Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists find pre-earthquake activity in central Alaska

06.06.2018

Earth scientists consistently look for a reliable way to forecast earthquakes. New research from University of Alaska Fairbanks Geophysical Institute professor Carl Tape may help in that endeavor, due to a unique set of circumstances.

"Our observations have recorded an unequivocally interesting sequence of events," Tape said.

Tape and his colleagues found evidence for accelerating activity before a 2016 earthquake in a laterally moving fault zone in central Alaska. The activity included a phenomenon known as very low-frequency earthquakes, referring to the type of energy waves associated with it.


Lakes in the roadless Minto Flats surround the Tanana River in this photo from July 2014. The ridge on the horizon leads down to the town of Nenana, Alaska. Seismic stations placed in this unique region detected some intriguing pre-earthquake activity.

Credit: UAF Photo by Carl Tape


University of Alaska Fairbanks doctoral student Kyle Smith installs a T120 posthole seismometer at a site in the Minto Flats of central Alaska in September 2015.

Credit: UAF photo by Carl Tape

Typical earthquakes have two associated energy waves, called the P and S waves. Very low-frequency earthquakes do not have such signals. Instead, their waves occur on much lower frequencies.

"Most earthquakes start abruptly, but not always," said Luciana Astiz, a program director in the National Science Foundation's Division of Earth Sciences, which supported the research. "A fault zone in central Alaska monitored by new scientific instruments offers a look at a more complex process.

This study reports the first observations of a slow process that transitions into an earthquake -- something previously observed only in laboratory experiments. These new observations contribute toward understanding the physics of earthquakes."

In 2015, Tape installed 13 seismic stations in the Minto Flats of central Alaska to capture the area's fault activity. Nine days later, the instruments recorded a long-duration, very low-frequency process, normally only seen in deep subduction zones. This event showed a small amount of activity gathering, or nucleating, in a central area below the surface. It did not lead to an earthquake.

A second, similar event in 2016 led to a key observation. At Minto Flats, a magnitude 3.7 quake occurred at a depth of about 10.5 miles, not an unusual event in itself. However, the event was preceded by a 12-hour accelerating sequence of earthquakes and 22 seconds of distinct high- and low-frequency waves in a concentrated area.

Tape said that this kind of slow event transitioning into a rupture had previously only been seen in laboratory experiments.

"The rupture process started, then it found a patch of the fault that was ready to go, and that's what people have not seen. It's really exciting," Tape said.

"The leap we make, and maybe the more controversial thing, is that this emergent long-period signal only seen on top of the fault is a low-frequency signal that can sometimes turn into an earthquake and sometimes not," Tape said.

Tape and his colleagues may have seen this kind of activity before. In 2012, there was a similar small event recorded in central Alaska. At that time, a magnitude 8.6 earthquake took place under the Indian Ocean and its energy was felt around the world. Because of the magnitude of this event, the smaller activity from central Alaska was overshadowed. Whatever signal the Minto Flats site gave off could not be confirmed. However, it was intriguing enough to help justify putting sensors in the area.

"Never in my wildest dreams did I expect we'd see something like that again," Tape said. "I assumed that the conditions that happened in 2012 were somehow unique and that huge surface waves led to this nucleation. Even though I proposed putting instruments on the area in a proposal, it was the last item I put on. I thought, "Maybe we'll see something crazy out there.'"

By 2016, Tape had high-quality stations on top of the Minto Flat faults, around 18 miles from the main events, and no triggering earthquake to complicate the data.

"We are staring right at this process, and what it showed was that exactly during the tremor-like signal there is this emergent long-duration signal that hints at what's driving this nucleation phase," he said.

Geologists have been looking for something like this for a long time. So why hasn't anyone seen it?

"I'm left saying 'I don't know,'" Tape said. "I'm going to assume everyone has been looking for something before the P wave forever. It leads me to believe there is something special about this fault zone."

Minto Flats has a deep sedimentary basin, strike-slip faulting, active tectonics and deep earthquakes; it is an unusual site.

"In some ways, I wish there wasn't anything special. I wish it was a global phenomenon that we discovered, but it's not," Tape said. "It appears there is something special about the conditions in Minto Flats."

The results of the research will appear in the latest issue of the journal Nature Geoscience. The paper is titled "Earthquake Nucleation and Fault Slip Complexity in the Lower Crust of Central Alaska."

The project was primarily funded by a National Science Foundation CAREER project that supported Tape and his student co-authors, Vipul Silwal and Kyle Smith.

Media Contact

Fritz Freudenberger
ffreudenberger@alaska.edu
907-474-7185

 @uafairbanks

http://www.uaf.edu 

Fritz Freudenberger | EurekAlert!
Further information:
https://news.uaf.edu/scientists-find-pre-earthquake-activity-in-central-alaska/
http://dx.doi.org/10.1038/s41561-018-0144-2

More articles from Earth Sciences:

nachricht New Measurement Device: Carbon Dioxide As Geothermometer
21.05.2019 | Universität Heidelberg

nachricht Cause for variability in Arctic sea ice clarified
14.05.2019 | Max-Planck-Institut für Meteorologie

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Self-repairing batteries

UTokyo engineers develop a way to create high-capacity long-life batteries

Engineers at the University of Tokyo continually pioneer new ways to improve battery technology. Professor Atsuo Yamada and his team recently developed a...

Im Focus: Quantum Cloud Computing with Self-Check

With a quantum coprocessor in the cloud, physicists from Innsbruck, Austria, open the door to the simulation of previously unsolvable problems in chemistry, materials research or high-energy physics. The research groups led by Rainer Blatt and Peter Zoller report in the journal Nature how they simulated particle physics phenomena on 20 quantum bits and how the quantum simulator self-verified the result for the first time.

Many scientists are currently working on investigating how quantum advantage can be exploited on hardware already available today. Three years ago, physicists...

Im Focus: Accelerating quantum technologies with materials processing at the atomic scale

'Quantum technologies' utilise the unique phenomena of quantum superposition and entanglement to encode and process information, with potentially profound benefits to a wide range of information technologies from communications to sensing and computing.

However a major challenge in developing these technologies is that the quantum phenomena are very fragile, and only a handful of physical systems have been...

Im Focus: A step towards probabilistic computing

Working group led by physicist Professor Ulrich Nowak at the University of Konstanz, in collaboration with a team of physicists from Johannes Gutenberg University Mainz, demonstrates how skyrmions can be used for the computer concepts of the future

When it comes to performing a calculation destined to arrive at an exact result, humans are hopelessly inferior to the computer. In other areas, humans are...

Im Focus: Recording embryonic development

Scientists develop a molecular recording tool that enables in vivo lineage tracing of embryonic cells

The beginning of new life starts with a fascinating process: A single cell gives rise to progenitor cells that eventually differentiate into the three germ...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

Summit charts a course to uncover the origins of genetic diseases

22.05.2019 | Life Sciences

New study finds distinct microbes living next to corals

22.05.2019 | Life Sciences

Stellar waltz with dramatic ending

22.05.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>