(CNN) -- The U.S. government Thursday announced its highest penalty for coal mine safety violations, $1.85 million, for a collapse that killed six miners in Utah last year.
Insufficient pillar support and activity in areas that should not have been mined caused the August Crandall Canyon mine collapse, federal investigators found.
The government fined the mine operator, Genwal Resources, $1.34 million "for violations that directly contributed to the deaths of six miners last year," plus nearly $300,000 for other violations.
The government also levied a $220,000 fine against a mining consultant, Agapito Associates, "for faulty analysis of the mine's design."
The mine's owner had insisted that earth movement detected at the time of the collapse had caused the disaster. But investigators found instead that the collapse caused the earth movement.
"It was not -- and I repeat, it was not -- a natural occurring earthquake," said the government's top mine safety official, Richard E. Stickler.
Stickler, the acting assistant secretary of labor for mine safety and health, said, "pillars failed under excessive load and ejected coal very violently."
Stickler also said the mine's operator "was taking more coal than allowed from the barrier pillars and the floor."
"This dangerously weakened the strength of the roof support," Stickler said.
In addition to the six miners killed in the initial cave-in August 6 in northwest Emery County, three would-be rescuers died 10 days later in a subsequent collapse. The bodies of the six miners killed in the initial collapse were never recovered.
Richard Gates, the lead investigator for the government, said the pillars in the mine "simply were not large enough to support the load."
That resulted in a "catastrophic failure of pillars over a broad area," as large as half a mile, he said.
University of Utah scientists said in June that the collapse was not the result of an earthquake.
"As seismologists, we're as certain as we can be that the seismic event registered as a magnitude-3.9 shock was due to the collapse of the mine and not a naturally occurring earthquake," said Walter Arabasz, director of the university's Utah Seismograph Stations, in a written statement.
Earlier this year, a Labor Department report criticized Mine Safety and Health Administration officials for approving plans for a risky mining technique, known as retreat mining, that was in use before the collapse. In the process, miners remove pillars of coal that support the roof of a chamber one by one, allowing the roof to collapse behind them.
Mine owner Bob Murray repeatedly denied in the days after the disaster that his company practiced retreat mining at Crandall Canyon. He later admitted that the practice had been used at the mine but said it was not being done at the time of the disaster.