A moderate earthquake measuring 5. 3 on the Richter scale jolted Sumatra island of Indonesia on Friday, the country\'s Meteorology and Geophysics Agency reported. The quake struck at 15:51 p.m. Jakarta time (0851 GMT) with epicenter at 99 km southeast Krui of Lampung province and with the depth at 18 km, it said. Indonesia is vulnerable on earthquake as it sits on a vulnerable quake-hit zone so called \"the Pacific Ring of Fire,\" where two continental plates meet that frequently caused seismic and volcanic movement in the country.