Deadly M7.8 earthquake hits southern Philippines

To read this article in Filipino (automatically translated by Google), click here.

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See the bulletin issued by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) here.

At 7:37 AM local time on June 8, 2026 (06/07/2026 UTC), a 7.8 magnitude earthquake struck beneath southern Mindanao in the Philippines.

The USGS PAGER estimates that more than 1 million people were exposed to severe (severe) shaking, and that deaths are likely. These numbers are preliminary calculations, taking into account estimated tremors, population density, and general infrastructure vulnerability. They are occasionally updated over time as new data emerges.

Normally, we start to see severe damage caused by magnitude VII+ earthquakes. The level of damage is related to the resilience of the structure: at severity 7, there can be significant damage to poorly constructed buildings. At intensity 8, even ordinary buildings can undergo partial collapse. Since most earthquake deaths are related to damage to buildings, these types of impacts are particularly dangerous.

Indeed, reports, photos and videos from Mindanao indicate that some buildings have collapsed, including in nearby General Santos City. One person in General Santos wrote to EMSC to report: “Severe damage.”

It usually takes days to months to get a full accounting of the damage from a major earthquake. We are aware of only one reported death to date; The authorities explained that this was only a preliminary report. It is very likely that this number will rise.

A number of aftershocks were recorded, including three aftershocks with a magnitude higher than 6 magnitude. The largest aftershock to date was M6.5; This happened about an hour after the main shock. While such aftershocks are normal, they can cause further damage, especially to buildings that have already been weakened or damaged.

A tsunami warning was issued in the wake of the quake, indicating the possibility of waves between 1-3 meters high in part of the Philippines, with more modest waves further afield. The latest report from tsunami.gov includes a 0.8 meter wave in Sulawesi, Indonesia, and 0.5 meter water in Davao, Philippines.

The USGS also noted that large areas of landslides or liquefaction are possible. Both can cause further damage to roads and infrastructure. Landslides are more common in areas with steep slopes. Liquefaction is more common in coastal areas or in low-lying areas with high water levels.

The Philippines is one of the most seismically active places in the world. Since we started this Substack in 2023, we’ve written twelve posts about earthquakes in the Philippines (including this one); This is the third reported earthquake above M7.

Why so many earthquakes? The Philippines is a highly tectonically active region. The entire country is stuck between dueling subduction zones. To the east, the Philippine Sea plate collides with the archipelago and sinks beneath it. In the West, different marginal seas are trying to do the same thing, with varying levels of success. If that’s not enough, because the collision/subduction is not perpendicular to the subduction zones, a massive strike-slip fault (the Philippine Fault) has ripped the country in half, with many other minor faults helping to accommodate the deformation.

Figure 5: Generalized tectonic map of the Philippines. The M7.8 earthquake is shown as a yellow star. Ignore the yellow box — this map was originally designed for a different project! The map is based on Yumul et al. (2008). Red lines are errors. The red toothed lines are large thrusts or large thrusts, with teeth on the hanging wall side. Note that most of the Philippines is bounded by megathrusts where offshore plates dip below the Philippine Mobile Belt.

In 2023, we wrote about an earthquake that occurred in roughly the same location as this most recent event: the M6.7 earthquake on November 27, 2023. We’ve removed the paywall on this post; Read it to learn more about the (very complex) tectonics of this region.

Below is an updated map of earthquakes in this area, showing how close the 2023 and 2026 earthquakes are. Data are from USGS and PHIVOLCS catalogs.

Figure 6: Seismic activity in the southern Philippines. Earthquakes are colored by depth. The colored lines are the depth lines of the two overlapping subduction zones here.

Based on the locations and depths of these earthquakes, they appear to be associated with the east-dipping Cotobato Trench. This opens up some possibilities: either (1) earthquakes occur at the plate interface (also known as macrothrust), effectively absorbing the downward motion of the slab; (2) occurred in the dominant plate as an associated deformation; Or (3) they occurred within the descending slab, where it bends and deforms on its way into the mantle.

The cross-section below helps us work through these choices.

Figure 7: Cross section of the map above. Here only one subduction zone is visible – the Cotabato Trench. The west-dipping Philippine Sea plate lies below this cross section.

The focal mechanisms (“beach balls”) of the two earthquakes are similar. Both show that the earthquake occurred on a steep fault, sloping either east or west. While the eastward direction of this fault is similar to plate interface dip, the M6.7 and M7.8 earthquakes originated at a much greater depth. This indicates that the bending of the subducting plate, rather than the sliding between the two plates, is what caused these earthquakes. The north-south orientation of the fault planes also does not fit well with the curve of the Cotabato Trench, indicating a different fault.

In 2023, we conclude that the M6.7 earthquake was probably a laboratory event. This conclusion is supported by the depth of the M7.8 earthquake.

These types of earthquakes, known as “in-slab” events, are relatively common. Subduction zones generate many types of earthquakes, not just those associated with slip along plate boundary faults. Intraplate earthquakes are usually attributed to folding of the slab as it bends downward and sinks, causing fractures along different directions. While in-lab earthquakes never reach the same magnitude as large quakes, they can still be quite devastating if they occur near populated land, as in this case.

This appears to be among the largest earthquakes recorded in the Cotabato Trench, and may be the largest earthquake recorded within the laboratory associated with this subduction zone. The 1976 M7.9 Morro Bay earthquake, which occurred to the west, was a powerful event. In 1918, an 8.3 magnitude earthquake occurred off the coast of the western island of Mindanao. It cannot be pinned to a specific error.

We will certainly learn more about the effects of this devastating event in the coming days.

Beck, S.L. and Ruff, L.J., 1985. Rupture process of the 1976 Mindanao earthquake. Journal of Geophysical Research: Solid Earth, 90(B8), pp. 6773–6782. https://doi.org/10.1029/JB090iB08p06773

Hubbard, J. and Bradley, K., 2023. M6.7 earthquake shakes southern Mindanao, Philippines. Earthquake Insights, https://doi.org/10.62481/839033b6

Yumol, J.P., Dimalanta, C.P., Maglambayan, V.P., and Marquez, E.J., 2008. Journal of Earth Sciences, 12, pp. 7-17. https://doi.org/10.1007/s12303-008-0002-0

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