CSEDI: Testing Resolution of Deep Earth Seismic Structure Under the Pacific Using Geodynamic Models

地球下地幔中的温度和成分结构为地球的化学分化和动力学提供了重要线索，特别是关于热量如何从地核传输到地幔的线索。在层析成像研究中，太平洋下地幔中出现了一种大范围、慢地震速度的异常。这一异常的热结构和成分结构仍然知之甚少。这项研究结合了地震学和地球动力学的努力，以调查了解这一深部地震异常结构的重要问题。我们将使用热化学对流模型来开发候选地幔结构，这些结构可以通过使用真实地震和接收器几何形状的地震波传播模拟来研究。这将使我们能够识别对候选地幔结构之间的差异敏感的地震相，并调查有限频率理论是否为这些结构的几何形状提供了超出射线理论的额外洞察力，以及三维衰减结构如何影响我们对层析图像的解释。这项研究解决了在热化学羽流模式中通过地震波传播了解太平洋下地幔的热和化学结构的几个具有挑战性的问题，重点是：(1)地震波对下地幔温度和成分的三维变化的敏感性；(2)温度和成分异常之间转换的不同尺度参数对地震波速和滞弹性衰减的影响；(3)当前地震数据(包括US阵数据)和地震层析成像方法(射线理论和有限频率理论)在成像太平洋下地幔结构和区分不同羽流模式方面的分辨率限制，这些模式包括：1)标准的全地幔等化学模型，在中太平洋下方有一簇窄的羽流；2)中太平洋下的热化学‘穹顶’(或堆)，从界面产生羽流；以及3)孤立、迟滞的下地幔和来自上地幔的热柱。地震方面的挑战，包括量化滞弹性衰减和聚焦-散焦效应的相对重要性，以及弹性和滞弹性结构之间的权衡，将通过在各种热化学羽流模型中的全波传播模拟来解决。

The temperature and composition structure in the Earth's lower mantle provides important clues to the chemical differentiation and dynamics of the planet, especially in regard to how heat is transported from the core to the mantle. A large-scale, slow seismic-velocity anomaly in the lower mantle beneath the Pacific has been imaged in tomographic studies. The thermal and compositional structure of this anomaly remains poorly understood. This research integrates seismological and geodynamical efforts to investigate important issues in understanding the structure of this deep seismic anomaly. We will use thermochemical convection models to develop candidate mantle structures that can be investigated with seismic wave propagation simulations using realistic earthquake and receiver geometries. This will allow us to identify seismic phases that are sensitive to differences between the candidate mantle structures and to investigate whether finite-frequency theory provides additional insight beyond ray-theory for the geometry of these structures, and how 3-D attenuation structure affects our interpretation of tomographic images. This research addresses several challenging problems in understanding the thermal and chemical structure in the Pacific lower mantle through seismic wave propagation in thermo-chemical plume models with focuses on (1) the sensitivity of seismic waves to 3-D variations in temperature and compositional in the lower mantle; (2) the effects of different scaling parameters in translation between temperature and compositional anomalies to seismic wave speed and anelastic attenuation and (3) the resolution limits of current seismic data (including USArray data) and seismic tomographic methods (ray theory and finite-frequency theory) in imaging the structure of the Pacific lower mantle and distinguishing between different plume models including 1) the 'standard' isochemical whole mantle model, with a cluster of narrow plumes under the central Pacific, 2) a thermochemical 'dome' (or pile) under the central Pacific with plumes arising from the interface, and 3) an isolated, sluggish lower mantle with upper mantle derived plumes. Seismological challenges, including quantifying the relative importance of anelastic attenuation and focusing-defocusing effects, and tradeoffs between elastic and anelastic structure will be addressed with full wave propagation simulations in a variety of thermochemical plume models.