Harold Tobin of the University Washington inspects drilling pipes.
Harold Tobin of the University Washington inspects drilling pipes. Researchers used similar equipment during a record-breaking attempt to drill Japan’s Nankai fault in 2018.University of Washington

Scientists who drilled deeper into an undersea earthquake fault than ever before have found that the tectonic stress in Japan’s Nankai subduction zone is less than expected.

The results of the study led by the University of Washington and the University of Texas at Austin, published Sept. 5 in Geology, are a puzzle, since the fault produces a great earthquake almost every century and was thought to be building for another big one.

Although the Nankai fault has been stuck for decades, the findings reveal that it is not yet showing major signs of pent-up tectonic stress. Authors say the result 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.

The findings will help scientists home in on the link between tectonic forces and the earthquake cycle. This could potentially lead to better earthquake forecasts, both at Nankai and other megathrust faults, like the Cascadia subduction zone off the coast of Washington and Oregon.

“Right now, we have no way of knowing if the big one for Cascadia — a magnitude-9 scale earthquake and tsunami — will happen this afternoon or 200 years from now,” said lead author Harold Tobin, a UW professor of Earth and space sciences and co-chief scientist on the drilling expedition. “But I have some optimism that with more and more direct observations like this one from Japan 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.

Read more at UW News »