M7.1 Deep Earthquake Strikes Offshore Sabah, Malaysia: A Rare Mantle Event in a Complex Tectonic Setting

On February 22, 2026, at 16:57 UTC, a magnitude 7.1 earthquake struck approximately 55 km north-northwest of Kota Belud in Sabah, Malaysia. The event originated at a significant depth of 619.8 km within the Earth's upper mantle. Located beneath the Sulu Sea near northern Borneo, this intraslab earthquake produced felt shaking across northern Borneo, parts of Brunei, and southern Philippines but caused no significant damage or tsunami due to its great depth.

This earthquake ranks as one of the strongest recorded near Malaysia in modern history, surpassing most recent events in the region. It highlights the unique seismic characteristics of Sabah, situated in a tectonically active zone influenced by the interaction of major plates.

Tectonic Context of Sabah and the Sulu Sea Region

Sabah, on the northern part of Borneo Island, lies at the junction of several tectonic features. The region forms part of the complex boundary between the Sunda Plate (part of the Eurasian Plate) and the Philippine Sea Plate. To the north and east, active subduction zones along the Sulu and Philippine Trenches drive ongoing deformation. The Sulu Sea itself is a marginal basin that opened during the Neogene as a result of back-arc extension and later experienced closure processes related to arc-continent collisions.

The area's tectonic evolution involves the subduction of the Proto-South China Sea beneath Borneo during the Eocene to Miocene, followed by collisions involving continental fragments and island arcs. These processes created fold-and-thrust belts, such as the Crocker Range in Sabah, and influenced basin development. Deep earthquakes like the M7.1 event often occur within subducted slabs that have descended into the mantle, where stress accumulates in cold, rigid oceanic lithosphere. Such deep-focus events are relatively rare beneath Borneo but can generate broad-area shaking because seismic waves travel efficiently from mantle depths.

Historical Seismic Activity in Sabah

Malaysia generally experiences low to moderate seismicity compared to neighboring Indonesia and the Philippines. However, Sabah has a more active record due to its proximity to plate boundaries and intra-plate faults. Notable historical events include:

• The 2015 M6.0 Ranau earthquake, which struck at shallow depth (~18 km) and caused 18 deaths, primarily from rockfalls on Mount Kinabalu.
• Earlier significant quakes, such as the 1976 M6.2 Lahad Datu event and the 1923 M6.6 Lahad Datu earthquake.

Instrumental records show few M6+ events since 1950 in the immediate offshore area near Kota Belud, with prior notable ones at shallower depths (e.g., M6.0 in 2015 and M6.1 in 1951). The 2026 M7.1 stands out as the largest in the vicinity since at least the 1920s, underscoring the potential for infrequent but powerful deep events.

Shallow earthquakes in Sabah are often linked to active faults within the Crocker Range and surrounding areas, exhibiting both compressional and extensional mechanisms. Deep events, by contrast, reflect stresses in descending slabs from past subduction. Overall, seismic activity in the region has been documented since the late 19th century, with most events below magnitude 5, but capable of local impacts.

Impacts and Response to the 2026 Event

Given its depth, the M7.1 earthquake produced light to moderate shaking (up to intensity IV–VII in some reports) over a wide area without generating a tsunami. The U.S. Geological Survey issued a Green alert, indicating low likelihood of casualties or economic losses. Populations in Kota Belud, Kudat, and Kota Kinabalu felt the event, but no major structural damage was widely reported. Coastal monitoring confirmed no tsunami threat from the National Tsunami Warning Center.

This event serves as a reminder of seismic preparedness in Sabah. Local authorities emphasize building codes resilient to both shallow crustal and deeper mantle quakes. The region's mix of vulnerable unreinforced structures and more resistant modern construction influences overall risk.

Geological Significance and Future Outlook

The 2026 earthquake provides valuable data for understanding mantle dynamics in Southeast Asia. Deep intraslab seismicity in this setting relates to the remnants of subducted lithosphere from the closure of ancient ocean basins. Ongoing GPS and seismic monitoring help refine models of plate interactions in the Sulu Sea–Sabah area, where collision and extension have shaped the landscape over millions of years.

While large deep earthquakes are less likely to cause surface damage, they contribute to the stress regime that can trigger shallower, more hazardous events. Continued research into Sabah's active faults and historical seismicity remains essential for mitigating risks in this geologically dynamic part of Malaysia.

In summary, the February 22, 2026, M7.1 deep earthquake off Kota Belud exemplifies the interplay of deep mantle processes and regional tectonics. It reinforces the importance of sustained monitoring and preparedness in Sabah, a region with a rich geological history shaped by plate convergence and basin evolution.

References

• USGS Earthquake Event Page: us6000sasz (2026).
• The Watchers: Rare deep M7.1 earthquake hits beneath the Sulu Sea near Sabah, Malaysia (Feb 22, 2026).
• Additional sources on Sabah tectonics: Scientific literature on Sulu Sea evolution and regional seismicity (e.g., Tongkul, Rangin et al.).