Bubble, bubble, more earthquake problems? Geo

Photo: Utah State University geochemist Dennis Newell collects data from a spring along the Cantwell section of the Denali Fault in Alaska. He and his colleagues published the findings in the journal Geology, citing evidence of mantle-to-crust connections that increase the likelihood of a major earthquake in the future. Show more

Credit: Jeff Benowitz

LOGAN, UT, USA – The 1,200-mile-long Denali Fault extends in an upward arc from southwestern Alaska and the Bering Sea east to the Yukon Territory of western Canada and British Columbia. The active and perennial slip fault system, which cuts through Denali National Park and Preserve, is responsible for shaping the Alaskan mountain range.

“It is a large sweeping fault and the source of a magnitude 7.9 earthquake in 2002, which tore through more than 200 miles of the Denali Fault, along with the Tochunda Fault to the east, causing massive damage to remote villages and infrastructure in central Alaska,” says the chemist. Utah State University geologist Dennis Newell.

Understanding the mantle-crust connections of the Restless Fault provides important information for understanding the seismic cycle of lithosphere faults, says Newell, associate professor in USU’s Department of Earth Sciences. He and colleagues Jeff Benowitz, Alaska chronogeologist Sean Regan of the University of Alaska Fairbanks, and doctoral candidate Coleman Hett of USU collected and analyzed helium and carbon isotope data from springs along a roughly 250-mile section of the fault and published their findings. To her, “Roadblocks and Velocity Limits: Mantle-to-Surface Vulcanizing Flow in Lithospheric Scale Denali Rift, Alaska,” in the June 1, 2023 print issue of the journal Geology.

The research was funded by a one-year National Science Foundation Early Concept Exploratory Research (EAGER) grant awarded to Newell and Regan in 2020.

“Active glide faults like Denali have three-dimensional geometries with potential channel connections deep below the Earth’s surface,” says Newell. “But we don’t know much about how and if these connections are maintained.”

To study these possible deep connections, Newell and Regan sampled 12 springs along the Denali and Tochunda Rifts, by helicopter and on foot, to remote mountainous regions within Alaska.

“Helium-3, a rare isotope of helium gas, in springs is a good indicator of whether or not the area is mantle-bound,” says Newell. Warm, bubbling springs west of the ruptured 2002 earthquake, along the Cantwell section of the Denali fault, have a strong helium-3 signature, indicating intact connections to the mantle. In contrast, springs along the fault section of the rupture contain only atmospheric gases, making indicates a “barrier” preventing mantle helium from flowing to the surface.”

He says these observations have implications for how groundwater tracks along the fault are altered by earthquakes, and the time scales on which they heal.

“The last major earthquake in the Cantwell sector was 400 years ago, and the helium data indicates that shelf connections have been re-established,” says Newell. “These bubbling springs indicate the potential for a major destructive earthquake in the future along the Denali Fault segment near Denali National Park, which receives about 600,000 visitors each summer.”

Geologists are also looking for data on how quickly helium moves from the mantle to the crust along active faults.

“This is the ‘velocity limit’ part of our research,” Newell says. “This is important because it reveals volatile flow from the mantle to the surface and how fluid pressure gradients can affect fault strength and seismicity along the fault.”

Mantle fluid flow rates for the fault fall in the range observed for other major and active slip faults in the world that form plate boundaries, he says, including the San Andreas fault in California and the North Anatolian fault zone in Turkey. These types of faults host large and destructive earthquakes, such as the deadly February 2023 earthquake on the East Anatolian fault, which caused widespread devastation in Turkey and Syria.

“Measuring crust-to-mantle connections along main strike slip faults is critical to understanding links between deep fluid flow, seismicity, and fault healing,” Newell says.

research method

Data/statistical analysis

Research topic

Not applicable

Article title

Roadblocks and speed limits: choppy flow from the mantle to the surface across the Denali Lithospheric Rift, Alaska.

The date the article was published

April 13, 2023

COI statement

The authors declare no conflicts of interest.

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