Furuichi Mikito, Nishiura Daisuke, Kuwano Osamu, Bauville Arthur, Hori Takane, Sakaguchi Hide
Department of Mathematical Science and Advanced Technology, Japan Agency for Marin-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku Yokohama, Japan.
R&D Center for Earthquake and Tsunami, Japan Agency for Marin-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku Yokohama, Japan.
Sci Rep. 2018 Jun 8;8(1):8685. doi: 10.1038/s41598-018-26534-x.
The stress states in accretionary prisms are important for understanding the building and releasing of seismic energy. Numerous researchers have conducted sandbox experiments as a scaled physical analog model to understand the formation of accretionary prisms. However, measuring stress states in laboratory sandbox experiments is still practically infeasible. Here we performed real-scale numerical sandbox experiments using the discrete element method to understand the 3D stress state in the accretionary prism. Despite the nearly uniform initial conditions, macro-scale undulations of faults, which are similar to those observed in the trenches of an accretionary prism, appear. We reveal that these undulations are caused by the formation of stress arches. We show that the mechanism behind the arch formation is the discontinuous change in the stress orientation during the rearrangement of the stress chain. Furthermore, analyses demonstrate that the in-situ stress orientation from borehole data can be a signal of either the regional direction of plate convergence or the local stress orientation associated with the stress arch. The results may greatly enhance the outcome of long term monitoring in areas, such as the Nankai Trough.
增生楔体中的应力状态对于理解地震能量的积累和释放至关重要。众多研究人员进行了砂箱实验，将其作为一种比例物理模拟模型来理解增生楔体的形成。然而，在实验室砂箱实验中测量应力状态在实际操作中仍然不可行。在此，我们使用离散元方法进行了真实尺度的数值砂箱实验，以了解增生楔体中的三维应力状态。尽管初始条件近乎均匀，但断层出现了宏观尺度的起伏，这与在增生楔体海沟中观察到的情况相似。我们揭示这些起伏是由应力拱的形成引起的。我们表明，拱形成背后的机制是应力链重新排列期间应力方向的不连续变化。此外，分析表明，来自钻孔数据的原地应力方向可能是板块汇聚区域方向或与应力拱相关的局部应力方向的信号。这些结果可能会大大提高对诸如南海海槽等地区长期监测的成果。
