SUMMARY Despite the well-established anisotropic nature of Earth’s upper mantle, the influence of elastic anisotropy on teleseismic P-wave imaging remains largely ignored. Unmodelled anisotropic heterogeneity can lead to substantial isotropic velocity artefacts that may be misinterpreted as compositional heterogeneities. Recent studies have demonstrated the possibility of inverting P-wave delay times for the strength and orientation of seismic anisotropy. However, the ability of P-wave delay times to constrain complex anisotropic patterns, such as those expected in subduction settings, remains unclear as synthetic testing has been restricted to the recovery of simplified block-like structures using ideal self-consistent data (i.e. data produced using the assumptions built into the tomography algorithm). Here, we present a modified parametrization for imaging arbitrarily oriented hexagonal anisotropy and test the method by reconstructing geodynamic simulations of subduction. Our inversion approach allows for isotropic starting models and includes approximate analytic finite-frequency sensitivity kernels for the simplified anisotropic parameters. Synthetic seismic data are created by propagating teleseismic waves through an elastically anisotropic subduction zone model created via petrologic-thermomechanical modelling. Delay times across a synthetic seismic array are measured using conventional cross-correlation techniques. We find that our imaging algorithm is capable of resolving large-scale features in subduction zone anisotropic structure (e.g. toroidal flow pattern and dipping fabrics associated with the descending slab). Allowing for arbitrarily oriented anisotropy also results in a more accurate reconstruction of isotropic slab structure. In comparison, models created assuming isotropy or only azimuthal anisotropy contain significant isotropic and anisotropic imaging artefacts that may lead to spurious interpretations. We conclude that teleseismic P-wave traveltimes are a useful observable for probing the 3-D distribution of upper mantle anisotropy and that anisotropic inversions should be explored to better understand the nature of isotropic velocity anomalies particularly in subduction settings.

中文翻译：

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远震 P 波延迟成像上地幔各向异性：俯冲模拟断层重建的见解

总结 尽管地球上地幔具有公认的各向异性性质，但弹性各向异性对远震纵波成像的影响在很大程度上仍然被忽视。未建模的各向异性异质性可能导致大量各向同性速度伪影，可能被误解为成分异质性。最近的研究已经证明了反转 P 波延迟时间以反映地震各向异性的强度和方向的可能性。然而，P 波延迟时间限制复杂各向异性模式（例如俯冲环境中预期的模式）的能力仍不清楚，因为合成测试仅限于使用理想的自洽数据（即数据使用断层扫描算法内置的假设生成）。这里，我们提出了一种改进的参数化，用于对任意方向的六边形各向异性进行成像，并通过重建俯冲的地球动力学模拟来测试该方法。我们的反演方法允许各向同性启动模型，并包括用于简化各向异性参数的近似解析有限频率灵敏度内核。合成地震数据是通过通过岩石热力学模型创建的弹性各向异性俯冲带模型传播远震波来创建的。使用传统的互相关技术测量跨合成地震阵列的延迟时间。我们发现我们的成像算法能够解决俯冲带各向异性结构中的大尺度特征（例如与下降板片相关的环形流动模式和浸渍织物）。允许任意定向的各向异性也可以更准确地重建各向同性的平板结构。相比之下，假设各向同性或仅方位角各向异性创建的模型包含可能导致虚假解释的显着各向同性和各向异性成像伪影。我们得出结论，远震 P 波走时对于探测上地幔各向异性的 3D 分布是一个有用的观测值，并且应该探索各向异性反演以更好地了解各向同性速度异常的性质，特别是在俯冲环境中。假设各向同性或仅方位角各向异性创建的模型包含可能导致虚假解释的显着各向同性和各向异性成像伪影。我们得出结论，远震 P 波走时对于探测上地幔各向异性的 3D 分布是一个有用的观测值，并且应该探索各向异性反演以更好地了解各向同性速度异常的性质，特别是在俯冲环境中。假设各向同性或仅方位角各向异性创建的模型包含可能导致虚假解释的显着各向同性和各向异性成像伪影。我们得出结论，远震 P 波走时对于探测上地幔各向异性的 3D 分布是一个有用的观测值，并且应该探索各向异性反演以更好地了解各向同性速度异常的性质，特别是在俯冲环境中。