Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa-noha, Chiba 277-8564, Japan.
Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan.
Nat Commun. 2014;5:3084. doi: 10.1038/ncomms4084.
Geophysical evidence suggests that fluids along fault planes have an important role in generating earthquakes; however, the nature of these fluids has not been well defined. The 2011 magnitude 9.0 Tohoku-Oki earthquake ruptured the interface between the subducting Pacific plate and the overlying Okhotsk plate. Here we report a sharp increase in mantle-derived helium in bottom seawater near the rupture zone 1 month after the earthquake. The timing and location indicate that fluids were released from the mantle on the seafloor along the plate interface. The movement of the fluids was rapid, with a velocity of ~4 km per day and an uncertainty factor of four. This rate is much faster than what would be expected from pressure-gradient propagation, suggesting that over-pressurized fluid is discharged along the plate interface.
地球物理证据表明，断层带中的流体在引发地震方面起着重要作用；然而，这些流体的性质尚未得到很好的定义。2011 年 9.0 级的东日本大地震沿着俯冲的太平洋板块和上覆的鄂霍次克板块之间的界面发生破裂。在这里，我们报告了在地震发生后 1 个月，破裂带附近底层海水中幔源氦的急剧增加。时间和位置表明，流体是从海底板块界面上的地幔中释放出来的。流体的运动速度很快，每天约 4 公里，不确定性因素为四。这个速度比预期的压力梯度传播速度要快得多，这表明超压流体是沿着板块界面排放的。
