The 16 October 2019 M6.3 Tulunan, Cotabato Earthquake Summary of QRT Investigation

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On 16 October 2019, 07:37 PM Philippine Standard Time (PST), a magnitude (Ms) 6.3 earthquake struck the provinces of Cotabato and Davao del Sur, and vicinity. The hypocenter was located 22 km southeast of Tulunan, Cotabato, with focal depth of 9 km. Initial earthquake information, including focal mechanism and aftershocks distribution, suggests that the earthquake was generated by northwest-trending strike-slip fault in the area. The strongest ground shaking was felt at PHIVOLCS Earthquake Intensity Scale (PEIS) VIl (Destructive) in Tulunan, M’lang, Makilala and Kidapawan City in the province of Cotabato; Magsaysay, Matanao, Digos City, Hagonoy and Bansalan in the province of Davao del Sur, and northwest portion of Columbio in the province of Sultan Kudarat. The rest of the municipalities from these provinces experienced PEIS VI (Very Strong) and V (Strong) ground shaking. Small to moderate earthquakes were recorded afterwards. As of 07:37 PM, 27 October 2019, a total of 874 aftershocks were recorded by the DOST-PHIVOLCS seismic monitoring network. The largest aftershock was recorded on 16 October 2019, at 08:09 PM with a magnitude (Ms) of 5.5

The DOST-PHIVOLCS Quick Response Team (QRT) was deployed from 18 to 24 October 2019 to conduct field surveys to determine the geologic impacts and damages brought about by the earthquake. Based on field investigations, the geologic impacts included liquefaction, tension cracks and earthquake-induced landslides. Liquefaction was manifested by lateral spreading, sandboils and subsidence in Brgy. Lepaga, M'lang, Cotabato; Brgy. Aplaya, Hagonoy, Davao del Sur; Brgy. Kasuga, Magsaysay, Davao del Sur; and Brgys. Kabasagan and Lower Marber, Matanao, Davao del Sur. Earthquake-induced landslides and tension cracks were observed in the mountainous areas of Tulunan and Makilala in Cotabato; Magsaysay and Matanao in Davao del Sur; and Columbio in Sultan Kudarat. Damages to buildings and infrastructures due to ground shaking were observed in areas where assessed intensities are PEIS VII (Destructive) and PEIS VI (Strong). Poor engineering has been a major contributing factor to these damages.

The team also conducted information dissemination activities for the local residents, teachers and local government officials. Discussions were centered on earthquakes and its hazards, as well as on earthquake preparedness. Recommendations were given to those severely affected by the earthquake, especially to those situated in areas with impending landslides.