A powerful earthquake struck near the Philippine city of Davao on Sunday, officials said, the latest in a series of tremors to strike the southern part of the country in recent months.A six-year-old girl died after a wall collapsed on her as a result of the quake, Vincent Fernandez, the mayor of Matanao town, told local radio.The magnitude 6.8 quake was centred 61km southwest of Davao on the island of Mindanao, at a depth of 28.2km, the US Geological Survey said, revising down the magnitude…