A DEVASTATING 9.3 magnitude earthquake powerful enough to unleash a tsunami could strike the west coast of America after a series of tremors on a major fault line.

Emergency services are already preparing for how to deal with a terrible off-shore earthquake in the Cascadia Subduction Zone, off the west coast of America near California.They were just completing their four-day major emergency test run when a 5.2 magnitude quake hit Borrego Springs, San Diego County, in California on Friday.

The mid-sized earthquake caused more than 200 aftershocks – some more than three on the richter scale – and could be felt from Santa Barbara to the Mexican border.

Egill Hauksson, a research professor of geophysics at Caltech, said of the 5.2 quake: “It was the biggest one for a while.”

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A 3.1 magnitude quake followed yesterday, 14 miles from Borrego Spring according to the US Geological Survey (USGS).And in the last 10 days there has been nine earthquakes of magnitude 3 or greater nearby according to the USGS, leading to fears of what may be to come.

The quakes have taken place on the San Jacinto fault, the region’s most active, Mr Hauksson said.

Scientists say both the California fault lines and the Cascadia Subduction Zone are long overdue a major earthquake of magnitude eight or above.

In a statement after the Cascadia Rising emergency tests a spokesman said: “Subduction zone earthquakes are said to be among the most powerful, and can exceed a 9 magnitude.”