What Caused the 1960s Denver Earthquakes?

In March 1962, the Rocky Mountain Arsenal, a chemical weapons plant northeast of Denver, had begun injecting contaminated wastewater down a 12,045-foot well. The earthquakes started the next month.

When the injections stopped temporarily in 1963, the number of earthquakes dropped. When the injections resumed in 1964, the number of earthquakes increased. The wastewater injections stopped permanently in early 1966, but the earthquakes didn’t stop until late 1968.

How did the wastewater injections cause earthquakes? Scientists think that the wastewater acted as a lubricant that reduced friction between underground rocks, allowing them move more easily. When movement occurred on a sufficiently large scale, an earthquake resulted.