Last December 15, 2019, the province of Davao del Sur, Philippines was struck by an earthquake measuring 6.9 magnitude and an intensity of 7 which is considered as very strong. About 13 people were killed and another 210 were injured.
According to PHIVOLCS, the earthquake was caused by the movement on the Tangbulan Fault. The individual faults last December earthquake include the NW-SE trending Makilala-Malungon Fault, Tangbulan Fault and the Central Digos Fault.
Right after that very strong earthquake, a series of aftershocks were experienced including nine of M ≥ 5.0 in the first 48 hours after the main shock, with the largest being an mb 5.7 event about an hour afterwards, which had a maximum felt intensity of 7.
Last October, a series of earthquakes already struck Mindanao. The sequence of three M>6 affected that area to the northwest of the December earthquake. What happened in December 15 was likely because of the earlier sequence due to stress transfer.
The greatest damage was in the area around the epicenter such as Matanao, Magsaysay, Hagonoy and Padada. There were significant damages reported in Davao del Sur, Sarangani, Sultan Kudarat and North Cotabato. In particular, a hospital was destroyed in Hagonoy and there was significant damage to a police station and fire station in Padada.
Still reeling from the series of strong earthquakes in October. The 6.9 magnitude earthquake on December 15, 2019 severely damaged Padada, Davao del Sur especially, Southern Grocery Store. Several persons were trapped in the collapsed store. There were four injured persons rescued by the people near the building. As to the accurate number of persons trapped in the store, it cannot be ascertained because it happened on a Sunday afternoon, the time when most of the residents of Padada and the nearby town like Sulop usually shop.
Aside from that, Canlas Commercial, a two-storey building also collapsed, but no casualties were reported. The old water reservoir at the public cemetery also collapsed, which injured some residents. That earthquake really left Padada in ruins.
Liquefaction was the reason why the first and second floors of Southern Trade commercial building sank. The foundation of the building went down or part of the building subsided. What happened was totally different when the frame of the building collapsed.
Liquefaction happens in sandy areas with low water table which means that the soil is soft. In fact, the ground opens in some parts of Padada. In other areas, like in Magsaysay, Davao del Sur, the water comes out apart from submerging the ground.
The government is now very strict in building procedures. The need to follow the building code in putting up structures in areas identified by experts as prone to liquefaction is really stressed!