More than 600 aftershocks have been recorded by the Philippine Institute of Volcanology and Seismology three days after a magnitude-6.3 earthquake hit Mindanao last Thursday.
According to Phivolcs science research specialist Dante Soneja, 663 small-to-strong magnitude aftershocks have been documented as of 8 a.m. Sunday. Three-hundred twenty-four were plotted from their original source, Tulunan, North Cotabato, while only 27 were felt.
Phivolcs said the destructive earthquake was generated by the movement of a northwest-trending strike-slip fault in Tulunan.
According to Phivolcs, four onshore earthquakes ranging from magnitude-five to magnitude-7.6 have occurred in Cotabato and nearby areas from 1924 to present. Small-magnitude earthquake swarms less than magnitude four were also recorded from April to May 1993 and August 2007.
Phivolcs said the most recent event that affected Cotabato is the magntiude-5.6 earthquake last July 9. The maximum intensity of this event was felt in Makilala, Kidapawan City, Matalam, M’lang, and Antipas, all in Cotabato, and Tulunan at Intensity 6.
It explained that Central Mindanao, which includes Cotabato, is one of the seismically active areas in the country because of the presence of the western extension of the Mindanao Fault or the Cotabato-Sindangan Fault.
This active fault traverses Sarangani to northwest of Zamboanga Peninsula. Cotabato Trench is also a major source of earthquakes which can affect the region, it also said.
In addition, there are other nearby local faults, some of which may be covered by recent deposits, and could be sources of small to strong magnitude earthquakes, it added. (Ellalyn V. Ruiz)
