M7.5 Mindanao Earthquake (02/12/2023) Aftermath and Report

A strong magnitude 7.5 earthquake struck Mindanao, Philippines, on Saturday the 2nd of December 2023, at 22:37 local time at a shallow depth of 10 km (6.2 mi). It happened in an area where we had issued an elevated seismic hazard exposure level (yellow alert). This report will provide additional information about the earthquake, its consequences, and incorporate Quantectum's official report. 

M7.5 Mindanao Earthquake Details

The M7.5 earthquake on the 2nd of December in Mindanao was triggered by the Earth's crust movement along the Philippine Trench. The long, narrow depression on the eastern seaboard of the Philippines forms the boundary of one tectonic plate pushing against another. The frequent aftershocks are produced by the continuous adjustment of the rocks that moved and caused the earthquake on the 2nd of December, the Philippine Institute of Volcanology and Seismology reported. 

Details of the mainshock are as follows: 
- Time: 2023-12-02 at 14:37:01 UTC 
2023-12-02 at 22:37:01 Manila 
- Location: 8.58° LAT, 126.45° LON 
- Magnitude: M7.5 
- Depth: 10 km (6.2 mi) 
- Provider: @EMSC 

Picture 1: Location of the magnitude 7.5 earthquake in Mindanao, Philippines, on the 2nd of December 2023.

M7.5 Mindanao Earthquake Aftermath

During a few hours after the magnitude 7.5 earthquake, several aftershocks of magnitude larger than 5.0 occurred in the same area, among which three were of a magnitude 6.0 or more: 
- M6.5 at 00:03 local time,  
- M6.2 at 01:40 local time, and 
- M6.2 at 02:09 local time.  

Due to big waves and tsunami threats danger, Japanese and Philippines authorities issued a tsunami alert, ordering residents near endangered coastal areas to leave their homes and go to higher grounds. The alerts were lifted a couple of hours. 

After the mainshock, many people already left their homes and ran out of the buildings to find safe places where they could spend the night. For example, the picture below shows an evacuation center in Hinatuan on Sunday night. Additionally, many people reported feeling the tremors and being scared on social media channels. 

Picture 2: Evacuation center in Hinatuan, Philippines. Credit: Hinatuan Local Government Unit, via Reuters.

In the last official report, disaster officials reported minor damage to some infrastructure and recorded damage to homes, while the aviation agency reported minor cracks on wall tiles in some regional airports. Some walls and roads cracked, while more than 100 homes were destroyed and the roof of an outdoor courtyard collapsed.  

Furthermore, the earthquake caused three fatalities, a pregnant woman lost her life in Tagum city in Davao del Norte province, in the northeastern part of the Mindanao island, and two others in Surigao del Sur, the southeastern part of the island, due to falling debris and a wall collapsing on top of him, the National Disaster Risk Reduction and Management Council reported. They further stated that 48 individuals were injured from the offshore earthquake. Altogether, the strong quake has affected nearly 530.000 residents of three regions. 

Quantectum’s Report on M7.5 Earthquake in Mindanao, Philippines 

Quantectum's models showed unstable tectonic zones, high seismic hazard exposure levels, high values of earthquake triggering potential as well as the presence of tectonic and critical instabilities in the region where the earthquake occurred. The combination of these factors made the region susceptible to strong earthquake triggering. Based on this we initially issued the increased seismic hazard exposure level (yellow alert) for the region and increased it to the heightened before the magnitude 7.5 earthquake occurred. 

Picture 3: Initially issued seismic hazard exposure levels for Indonesia region.

The image below illustrates that the average alert field in the southern Philippines shortly before the magnitude 7.5 earthquake was high to very high. These models indicated that the strong earthquake triggering potential was very high which then resulted in magnitude 7.5 earthquake and strong aftershocks. 

Picture 4: Average alert field in the southern Philippines before the M7.5 earthquake on the 2nd of December 2023.

The maximum intensity was classified as “IX”, which is connected to violent shaking and very heavy damage. However, the level of the damage can be reduced due to the quality and status of the infrastructure and buildings and ongoing evacuation plans etc... This means that even though the shaking was really strong, the buildings and structures didn't get damaged as much as expected.  

The maximum intensity was felt in Bislig (pop. 68,000) 38 km away from the earthquake epicenter, while it was slightly weaker in Bayugan (pop. 41,000), Monkayo (pop. 51,000), Compostela (pop. 43,000), Butuan (pop. 310,000), Libertad (pop. 250,000), and Buenavista (pop. 69,000).  

Picture 5: Macroseismic Intensity for the M7.5 earthquake in Mindanao on the 2nd of December 2023.

In addition, the map below provides a visual representation of the mean expected magnitude M0, as forecasted by Quantectum's advanced models. These values have experienced a significant elevation, primarily attributed to the intense chaotic synchronizations occurring along the regional fault system within the vicinity of the anticipated M7.5 earthquake. 

Quantectum's models take into account various seismic factors, enabling a more comprehensive understanding of the potential seismic activity in the region. The heightened values of M0 depicted on the map underscore the intensified seismic stress and potential impact of the impending earthquake. 

The strong chaotic synchronizations observed along the regional fault system suggest a complex interplay of tectonic forces, increasing the likelihood of a substantial seismic event. This information is crucial for local authorities, emergency responders, and the public to enhance preparedness measures and mitigate the potential impact on the affected areas. 

Picture 6: Visual representation of the mean expected magnitude M0.

The complete report of the earthquake is available here on our regional X profile for Indonesia and the P. Here, you can get the latest updates. 

Seismicity in the Philippines

The archipelagic Philippines has frequent seismic activities due to its location along the Pacific "Ring of Fire." Even though the region experiences daily earthquakes, most are too weak to be felt by humans.  

It is located at and near the junction of three major tectonic plates, namely; the stable Eurasian Plate to the west, the northwest-moving Philippine Sea Plate to the east, and the northward-moving Indo-Australian Plate to the south. The interaction between them makes the region prone to earthquakes. 

At Quantectum, our Operations Center operators are constantly watching over the seismic situation in Indonesia and the Philippines. They observe changes in seismicity based on various factors and different methods, and issue seismic events reports, and weekly earthquake forecasts. You can see our updates for the region of Indonesia here. 

Sources: 

1) The Strait Times. 2023. Death toll from Philippine quake rises to three. Accessed on 12-Dec-2023. Available at: https://www.straitstimes.com/asia/se-asia/magnitude-69-earthquake-strikes-off-southern-philippines