Study of the Nankai seismogenic fault using dynamic wave propagation modelling of digital rock from the Nobeoka Fault
Study of the Nankai seismogenic fault using dynamic wave propagation modelling of digital rock from the Nobeoka Fault
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DOI：
10.1071/eg17129
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发表时间：
2017-10
影响因子：
0.9
通讯作者：
Chandoeun Eng;Tatsunori Ikeda;T. Tsuji
中科院分区：
文献类型：
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作者：
Chandoeun Eng;Tatsunori Ikeda;T. Tsuji
为了了解南海孕震断层在板块会聚边缘的特征，我们计算了P-和S-波速度（VP和VS）的数字岩石模型构建的一个古老的板块边界断层在野冈，日本九州岛的岩心样品。我们首先从显微计算机断层扫描图像构建三维数字岩石模型，并确定其异质性纹理，如裂缝和静脉。我们用空气、水、石英、方解石和其他具有不同体积模量和剪切模量的材料代替裂缝和脉。采用旋转交错网格差分法，对不同裂隙填充矿物的三维数字岩石模型进行了动态波传播模拟，量化了有效VP、VS和VP/VS比值。我们的研究结果表明，水饱和的裂缝大大降低了地震速度和增加VP/VS。VP/VS的石英填充的岩石模型低于在水饱和的情况下，在方解石填充的岩石模型。通过将数字岩石模型的弹性性质与由野外地震资料估算的发震断层周围的地震速度（如VP和VP/VS）进行比较，描述了深部发震断层的演化过程。在南海海槽从平静向同震过渡区所观察到的高VP/VS和低VP可以用张开的裂缝（或裂缝）来解释，而在同震断裂带较深处所观察到的低VP/VS和高VP则表明石英填充的裂缝。在这项研究中，富含石英的断裂带的特点是低VP/VS和高VP可能部分涉及到同震的行为，如以前的研究所建议的，因为石英表现出滑动弱化行为（即不稳定的同震滑动）。我们量化了不同裂隙填充矿物的三维数字岩石模型的有效VP、VS以及VP与VS的比值。通过对南海孕震断层周围岩石弹性参数与地震速度的对比，揭示了该断层的演化过程。
To understand the characteristics of the Nankai seismogenic fault in the plate convergent margin, we calculated the P- and S-wave velocities (VP and VS) of digital rock models constructed from core samples of an ancient plate boundary fault at Nobeoka, Kyushu Island, Japan. We first constructed 3D digital rock models from microcomputed tomography images and identified their heterogeneous textures such as cracks and veins. We replaced the cracks and veins with air, water, quartz, calcite and other materials with different bulk and shear moduli. Using the Rotated Staggered Grid Finite-Difference Method, we performed dynamic wave propagation simulations and quantified the effective VP, VS and the ratio of VP to VS (VP/VS) of the 3D digital rock models with different crack-filling minerals. Our results demonstrate that the water-saturated cracks considerably decreased the seismic velocity and increased VP/VS. The VP/VS of the quartz-filled rock model was lower than that in the water-saturated case and in the calcite-filled rock model. By comparing the elastic properties derived from the digital rock models with the seismic velocities (e.g. VP and VP/VS) around the seismogenic fault estimated from field seismic data, we characterised the evolution process of the deep seismogenic fault. The high VP/VS and low VP observed at the transition from aseismic to coseismic regimes in the Nankai Trough can be explained by open cracks (or fractures), while the low VP/VS and high VP observed at the deeper coseismic fault zone suggests quartz-filled cracks. The quartz-rich fault zone characterised as low VP/VS and high VP in this study could partially relate to the coseismic behaviour as suggested by previous studies, because quartz exhibits slip-weakening behaviour (i.e. unstable coseismic slip). We quantified effective VP, VS and the ratio of VP to VS of the 3D digital rock models with different crack-filling minerals. By comparing the elastic properties derived from the digital rock models with the seismic velocities around the Nankai seismogenic fault, we characterised the evolution process of the seismogenic fault.