Broadband Seismological Investigations of Earth Structure and Earthquake Sources

这是一个为期四年的项目，支持加州大学圣克鲁斯分校的索恩·雷进行的地震学研究计划。研究工作的统一主题是使用宽带数字地震数据来解决关于地球结构和地震破裂过程的基本问题。研究集中在以下几个方面：(1)地震波叠加和偏移用于成像最低地幔结构，检验后钙钛矿相变发生在D“区顶部附近的假设，并寻找核幔边界上方钙钛矿发生更深层次逆变的证据，以约束CMB边界层中的温度梯度；(2)正在对大数据集进行分析，以分离震源、接收器和深层传播的复杂性，试图更好地了解近源(板条)对波形复杂性和横波分裂的贡献；(3)正在对深源地震的地震记录进行叠加和偏移，以形成俯冲带附近的上地幔反射率图像；(4)将分析苏门答腊岛-安达曼断裂带和其他斜向俯冲地区的中等规模震源性质，以评估摩擦性质的变化。目前与这项研究相关的进展包括：根据地震学和矿物物理约束首次直接确定通过核幔边界的热通量，探测核幔边界局部斑块中的强散射，以及对汤加之下上地幔的多个地震不连续面进行三维成像。这一总体研究工作涉及到PI和两名研究生，并与其他机构的同事继续合作。我们预计，在表征与地表附近和核幔边界附近的地球主要边界层有关的动力学过程方面将继续取得进展。

This is a four-year project supporting the seismological research program conducted by Thorne Lay at the University of California, Santa Cruz. The unifying theme of the research effort is the use of broadband digital seismic data to address fundamental questions about earth structure and earthquake rupture processes. The research is focused on the following areas: (1) seismic wave stacking and migration is being used to image lowermost mantle structure, testing the hypothesis that the post-perovskite phase transition occurs near the top of the D" region, and seeking evidence of a deeper reverse transformation to perovskite above the core-mantle boundary that can constrain thermal gradients in the CMB boundary layer; (2) analysis of large data sets to separate source, receiver and deep propagation complexity is being pursued, seeking to better understand near-source (slab) contributions to waveform complexity and shear wave splitting; (3) stacking and migration of seismograms from deep focus earthquakes is being performed to develop images of upper mantle reflectivity in the vicinity of subduction zones; and (4) analysis of moderate-size earthquake source properties along the Sumatra-Andaman rupture zone and other regions of oblique subduction will be conducted to assess variations in frictional properties. Current advances associated with this research include the first direct determination of heat flux through the core-mantle boundary based on seismological and mineral physics constraints, detection of strong scattering in localized patches at the core-mantle boundary, and three-dimensional imaging of multiple seismic discontinuities in the upper mantle beneath Tonga. This overall research effort involves the PI and two graduate students, with continuing collaborations with colleagues at other institutions. We anticipate continued progress in characterizing dynamical processes associated with the Earth's major boundary layers near the surface and near the core-mantle boundary.