On December 18, 2025, a 5.1 magnitude earthquake rattled the region off the coast of Hualien City in eastern Taiwan, briefly shaking buildings as far away as the capital, Taipei. According to Taiwan’s weather administration, the quake struck 18 kilometers (11 miles) offshore at a depth of 31.6 kilometers (19.6 miles), but, remarkably, no immediate reports of damage surfaced. For a place perched at the intersection of two tectonic plates, such tremors are a regular, if unnerving, part of life. Yet, the real story of the day stretched far beyond Taiwan’s shores, reaching into the depths of the Pacific Ocean, where scientists have been working to unravel the mysteries behind some of the world’s most devastating earthquakes.
In a timely coincidence, the same day saw the publication of a groundbreaking study in the journal Science that shed new light on the catastrophic 2011 megaquake northeast of Japan. That disaster, infamous for the tsunami that devastated coastal communities and crippled the Fukushima Daiichi nuclear power plant, has long puzzled experts with its unusual behavior. Now, thanks to an international research effort led in part by Cornell University, scientists are closer than ever to understanding why the 2011 quake was so destructive—and what it might mean for earthquake-prone regions like Taiwan.
The new study, as reported by Phys.org, confirms that a hidden, 30-meter-thick layer of pelagic clay beneath the seafloor at the Japan Trench played a pivotal role in intensifying the 2011 earthquake. This clay, soft and slippery, created a weak fault zone that allowed the earthquake’s rupture to reach the seafloor itself, resulting in an astonishing 50 to 70 meters of shallow slip—far greater than what’s typically observed in subduction zone earthquakes. In most cases, the slip starts deep and diminishes as it nears the surface. But in 2011, the opposite occurred: the slip actually grew larger as it approached the seabed, leading to the massive displacement that triggered the monstrous tsunami.
“This work helps explain why the 2011 earthquake behaved so differently from what many of our models predicted,” said Patrick Fulton, associate professor and Croll Sesquicentennial Fellow in the Department of Earth and Atmospheric Sciences at Cornell Engineering, and a co-author of the study. “By seeing exactly how the fault zone is constructed, we can better understand where slip is likely to concentrate and how much tsunami potential a given subduction zone might have.”
The research was the product of the International Ocean Discovery Program Expedition 405, also known as JTRACK, which in 2024 sent a deep-sea research vessel to drill through the fault and into the sediment of the Pacific Plate. The operation achieved a world record for scientific ocean drilling, reaching a staggering 7,906 meters beneath the sea surface—a feat recognized by Guinness World Records. This technical triumph was possible thanks to the close collaboration between the Japan Agency for Marine-Earth Science and Technology, industry partners, and an international team of scientists. Fulton, who spent nearly two months on the vessel, described the achievement as both a scientific and engineering milestone.
The JTRACK expedition built upon earlier work in the region, including the Japan Trench Fast Drilling Project launched one year after the 2011 earthquake. That earlier project had first hinted at the weak nature of the shallow plate boundary fault, but the new results provide a much more comprehensive picture of how the fault zone and its surrounding sediments are organized. The sediment samples revealed the presence of the pelagic clay—a material formed over millions of years from microscopic particles settling on the seafloor. Sandwiched between stronger layers, this clay acted like a natural “tear line,” focusing the rupture along its surface.
“At the Japan Trench, the geologic layering basically predetermines where the fault will form,” Fulton explained. “It becomes an extremely focused, extremely weak surface, which makes it easier for ruptures to propagate all the way to the sea floor.” This insight has sweeping implications: because the pelagic clay layer extends for hundreds of miles along the trench, the region may be far more prone to shallow-slip earthquakes—and, by extension, tsunamis—than previously believed.
Fulton emphasized the broader significance of the findings, stating, “Ultimately, our goal is to translate this kind of detailed fault zone knowledge into better assessments of earthquake and tsunami hazards for coastal communities around the world.” In other words, what happens beneath the waves off Japan could one day inform how places like Taiwan prepare for their own seismic threats.
To bring the scientific journey to a wider audience, a 30-minute documentary about the JTRACK expedition premiered alongside the study’s publication. The film follows Fulton and dozens of other scientists through 105 days at sea as they plan, drill, recover core samples, and install long-term observatories deep within the fault zone. For those eager to dig even deeper, more data from the expedition will soon be made publicly available through the International Ocean Discovery Program.
The urgency of such research is underscored by Taiwan’s own seismic history. The island, frequently rattled by earthquakes due to its tectonic setting, has endured its share of tragedy. In 2016, a quake in southern Taiwan killed more than 100 people, and the 1999 Jiji earthquake claimed over 2,000 lives. Each event is a stark reminder of the unpredictable power lurking beneath the Earth’s surface—and the need for ever-better science to help communities anticipate and withstand the worst.
While Thursday’s quake off Hualien mercifully resulted in no immediate damage, it served as yet another reminder of the region’s vulnerability. For residents of Taipei and beyond, the brief shaking was a familiar, if unsettling, occurrence. But for the scientists peering into the planet’s hidden layers, every tremor is a clue, every core sample a step closer to understanding—and maybe, just maybe, to safety.
As researchers continue to analyze the JTRACK data and refine their models, the hope is that these discoveries will lead to more accurate hazard assessments, smarter building codes, and better early warning systems. After all, as the events of 2011 and the daily realities in places like Taiwan show, the next big quake is not a matter of if, but when. Until then, the world will be watching—and learning—from the restless earth beneath our feet.