Mantle deformation beneath the Alps and the physics of the subduction polarity switch: Constraints from thermomechanical modelling, seismic anisotropy and waveform modelling

密集的AlpArray网络提供的大量高质量地震数据，加上新的地球动力学建模能力，为检验目前关于大陆碰撞深部动力学的假设提供了独特的机会。一个主要的突出目标是了解的原因和动力学负责的俯冲极性下东阿尔卑斯山的拟议时间开关。我们提出的假设，一般来说，这样的开关是不是一个长期的板块构造历史的巧合的结果，但在会聚板块边界的特定物理条件的直接结果。将通过研究这种规定的或自相一致的极性转换的物理学，并通过将热力学模型与地震学对地幔变形的约束结合起来，对这一假设进行检验，这些约束来自对地震各向异性造成的波形效应的观测和建模。限制阿尔卑斯山下地幔变形的现状带来了一些困难，这些困难与地壳对地壳的可能影响有关。地幔各向异性结构的深度变化也是造成这种现象的原因。我们建议解决这些问题，结合分析剪切波分裂从（1）Escherichia XKS相位和（2）转换Psx相位从莫霍面和上地幔不连续提供一个详细的图像的地幔和地壳变形模式下整个阿尔卑斯山碰撞带。地壳厚度和各向异性将在途中确定。 关于造山带岩石圈软流圈系统的地球动力学建模，我们的时间依赖性热化学有限元和有限差分模型的复杂性将逐步增加（从2D到3D），包括粘塑性非牛顿流变学，自由表面，侵蚀和沉积，耗散加热等一致的工具，以确定不断变化的晶格取向将被应用。由此，将预测不同的地震各向异性模型，并作为与地震观测和波形建模进行比较的测试模型。此外，热机械模型的输出将包括不断变化的地形、隆起、沉降和折返速率、应力等，并将与SPP MB-4D内的合作项目进行交换。

The enormous amount of high-quality seismological data that is becoming available from the densely-spaced AlpArray network in combination with new geodynamic modelling capabilities opens up unique opportunities to test current hypotheses about the deep dynamics of continental collision. A major outstanding goal is an understanding of the causes and dynamics responsible for the proposed temporal switch of subduction polarity beneath the Eastern Alps. We pose the hypothesis that in general such a switch is not a coincidental result of long-term plate tectonic history, but the direct result of specific physical conditions at a converging plate boundary. This hypothesis will be tested by studying the physics of such a prescribed or self-consistently evolving polarity switch and by combining thermomechanical modelling with seismological constraints on mantle deformation from observations and modelling of waveform effects due to seismic anisotropy.From a seismological perspective, constraining the current state of mantle deformation beneath the Alps poses a number of difficulties related to the possible influence of the crust on teleseismic waveforms and also due to depth variations of anisotropic structures in the mantle. We propose to tackle these problems by combining analyses of shear-wave splitting from (1) teleseismic XKS phases and (2) converted Psx phases from the Moho and upper-mantle discontinuities to provide a detailed image of mantle and crustal deformation patterns beneath the entire Alpine collision zone. Crustal thicknesses and anisotropies will be determined on the way. Regarding the geodynamical modelling of an orogenic lithosphere-asthenosphere system, the complexity of our time-dependent thermochemical Finite Element and Finite Difference models will be increased stepwise (from 2D to 3D) and include visco-plastic-non-Newtonian rheology, a free surface, erosion and sedimentation, dissipational heating, etc. Consistent tools to determine the evolving lattice-preferred orientations will be applied. From this, different models of seismic anisotropy will be predicted and serve as test models for the comparison with seismological observations and waveform modelling. Additionally, the output of the thermomechanical models will include the evolving topography, uplift-, subsidence and exhumation rates, stresses etc. and will be exchanged with cooperating projects within the SPP MB-4D.