Spectrum of slip behaviour in Tohoku fault zone samples at plate tectonic slip rates
Spectrum of slip behaviour in Tohoku fault zone samples at plate tectonic slip rates
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DOI：
10.1038/ngeo2547
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发表时间：
2015-11-01
影响因子：
18.3
通讯作者：
Kopf, Achim J.
中科院分区：
文献类型：
--
作者：
Ikari, Matt J.;Ito, Yoshihiro;Kopf, Achim J.
在2011年东北冲地震期间，极广泛的同震滑动使日本海沟俯冲带的浅部破裂，并破坏了海底（1，2）。俯冲带的这一部分也是慢滑动事件（SSE）的宿主（3，4）。因此，该断层似乎具有滑动不稳定或准不稳定的倾向，这在重要断层带的浅部是意想不到的。在这里，我们使用实验室实验来缓慢剪切从东北冲地震断层带恢复的岩石样品，作为日本海沟快速钻探项目的一部分。我们发现，在岩石强度的罕见的扰动出现自发的长期SSE时，样品被剪切约8.5厘米/年（-1），相当于板收敛率恒定速率。在约2至4小时内，岩石的剪切强度下降3至6%，或50 kPa至120 kPa。这些事件期间的滑动达到高达25厘米/年（-1）的峰值速度，类似于在几个环太平洋俯冲带中观察到的SSE。此外，剪切样品表现出全谱的断层滑动行为，从快速不稳定滑动缓慢稳定蠕变，这可以解释在日本海沟观察到的广泛的滑动风格。我们认为，发生在浅层的SSE可能有助于识别断层段是不稳定的，容易受到大同震滑动传播。
During the 2011 Tohoku-oki earthquake, extremely extensive coseismic slip ruptured shallow parts of the Japan Trench subduction zone and breached the sea floor(1,2). This part of the subduction zone also hosts slow slip events (SSE)(3,4). The fault thus seems to have a propensity for slip instability or quasi-instability that is unexpected on the shallow portions of important fault zones. Here we use laboratory experiments to slowly shear samples of rock recovered from the Tohoku-oki earthquake fault zone as part of the Japan Trench Fast Drilling Project. We find that infrequent perturbations in rock strength appear spontaneously as long-term SSE when the samples are sheared at a constant rate of about 8.5 cm yr(-1), equivalent to the plate-convergence rate. The shear strength of the rock drops by 3 to 6%, or 50 kPa to 120 kPa, over about 2 to 4 h. Slip during these events reaches peak velocities of up to 25 cm yr(-1), similar to SSE observed in several circum-Pacific subduction zones. Furthermore, the sheared samples exhibit the full spectrum of fault-slip behaviours, from fast unstable slip to slow steady creep, which can explain the wide range of slip styles observed in the Japan Trench. We suggest that the occurrence of SSE at shallow depths may help identify fault segments that are frictionally unstable and susceptible to large coseismic slip propagation.