Transient deformation and long-term shear zone activity

在数百万年的时间尺度上的造山过程中，地壳块体沿着剪切带错开了千米级的距离。地震滑动事件在几秒的时间尺度上可以触发剪切带在高应力下的瞬时变形，然后松弛。-从孕震带底部的地质记录中的多个地震事件的特征是什么？-如何区分特定岩石中不同的瞬时高应力变形事件？-瞬时变形对长期剪切带活动的作用是什么？为了解决这些问题，我们提出了一种基于现场的微观分析方法，以中央阿尔卑斯山的西尔维雷塔推覆为基础。在那里，相互交错的糜棱岩和假玄武岩暴露得很好。我们将分析由这些横切关系记录的形变历史，考虑到变形依赖于正在传播的地震活动断层的尖端。我们将测试它们是否表明(1)特定的加速蠕变序列，随后在瞬时高应力下变形，然后松弛应力，或(2)几个高应力变形事件的循环叠加。我们的目标是建立一个与地震活动断层尖端距离有关的时空尺度相关流变学的概念模型。这些发现将根据逆冲体制的具体特征进行讨论，并与不同构造体制的结果进行比较。预计这些发现将有助于更好地了解孕震带底部的地震滑动和相关形变在长期剪切带活动中的作用，这些活动抵消了千米尺度上的地壳块体。

During orogeny on the time scale of Millions of years, crustal blocks are offset over kilometre-scale distances along shear zones. Transient deformation at high and then relaxing stresses in shear zones can be triggered by seismic slip events taking place on the time scale of seconds. - What is the signature of multiple seismic events in the geological record from the base of the seismogenic zone? - How can different transient high-stress deformation events in a specific rock be distinguished? - What is the role of transient deformation on the long-term shear zone activity?To address these questions we propose a field-based and micro-analytical approach on the base of the Silvretta nappe in the Central Alps. There, mutually crosscutting mylonites and pseudotachylytes are well exposed. We will analyse the deformation history that is recorded by these crosscutting relations considering deformation in dependence to the tip of a propagating seismic active fault. We will test whether they indicate (1) a specific sequence of accelerated creep followed by deformation at transiently high and then relaxing stresses, or (2) a cyclic overprinting of several high-stress deformation events. We aim at a conceptual model for the temporal and spatial scale–dependent rheology related to the distance to the tip of a propagating seismic active fault. The findings will be discussed in the light of the specific characteristics in thrust regimes and compared to those of different tectonic regimes. The findings are expected to lead to a better understanding on the role of seismic slip and related deformation at the base of the seismogenic zone on the long-term shear zone activity offsetting crustal blocks over kilometre-scale distances.