Sloshing Of Earth’s Core May Spike Major Earthquakes

The world doesn’t stop spinning. But every so often, it slows down. For decades, scientists have charted tiny fluctuations in the length of Earth’s day: Gain a millisecond here, lose a millisecond there. Last week at the annual meeting of the Geological Society of America here, two geophysicists argued that these minute changes could be enough to influence the timing of major earthquakes—and potentially help forecast them.

During the past 100 years, Earth’s slowdowns have correlated surprisingly well with periods with a global increase in magnitude-7 and larger earthquakes, according to Roger Bilham of the University of Colorado (CU) in Boulder and Rebecca Bendick at the University of Montana in Missoula. Usefully, the spike, which adds two to five more quakes than typical, happens well after the slow-down begins. “The Earth offers us a 5-years heads up on future earthquakes, which is remarkable,” says Bilham, who presented the work.

Most seismologists agree that earthquake prediction is a minefield. And so far, Bilham and Bendick have only fuzzy, hard-to-test ideas about what might cause the pattern they found. But the finding is too provocative to ignore, other researchers say. “The correlation they’ve found is remarkable, and deserves investigation,” says Peter Molnar, a geologist also at CU.

The research started as a search for synchrony in earthquake timing. Individual oscillators, be they fireflies, heart muscles, or metronomes, can end up vibrating in synchrony as a result of some kind of cross-talk—or some common influence. To Bendick, it didn’t seem a far jump to consider the faults that cause earthquakes, with their cyclical buildup of strain and violent discharge, as “really noisy, really crummy oscillators,” she says. She and Bilham dove into the data, using the only complete earthquake catalog for the past 100 years: magnitude-7 and larger earthquakes.

In work published in August in Geophysical Research Letters they reported two patterns: First, major quakes appeared to cluster in time—although not in space. And second, the number of large earthquakes seemed to peak at 32-year intervals. The earthquakes could be somehow talking to each other, or an external force could be nudging the earth into rupture.

Exploring such global forces, the researchers eventually discovered the match with the length of day. Although weather patterns such as El Nino can drive day length to vary back and forth by a millisecond over a year or more, a periodic, decades-long fluctuation of several milliseconds—in particular, its point of peak slow down about every three decades or so—lined up with the quake trend perfectly. “Of course that seems sort of crazy,” Bendick says. But maybe it isn’t. When day length changes over decades, Earth’s magnetic field also develops a temporary ripple. Researchers think slight changes in the flow of the molten iron of the outer core may be responsible for both effects. Just what happens is uncertain—perhaps a bit of the molten outer core sticks to the mantle above. That might change the flow of the liquid metal, altering the magnetic field, and transfer enough momentum between the mantle and the core to affect day length.

Seismologists aren’t used to thinking about the planet’s core, buried 2900 kilometers beneath the crust where quakes happen. But they should, Bilham said during his talk here. The core is “quite close to us. It’s closer than New York from here,” he said.

At the equator, Earth spins 460 meters per second. Given this high velocity, it’s not absurd to think that a slight mismatch in speed between the solid crust and mantle and the liquid core could translate into a force somehow nudging quakes into synchrony, Molnar says. Of course, he adds, “It might be nonsense.” But the evidence for some kind of link is compelling, says geophysicist Michael Manga of the University of California, Berkeley. “I’ve worked on earthquakes triggered by seasonal variation, melting snow. His correlation is much better than what I’m used to seeing.”

One way or another, says James Dolan, a geologist at the University of Southern California in Los Angeles, “we’re going to know in 5 years.” That’s because Earth’s rotation began a periodic slow-down 4-plus years ago. Beginning next year, Earth should expect five more major earthquakes a year than average—between 17 to 20 quakes, compared with the anomalously low four so far this year. If the pattern holds, it will put a new spin on earthquake forecasting.

Earthquake Risk Elevated With Detection Of Spontaneous Tectonic Tremor In Anza Gap

Scientists at the University of California, Riverside have detected spontaneous tectonic tremor—a signature of slow earthquakes deep below the earth’s surface—in the Anza Gap region of the San Jacinto Fault. Tectonic tremors are believed to increase the likelihood of a moderate to large, damaging earthquake occurring close to the earth’s surface by altering the stress along the fault.

