The operator of a collapsed Utah mine violated safety protocols by cutting coal pillars that should have been left standing to prevent cave-ins, federal regulators said Thursday.

A subsidiary of Ohio-based Murray Energy Corp. undermined other pillars by excavating coal from tunnel floors, a federal report said.

The disaster was caused by poor planning, inadequate design and decisions not to adapt to conditions inside the mine, MSHA Chief Richard Stickler said at a news conference.

“It was not, and I’ll repeat, not a naturally occurring earthquake,” Stickler said. “But in fact a catastrophic outburst of the coal pillars.”

The first details of the Mine Safety and Health Administration report came from a summary issued to reporters and interviews with family members and one of their lawyers.

The Aug. 6 collapse trapped six miners whose bodies have never been recovered. Three others were killed during a rescue attempt.

MSHA said Murray Energy misled regulators about the dangers and violated its approved mining plan. The company says it is preparing a response.