This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In 2011, a huge earthquake struck eastern Japan. The magnitude 9.1 earthquake caused shaking at its epicenter for almost six minutes.
However, its effects didn't end there, as the movement of the plates displaced the seafloor enough to cause a devastating tsunami. Understanding how such earthquakes cause tsunamis is an important part of early-warning systems. One proposed mechanism is that the rapid movement of the plates generates large amounts of heat through friction.
As the temperature increases, heated water trapped within the pores of rocks increases pressure, which makes the fault boundaries increasingly slippery. The fault subsequently slips an exceptionally large distance, displacing the seafloor enough to cause a tsunami. To understand how these massive events happen, researchers often turn to similar occurrences preserved in rock faces from Earth's ancient past.
Looking at rocks exposed on the Boso Peninsula in Japan that were once part of an ancient seafloor environment, a research group led by professor Tetsuro Hirono of Osaka Metropolitan University has identified vortex-like structures in an ancient fault that suggest the material underwent fluid-like flow during an earthquake approximately 15 million years ago. The researchers called the rock layers "turbulent-flow-like," as they showed wavy and curved laminations and vortex-like structures. When they performed fluid-dynamical analyses of the structures, their findings suggested that thermal pressurization had been enough to fluidize the clay in the fault.
The findings are published in the journal Scientific Reports. "Our analysis suggests that the viscosity approached that of water," Hirono explained. "This would have been a dramatic reduction.
The fluidized state would have acted as a form of dynamic lubrication, causing the fault to weaken dramatically. The resulting large-scale slip would have produced a large displacement on the fault near the seafloor, potentially causing a tsunami." Using their insights, the group hopes to apply the same methodology to modern faults to improve scientists' ability to estimate fault-slip magnitude. "Understanding the change in viscosity in fault slips may allow us to more accurately recognize the magnitude of fault slips, which would support tsunami mitigation efforts," Hirono concluded.
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