A Strange Swarm of More Than 22,000 Earthquakes Has Rattled South California for the Last Four Years and Scientists Finally Know Why

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Early in 2016, without any fanfare, a swarm of earthquakes silently revved up in Southern California.

4 years after, scientists recorded more than 22,000… And now they seem to have discovered what’s behind the strange seismic event.

Cahuilla earthquake swarm, mysterious earthquake swarm south california, A strange earthquake swarm with more than 22,000 tremors lasted for years in Southern California and scientists finally know why
Cahuilla earthquake swarm: A strange earthquake swarm with more than 22,000 tremors lasted for years in Southern California and scientists finally know why. Science

The quakes didn’t occur every day, and most were too small for humans to feel, but month after month the tremors continued to rumble and multiply.

By the spring of 2018, thousands of little quakes were striking each month, some large enough to set lamps swaying and put residents of nearby towns on edge.

Over the past four years there have been more than 22,000 temblors. Yet the source behind all this activity has been a mystery.

Seismologists examined a cluster of 22,698 tiny earthquakes that lasted nearly four years.
Seismologists examined a cluster of 22,698 tiny earthquakes that lasted nearly four years. Picture: NatGeo

Now, in one of the highest resolution looks at a seismic swarm yet, scientists have zeroed in on a likely cause.

The analysis used a computer algorithm to tease out the locations and timing of the tiny temblors, creating a stunningly detailed portrait of the swarm activity as it unfolded along a spidery network of fractures.

This intimate picture of the swarm’s progression suggests that the cluster of quakes was triggered by fluids being naturally injected into the fault system.

The work hints that fluids may play a role in other swarms detected around the world.

Spotting a swarm of tremors

Along a fault line, the fissures in Earth’s crust were once imagined as simple structures, but in reality, fault zones are very complicated places. Some faults can bend. Others crisscross under the ground. The fractures analyzed in the new study weave together in a subterranean labyrinth sprawling across several miles.

The earthquake swarm that revealed this intricate structure passed unnoticed until 2017, when an email from a curious citizen landed in the mailbox of Southern California Seismic Network. That email requested information about a cluster of tiny quakes in a sparsely populated stretch of the state.

A cursory look at the region didn’t reveal anything extraordinary. Located about 10 miles from the highly active San Jacinto fault zone, the area is often subject to tiny tremors.

But by digging deeper into the region’s seismic history, the researchers realized that the email’s author was on to something: Starting nearly a year before, in 2016, a swarm of tiny earthquakes had rippled along the edge of the Cahuilla Band of Mission Indians reservation.

Such swarms of small quakes are distinct from large earthquakes, which often follow a familiar pattern: An intense event, or main shock, is followed by a series of aftershocks that taper off in magnitude and frequency over a predictable period of time.

Earthquake swarms are another geologic beast entirely. These events have little rhyme or reason to their progression, and they are sometimes made up of hundreds or thousands of small or moderate but similarly sized earthquakes. Most swarms occur as a burst of quakes over hours, days, or even months.

While many swarms are associated with burbling volcanoes, others roll across landscapes far from any major activity. The potential for destruction from these events varies widely.

The Cahuilla swarm pumped out quakes from early 2016 through last year — but all of the shakes were itty bitty, and they never generated significant damage in four years.

The subterranean labyrinth

The result of the team’s work is a remarkably complex look at how the Cahuilla swarm unfolded.

The researchers conclude that a reservoir of fluid — such as water or liquid carbon dioxide — lingered beneath the fault structure. For many years, that fluid was sealed off from the fault system, but in 2016 something breached the rocky divide. Fluid was injected into the fault, altering the pressures of the system and lubricating the cracks, which triggered the swarm’s first quakes some five miles deep.

Over the following months, the swarm slowly migrated upward and outward from this narrow starting point. A radiating front of quakes fanned out along underground fractures in the rock — precisely the way a fluid spreads. Some paths of the quake front eventually died out, perhaps as the fluids reached the end of a crack. Other times, the quakes seemed to pause at a boundary, migrating sideways before resuming their trajectory, like a river flowing around a rock.

