A strong undersea earthquake has hit parts of eastern Indonesia, but there were no immediate reports of damage or casualties. The US Geological Survey says today's 6.3-magnitude quake struck at a depth of 21 miles. It said it was 86 miles southeast of Ambon, the provincial capital of Maluku. Indonesia's meteorology and geophysics agency said there was no danger of a tsunami. Indonesia is prone to seismic upheaval due to its location on the Pacific's Ring of Fire, an arc of volcanoes and fault lines encircling the Pacific Basin.