A M6.5 subduction earthquake strikes near Acapulco, Mexico

To read this post in Spanish (automatically translated by Google), click here.

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At 7:58 a.m. local time on January 2, 2026, a 6.5 magnitude earthquake struck down the west coast of Mexico, near the city of Acapulco de Juarez. The USGS estimates a maximum shaking intensity of ~V-VI (moderate to strong) in the area surrounding the epicenter. In Mexico City, about 280 kilometers to the north, seismometers recorded the intensity of the fourth (light) shaking.

Although the strongest tremors occurred near the coast, many news reports focused on the experience in Mexico City, in part because of the high population density there. The earthquake interrupted President Claudia Sheinbaum's first press conference this year. Feeling the tremors, the president calmly led an evacuation, accompanied by sirens from Mexico's seismic warning system. The footage also shows the high-rise brick buildings swaying in a disturbing manner, with some minor debris falling from the sides.

We are not aware of any reports of major damage, although some minor structural damage may have occurred. With the spread of AI-generated videos, as well as footage from previous earthquakes affecting Acapulco, we caution our readers against giving credence to images or videos from unknown sources.

The earthquake occurred within the Mexican subduction zone. Here, the oceanic crust of the Cocos (marine) plate is moving northeast, subducting beneath the continental crust of southern Mexico, at a rate of about 6-7 centimeters per year.

Figure 2: Earthquakes since 1980 around the Mexican subduction zone. The arrows show the movement of the Cocos and Pacific Plate relative to the North American Plate, in millimeters per year.

Subduction zones like these are responsible for many earthquakes recorded around the world every day. These earthquakes are associated with a variety of faults: most notably the Megathrust Fault, the fundamental fault that separates tectonic plates, but also a whole host of faults in both the underlying and overriding plates as they respond to tectonic collision.

The most recent earthquake occurred within this broad deformation zone, although it is currently unclear which fault has actually slipped. The focal mechanism of the earthquake shows a thrust event where one decadal level dips approximately 12° to the northeast, which is consistent with slip on the large thrust fault itself. However, the USGS reported origin depth of 35 km places the rupture below the plate interface mapped in the Slab2.0 model, which at this location is only about 21 km deep.

Figure 3: Map and cross section showing seismic activity around the recent M6.5 earthquake (highlighted with the bull's eye). Earthquakes are classified M7+.

It is possible that the USGS origin depth is wrong; The depths of reported focal mechanisms tend to be significantly shallower (NEIC: 12 km, SC4 18 km, CPPT 20 km, GFZ 24 km). This would be much closer to the depth of the large thrust fault, and we believe thrust slip is the best explanation. It is not uncommon for there to be mismatches between early reports, which is why it is always a good idea to keep multiple working hypotheses in mind.

While this particular M6.5 earthquake does not seem to require much discussion, we can also consider the history of large earthquakes in the region, and the impact of large but distant earthquakes on Mexico City.

In 1985, the Mw8.0 Michoacán earthquake occurred down the west coast of Mexico, about 380 kilometers from Mexico City. This earthquake caused significant damage within Mexico City, due to the classic dangerous combination of weak architecture and near-surface geological formations that amplified low-frequency vibrations. Many high-rise buildings collapsed completely, and the number of casualties reached tens of thousands. The slow swaying of tall buildings recorded in the recent M6.5 earthquake is consistent with this effect. The devastation caused by the 1985 earthquake led to the creation of the Mexican Earthquake Alert System, which was activated during today's less damaging event.

Near Acapulco, there is a long history of huge earthquakes. Most of these major events occurred long before the 21st century. Below is a map of the region showing events above M6.5, labeled as M7+ events.

Figure 4: Earthquakes above M6.5; Events are classified as M7+. The earthquake timeline is shown below the map. The latest M6.5 is highlighted with a bull's eye.

More recently, the M7.0 Guerrero earthquake on September 8, 2021 struck northeast of Acapulco. This earthquake was also a powerful event, causing widespread damage and killing 13 people. As usual, the shaking affected Mexico City, causing a power outage. This earthquake occurred near the epicenter of the M7.0 earthquake in 1962.

While a shallow 7.0 magnitude earthquake will always be very scary, the experiences of 1962 and 2021 suggest that Acapulco's current infrastructure should be fairly resilient to that level of shaking. However, a different type of tear, or even a less superficial event, can cause more damage.

More importantly, M7.0 is certainly not the strongest event that could occur along this section of the large thrust. This region has a long history of larger earthquakes, including a number of events approaching or possibly exceeding M8. It is important to remember that the magnitude scale is logarithmic, and each step in unit magnitude reflects an earthquake thirty times stronger. In other words, a magnitude 8 earthquake would release about 170 times the energy of an M6.5 earthquake that just occurred.

When did earthquakes approaching this size occur? About 200 km from Acapulco, earthquakes of magnitude M7.5+ occurred in 1697, 1754, 1820, 1845, 1899, 1908, 1909, and 1957. The largest of these earthquakes is believed to have been an 8.3 magnitude earthquake in 1845.

Given the scale of these events, we found it extremely difficult to obtain information about them. However, we have come across this rather horrific illustration, which purports to show the submergence of Acapulco in 1820, following a major earthquake:

Figure 5: Illustration of the inundation of Acapulco following the 1820 earthquake. Source: Sunrail (1868).

The description comes from Sánchez-Devora and Ferreras-Sánz (1993) and they describe the event (excluding the lightning bolt and objects):

In Acapulco, the sea receded into the middle of the bay, exposing coral reefs. Quiet floods and tides were observed, with some stops in water movement when reaching the highest and lowest levels. Two hours later, the tide was so great that the water reached the doors of the church at the top of the town square. The arena was flooded. The ocean advanced inward like a wall at great speed, sweeping away everything in its path. Then, in a strong tide, stronger than in 1787 [?]most of the bottom of the Gulf was exposed. After that, sea level gradually began to return to its natural state. After the tsunami, the entire breakwater was covered with sand by 1/2-2 m (5-6 ft), while the beach expanded by 17 m (20 var).

Large earthquakes along the coast are clearly capable of causing large tsunamis and localized damage, along with large tremors in Mexico City, as seen in 1985, with hints again today.

The subduction earthquakes we have seen in living memory do not represent the greatest seismic hazard: earthquakes along this part of the subduction zone have reached M8+ in historical times, and can be larger than the historically observed maximum.

To reduce the effects of these inevitable large earthquakes, there is no alternative to strong, earthquake-resistant buildings. A research paper published last month addressed this topic in some detail, outlining advances in Mexico's building codes and the challenges of implementing them.

Alcocer, SM and Fernández-Sola, LR, 2025. Towards urban resilience-based management: the case of Mexico after the 2017 earthquakes. Resilient Cities and Structures, 4(4), pp. 97-116.

Sanchez-Devora, Antonio J., Sanz, Sanz, Noah

Sonrel, Léon (1868). The bottom of the sea / by L. Sunrail; Photographer's work… Layan Dargent, Furat, and A. Mesnil (in French). Paris, France: L. Hachette et Cie. p. 59, 60.

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