September 22 2022
Scientists who have delved deeper into an undersea earthquake fault than ever before have discovered that tectonic stress in Japan’s Nankai region is lower than expected.
consequences study Led by the University of Washington and the University of Texas at Austin, published September 5 in Geology, is a mystery, because the fault produces a great earthquake roughly every century and was thought to build for another major earthquake.
Although the Nankai fault has been stuck for decades, the results reveal that it has not yet shown major signs of pent-up tectonic stress. The authors say the finding does not change the long-term view of the fault, which last erupted in 1946, when it caused a tsunami that killed thousands, and is expected to happen again within the next 50 years.
The findings will help scientists understand the link between tectonic forces and the earthquake cycle. This may lead to better predictions of earthquakes, both in Nankai and in other mega faults, such as the Cascadia subduction zone off the coasts of Washington and Oregon.
“Right now, we have no way of knowing if the big Cascadia earthquake – a magnitude 9 earthquake and tsunami – will happen this afternoon or 200 years from now,” said the lead author. Harold Tobin, UW Professor of Earth and Space Sciences and Senior Scientist involved in the Expedition Drilling expedition. “But I have some optimism that with more and more direct observations like this from Japan, we can begin to recognize when something abnormal has occurred and that the risk of an earthquake is increasing in a way that can help people prepare.
“We are learning how these bugs work by studying them around the world, and this knowledge will translate directly into insight into the risks of Cascadia as well.”
Giant trust faults like Nankai and Cascadia, and the tidal waves they generate, are among the most powerful and damaging in the world. Scientists say they don’t currently have a reliable way to know when and where the next big blow will strike.
The hope is that by directly measuring the perceptible force between tectonic plates pushing each other – tectonic stress – scientists can tell when a great earthquake is ready to strike.
“This is the core of the subduction zone, directly above where the fault was locked, as the expectation was that the system should store energy between earthquakes,” said the co-author. Damian Sapphire at the University of Texas at Austin, who also co-led the scientific exploration expedition. “It changes the way we think about stress in these systems.”
The nature of tectonics means that large earthquake faults are found in the depths of the ocean, miles below the sea floor, making them incredibly difficult for direct measurement. Tobin’s excavation journey and traveled are the earliest scholars to have come.
they He broke the record in 2018 On board a Japanese science drill ship, the Chikyu, it drilled nearly 2 miles, or just over 3 kilometres, into the tectonic plate before the well became very unstable — one mile from the rift.
Nevertheless, researchers have collected invaluable data about subsurface conditions near the fault, including stress. To do this, they measured how much the shape of the well changed when the earth pressed against it from the sides, then pumped out water to see what it took to force its walls back down. This told them about the direction and strength of the horizontal pressure felt by the plate pressing on the fault.
Contrary to expectations, horizontal pressure since the last major earthquake is expected to build close to zero, as if the system had already released its pent-up energy.
The researchers suggested several explanations: It could be that the fault simply needed less pent-up energy than was thought to slip in a major earthquake, or that stresses lie closer to the fault than the craters have reached. Or a tectonic thrust could come on suddenly in the coming years. Either way, the researchers said, the drilling demonstrated the need for further investigation and long-term monitoring of the fault.
“Results like these may seem to blur the picture, because things are not as simple as our theory or models predicted,” Tobin said. “But it does mean that we gain more understanding of how the real world works, and the real world is chaotic and complex.”
The research was funded by the Integrated Ocean Drilling Program and the Japan Agency for Marine Earth Science and Technology, or JAMSTEC. Other co-authors are Takehiro Hirose at JAMSTEC and David Castillo at Insight GeoMechanics in Australia.
For more information, contact Tobin at email@example.com or Saver at firstname.lastname@example.org.
Adapted from Article – Commodity from the University of Texas at Austin.