On August 9, 1967, a 5.5 magnitude earthquake struck Northglenn, a northern suburb of Denver, Colorado.
The Associated Press wrote that it was “the severest earthquake ever recorded” in the city’s history. Building foundations cracked, windows broke, bricks flew off of downtown rooftops.
A year later in the prominent academic journal “Science,” geophysicist J.H. Healy and his associates proposed that humans, not nature, were responsible for the quake.
“We attempt here to present the statistical evidence for correlating the two events — fluid injection and earthquakes — and to develop a hypothesis relating the two as cause and effect,” Healy wrote.
The “fluid injection” Healy was referencing had been taking place two miles from Northglenn at the U.S. Army’s Rocky Mountain Arsenal manufacturing plant. In 1961, the army drilled a “disposal waste well” through 2.2 miles of sedimentary rock, and had begun injecting it with contaminated industrial wastewater.