Cahuilla swarm earthquake south california
The Cahuilla earthquake swarm in South California counts more than 22,000 tiny tremors. When the strongest earthquake of the swarm hit, the rate of tremors increased rapidly. Picture NatGeo

In August 2018, nearly three years after the swarm began, one particularly stalwart blockage seemed to stall out the fluid’s upward progression. The quakes took a turn before eventually finding a new path to resume their spread toward the surface.

That’s when the flow triggered the biggest earthquake measured in the swarm — a magnitude 4.4 event that anyone just above it would have felt rippling through the ground. The temblor was a huge kick to the system, triggering a spike of smaller quakes in one last burst of energy before the swarm died out.

In total, the study provides a convincing picture of fluids rushing into a fault zone and sending a four-year shudder through the rock beneath Southern California. Similar injections of fluid may cause many other swarms around the world, though there are likely multiple causes for clusters of quakes.

Each earthquake is like a dot of a pointillist painting. By studying just the largest quakes, you see only a smattering of spots. But by filling in the tiny tremors, a complete portrait of the complex physics behind our planet’s many creaks and quivers begins to emerge. [Science, NatGeo]

6 COMMENTS

  1. Actually strange sounds since last 4 of July double quakes in
    Ridgecrest we have had closer to 400,000 . I do remeber 4 months ago Steve Quayle said 300 K . Can you please kindly
    say why so much difference in numbers? I go with closer to 400 K even i accept Steve 300K but you are too low without predjudice. So i hope you do not fire me lol.. Peace to you all
    happy 4 of July with lots of beers, Corona beers are lowest ever
    been. There has been already 2 people in Seattle died or injured as a result of a car running to protestors in freeway 5N?
    More report of clashes for 4 of July watch your news world wiide? I suggest see any channels you trust? This will be last
    4 of July in USA, due to Corona and mass vaccinations we all
    die? So enjoy this holiday be last ever seen on planet be nice to each others?

  2. Bill Gates want every one have digital certificates that took vaccines? Also Donald trump said he will mobilse his army to vaccinate all Americans then he backed off so far.

  3. So everything i said so far came through, We had Disunited States of America with over 500 people shot dead or injured in NYC, ATL, PDX, SEA, LAX , CHI, ORD, and many more cities.
    Is this USA we want of course not , We invite all be calm in this age and time , be nice to each others, Either i have told before documented in this beautiful site that we will become 51 new nations or we need stop and go back home and find better solutions to discriminations and racism we see every day in the world. Other wise we loose USA and become weaker weaker specially with plagues such as black death, and new swine flue.
    China and Russia will invade us from Alaska and North America will fall under China and Russia . We know fact Iran is responsible for riots in USA as a result of death of Ghasem S.
    We know the fact Iran sent Bitcoins to Linda Sarsour a PLO born in USA with help of CAIR to dismental bill of rights. The explosions in Iran was caused by either by sabotage from MKO forces inside Iran. MKO is partial Islamist and also are communist partially so i call them ComoIslamists follower of Maryam Rajavi now lives in Paris France. Another theory is this the explosion in Tehran was caused by Laser new high Tech by Israel or USA from space. We must Nuke Iran before is too late ?Or we will loose USA indeed.

  4. Emergency News Another Multiple Explosions in IRAN? IS WWW3 in progress ?

    Kahrizak district governor announced; At least two people were killed and three others were injured in a bomb blast near the Iran Capital, Tehran?

    Kahrizak district governor confirmed the explosion in Baqershahr and said that the explosion took place on Tuesday morning in the factory building called “Sepahan Barish”, caused damage to the “Saipa Press” factory and left at least two dead and three injured.

    On Tuesday morning, after hearing the sound of a terrible explosion in areas south of Tehran and in the Kahrizak area, many residents of these areas were worried and at the same time local sources in Baqershahr reported that the sound of the explosion that terrified the people of this area was caused by the explosion. He was in a factory.

