CSEDI Collaborative Research: 3D Temperature and Composition Structure of the Upper Mantle Using Seismological and Mineral Physics Constraints

这是加州大学伯克利分校和密歇根大学的地震学家、矿物物理学家和地球动力学家之间的一项合作研究，其目标是将各自领域的观测约束和理论工具联合收割机结合起来，直接从地震波形反演中研究地球上地幔温度和主要元素化学的大尺度三维变化。 本研究的核心是一个猜想，该猜想得到了理论上的支持，即对于成分C和温度T等物理参数的地震波形的一步反演，应该比首先分别反演速度和衰减结构，然后根据物理参数解释所获得的地图的标准方法产生更稳定的结果。后者目前被抑制的三维上地幔衰减，Q，由于污染的振幅很大程度上未建模的，但显着的，聚焦和散射的影响，分辨率差。一步法中方程组的耦合性，以及振幅对T的强烈敏感性，（通过滞弹性项）应抵消现有矿物物理偏导数的近似特征以及由于聚焦的理论处理不充分而引起的误差。1）利用最近的上地幔弥散和衰减的实验约束，反演全球长周期地震波形的T和径向各向异性; 2）从（1）中获得的模型开始，他们将测试其反演成分横向变化（以玄武岩消耗表示）的能力。 关于C的偏导数及其不确定性将由团队中的矿物物理学家使用自洽的形式主义进行评估和提供，该形式主义结合了实验和第一原理计算的结果。 在这一点上，他们还将纳入地球动力学约束，以提高反演的成分分量的分辨率。 在反演过程中的每一步都需要迭代过程，因为各种偏导数对温度的依赖性，由于存在强衰减和相位变化，以及在估计这些偏导数时存在很大的不确定性。 该项目包括资助两名学生和一名博士后，他们将接受跨学科方法的培训。

This is a collaborative study between seismologists, mineral physicists and geodynamicists at UC Berkeley and at the Univ. of Michigan, the goal of which is to combine observational constraints and theoretical tools from their respectivefields and investigate large scale 3D variations in temperature and major element chemistry in the earth's upper mantle directly from the inversion of seismic waveforms. At the heart of this proposed study is the conjecture, supported by theoreticalconsiderations, that the one step inversion of seismic waveforms for physical parameters such as composition C and temperature T, should yield more stable results than the standard approach of first inverting for velocity and attenuation structure separately, and then interpreting the obtained maps in terms of physical parameters. The latter is currently inhibited by the poor resolution in 3D upper mantle attenuation, Q, due to contamination of amplitudes by largely unmodelled, butsignificant, effects of focusing and scattering. The coupled character of the equations in the one step approach, combined with the strong sensitivity of amplitudes to T (through anelastic terms) should offset the approximate character of the available mineral physics partial derivatives as well as the errors due to inadequate theoretical treatment of focusing.The investigators will: 1) invert a global collection of long period seismic waveforms for T and radial anisotropy, using recentexperimental contraints on dispersion and attenuation in the uppermost mantle; 2) starting from the model obtained in (1), they will test their ability to invert for lateral variations in composition (as expressed in terms of basalt depletion). Partial derivatives with respect to C and their uncertainties will be evaluated and provided by the mineral physicists in the team using a self-consistent formalism which incorporates results from experiments and first principles calculations. At this point, they will also incorporate geodynamical constraints to increase resolution of the compositional component of the inversion. An iterative procedure will be required at each step in the inversion process, because of the dependence of various partial derivatives on temperature, due to the presence of strong attenuation and phase changes, as well as the large uncertainties remaining in the estimation of these partial derivatives. The project includes funding for two students and a post doc, who will be trained using a cross-disciplinary approach.