QUETTA : A 5.1-magnitude earthquake struck Balochisan on Friday, but officials said there were no immediate reports of damage or casualties. The epicentre was close to Sibi at a depth of 71 kilometres, a meteorological official, Mahwish Ahmad told AFP.  The quake, measured by the US Geological Survey at a 4.9 magnitude, comes a week after one person was killed and 30 injured in a series of small tremors in southern Pakistan.