Continental rifts are characterized by up to 30 km wide rotated fault blocks with stratigraphic dip away from the central rift axis. Although gravity‐induced mass movements are well known features of collapsed fault block crests, I here demonstrate the occurrence of polymodal gravity‐driven mass transport down the back slope of a first‐order rift fault block. I identify (1) early sliding related to syntectonic crestal collapse of second‐order rift faults, (2) large‐scale bed‐parallel sliding of the L‐M Jurassic sedimentary package, and (3) the accumulation of two 7 km long, 1–2 km wide and up to 750 m thick volumes of complexly slumped material in the hanging walls of two ramp‐forming faults. Early sliding is documented by 100 m of repeated Brent Group stratigraphy in a cored well in the study area (well 34/4‐15A). These smaller slides have intact internal stratigraphy but show elevated deformation band densities. The seismic data also show evidence for ca. 2 km of massive translational sliding of the ca. 400 m thick and ca. 300 km2 large Jurassic section above a lowermost Jurassic bedding‐parallel detachment. This translational slide did not deform much internally, except for ductile folding where it slid over underlying active rift faults. Chaotic seismic facies in fault hanging walls are interpreted as contorted Jurassic beds, formed by multiple slumping and sliding events that stacked mobilized sediments into a 750 m thick column. These complex slump volumes occur where fault displacement is highest along two relayed faults. A model is favoured where the large translational slide ruptured with an opening of space against the fault that was progressively filled with slumped material from the footwall. While the large‐scale translational sliding only caused moderate internal subseismic deformation, early sliding and, particularly, the complex slumping caused significant internal deformation. This study shows the importance of carefully searching for and distinguishing between different types of mass movement in rift systems.

中文翻译：

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北海北部裂谷期间的多模态重力构造：Snorre 断块案例


大陆裂谷的特点是长达 30 公里宽的旋转断层块，地层倾斜远离中央裂谷轴线。尽管重力引起的质量运动是坍塌断块波峰的众所周知的特征，但我在这里演示了多峰重力驱动的质量传递沿着一阶裂谷断层块的后坡发生。我确定了 （1） 与二级裂谷断层的构造状脊坍塌有关的早期滑动，（2） L-M 侏罗纪沉积包的大规模河床平行滑动，以及 （3） 两个 7 公里长、1-2 公里宽、厚达 750 米的复杂坍塌物质在两个斜坡形成断层的上壁中堆积。在研究区域的一口取芯井（34/4-15A井）中，100米的重复布伦特群地层记录了早期滑动。这些较小的滑坡具有完整的内部地层，但显示出较高的变形带密度。地震数据还显示，在最底层的侏罗纪层理平行分离上方，约 400 m 厚和约 300 km2 的大型侏罗纪剖面发生了约 2 公里的巨大平移滑动。这个平移滑坡内部没有太大变形，除了它在下面的活动裂谷断层上滑动的延性折叠。断层上盘中的混沌地震相被解释为扭曲的侏罗纪床，由多次坍塌和滑动事件形成，这些事件将移动的沉积物堆积成一个 750 m 厚的柱状物。这些复杂的坍落度体积发生在沿两个中继断层的断层位移最高的地方。当大型平移滑坡破裂时，断层上的空间开口逐渐被下盘的坍塌材料填充，则倾向于采用模型。 虽然大规模的平移滑动只引起了中度的内部亚震变形，但早期滑动，特别是复杂的坍塌导致了严重的内部变形。这项研究表明了仔细寻找和区分裂谷系统中不同类型的质量运动的重要性。