From when records began in 1776 until 2011, the residents of Youngstown, Ohio, had never experienced an earthquake. However, in December 2010, Northstar 1, a well built to pump wastewater produced by fracking in the neighbouring state of Pennsylvania, came online. Over the following year, seismometers in and around Youngstown recorded 109 earthquakes, including a 3.9-magnitude tremor on 31 December 2011.
When a team led by Won-Young Kim of Columbia University analysed the Youngstown earthquakes, they found that their onset, cessation and even temporary dips in activity were all tied to the activity at the Northstar 1 well. The first earthquake occurred 13 days after pumping began, and the tremors ceased shortly after the Ohio Department of Natural Resources shut down the well in December 2011. Earthquake activity dipped in the periods after US public holidays and when injection at the well was temporarily stopped.
‘The earthquakes were centred in subsurface faults near the injection well,’ Kim said. ‘These shocks were likely due to the increase in pressure from the deep waste water injection, which caused the existing fault to slip. Throughout 2011, the earthquakes migrated from east to west down the length of the fault away from the well – indicative of the earthquakes being caused by an expanding pressure front.’
This story was published in the October 2013 edition of Geographical Magazine