Natural gas is a clean burning fuel compared to electricity.

However, don't worry too much about those underground gas lines, all of which have redundant shut off valves every few meters. Worry about naturally occurring pockets of natural gas, or large deposits of Methane gas at the bottom of large lakes, or the ocean. Those, worry about.

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The evidence comes from cores of sediment drilled from the bed of the northern Arabian Sea during a research trip by marine scientists in 2007.

One of the cores has now been found to contain methane hydrates—a solid ice-like crystalline structure of methane and water—only 1.6 metres (5.2 feet) below the sea floor.

Also uncovered were tell-tale signatures from water between sediment grains, and concentrations of a mineral called barite.

Together, these suggested that methane had surged up through the sea bed in recent decades.

"We started going through the literature and found that a major earthquake had occurred close by, in 1945," said David Fischer from the MARUM Institute at the University of Bremen.

"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."

Their search names the culprit as an 8.1-magnitude quake, the biggest ever detected in the northern Arabian Sea.

It ruptured a shallow gas reservoir at a location called Nascent Ridge, according to their paper, appearing in the journal Nature Geoscience.

Over a likely period of decades, around 7.4 million cubic metres (261 million cubic feet) of methane—equivalent roughly to 10 large natural-gas holding tanks—belched to the surface, the authors calculate.