Broadband Seismological Investigations of Earth Structure and Earthquake Sources

这是一个为期四年的项目，支持圣克鲁斯的加州大学的索恩·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有关地球结构和地震破裂过程的基本问题。 研究的重点是：（1）地震波叠加和偏移用于地幔最下部结构成像，检验后钙钛矿相变发生在D”区顶部附近的假设，并寻找核幔边界以上更深的钙钛矿逆相变的证据，这可以限制CMB边界层中的热梯度;（2）正在对大型数据集进行分析，以区分震源、接收器和深层传播的复杂性，力求更好地了解近源（板）对波形复杂性和剪切波分裂的影响;（3）正在对深源地震的地震图进行叠加和迁移，以制作俯冲带附近上地幔反射率的图像;以及（4）将对沿着苏门答腊-安达曼断裂带和其他斜向俯冲区域的中等规模地震震源特性进行分析，以评估摩擦特性的变化。目前与这项研究有关的进展包括第一次直接确定热通量通过核幔边界的基础上地震和矿物物理学的限制，检测强散射局部补丁在核幔边界，和三维成像的多个地震不连续性在上地幔下汤加。 这项整体研究工作涉及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球表面附近和核幔边界附近的主要边界层相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.