Plate motion is driven by water in the mantle asthenosphere
Summary
A research team led by Professor Takashi Yoshino of the Institute for Planetary Materials, Okayama University, and a joint research group led by Senior Scientist Yuji Higo of the Japan Synchrotron Radiation Research Institute (JASRI) has forcibly vibrated rocks under high temperature and pressure. They succeeded in observing the phenomenon of attenuation, in which the energy of seismic waves is lost. They also found that the presence of water in mantle rocks softens the asthenosphere deeper in the mantle, allowing plates (lithosphere) to move over it more smoothly.
In plate tectonics theory, the reason why the asthenosphere becomes soft has not been well understood, but in this study, they conducted vibration experiments over a wide range of frequencies under high pressure to clarify the effect of water on the attenuation of seismic waves in mantle rocks. The presence of water in the asthenosphere could explain both the sharp drop in shear wave velocity at the oceanic lithosphere-asthenosphere interface and the frequency-independent damping in the asthenosphere beneath the old oceanic plate. These research results were published on July 31st (local time) in the American scientific journal “The Proceedings of the National Academy of Sciences”.
For more details, see the Okayama University press release [ JP | EN ].
Reference
Title: Effect of water on seismic attenuation of the upper mantle: the origin of the sharp lithosphere–asthenosphere boundary
Journal: The Proceedings of the National Academy of Sciences (PNAS)
Authors: Chao Liu, Takashi Yoshino, Daisuke Yamazaki, Noriyoshi Tsujino, Hitoshi Gomi, Moe Sakurai, Youyue Zhang, Ran Wang, Longli Guan, Kayan Lau, Yoshinori Tange, Yuji Higo
DOI: 10.1073/pnas.2221770120
