Extraction of natural gas from the deep soil in a region of the Netherlands has triggered an increase in minor earthquakes, similar to seismic effects that have raised concerns about drilling operations, including hydraulic fracturing, in other countries. While the extraction of gas has occurred for decades in the northern Netherlands, including in the province of Groningen, quakes have become more frequent in the last few years, the New York Times reports. The region experienced as few as 20 quakes a year before 2011, but there were 18 during the first six weeks of 2013, with some strong enough to cause significant property damage. According to Chiel Seinen, a spokesman for a local gas consortium known as NAM, natural gas extraction has created at least 1,800 faults in the region’s subsoil, although he said the controversial drilling technique known as fracking is not used in the Dutch region. A new study by Columbia University’s Earth Institute found that a 5.7-magnitude earthquake that occurred in Oklahoma in 2011 may have been the largest quake yet that can be linked to the injection of wastewater as part of an energy extraction project.