Scientists drilled two miles into the tectonic plate to understand Japan’s ‘great earthquake’

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“It changes the way we’re thinking about stress in these systems,” added Saver, who co-led the research and scientific mission that drilled the fault.

In geology, a fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture.

The results, documented in the journal Geology, are intriguing because it was thought that the fault was getting ready for a significant earthquake, which usually happens almost every century.

Despite the Nankai fault being stalled for years, the analysis reveals that there aren’t any significant indications of tectonic stress that haven’t yet been released.

But “that doesn’t alter the long-term outlook for the fault, which last ruptured in 1946—when it caused a tsunami that killed thousands—and is expected to do so again during the next 50 years,” warned Saver.

Understanding the relationship between tectonic forces and the earthquake cycle

Seismic section showing location of all Integrated Ocean Drilling Program (IODP) drill sites.

The discoveries will help researchers better understand the relationship between tectonic forces and the earthquake cycle, which could improve earthquake forecasts for both the Nankai and other megathrust faults like Cascadia in the Pacific Northwest.

“Right now, we have no way of knowing if the big one for Cascadia—a magnitude nine scale earthquake and tsunami—will happen this afternoon or 200 years from now,” said Harold Tobin, a researcher at the University of Washington and the first author of the paper.

“But I have some optimism that with more and more direct observations like this, we can start to recognize when something anomalous is occurring and that the risk of an earthquake is heightened in a way that could help people prepare.”

According to scientists, there is currently no accurate technique to predict when and where the next major earthquake or tsunami will occur, despite the fact that megathrust faults like Nankai and the tsunamis they produce are among the most destructive on the planet.

The researchers hope to measure the tectonic stress directly—the force felt when tectonic plates are pushed against one another—to determine when a major earthquake is about to occur.

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