WASHINGTON (AFP) - A rare 5.6 earthquake considered to be the stongest on record in the area shook the central US state of Oklahoma late Saturday, reportedly causing significant damage. After initially putting the magnitude of the temblor at 5.2, the US Geological Survey revised the strength of the seismic event, the second of the day, saying it had reached magnitude 5.6. The epicenter of the tremor, which occurred at 10:53 pm local time (0353 GMT Sunday), was located just six kilometers (four miles) east of the town of Sparks at a depth of five kilometers. KJRH television said the Lincoln County Emergency Management agency was reporting significant damage, but offered no details.