Large earthquakes around the world have been found to trigger tremors at US sites where wastewater from gas drilling operations is injected into the ground, a US study said Thursday.

For instance, the massive 9.0 magnitude earthquake in Japan in 2011 set off a swarm of earthquakes in the western Texas town of Snyder near the Cogdell oil field, culminating in a 4.5 magnitude quake there about six months later, said the research in the journal Science.

Similarly, small to mid-sized quakes were observed near active injection wells in Prague, Oklahoma following an 8.8 magnitude quake in Chile in 2010.

Uncommon seismic activity stirred that region 16 hours after the Chile quake with a 4.1 magnitude tremor, and it continued until a 5.7 magnitude quake in November 2011, said researchers at Columbia University’s Lamont-Doherty Earth Observatory.

The 2010 Chile quake also led to heightened seismic activity in Trinidad, Colorado, including a 5.3 magnitude quake in August 2011, in an area where methane is extracted from the coal bed and wastewater is reinjected into the Earth.

‘We weren’t really confident until we found the same pattern of little bursts of seismicity following the passage of seismic waves from several of these big earthquakes,