CSEDI: Collaborative Res.: Toward Mapping 3D Variations in Temperature and Chemical Composition in the Upper Mantle through a Mineral Physics-based Inversion of Seismic Waveforms

这是加州大学伯克利分校的地震学家和耶鲁大学的矿物物理学家之间的一项合作研究，旨在探索直接反演地震长周期波形数据的可行性，以获取上地幔有效温度和主要元素化学成分的三维变化。有效温度将包括温度和含水量的影响，这两个因素很难单独从地震数据中分离出来。含水量可能对流变性有很大影响，因此对地幔的动力学有重大影响。他们将使用矿物物理框架来描述这些不同因素的贡献，并提供相关偏导数的估计。主元素化学的影响可以与水的影响区分开来，因为水对非弹性有很大的影响，而主元素化学则没有。另一方面，与地震速度相比，非弹性对温度的依赖性更强。本研究的核心是一个猜想，该猜想得到了理论考虑的支持，即对物理参数（如成分C和（有效）温度T*）的地震波形进行一步反演，应该比先对速度和Q结构进行反演，然后根据物理参数解释获得的图的标准方法产生更稳定的结果。后者目前受到三维上地幔Q分辨率较差的抑制，这是由于振幅受到很大程度上未建模但重要的聚焦和散射效应的污染。在一步反演中，C和T*的影响在反演矩阵元素中耦合，而在标准方法中，只有振幅取决于非弹性项，而相位和振幅都取决于弹性项，导致推断出的Q分布有很强的偏差。一步法方程的耦合特性，加上振幅对T*的强敏感性（通过非弹性项），应该抵消现有矿物物理偏导数的近似特性和由于聚焦理论处理不足而产生的误差。

Romanowicz Karato This is a collaborative study between seismologists at UC Berkeley and mineral physicists at Yale University, to explore the feasibility of inverting seismic long period waveform data directly for 3D variations in effective temperature and major element chemistry in the upper mantle. Effective temperature will include the effects of temperature and water content, which cannot be easily separated from seismic data alone. Water content is likely to have large effects on rheology and therefore has significant influence on the dynamics of the Earth's mantle. They will use the mineral physics framework to delineate contributions from these various factors and provide estimates of relevant partial derivatives. Effects of major element chemistry can be distinguished from that of water, because water has a large influence on anelasticity whereas major element chemistry does not. On the other hand anelasticity is more strongly dependent on temperature than seismic velocity. At the heart of this study is the conjecture, supported by theoretical considerations, that the one step inversion of seismic waveforms for physical parameters such as composition C and (effective) temperature T*, should yield more stable results than the standard approach of first inverting for velocity and Q structure and then interpreting the obtained maps in terms of physical parameters. The latter is currently inhibited by the poor resolution in 3D upper mantle Q, due to contamination of amplitudes by largely unmodelled, but significant, effects of focusing and scattering. In the one step inversion the effects of C and T* are coupled in the inversion matrix elements, whereas in the standard approach, only the amplitudes depend on anelastic terms, while both phase and amplitudes depend on the elastic ones, leading to strong biases in the distribution of Q inferred. 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 and the errors due to inadequate theoretical treatment of focusing.