AsianScientist (Nov. 1, 2017) – A team of researchers at Kyushu University in Japan have identified the root cause of the massive 1944 Tonankai earthquake and the smaller Off-Mie earthquake that struck almost the same area on April 1, 2016. They have published their findings in Earth and Planetary Science Letters.
The islands of the Japanese archipelago are affected both by frequent, low-magnitude earthquakes and tremors as well as larger, highly destructive events. One of the largest quakes to strike Japan occurred in 1944, leading to the loss of more than 1,200 lives on the main and most populated island of Honshu. Its strength resulted from the abrupt release of plate tectonic forces, a process known as subduction, centered on an area beneath Honshu where it slides over the top of oceanic crust.
Highly destructive earthquakes caused by subduction occur because of excessive friction that develops during the sliding process, resulting in a build-up of stress. Sudden release of this stress, a condition called rupturing, leads to the violent shaking felt during an earthquake.
In this study, researchers at the International Institute for Carbon-Neutral Energy Research at Kyushu University in Japan, focused on the Nankai Trough, one of three major subduction zones offshore of Japan. The researchers used advanced 2D and 3D seismic profiles to reveal the detailed structure of the trough, in particular, that of an ancient accretionary prism—a large mass of rock and sediment accumulated in the trough.
The researchers revealed that the added mass of this rock and sediment impeded subduction, ultimately causing stress to build up over time. The build-up of stress, and rupturing, was the root cause of the massive 1944 Tonankai earthquake and the smaller Off-Mie earthquake that struck almost the same area on April 1, 2016.
“Along with evidence of frictional obstruction to subduction, the fault structure appears to have also impacted earthquake location and behavior,” said Professor Takeshi Tsuji of Kyushu University. “We found that aftershocks of the 2016 quake only occurred in front of the accretionary prism, where stress accumulation is greatest.”
The findings suggest that large earthquakes in Japan are most likely to occur in this very same region of the Nankai Trough in the future.
The article can be found at: Tsuji et al. (2017) 3D Geometry of a Plate Boundary Fault Related to the 2016 Off-Mie Earthquake in the Nankai Subduction Zone, Japan.
Source: Kyushu University; Photo: Shutterstock.
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