Episodic imbricate thrusting and underthrusting: Analog experiments and mechanical analysis applied to the Alaskan Accretionary Wedge
Episodic imbricate thrusting and underthrusting: Analog experiments and mechanical analysis applied to the Alaskan Accretionary Wedge
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幕式叠瓦逆冲和逆冲：应用于阿拉斯加增生楔的模拟实验和力学分析
DOI：
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发表时间：
1998
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影响因子：
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通讯作者：
S. Lallemand
中科院分区：
文献类型：
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作者：
M. Gutscher;N. Kukowski;J. Malavieille;S. Lallemand
富沉积的阿拉斯加俯冲带的地震反射剖面图像为短的、前缘增生的、叠瓦状逆冲片和长逆冲下片的重复序列。观察到楔体厚度快速向陆增加、逆冲和前弧隆起，表明楔体下方有逆冲作用。这些特征和锋面楔形态的广泛变化被解释为是由沿海沟在不同位置同时活动的不同模式的吸积引起的。在以砂为模拟材料的高基础摩擦试验中，观察到楔形生长的偶发性。一个增生旋回的两个阶段可以被区分开来：短叠瓦状逆冲片的前缘增生与长而未变形的逆冲片的交替。实验表明，相位取决于楔形的表面斜率。在工作的力的力学分析预测这两种模式的变形，由于变化的摩擦力和屈服强度的楔形暂时变化的几何形状。在实验条件下计算了推力片的最大长度，并得到了观测结果的证实。对于一个陡峭的锋面斜坡（在莫尔-库仑锥稳定场的上限），覆盖层太大而不允许下冲，并且在楔形前缘反复发生破坏，产生短瓦叠瓦状薄片。楔形向前增长，降低表面角度到最小的临界锥度。对于一个浅锋面斜坡，沿着活跃的顶板冲力减少的覆盖层允许持续的逆冲，导致锋面侵蚀和逆冲，使楔变陡，从而完成循环。
Seismic reflection profiles from the sediment rich Alaska subduction zone image short, frontally accreted, imbricate thrust slices and repeated sequences of long, underthrust sheets. Rapid landward increases in wedge thickness, backthrusting, and uplift of the forearc are observed, suggesting underthrusting beneath the wedge. These features and a widely varying frontal wedge morphology are interpreted to be caused by different modes of accretion active concurrently along the trench at different locations. Episodic wedge growth is observed in high basal friction experiments using sand as an analog material. Two phases of an accretionary cycle can be distinguished: frontal accretion of short imbricate thrust slices, alternating with underthrusting of long, undeformed sheets. The phase is shown experimentally to depend upon the surface slope of the wedge. Mechanical analysis of the forces at work predicts these two modes of deformation due to the varying frictional forces and yield strengths for a temporally varying wedge geometry. Maximum length of thrust slices is calculated for experimental conditions and confirmed by the observations. For a steep frontal slope (at the upper limit of the Mohr-Coulomb taper stability field) the overburden is too great to permit underthrusting, and failure occurs repeatedly at the wedge front producing short imbricate slices. The wedge grows forward, lowering the surface angle to the minimum critical taper. For a shallow frontal slope the reduced overburden along an active roof thrust permits sustained underthrusting, causing frontal erosion and backthrusting, steepening the wedge and thus completing the cycle.