| 英文摘要: | 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. |