Evolution of uphill-facing scarps by flexural toppling of slate with high-angle faults
Evolution of uphill-facing scarps by flexural toppling of slate with high-angle faults
复制标题
高角度断层板岩弯曲倾倒导致上坡陡坡的演化
DOI：
10.1016/j.geomorph.2019.106977
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
O. Yokoyama
中科院分区：
文献类型：
--
作者：
O. Yokoyama
上坡陡坎是深部重力斜坡变形的典型地表表现形式，通常由挠曲倾倒造成。然而，由于难以观察其内部结构，其演化机制还不清楚。因此，本研究进行了高分辨率的地貌分析和全面的地质测绘在板岩丰富的地区，弯曲倾倒发生，上坡面临的悬崖已经发展。斜坡坍塌后，在倒塌区域中暴露倒塌石板的内部至关重要。当板岩含有高角度断层的破碎带作为软弱层时，发育向上陡坎。向上陡坎的发育与楔体的旋转有关，楔体的旋转是由高角度断层和劈理通过断层与倾倒基底铰链面的相交而形成的。楔形体在断层的上坡或下坡发展，取决于断层是向斜坡还是向山谷倾斜。在楔体旋转过程中，断层发生了沿着位移，并沿断层沿着发育了一个仰坡陡坎。当劈理向斜坡倾斜，断层向山谷倾斜时，上坡陡坎变高。当断层向斜坡内倾斜时，仰坡陡坎不明显增长。当一个高角度的故障不涉及，弯曲倾倒板岩不断变形的斜坡，是不太可能形成一个上坡面临的悬崖。当挠曲倾倒延伸到脊顶时，无论是否有断层参与，一般都形成脊顶坳陷。岩体的弯曲倾倒产生了许多开口，使岩石具有高度的渗透性。然而，当涉及到一个高角度的断层与厚破碎带，地下水存储在断层破碎带和弯曲倾倒铰链面，这可能倾向于弯曲倾倒在暴雨和/或地震的灾难性故障。
Uphill-facing scarps are typical surface expressions of deep-seated gravitational slope deformations and are commonly created by flexural toppling. However, their evolution mechanisms are not well-understood partly because of the difficult in observing their internal structures. This study therefore performed high-resolution geomorphic analyses and thorough geological mapping in a slate-rich area where flexural toppling has occurred, and uphill-facing scarps have developed. Following slope failures was crucial in exposing the inside of the toppled slate amid the toppled area. Uphill-facing scarps developed when slate contained a crush zone of a high-angle fault as a weak layer. Uphill-facing scarps developed with the rotation of a wedge, which was defined by the high-angle fault and cleavage that passed through the intersection of the fault and basal hinge surface of the toppling. The wedge developed up- or downslope of the fault, depending on whether the fault dipped into the slope or valleyward. During wedge rotation, displacement occurred along the fault, and an uphill-facing scarp developed along the fault. The uphill-facing scarp became higher when the cleavage dipped into the slope and the fault dipped valleyward. When the fault dipped into the slope, the uphill-facing scarp did not grow significantly. When a high-angle fault was not involved, flexural toppling of slate continuously deformed the slope and was unlikely to form an uphill-facing scarp. When flexural toppling extended to the ridge top, it generally formed a ridge-top depression, regardless of whether a fault was involved. Flexural toppling of rock mass created many openings, making the rock highly permeable. However, when a high-angle fault with a thick crush zone was involved, groundwater was stored between the fault crush zone and flexural toppling hinge surface, which could predispose the flexural toppling to catastrophic failure during a rainstorm and/or earthquake.