The first tremor occurred about 37 kilometers 23 miles north northwest of the city of Concepcion at 0851 GMT, according to the US Geological Survey.

It was followed an hour and a half later by a 6.0 temblor 25 kilometers (16 miles north northwest of the same city.The region that was heavily damaged by an 8.8 magnitude quake nearly a year ago.

The reading was based on the open-ended Moment Magnitude scale, now used by US seismologists, which measures the area of the fault that ruptured and the total energy released.

Two quakes strike off Chile coast: US