Collaborative Proposal: Understanding Subduction Systems by Linking Anisotropic Seismic Imaging and Geodynamic Modeling

这个项目将使用遥远地震的记录来推断地震波在地表下传播的速度。反过来，我们利用这些信息来了解地球的结构，特别是俯冲作用（一个古老的构造板块下降到地幔中）是如何产生火山活动并影响地表地形的。在进行这种类型的研究时，目前通常假设波的传播速度与它们的方向无关。实际上，地震波以不同的速度传播，这取决于它们的方向与地幔中矿物的方向的关系。这种现象被称为各向异性，如果不加以考虑，它可能会使地下图像产生偏差，从而损害对俯冲过程的理解。在这个项目中，地震学家将通过将基于物理的各向异性分布估计纳入成像程序来研究减少这一问题的方法。通过这种方式，将确定更准确的地下图像，促进对俯冲作用如何影响地表的理解，包括火山活动的分布。该项目将结合走时层析成像、SKS分裂观测和地球动力学流模型，在两个俯冲带附近建立自一致的地幔结构模型（各向同性和各向异性）。新方法将使我们能够将地幔各向异性完全整合到俯冲带的远震层析成像中。通过将各向异性场的估计结合到走时断层扫描中，科学家们将大大减少各向同性假设产生的主要伪影，并获得地幔楔和俯冲板块下方应变的物理模型。改进后的成像技术可以更好地恢复地幔的物理状态（温度、成分和熔体分数）。这种方法将应用于西地中海和卡斯卡迪亚俯冲带的现有数据。

Recordings of distant earthquakes will be used in this project to infer the velocity at which the waves traveled beneath the Earth's surface. In turn, we use this information to understand the Earth's structure and, in particular, how subduction (the descent of an old tectonic plate into the Earth's mantle) produces volcanism and affects surface topography. When conducting this type of study, it is currently common to assume that the speed at which the waves travel is independent of their direction. In reality, seismic waves travel at different speeds depending on what their direction is relative to the orientation of minerals in the mantle. This phenomenon is known as anisotropy, and when not taken into account, it can bias the image of the subsurface in ways that can compromise the understanding of the subduction processes. In this project, seismologists will investigate ways to reduce this problem by incorporating physically-based estimates of the distribution of anisotropy into the imaging procedures. In this way, more accurate images of the subsurface will be determined advancing the understanding of how subduction affects the surface, including the distribution of volcanism.The project will combine travel-time tomography, SKS splitting observations and geodynamic flow modeling to produce self-consistent models of mantle structure (isotropic and anisotropic) in the vicinity of two subduction zones. The new approach will allow us to fully integrate mantle anisotropy into teleseismic tomography of subduction zones. By incorporating estimates of the anisotropy field into travel-time tomography the scientitists will significantly reduce major artifacts stemming from the isotropic assumption and obtain a physically-based model for the strain in the mantle wedge and beneath the subducting plate. The improved imaging will allow to better recover the mantle physical state (temperature, composition and melt fraction). This methodology will be applied to existing data from the western Mediterranean and Cascadia subduction zones.