The Denali Fault System is a 1,200-mile-long fault that runs in an upward arc from southwestern Alaska and the Bering Sea into western Canada’s Yukon Territory and British Columbia. The active strike-slip fault system, which runs through Denali National Park and Preserve, is responsible for the formation of the Alaska Range. In 2002, the Denali Fault ruptured, causing significant damage to remote villages and central Alaska’s infrastructure. To better understand the fault system, Dennis Newell, a geochemist at Utah State University, and his colleagues collected and analyzed helium and carbon isotopic data from springs along a nearly 250-mile segment of the fault.

Mantle-to-Surface Volatile Flux

Newell and his colleagues collected samples from 12 springs along the Denali and Totschunda Faults, using both helicopters and on-foot expeditions to access remote, mountainous regions of Alaska’s interior. The team analyzed the helium-3 levels in the springs to determine whether an area had connections to the Earth’s mantle. They found that warm, bubbling springs west of the 2002 earthquake rupture, along the Cantwell segment of the Denali Fault, had a strong helium-3 signature, indicating intact connections to the mantle. Conversely, springs along the ruptured fault segment only had atmospheric gases, suggesting a “roadblock” preventing the flow of mantle helium to the surface. These observations have implications for how groundwater pathways along the fault are changed by earthquakes and the timescales on which they heal.

Newell and his colleagues also sought data on how fast helium can move from the mantle to the crust along active faults. By examining these mantle-to-surface volatile flux rates, the team could determine how fluid pressure gradients may impact fault strength and seismicity along the fault. They found that the fault’s mantle fluid flow rates fall within the range observed for the world’s other major and active strike-slip faults, including California’s San Andreas Fault and Turkey’s North Anatolian Fault Zone.

Newell and his team’s study provides insight into the Denali Fault System, an active strike-slip fault system that runs through Denali National Park and Preserve. The team’s analysis of mantle-to-surface volatile flux rates helps researchers understand how fluid pressure gradients may impact fault strength and seismicity along the fault. By better understanding the fault system, researchers can make more informed predictions about future earthquakes along the fault, which is especially important as the Denali National Park receives some 600,000 visitors each summer.

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