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增多使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记录，通常有可能解决数据中的新特征，或者对以前在较小规模上解决的问题进行更全面的分析。该项目将继续在加州大学圣地亚哥分校对全球地震数据进行分析，以检查各种地球物理问题。包括：(1)利用反射震相和转换震相研究上地幔的地震不连续性。解决地幔不连续性质的细节对于模拟地幔成分和理解不连续对地幔对流的影响都是重要的。(2)利用反投影法对地震破裂进行成像。这些方法有可能提供大地震破裂程度的近乎实时的图像，这将有助于规划救灾行动。(3)解决方向性和应力降问题的地震谱分析。这将有助于确定破坏性的大地震是否是较小地震的简单“放大”版本，在这种情况下，可以通过研究仪器检测到的更多较小地震的记录来预测未来大地震的强烈地面运动。(4)小尺度地幔和核结构散射高频波的研究与模拟。这将在比其他地震方法可能的更精细的尺度上提供关于地幔成分变化的信息，并将对地幔的地球化学模型提供约束。(5)波形互相关和聚类分析技术在长周期波形中的开发和应用。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，并将导致改进的三维地震速度变化模型。(6)观测和模拟地幔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。这项研究将改进地球结构和地震破裂过程的模型，这将对构造学、地球动力学和矿物物理学产生兴趣。结果将通过出版物、会议报告以及提供给教育和外展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.