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

地球下地幔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。 一个大规模的，缓慢的地震速度异常下地幔在太平洋已成像层析成像研究。 这种异常的热结构和成分结构仍然知之甚少。这项研究整合了地震学和地球动力学的努力，以调查了解这种深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，可以使用真实的地震和接收器几何形状与地震波传播模拟进行研究。 这将使我们能够识别地震相，是敏感的候选地幔结构之间的差异，并调查有限频率理论是否提供了额外的洞察力超越射线理论的几何结构，以及如何3-D衰减结构影响我们的层析成像图像的解释。本研究旨在通过地震波在热化学柱模型中的传播来了解太平洋下地幔的热化学结构，主要研究了以下几个具有挑战性的问题：（1）地震波对下地幔温度和成分三维变化的敏感性;（2）温度和成分异常之间转换的不同标度参数对地震波速度和滞弹性衰减的影响;现有地震资料的分辨率极限（包括USAray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地幔柱模型中的应用，包括1）“标准”等化学全地幔模型，在中太平洋下有一簇狭窄的地幔柱，（2）中太平洋下的热化学“穹丘”（或堆），地幔柱从界面上产生;（3）孤立的、缓慢的下地幔，上地幔源地幔柱。 地震学的挑战，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，将在各种热化学羽流模型中进行全波传播模拟。

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.