Toward Seismic Tomography Based Upon Adjoint Methods

来自全球地震台网的大量高质量数字记录的日益可用性，使得研究地震和地球深部结构的各种新方法成为可能。通过分析成百上千的地震图，通常可以解决数据中的新特征，或者对以前在较小尺度上解决的问题进行更全面的分析。该项目将继续分析加州大学圣地亚哥分校的全球地震数据，以研究各种地球物理问题。这包括：(1)利用反射和转换地震相研究上地幔地震不连续面。解决地幔不连续特性的细节对于地幔组成的建模和理解不连续对地幔对流的影响都是重要的。(2)反演地震破裂成像方法。这些方法有可能提供大地震破裂程度的近实时图像，这将有助于规划救灾行动。(3)利用地震谱分析解决指向性和应力降问题。这将有助于确定大的破坏性地震是否仅仅是小地震的“放大”版本，在这种情况下，通过研究仪器检测到的数量多得多的小地震的记录，可以预测未来大地震的强烈地面运动。(4)小尺度地幔-岩心结构高频波散射研究与模拟。这将提供比其他地震方法更精细的地幔成分变化信息，并将为地幔的地球化学模型提供约束。(5)波形互相关与聚类分析技术在长周期波形中的发展与应用。这为处理目前可用的大量地震数据提供了一种实用的方法，并将改进三维地震速度变化模型。(6)观测和模拟地幔中地震衰减的横向变化，这将为地幔温度和化学提供有价值的约束。该项目通过为研究生和博士后提供资金来支持加州大学圣地亚哥分校的教育项目。这项研究将导致地球结构和地震破裂过程模型的改进，这将对构造学，地球动力学和矿物物理学界感兴趣。研究结果将通过出版物、会议报告以及提供给教育和推广项目的材料广泛传播。

The increasing availability of large numbers of high-quality digital records from the global seismic networks has made possible a variety of new ways to study earthquakes and deep Earth structure. By analyzing hundreds or thousands of seismograms, it is often possible to resolve new features in the data, or to perform more comprehensive analyses of problems that were previously addressed on smaller scales. This project will continue analyses of global seismic data at U.C. San Diego to examine a variety of geophysical issues. These include: (1) Study of seismic discontinuities in the upper mantle using reflected and converted seismic phases. Resolving details of mantle discontinuity properties is important, both for modeling of mantle composition and for understanding the effect that the discontinuities can have on mantle convection. (2) Imaging earthquake rupture using back-projection methods. These methods have the potential to provide near-real-time images of the rupture extent of large earthquakes, which will help in planning disaster relief operations. (3) Analyses of earthquake spectra to resolve directivity and stress drop. This will help determine whether large, damaging earthquakes are simply "scaled up" versions of smaller earthquakes, in which case strong ground motions could be predicted for future large quakes by studying records of the much more numerous smaller earthquakes that are detected instrumentally. (4) Study and modeling of high-frequency waves scattered from small-scale mantle and core structure. This will provide information on compositional variations in the mantle at much finer scales than are possible from other seismic methods and will provide constraints on geochemical models of the mantle. (5) Development and application of waveform cross-correlation and cluster analysis techniques to long-period waveforms. This provides a practical way to process the large volumes of seismic data that are currently available and will lead to improved models of three-dimensional seismic velocity variations. (6) Observing and modeling lateral variations of seismic attenuation in the mantle, which will provide valuable constraints on mantle temperatures and chemistry. This project supports the educational program at U.C. San Diego by providing funds for graduate and postdoctoral students. This research will lead to improved models of Earth structure and earthquake rupture processes, which will be of interest to the tectonics, geodynamics and mineral physics communities. Results will be widely disseminated through publications, conference presentations, and material provided to education and outreach programs.