes on land.

The paper’s co-authors are UCLA doctoral students Han Bao and Liuwei Xu of UCLA and Jean-Paul Ampuero, a senior researcher at Université Côte d’Azur in Nice, France.

The scientists used a method called backprojection to determine the direction in which seismic waves arrived to infer how fast an earthquake moves along the fault. The technique applies an algorithm to analyze brief time delays between seismic waves as they’re detected by a group of sensors. The method is similar to how one can locate a person by tracking the signals their smartphone sends to cell towers.

The data revealed supershear earthquakes tend to occur on mature strike-slip faults, in which the edges of two continental plates rub laterally against each other. In a mature fault, that action has been happening for long enough to create a zone of damaged rocks that act like a dam around the fault, slowing or blocking seismic wave propagation and concentrating their energy.

Ampuero said the findings could help scientists better understand what it takes for a fault to produce the kinds of ruptures that lead to supershear earthquakes.

In the past century, at least one large supershear earthquake has occurred in California: In 1979, a 6.5-magnitude quake in Southern California’s Imperial Valley region injured people as far away as Mexico and caused extensive damage to irrigation systems. And, although it predated scientific monitoring, the 1906 earthquake that caused extensive damage in San Francisco likely also fell into the supershear category.

Not all supershear earthquakes are that disastrous. The shape of the fault, the rocks around it, and other factors can affect the propagation of seismic waves and limit the accumulation of energy. Faults that curve tend to slow, deflect or absorb seismic waves, while straight faults let them flow freely.

In a previous study, Meng’s research group identified the catastrophic 7.5 magnitude earthquake that hit the Indonesian island of Sulawesi in 2018 as a supershear event. The temblor and ensuing tsunami killed at least 4,000 people. Despite the curve in the Indonesian earthquake fault, the horrific damage occurred because the fault moved faster than any previously recorded and energy from earlier temblors likely was stored up in the rocks, awaiting a moment to burst, Meng said.

Fortunately, Meng said supershear earthquakes in the ocean are less likely than earthquakes that cause the sea floor to move vertically to produce tsunamis.

The San Andreas Fault, on the other hand, is mostly straight and could experience an even more explosive rupture than the Sulawesi quake.

References: “Global frequency of oceanic and continental supershear earthquakes” by Han Bao, Liuwei Xu, Lingsen Meng, Jean-Paul Ampuero, Lei Gao, and Haijiang Zhang, 31 October 2022, Nature Geoscience.
DOI: 10.1038/s41561-022-01055-5

“Early and persistent supershear rupture of the 2018 magnitude 7.5 Palu earthquake” by Han Bao, Jean-Paul Ampuero, Lingsen Meng, Eric J. Fielding, Cunren Liang, Christopher W. D. Milliner, Tian Feng, and Hui Huang, 4 February 2019, Nature Geoscience.
DOI: 10.1038/s41561-018-0297-z

NEWS RELATED

EPA blocks mine project that threatened crucial Alaskan salmon runs

The Environmental Protection Agency moved to block the Pebble Mine in Alaska on Tuesday, preventing mining waste discharges into the Bristol Bay watershed. It’s a decision the agency says will preserve the thriving ecosystem and safeguard Alaska’s Sockeye salmon fishery, which produces about half of the world’s harvest of ...

View more: EPA blocks mine project that threatened crucial Alaskan salmon runs

Giant sea scorpion species discovered in New Mexico

Scientists have discovered a giant ancient sea scorpion species in New Mexico that lived between 307 and 303 million years ago. Hibbertopterus lamsdelli was over a metre long and likely lived in a marine-influenced estuary fed by a river delta, according to a new study published in the journal ...

View more: Giant sea scorpion species discovered in New Mexico

Tyre Nichols' death has reignited the debate around police brutality. Here are 5 proven ways to reduce it - and 2 strategies that don't work.

Business Insider Protesters rally as Philadelphia Police officers and Pennsylvania National Guard soldiers look on, June 1, 2020.AP Photo/Matt Slocum Tyre Nichols, 29, died after he was beaten by police at a traffic stop January 7. Campaign Zero, a police-reform initiative, suggested six ways to reduce police violence. Research ...

View more: Tyre Nichols' death has reignited the debate around police brutality. Here are 5 proven ways to reduce it - and 2 strategies that don't work.

Northern Lights Glimmer in Manitoba Night Sky

A Manitoba-based photographer captured the green glow of the aurora borealis over South Indian Lake on Friday, January 27, as the temperature fell to -23 degrees Fahrenheit (-30 Celsius). Timelapse footage published to Twitter by RJ Roldan shows the northern lights on display as the Canadian region was hit ...

View more: Northern Lights Glimmer in Manitoba Night Sky

Amid high levels of contamination, Puerto Rico town's residents plead for action

SALINAS, Puerto Rico — Shuttered windows are a permanent fixture in Salinas, an industrial town on Puerto Rico’s southeast coast that is considered one of the U.S. territory’s most contaminated regions. For years, toxic ash and noxious chemicals from coal-fired and thermoelectric power plants have enveloped this community, and ...

View more: Amid high levels of contamination, Puerto Rico town's residents plead for action

COVID flashback: Here's how NPR reported on the coronavirus at a turning point

On Jan. 23, 2020, as the coronavirus spread in China, residents of Wuhan, where it was first identified, donned masks to go shopping. The U.S. didn’t officially endorse masks as a preventive measure for the public for a number of weeks. Stringer/Getty Images hide caption toggle caption Stringer/Getty Images ...

View more: COVID flashback: Here's how NPR reported on the coronavirus at a turning point

9 diseases that keep epidemiologists up at night

Thinking about the next pandemic keeps lots of researchers busy. Peter Zelei Images/Getty Images hide caption toggle caption Peter Zelei Images/Getty Images Just three years ago, on Jan. 30, 2020, the head of the World Health Organization made a landmark declaration: A “novel coronavirus” that had first been identified ...

View more: 9 diseases that keep epidemiologists up at night

Women who snore struggle to orgasm, new study suggests

(Getty Images) Woman who snore are more likely to suffer from sexual dysfunctions, according to a new study. Sexual disorders are more common among women who suffer from obstructive sleep apnoea (which can cause loud snoring), insomnia, or circadian rhythm sleep disorder according to a study published in the ...

View more: Women who snore struggle to orgasm, new study suggests

Huge meteorite discovered in Antarctica contains oldest material in solar system

My night in a 'gaming suite' forced me to reckon with the time I spend playing video games

Crowdfunded DNA effort helps identify woman found murdered 50 years ago

Peloton instructor Leanne Hainsby, 35, said she was diagnosed with breast cancer after a doctor told her not to worry about a lump in her breast

ChatGPT creator OpenAI might be training its AI technology to replace some software engineers, report says

Fossilized eggs reveal new secrets about one of the world's largest dinosaurs

Rotation of Earth’s inner core may have slowed, puzzling new discovery suggests

How a good teacher can boost your child's future INCOME: Kids in the most effective reception class earn up to £7,500 more, study finds

Study reveals how you can find out if your cats are about to fight

Scientific journals ban ChatGPT use by researchers to author studies

New blood test could detect Alzheimer’s disease years before diagnosis

Is cannabis the secret to ORGASMS for women? Females who smoke before sex are more likely to climax multiple times, study suggests

OTHER NEWS