Mindanao lies across the complex convergent boundary between the Sunda Plate and the Philippine Sea Plate. Part of the oblique convergence between these plates is taken up by subduction along the Cotabato Trench. The strike-slip component of the convergence is accommodated partly by the Philippine Fault System and partly by the Cotabato Fault System, a network of mainly NW-SE trending sinistral (left-lateral) strike-slip faults that form the boundary between the Cotabato Arc and the Central Mindanao Volcanic Belt. In the area of the October 2019 earthquakes series, the individual faults include the NW-SE trending South Columbio Fault, North Columbio Fault, M'Lang Fault, Makilala–Malungon Fault and Tangbulan Fault, and the SW-NE trending Makilala Fault and Balabag Fault.
Events at or above Mw 5.0 associated with the 2019 Cotabato earthquakes
Philippine government seismologist Renato Solidum described the quake as "moderately powerful". The National Tsunami Center issues a statement saying no present tsunami threat from the earthquake.
Three malls in Davao City reported damage following the earthquake. In General Santos, the Gaisano Mall was mostly gutted following a fire triggered by the earthquake. 143 buildings were damaged and one was destroyed. The damaged buildings included 40 houses, 70 schools, 7 health facilities, 10 commercial buildings, and 2 places of worship.
On October 29, 2019, a 6.6-magnitude earthquake struck the island of Mindanao in the Philippines at a depth of 14.1 km, according to the USGS, and 7 km according to PHIVOLCS. The maximum perceived shaking was VII on both the PEIS and MMS scales. This intensity was reached in Tulunan, Makilala, Kidapawan City, Digos City, and Malungon. This earthquake was caused by movement on a different, but related, strike-slip fault to the October 16 event.
A major fire broke out in General Santos City. There were power outages in many parts of Cotabato and locally in South Cotabato, Sultan Kudarat, and Sarangani. At least ten deaths were reported, with a minimum of another four hundred injured. The fatalities were reported in Arakan, Carmen, Tulunan, Makilala, Digos City, and Magsaysay. School classes were suspended in parts of North Cotabato, South Cotabato, and Sultan Kudarat.
On October 31, 2019, a 6.5 magnitude earthquake struck the island of Mindanao in the Philippines at a depth of 10 km according to the USGS, with the epicenter located 1 km south of Kisante. A maximum perceived shaking of VII (PEIS) was reported from Tulunan, Makilala, Kidapawan City, Santa Cruz, Matanao, Magsaysay, Bansalan and Digos City. Some buildings in Davao and Soccksargen were seriously damaged and some collapsed. The death toll of these two quakes (October 29 and 31) was raised to 24, with 563 people injured, and 11 still missing. More than 300 aftershocks were recorded after the earthquake.
The earthquake sequence triggered a large number of landslides and rockslides. Municipalities affected by landslides include Kidapawan City, Antipas, Arakan, Makilala, M'Lang and Tulunan in Cotabato province; Magsaysay, Bansalan, Malalag, Matanao and Kiblawan in Davao Del Sur. Three fatalities were caused by landslides triggered by the October 29 shock with a further six people reported missing. Two fatalities were caused by landslides triggered by the October 31 shock, with a further five people reported missing.
Effects on infrastructure
Damage to infrastructure in the eight most badly affected areas from the earthquakes on October 29 and October 31
The Provincial Government of South Cotabato, Sarangani and the City of General Santos was one of the first to initiate to help the citizens with blankets, trapal, food and water near the epicenter of the earthquake swarm, most especially in the Municipalities of Makilala, Tulunan, M'lang and City of Kidapawan. Local citizens in Soccsksargen acted in both giving donations in the government processes and privately giving donations across the highway in Makilala, Tulunan and Kidapawan. The Davao City Government also helped the affected areas headed by Mayor Sara Duterte. The Island Garden City of Samal Government also went to Cotabato Province to give relief goods and drinking water. The Bangsamoro Government also went to the affected areas to give relief goods. The municipality of Datu Saudi Ampatuan Government also went to the area to share donations to help the affected people. Among other institutions that immediately helped where banks, malls, universities and schools in Soccsksargen and Davao Region to assist their fellow Mindanaoans in crisis.