By Ellalyn De Vera-Ruiz  The 6.1-magnitude earthquake that jolted parts of Luzon, including Metro Manila on Monday had spawned close to 500 lesser-sized tremors in a span of 15 hours. According to Philippine Institute of Volcanology and Seismology (Phivolcs) science research assistant Maila Advincula, as of 8 a.m. Tuesday, 491 aftershocks have been recorded close to the original source of the 6.1-magnitude earthquake. Rescue workers search for survivors in a collapsed Chuzon Super Market in Porac, Pampanga, after a powerful earthquake hit northern Philippines on April 22, 2019.
(Photo by Noel CELIS / AFP / MANILA BULLETIN) Of the recorded aftershocks, 62 were plotted and only eight were felt, ranging between magnitudes 1.4 and 3.4 and intensities 1 and 3. Advincula explained that the earthquakes occurred at shallow depths and can be possibly attributed to the movement of an unnamed local fault in the vicinity of Zambales province. She warned the public that aftershocks, mostly with smaller magnitudes, may persist for the next one to two weeks. The 6.1-magnitude tremor on Monday caused panic in Luzon, especially in the metropolis as Phivolcs has repeatedly warned that Metro Manila is due for a "big one," a term used to describe a destructive earthquake, which could measure 7.2-magnitude and can occur along the West Valley Fault System located in eastern Metro Manila. Advincula clarified that Monday’s quake was not generated by the West Valley Fault nor the Manila Trench—an ocean trench west of the country that could cause tsunami after a powerful earthquake. On average, around 20 earthquakes daily are recorded by Phivolcs all over the country, but some of them are too weak to be felt. Earthquakes are frequent in the Philippines because of several active faults surrounding or crisscrossing the country. Read more: Strong 6.1 quake jolts Metro, Luzon