State lets seismic survey near Beluga reach across the Castle Mountain Fault

Alaska's Division of Oil and Gas on Friday approved a change that lets a seismic survey in the Susitna Flats Game Refuge reach across the Castle Mountain Fault this winter.

Explor Geoscience USA, a Houston company, asked to extend two survey lines near Stump Lake by a combined 9.7 miles. The work is about 13 miles northeast of the Beluga airstrip on the west side of Cook Inlet, according to the state's notice. One line would run 6.1 miles farther northwest, past the fault. The other would stretch 3.6 miles to cover more of the Stump Lake anticline, an arch-shaped fold in the rock layers, according to the approval letter and Explor's application.

The survey will total about 20 miles either way, the application says. Explor will do one of two layouts: the new Stump Lake lines, which it prefers, or the four lines between the Susitna Flats and the Beluga River that the state approved in March 2025. The approval letter describes the change as bringing the survey to 20 miles, as did the state's public notice and Alaska News' Oct. 7 story.

Crews will work on foot, the application says. With portable hand drills, they'll bore holes 5 feet deep and just under 2½ inches wide, load each with a 130- or 230-gram explosive charge and plug it with the drill cuttings. Charges are planned every 66 feet, about 80 to a mile.

Explor plans to mobilize Nov. 1, set out receivers in early January, set off charges Jan. 9 to 24 and finish pulling the data by Feb. 16.

The Alaska Department of Fish and Game limits the work to Nov. 1 through March 31 each year. Explor must coordinate with local subsistence and personal-use harvesters and make a good-faith effort to reach known trapline owners. Where its lines cross snowmachine and dogsled trails, the trails should be marked and Explor must post notice of hazardous work. The division waived its usual performance bond, deciding Explor's liability insurance was enough. The permit runs through March 2030.

The division asked five agencies, including Fish and Game, the Army Corps of Engineers and the Matanuska-Susitna Borough, to weigh in, and posted public notice Oct. 7. No one commented. Only someone who commented can appeal the decision.