Both earthquakes, which came within hours of each other, were on the “Ring of Fire”, fault lines along the Pacific coasts of America and Asia. But scientists said that the second was a “tragic coincidence” rather than a consequence of the first.

“The chances of there being a connection between these two earthquakes is extremely slim,” said Professor John McCloskey, a geophysicist at the University of Ulster. The distance between the quakes — 6,200 miles —and the orientation of the tectonic plates made a causal link physically implausible, he said.

Early estimates suggest that the Sumatra quake occurred about 50 miles beneath the Earth’s crust, so deep that there was little or no movement on the ocean floor, and no resultant tsunami.

A key concern is that the quake could have led to an increase in pressure at other points along the fault line, which could trigger a second tremor closer to the surface.

“The real danger in the coming days is that a second larger quake with a magnitude of around 8.5 could occur just off the coast of Padang,” Professor McCloskey said. That could result in a huge tsunami submerging the town and surrounding coastline, which has a population of about 1.5 million.

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