A strong undersea earthquake measuring 7.4 on the Richter scale struck off Indonesia's north Sulawesi province early Saturday, but there were no immediate reports of injury or damage. The quake's epicentre was about 410 km north-west off North Sulawesi province, Indonesia's National Meteorology and Geophysics Agency said. There was no tsunami warning, reported DPA. Indonesia, the world's largest archipelago nation, sits atop the Pacific Ocean's Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity