By Mike Crismundo BUTUAN CITY — A 4.2-magnitude earthquake struck Siargao Island again, the Philippine Institute of Volcanology and Seismology (Phivolcs) said. It was an aftershock of the April 26 magnitude-5.5 earthquake in Siargao Island, Surigao Del Norte province, the state agency said. The provincial disaster risk reduction and management council did not report any damage or injury after the Thursday night tremor. In its bulletin, Phivolcs said the new tremor was registered at 7:34 p.m. on Thursday (May 2). The epicenter was plotted 55 kilometers (km) northeast of Pacific Ocean facing town of General Luna, Siargao Island, Surigao del Sur province, it said. The tremor had a shallow depth of only 8 km, Phivolcs said. On Friday (May 3), three mild tremors – magnitudes 3.4, 2.2 and 2.1 – were also registered in the same town, island and province. The series of earthquakes were all tectonic in origin and no tsunami alert was raised by the state agency. All rescue teams and personnel of the disaster risk reduction and management councils (DRRMCs) there are still on “standby alert” due to series of tremors for almost three weeks now. The Philippines lies in the Pacific “Ring of Fire”, where colliding plates in the Earth’s crust cause frequent earthquakes and volcanic activity.