We use three-dimensional seismic reflection data from the southern German Molasse Basin to investigate the structural style and evolution of a geometrically decoupled fault network in close proximity to the Alpine deformation front. We recognise two fault arrays that are vertically separated by a clay-rich layer – lower normal faults and upper normal and reverse faults. A frontal thrust fault partially overprints the upper fault array. Analysis of seismic stratigraphy, syn-kinematic strata, throw distribution, and spatial relationships between faults suggest a multiphase fault evolution: (1) initiation of the lower normal faults in the Upper Jurassic carbonate platform during the early Oligocene, (2) development of the upper normal faults in the Cenozoic sediments during the late Oligocene, and (3) reverse reactivation of the upper normal faults and thrusting during the mid-Miocene. These distinct phases document the evolution of the stress field as the Alpine orogen propagated across the foreland. We postulate that interplay between the horizontal compression and vertical stresses due to the syn-sedimentary loading resulted in the intermittent normal faulting. The vertical stress gradients within the flexed foredeep defined the independent development of the upper faults above the lower faults, whereas mechanical behaviour of the clay-rich layer precluded the subsequent linkage of the fault arrays. The thrust fault must have been facilitated by the reverse reactivation of the upper normal faults, as its maximum displacement and extent correlate with the occurrence of these faults. We conclude that the evolving tectonic stresses were the primary mechanism of fault activation, whereas the mechanical stratigraphy and pre-existing structures locally governed the structural style.

中文翻译：

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德国南部莫拉西盆地的多相解耦断层-来自3-D地震数据的证据

我们使用来自德国南部莫拉西盆地的三维地震反射数据，研究了紧邻阿尔卑斯山变形锋的几何解耦断层网络的构造样式和演化。我们认识到由富粘土层垂直分隔的两个断层阵列-下正断层以及上正断层和反向断层。额叶逆冲断层部分覆盖了上部断层阵列。地震地层，运动学上的地层，投掷分布以及断层之间的空间关系分析表明多相断层演化：（1）渐新世早期在上侏罗统碳酸盐岩台地下正断层的萌发，（2）渐新世晚期新生代沉积物中的上正断层 （3）中新世中期上正断层逆冲和逆冲作用。这些不同的阶段记录了高山造山带在前陆上传播时应力场的演变。我们假定，由于同沉积物的作用，水平压缩和垂直应力之间的相互作用导致了间歇性的正断层。弯曲的前深部内的垂直应力梯度确定了上断层在下断层之上的独立发展，而富含粘土的层的力学行为阻止了断层阵列的后续联系。推力断层一定是由上部正常断层的逆向激活所推动的，因为其最大位移和范围与这些断层的发生有关。