Earthquakes can create pathways for methane to escape from underground reservoirs, a new study has found.
The researchers suggest quake-released methane should be considered as another cause of climate change, describing methane as a "potent greenhouse gas".
But they did not know how much of the gas might be escaping as a result of earthquakes.
Results of the study by German and Swiss scientists have been published in the journal Nature Geoscience.
Evidence for the findings came from cores of sediment drilled from the bed of the northern Arabian Sea off Pakistan during a research trip in 2007. One core contained a solid ice-like crystalline structure of methane and water, called methane hydrates, just 1.6 metres below the sea floor.
That discovery, along with others suggested methane had surged up through the seabed in recent decades.
The researchers found an 8.1-magnitude quake had occurred nearby in 1945. Their paper said the quake had ruptured a shallow gas reservoir at a place called Nascent Ridge.
"Based on several indicators, we postulated that the earthquake led to a fracturing of the sediments, releasing the gas that had been trapped below the hydrates into the ocean, David Fischer from the University of Bremen said.
The study calculated around 7.4 million cubic metres of methane - equivalent roughly to 10 large natural gas tankers - reached the surface during a period likely to have taken decades. That estimate was conservative and other sites in the area could have been breached by the quake.
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