Over the past decade, Japan has been hit by more than 27 major earthquakes measuring at least a lower 6 on the country seismic intensity scale. As scientists and researchers have struggled to understand why the region sits on such fragile ground, a recent study brought a glimmer of hope.
Researchers at the University of Texas believe they’ve found the culprit: a mountain-sized mass of igneous rock just below the coast of southern Japan. The mass, known as Kumano Plutohas been first discovered in 2006 . However, the details have remained a mystery until now.
Recent findings reveal that the mass acted as a magnet for earthquakes in the region. What does this discovery mean for the future of this vulnerable region? Let’s take a closer look.
What lies beneath
The beautiful island country of Japan falls along the Pacific Ring of Fire, a region as deadly as it may seem. Shaped like a long horseshoe, the Ring of Fire spans the shores of the Pacific Ocean and is home to some of the most active volcanoes and earthquakes in the world. The unstable nature of the region is largely due to its location along plate boundaries. Essentially, plate boundaries are the edges where two slabs of rock called tectonic plates meet. When these blocks of rock move or shift, it can create a very unstable environment that gives rise to volcanoes and earthquakes.
Japan’s position along the Ring of Fire was no secret to scientists and researchers. However, one specific region in southwestern Japan stood out – the Nankai Subduction Zone. The area has experienced a huge number of earthquakes compared to other regions, making it an area of particular interest for researchers. When the Kumano pluton was discovered, it was found in the Nankai subduction zone through seismic imagery. The imagery indicated that there was a mass of different density in the surrounding rock just off the coast of southern Japan – imagine a mountain-sized slab of solidified rock at the bottom of the Pacific Ocean.
Initially, the discovery did not lead to concrete answers about what could cause many earthquakes in the region. Now, after two decades of analyzing seismic data from the Nankai Subduction Zone, scientists are able to fully visualize the destructive structure with a complete and high resolution model of the rock.
Preparing for shaky ground
How does a mass the size of a mountain act like a magnet to mega-earthquakes? The answer was discovered when a team of experts led by the University of Texas used a supercomputer to sift through more than 20 years of data and locate the Kumano pluton between 3 and 12 miles (4.8 to 19.3 kilometers) below the coast of southern Japan. The study indicates that the giant boulder may have been redirection of tectonic energy at several points on its sides. This, combined with new images of the Kumano Pluton which reveal just how dense and rigid the rock is, shows us how this massive structure was responsible for the massive destruction.
Between 1944 and 1946, mega-earthquakes greater than magnitude 8 occurred just along the sides of the Kumano pluton. While earthquakes are common in this region, the threat of a massive mega-earthquake still haunts the Nankai subduction zone.
Fortunately, geophysicist Shuichi Kodaira from Japan Agency for Marine and Land Science and Technology in Japan notes that this discovery could help future earthquake prevention efforts. “We can’t predict exactly when, where, and how big future earthquakes will be, but by combining our model with monitoring data, we can begin to estimate future processes,” Kodaira said. in a press release. “It will provide very important data for the Japanese public to prepare for the next big earthquake.”
The discovery of this mountain-sized mass shows how little we know about the pieces of Earth causing such massive destruction. But with the right tools, we can stand a chance of stabilizing a fragile disaster.