A series of new studies by U.S. seismological experts is drawing a closer link between drilling for oil and gas and the disturbing rise in the number of earthquakes in areas not usually prone to seismic activity.
It is by no means breaking news that certain aspects of oil and gas drilling can lead to small earthquakes. But the problem is taking on a new urgency as the U.S. has rapidly expanded oil and gas production in recent years.
The main culprit is the increased use of a controversial drilling technique known as hydraulic fracturing, or fracking. The process involves pumping high-pressure water, sand and chemicals into rock formations deep underground.