Suva, May 14 (Reporter) A 6.4-magnitude earthquake jolted 137 km West of Neiafu, Tonga at 17:15 local time (0415 GMT) on Wednesday, the U.S. Geological Survey (USGS) said. There were no immediate reports of casualties or damage. The epicenter, with a depth of 243.1 km, was initially determined to be at 18.720 degrees south latitude and 175.283 degrees west longitude, according to the USGS. The Pacific Tsunami Warning Center did not immediately issue a tsunami warning based on the quake. Pacific island countries such as Fiji, Tonga and Vanuatu lie on the so-called Pacific "Ring of Fire," an arc of earthquake and volcanic zones where continental plates collide, producing frequent seismic activities...////...