Oklahoma earthquakes and the price of oil

The process of hydraulic fracturing has unlocked an unprecedented amount of oil and gas in the United States. Hydrocarbons are not the only output from this process, though, as billions of barrels of "produced" water are extracted and subsequently pumped back underground. This process of injecting produced water into disposal wells has been causally linked to the rise in earthquakes. Here I show how the amount of earthquakes in Oklahoma are positively linked to the price of oil, and further find that the decrease in earthquake activity in Oklahoma is due to both the drop in oil prices and the regulatory directives of regional authorities. The estimated impact of the various shut-in policies have been small compared to the reduction in earthquakes due to the broad price decline, though. I find that the drop in oil prices that began in mid-2014 led to as large of a reduction in earthquakes as the combined effect of new policies that started in March of 2015.