Collaborative Research: Developing a Three-Dimensional Seismic Reference Earth Model (REM-3D) in Collaboration with the Community

地球内部的弹性性质(如密度、刚性、可压缩性等)因温度、压力、成分和流量的变化而不同的位置。在20世纪，地球科学家利用地震和爆炸发出的地震波来开发地球特性如何随深度变化的模型。从这些努力中产生的社区参考模型已被证明在地震定位、内部结构成像、了解极端条件下的材料性质以及在粒子物理和天文学等其他领域作为参考是不可或缺的。在过去的三十年里，全球地震学家的更复杂的努力已经产生了几代人的模型，这些模型不仅研究了属性如何随深度变化，而且还研究了其横向变化。然而，尽管这些三维(3D)模型在大尺度上表现出令人信服的相似性，但它们所基于的方法、结构表示和数据集的差异阻碍了3D社区参考模型的创建。研究人员建议通过汇编、协调和分发长周期参考地震数据集来克服这些挑战，他们将根据该数据集构建地球地幔的三维地震参考模型(REM-3D)。作为一个社区参考模型，REM-3D具有完全量化的不确定性和权衡，将促进地球成像研究、地震特征、对深部温度和成分的推断，并将提高对诸如中微子地球科学等新兴科学努力的效用。研究人员将设立社区工作组，在参考模型和数据集开发过程中提供咨询意见，并将组织一次讲习班，以评估进展情况，评价模型和数据集的性能，确定改进途径，并为最大限度地扩大模型在地球深处社区的采用和利用提出战略建议。为此，调查人员征求了来自美国和国际各地的地震学家、矿物物理学家、地球动力学和地球化学家的意见。研究人员提议为地幔开发一个三维地震参考模型(REM-3D)，该模型以剪切波速(Vs)、纵波速度(Vp)、密度(&amp；#961；；)和表示径向各向异性的3个附加参数为参数。将开发两个版本的模型，以明确拟合社区贡献的综合长周期地震数据集，一个版本以球面调和为参数，另一个版本作为与主要地理省份对应的规范剖面。此外，他们将汇编、协调和分发长周期参考地震数据集，包括面波频散测量、长周期绝对体波和差分体波测量以及自由振荡频率/衰减/和分裂。与以前的地球结构参考模型不同，REM-3D将完全量化。研究人员还将创建在线工具，用于模型分布和预测各种地震观测数据，包括完整的波形，以及主要设计用于使矿物物理学家和地球动力学家能够以直接方式对照该参考模型或直接对照参考数据集验证测试模型的工具。最后，研究人员将设立社区工作组并组织讲习班，就模型和数据集的性能提供咨询意见并对其进行评估，确定改进途径，并建议最大限度地扩大模型在地球深处社区的采用和利用的战略。REM-3D将有助于更广泛的科学界：1.地震速度和密度的矿物学和热化学解释；2.查明地幔中的异常/非典型结构；3.全球和区域层析模型的比较；4.地震波形解释，例如确定特定的地震震相；5.对三维地球结构的反演需要一个起始或背景模型；6.利用长周期数据描述震源特征。社区贡献的参考数据集的构建将使识别异常地震波走时、面波频散、正常模式分裂和波形特征成为可能。此外，我们将创建的用于从输入结构预测地震观测值的工具将能够直接评估矿物物理和地球动力学实验和计算预测的潜在速度结构。

Elastic properties of the Earth's interior (e.g. density, rigidity, compressibility, etc.) vary with location due to changes in temperature, pressure, composition, and flow. In the 20th century, Earth scientists have used seismic waves emitted by earthquakes and explosions to develop models of how Earth properties vary with depth. Community reference models that grew out of these efforts have proven indispensable in earthquake location, imaging of interior structure, understanding material properties under extreme conditions, and as a reference in other fields, such as particle physics and astronomy. Over the past three decades, more sophisticated efforts by seismologists across the globe have yielded several generations of models of how properties vary not only with depth, but also laterally. Yet, though these three-dimensional (3D) models exhibit compelling similarities at large scales, differences in the methodology, representation of structure, and dataset upon which they are based, have prevented the creation of 3D community reference models. The investigators propose to overcome these challenges by compiling, reconciling, and distributing a long period reference seismic dataset, from which they will construct a 3D seismic reference model (REM-3D) for the Earth's mantle. As a community reference model and with fully quantified uncertainties and tradeoffs, REM-3D will facilitate Earth imaging studies, earthquake characterization, inferences on temperature and composition in the deep interior, and be of improved utility to emerging scientific endeavors, such as neutrino geoscience. The investigators will set up community working groups that will serve to advise during the process of reference model and dataset development, and will organize a workshop to assess progress, evaluate model and dataset performance, identify avenues for improvement, and recommend strategies for maximizing model adoption in and utility for the deep Earth community. To this end, the investigators have solicited input from seismologists, mineral physicists, geodynamics, and geochemists from around the United States and internationally. The investigators propose to develop a three-dimensional seismic reference model (REM-3D) for the Earth's mantle, parameterized in terms of shear wavespeed (Vs), compressional wavespeed (Vp), density (ρ), and the 3 additional parameters representing radial anisotropy. Two versions of the model will be developed to explicitly fit the comprehensive, community-contributed long period seismic dataset, one parameterized in terms of spherical harmonics, and the other as canonical profiles corresponding to major geographic provinces. Furthermore, they will compile, reconcile, and distribute a long period reference seismic dataset, including surface wave dispersion measurements, long period absolute and differential body wave measurements, and free oscillation frequencies / attenuation / and splitting. Unlike previous reference models of Earth structure, REM-3D will have fully quantified. The investigators will also create online tools for model distribution and for predicting various seismic observables, including full waveforms, as well as tools designed primarily to enable mineral physicists and geodynamicists a straightforward way of (in)validating test models against this reference model or directly against the reference dataset. Finally, the investigators will set up community working groups and organize workshops that will advise on and evaluate model and dataset performance, identify avenues for improvement, and recommend strategies for maximizing model adoption in and utility for the deep Earth community. REM-3D will benefit the broader scientific community by facilitating: 1. Mineralogical and thermo-chemical interpretation of seismic velocities and density; 2. Identification of anomalous / atypical structures in the Earth's mantle; 3. Comparison of global and regional tomographic models; 4. Seismic waveform interpretation, such as the identification of particular seismic phases; 5. Inversion for 3D Earth structure requires a starting or background model; 6. Earthquake source characterization using long period data. The construction of a community-contributed reference dataset will make possible the identification of anomalous seismic wave travel times, surface wave dispersion, normal mode splitting, and waveform features. Furthermore, the tools for predicting seismic observables from input structures that we will create will enable direct evaluation of potential velocity structures predicted by mineral physics and geodynamics experiments and calculations.