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THE recent 6.8-magnitude earthquake that struck off the coast of Kota Kinabalu, Sabah, in the early hours of 23 February was among the strongest ever recorded in Malaysia, yet miraculously caused no fatalities or major structural damage.
The incident contrasts starkly with the 5 June 2015 Ranau earthquake, which, despite registering a lower magnitude of 6.0, claimed 18 lives and left widespread destruction.
The key difference lies in the depth of the earthquake’s focus, explained seismic geologist Navakanesh M Batmanathan.
“In seismology, depth is as critical as magnitude,” he said.
The Malaysia Meteorological Department (MetMalaysia) reported the recent earthquake’s focus at approximately 678 kilometres below the surface, while the United States Geological Survey (USGS) estimated around 620 kilometres. Both classify it as a deep-focus earthquake.
“For context, earthquake depths are categorised as shallow (0–70 km), intermediate (70–300 km), and deep (300–700 km).
“This recent quake occurred near the maximum depth, which is extremely rare. If it had been shallow – less than 30 km – the scenario would likely have involved serious property damage and loss of life,” Batmanathan added, noting his affiliation with the Southeast Asia Disaster Prevention Research Institute at the National University of Malaysia.
By contrast, the 2015 Ranau earthquake occurred at an exceptionally shallow depth of around 10 kilometres. Its proximity to populated areas amplified its destructive force, triggering landslides on Mount Kinabalu that claimed 18 lives.
Batmanathan illustrated the effect with an analogy: “Imagine a tall table with a thick top. A blow to the surface produces sharp, immediate vibrations, whereas a strike from underneath shakes it less perceptibly.
“Similarly, seismic waves from deep earthquakes lose much of their destructive energy before reaching the surface.”
The deep-focus nature of the Sabah quake also prevented significant seafloor displacement, reducing the risk of a tsunami.
Magnitude readings differed slightly: MetMalaysia recorded 6.8 while USGS measured 7.1. Batmanathan explained, “Local agencies use nearby monitoring stations, while USGS calculates a global average from hundreds of stations. Variations of 0.2 to 0.3 are normal in seismic reporting.”
Magnitude quantifies total energy released underground. For example, a magnitude 7.0 earthquake releases roughly 32 times more energy than a 6.0 tremor.
Despite the higher energy released by the Sabah quake, the extreme depth limited surface impact. Other factors influencing destruction include distance from populated areas, soil and terrain characteristics, building design, and the duration and intensity of shaking.
Sabah’s unique geology contributes to frequent earthquakes while often sparing high casualties. Situated near a “triple junction,” where the Eurasian, Indo-Australian, and Philippine Sea tectonic plates meet, the state experiences complex interactions that generate seismic activity.
Ancient subduction processes, where one plate sinks beneath another, also create deep subterranean stress capable of triggering earthquakes hundreds of kilometres below the surface.
Batmanathan noted that the February quake was likely linked to such ancient tectonic processes rather than surface fault movements. “While strong, deep earthquakes like this rarely produce damage comparable to shallow events, Sabah remains Malaysia’s most seismically active region,” he said.
Understanding the science behind earthquake depth can help communities and authorities better assess risk and enhance preparedness.
Deep-focus tremors, though less visibly destructive, remind us that the Earth’s crust behaves like a giant, interlocking jigsaw of slow-moving tectonic plates.
Subduction zones, where denser oceanic plates sink beneath lighter continental plates, generate extraordinary subterranean pressures released over time as earthquakes or volcanic activity.
This latest event underscores the critical importance of depth in determining the destructive potential of seismic activity, even when the energy released is immense. - February 28, 2026