Abhijit Ghosh, an assistant professor of earth sciences in UCR’s College of Natural and Agricultural Sciences, and Alexandra Hutchinson, an earth sciences graduate student, published the research in the Bulletin of the Seismologic Society of America.

The paper is titled “Ambient Tectonic Tremor in the San Jacinto Fault, Near the Anza Gap, Detected by Multiple Mini Seismic Arrays.”

The San Jacinto Fault zone, which is part of the San Andreas Fault system, runs underneath densely populated areas of Inland Southern California, including San Bernardino, Redlands, and Moreno Valley. It is the most active fault in Southern California and sits five miles from the UCR campus. While it is technically not a plate boundary, the San Jacinto Fault accommodates some of the movement that occurs as the North American Plate and the Pacific Plate grind together at the San Andreas Fault.

Over the past 200 years, the 20-km region known as the Anza Gap is the only stretch along the 200-km fault line that has not experienced an earthquake of magnitude 5.5 or greater.

“While other regions of the San Jacinto fault give rise to small and moderate earthquakes on a regular basis, the Anza Gap is surprisingly quiet, which raises questions about how it is releasing the stress it accumulates,” Ghosh said. “For that reason, many experts suspect that this area is ripe to produce a damaging earthquake.”

Using data from 2011 and a new, highly sensitive detection method developed by Ghosh called “multibeam backprojection,” the researchers uncovered the first evidence of a spontaneous tectonic tremor in the Anza Gap. Relatively little is known about tectonic tremors, which were first identified in Japan in 2001. Researchers now know they are associated with a phenomenon called “slow slip,” a slow and transient movement of plates deep below the earth’s surface that can last from several minutes to several years and may occur daily, annually, or anywhere between, depending on the fault.

“While relatively little is known about tectonic tremors, in part because they have historically been difficult to detect, we know that these tremors are being caused by slow slip deep in the fault, and that when the deep part of the fault slips it adds stress to the shallow part. This may ultimately help to cause a damaging earthquake,” Ghosh said.

Ghosh said seismologists should further study tremor activity in the area to learn how the deep roots of fault zones impact activity closer to the earth’s surface and affect earthquake hazard.

“Tectonic tremors and slow slip will change the way we view faults. For example, our research on the Anza gap shows that the fault is spontaneously slipping at a greater depth than we previously thought, with slow earthquakes occurring between 13 and 24 km deep.”

“Since there is a connection between deep slow slip and damaging earthquakes closer to the surface, it may be possible that tectonic tremors will enable us to forecast major earthquakes in the future. Much more research is needed before that can happen, though.”

Low-Pitched, Rumbling Rocks Could Help Predict When Earthquakes Strike: Research Says

TEPIC, Mexico – Rocks under increasing pressure before earthquakes strike send out low-pitched rumbling sounds that the human ear cannot detect but could be used to predict when a tremor will strike, scientists said on Monday.

Researchers recreated powerful earthquake forces in a laboratory and used high-tech algorithms to pick out the acoustic clues amid all the other noise of a pending quake, according to findings published in Geophysical Research Letters, a journal published by the American Geophysical Union.

The sounds are emitted typically a week before an earthquake occurs, so deciphering them would allow scientists to pinpoint the timing of a tremor, the research paper said.

Scientists currently can calculate the probability of an earthquake in a particular area but not when it will happen, according to the U.S. Geological Survey.

“People have said you can’t predict earthquakes. People have tried. We’re now saying we believe for the first time we can predict an earthquake in a laboratory,” said Colin Humphreys, professor of materials science at Cambridge University and one of the paper’s authors.

“What happens before an earthquake is that rocks emit noise because one grain of rock is rubbing against another grain of rock…. It’s a little like a squeaky door,” Humphreys told the Thomson Reuters Foundation

“This noise is emitted typically one week before an earthquake happens,” he said. “You get one week’s warning so you get time to evacuate people and get many fewer deaths.”

