A moderate 5.7-magnitude earthquake hit Japan's remote Volcano Islands today. The US Geological Survey said the quake hit at 86 kilometres south-east of Iwo Jima, at a depth of 138 kilometres. It said, although there was no tsunami warning and no immediate reports of damage or injuries. Around 20 percent of the world's most powerful earthquakes strike Japan, which sits on the Ring of Fire surrounding the Pacific Ocean. But high building standards, regular drills and a sophisticated tsunami warning systems mean that casualties are often minimal.