University of Tokyo researchers studying sediment cores from the Kumano Sea have found evidence of several hidden disasters in the country’s past, including previously unrecorded earthquakes, tsunamis, and typhoons.
The team behind the findings said the evidence for unknown earthquakes and other hidden natural disasters was found in the Nankai Trough, where experts expect the country’s next megaquake to occur. They also suggested that reconstructing a more accurate picture of the region’s geophysical past will help officials prepare for future disasters.
Searching for Hidden Disasters Lurking in Japan’s Past
Due to its location along the so-called “Ring of Fire,” Japan experiences an inordinately high number of earthquakes and tsunamis compared to the rest of the world. The island nation also experiences its share of typhoons and powerful storms, adding to its history of enduring nature’s wrath.
Fortunately, advances in monitoring and infrastructure have helped modern Japanese citizens endure these periodic disasters better than ancient human populations from the same regions. Still, the research team behind the new study argues that a better understanding of these “hidden” disasters in the country’s past could help modern populations prepare for future natural catastrophes. This includes preparing for a megaquake most experts predict will hit Japan sometime in the next 30 years.
In many cases, scientists examine the geological record left behind by such events to better understand their effects. However, the University of Tokyo team notes that “not all events are easy to spot.” For example, evidence of past earthquakes could be hidden beneath hundreds of feet of water, making it difficult to spot without costly equipment.
Carbon-14 Testing Provides a Geophysical Calendar
Scientists use carbon-14, a material all living things absorb while alive, as a timeline marker because it decays at a known rate. For example, researchers can examine the carbon-14 levels in an ancient animal and determine when it died and when the carbon-14 inside it began to decay.
Archaeologists often use this method to determine when plants were harvested or when ancient humans inhabited certain regions. Depending on the level of decay, this approach can give an accurate date as far back as 50,000 or 60,000 years before present.
According to Professor Yusuke Yokoyama from UTokyo’s Atmosphere and Ocean Research Institute, the team began its investigation by collecting cores from the Kumano Sea floor. Next, they examined the core using radiocarbon dating. To examine the 40-centimeter-long core, the team collected carbon-14 samples at half-centimeter and one-centimeter intervals.
Professor Yokoyama said the team used a new, “ultrasensitive method to measure the trace amounts of carbon-14 contained in sediment from the ocean floor, at a very high resolution of 1 centimeter or less.”
Multiple Events Correlated with Historical Records
After examining the test results, the team found that the oldest part of the core from a depth of 37-38 centimeters dated back roughly 600 years to approximately 1440 C.E. A closer examination also revealed a history of geophysical evidence across the entire period, including disasters hidden from earlier efforts.
“This revealed multiple events which were not found through previous visual observations, X-ray or CT analysis,” the professor explained.
For example, the researchers found evidence that seafloor sediment was mixed, shifted, and repositioned. They suspect this reflects several severe floods, storms, and underwater earthquakes.
“We found several new geological layers that were not visible before, derived from submarine landslides possibly triggered by earthquakes in the Nankai Trough,” Professor Yokoyama said, adding that the layers being mixed together removed any structural features, “making the event layers invisible.”
Still, the team said its approach revealed dates along the entire core’s length, offering a calendar of ancient and hidden catastrophes that had remained undiscovered before now. This allowed the team to correlate its findings with documented historical events over the last 600 years.
“We could determine the occurrence of multiple events and were able to correlate some of these with written historical records of submarine earthquakes from the 13th to the 20th century,” the professor explained.
Future Efforts Could Look Deeper into the Past
When discussing the potential impact of its findings, the research team said the technique could help Japanese planners and officials refine their prediction models and prepare for potential future disasters. The team said the approach could also help other countries improve their hidden disaster dataset, resulting in better models of future events.
Going forward, Professor Yokoyama and colleagues hope to look deeper into the ocean to reveal a much older timeline of hidden disasters. The professor also plans to expand the effort “more widely across the Kumano Sea and beyond,” hoping to paint a clearer picture of Japan’s hidden disasters and prepare the nation for likely future events.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.