An earthquake measuring 6.3 on the Richter scale shook northern Pakistan today though there were no reports of damage or casualties due to the second major tremor to hit the country within a week.Meteorological Department chief Arif Mehmood said the quake had its epicenter in Tajikistan at a depth of 89 km.Tremors lasting about 10 seconds were felt in cities like Islamabad, Rawalpindi and Peshawar at 7.45 am. A 7.3-magnitude temblor rocked southwest Pakistan on January 19.