The research simulating multiple earthquake scenarios using steel blocks and pistons and machine-learning algorithms systems was conducted at New Mexico’s Los Alamos National Laboratory, where the world’s first nuclear bomb was designed and built.

The seismic signals generated in the simulations were analyzed by machine-learning systems that could identify the low rumblings that strengthen as tremors approach, Humphreys said.

The acoustic clues had previously been detected by scientists but rejected as random noise, he said.

The Los Alamos experiment will be applied to quake-prone areas such as the San Andreas fault in California, he said.

The next challenge is determining a quake’s magnitude in advance, Humphreys told the Foundation.

“There is hope that we can solve these problems, and this is a first step,” he said.

The sounds also could be used to warn of landslides or avalanches.

Strong 6.7 Earthquake Hits East Nusa Tenggara, No Tsunami Warning

A strong 6.7-magnitude earthquake struck off the coast of East Nusa Tenggara on Tuesday, US seismologists said, but no tsunami warning was issued and there were no immediate reports of casualties or damage.

The quake hit East Nusa Tenggara about 318 kilometres kilometres northwest of the provincial capital Kupang at a depth of 549 kilometres, according to the US Geological Survey.

“We are collecting reports about potential damages but the earthquake was very deep, and there was tsunami potential,” a spokesman for Indonesia’s geophysics and meteorological agency told AFP.

Indonesia experiences frequent seismic and volcanic activity due to its position on the Pacific “Ring of Fire”, where tectonic plates collide.

An earthquake struck the country’s western Aceh province in December 2016, killing more than 100 people, injuring many more and leaving tens of thousands homeless.

New Zealand Hit By ‘Big’ 5.4 Magnitude Earthquake, Causing Landslides

New Zealand’s South Island has been struck by a “big” 5.4 magnitude earthquake, causing landslides.

The quake struck near the town of Kaikoura on Sunday, at a depth of 13km, causing strong shaking.

No casualties were reported after the earthquake struck.

“Looks like that was a bit of a rattle. Hope everyone who felt that is doing ok,” tweeted the New Zealand Ministry of Civil Defence and Emergency Management.

Residents and tourists were shaken but unhurt by the quake, which was followed by number of lighter aftershocks.

Hotel manager Ross James said it was “a big one”.

He told the New Zealand Herald: “It certainly felt like a [magnitude] five… It was short and sharp. It was very, very sharp, quick and then it was over.

“There are people here from China who only just arrived but they took it extremely well – they said ‘We’ve got earthquakes in China as well’ so they’re all happy.”

Another Kaikoura hotel employee, named Warren, told Stuff: “We’ve got eight rooms full – all bar one couple are from overseas and they weren’t sure what it was all about.

Magnitude 6.3 Earthquake Shakes Northern Chile

SANTIAGO, Chile – The U.S. Geological Survey says a magnitude 6.3 earthquake has struck northern Chile.

The quake, which was moderately deep at 82 kilometers (51 miles), struck at 3:32 a.m. local time Tuesday. The epicenter in Tarapaca was 73 kilometers (45 miles) east of the port city of Arica, and 87 kilometers (54 miles) southeast of the larger Peruvian city of Tacna.

No further information was immediately available.

Magnitude 6.3 Earthquake Strikes Northern Chile: USGS

WASHINGTON, United States – A 6.3-magnitude earthquake struck northern Chile early Tuesday, the US Geological Survey said.

The tremor hit 70 kilometers (43 miles) east of the coastal city of Arica, which is near the border with Peru, the US agency said.

The quake struck at a depth of 82 kilometers, it added.

Chile is one of the world’s most earthquake-prone countries. In the past seven years, it has had three quakes of a magnitude greater than eight.

The 1960 Valdivia earthquake in Chile was the strongest quake ever recorded at 9.5 on the magnitude scale, according to the US Geological Survey.

Chile lies on what is known as the Ring of Fire — an arc of fault lines that circles the Pacific Basin and is prone to frequent earthquakes and volcanic eruptions.

The north of Chile was struck by an 8.3-magnitude quake, followed by a tsunami in September 2015, killing 15 people.