    Local sources in Baqershahr said the blast was heard from Sepahan Bresh Company and that firefighters and paramedics were immediately dispatched to the scene.

    Local sources also cited the cause of the fire as “caused by the explosion of cutting air capsules” and said that two people had been killed and a number of others injured in the blast at Sepahan Bresh in Baghershahr.

    Hours after the blast, the Islamic Republic Radio and Television News Agency confirmed the blast, quoting Kahrizak district governor, as saying that “an explosion occurred in a workshop following the failure to fill oxygen caps in Baqershahr, Kahrizak.” “Two people were injured and three were injured.”

    The IRIB news agency announced the time of the explosion at 3:20 AM on Tuesday and its location as Baghershahr Tourism Street, and quoted the Kahrizak district governor as saying that the “Saipa Press” complex was located next to the exploded workshop.

    Kahrizak district governor said that as a result of the explosion in Sepahan Bresh company, the walls of Saipa Press complex were destroyed and the workshop itself was damaged.

    The names of the victims of the explosion, as well as more details about the activities of Sepahan Barsh Company, have not been provided by Kahrizak district.

    Numerous fires and explosions in recent days have fueled speculation about the connection between the blasts and the fires in public opinion and among social media users.

    Officials in Iran, such as the Sina Athar and Sina Mehr medical centers in northern Tehran, which killed 19 people, said the building was unsafe and that gas and oxygen capsules were being stored in unsafe conditions.

    The explosion of missile facilities in the east of Tehran was also called “gas tanker explosion” by the officials of the Islamic Republic and the Islamic Republic Broadcasting.

    Government officials in Iran have not explicitly confirmed the connection between any of the explosions and the fires.

    The only blast ever reported by Islamic Republic officials other than the blasts and fires was last Thursday’s explosion at the Natanz nuclear facility.

    Behrouz Kamalvandi, a spokesman for the Atomic Energy Organization of Iran, specifically described the site of the explosion at the nuclear facility as a center for the development of advanced centrifuges, describing its importance as saying that the explosion could interrupt the activities of the Atomic Energy Organization.
    Please send it to Jason A.
    Discalimer always apply

  5. Israeli Channel 12 TV: Mossad thwarts Iranian attacks on several Israeli diplomatic missions

    Israel’s Channel 12 television reported that “Mossad has recently thwarted a number of Iranian-sponsored attacks on Israeli diplomatic missions in several European countries and other parts of the world.”

    According to the report, which was released on Monday, the names of the countries where the attacks were foiled were not disclosed, but “cooperation with these countries helped to thwart the attacks.”

    Israel’s Channel 12 television also quoted Western intelligence sources as saying that the attack on the Natanz nuclear facility, which has been attributed to Israel, had “delayed Tehran’s plan to enrich uranium for two years.”

    On the other hand, a report broadcast on Israel’s Channel 13 states that the attack “just one year” delayed Iran’s nuclear program.

    On Sunday, the New York Times quoted a Middle East intelligence official as saying that Israel had been involved in the blaze. The bomber struck shortly after noon in front of a police station, officials said. The Middle East official, meanwhile, said other recent suspicious fires in Iran had nothing to do with Israel.

    The New York Times also confirmed that a Revolutionary Guards member had used an explosive device in the incident, but did not say who was involved in the attack.

    Meanwhile, Israeli Defense Minister Benny Gantz rejected the hypotheses about Israel’s role, saying, “Everything that happens there (Iran) cannot be attributed to Israel.”

    Analysts say the fire destroyed a laboratory used to make advanced centrifuges. However, Iran has tried to minimize the damage.

    The Natanz incident came as tensions between Tehran and Western countries over arms embargoes and the nuclear program escalated.

    Reuters quoted three Iranian officials who did not want to be named as saying the blaze was caused by a cyber attack.

    The head of Iran’s passive defense organization also did not rule out the possibility of a cyber attack and spoke of the possibility of “enemy and counter-revolutionary elements” interfering in the blast.

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