A strong earthquake measuring 6.4 on the Richter scale struck the southern Philippine island of Mindanao on Friday, according to the German Research Centre for Geosciences (GFZ). The quake hit at a depth of 29 kilometres (18.02 miles), GFZ said in a preliminary assessment. There were no immediate reports of casualties, damage, or tsunami warnings following the tremor. The Philippines lies along the Pacific "Ring of Fire," a seismically active zone where earthquakes and volcanic eruptions occur frequently due to the movement of tectonic plates.