Mantle Discontinuity Structure From 3D ScS Reverberation Mapping

地幔是地球表面薄地壳和深层铁核之间的部分，是驱动表面板块运动的活跃“引擎”。 由于化学变化和温度波动，它在所有长度尺度上都是不均匀的，并不断演变。 地震学为探索地幔提供了一种强有力的手段，而断层扫描图，类似于医学断层扫描，是我们最好的工具。 但层析成像忽略了地幔结构的重要方面，最明显的是局部反射。 该项目提供了一个经典的地幔勘探工具，使用非常低的频率剪切波“反射”通过地幔，作为石油工业风格的“散射波”成像技术的重新制定。 其结果将利用新的地震记录数据集和俯冲带中丰富的地震来绘制地幔中清晰的边界-"反射体"。地幔中的地震反射体是地幔矿物晶体结构变化、成分突变、地幔熔融区域和各向异性组构快速转变（材料性质的方向变化，与灯芯绒织物的纹理不同）的结果。 每一个都是地幔成分、状态（固体、液体或两者的混合）和动力学（它在哪里移动以及移动速度有多快）的重要诊断，它们的地图为断层扫描提供了关键的补充信息。 我们推荐的新方法很好地利用了这些波携带的信息，并承认地幔在所有三个维度上都是复杂多变的。 它将应用于两个独立的数据集，一个是由日本的“Hi-Net”台阵的近500台仪器，日本及其周围的F-net地震台的60多个地震台，以及中国东部，朝鲜和俄罗斯东南部的其他地震台产生的。 这里的目标包括在地幔过渡区（400和700公里深的层），熔融层顶部的过渡区，和中地幔反射可能与过去的俯冲的证据，停滞的太平洋“板”。 研究的第二个地理区域是西南太平洋和珊瑚海。 虽然那里的台站覆盖范围要有限得多，但中深地震活动的丰富性和多个中心足以弥补这一点。 这里的目标与日本相似。 在这两种情况下，一个改进的成像工具和密集的数据相结合，提供了发现反射体没有类似物在文献中的其他地方的可能性。 更广泛的影响的建议是两个研究生的支持和培训，以及这项工作的效用，了解地幔流动，也许水在地幔中的分布。

Earth's mantle, the portion of the planet between the thin surface crust and the deep iron core, is an active "engine" driving movement of the surface plates. Because of chemical variability and temperature fluctuations, it is heterogeneous at all length scales and constantly evolving. Seismology provides a powerful means of exploring the mantle, and tomographic maps, akin to medical cat-scans, are our best tool. But tomography misses important aspects of mantle structure, most notably localized reflectors. This project offers reformulation of a classic mantle exploration tool, using very low frequency shear waves "reverberating" through the mantle, as an oil-industry style "scattered-wave" imaging technique. The result will make use of new seismogram datasets and abundant earthquakes in subduction zones to map out sharp boundaries--"reflectors"--in the mantle. Seismic reflectors in the mantle are the result of changes in crystal structure of mantle minerals, abrupt changes in composition, regions of mantle melting, and rapid transitions in anisotropic fabric (directional variation in material properties, not unlike the grain of corduroy fabric). Each is an important diagnostic of mantle composition, state (solid, liquid or a mix of both) and dynamics (where is it moving and how fast), and maps of them provide critical complimentary information to tomography. The new method we recommend makes good use of the information these waves carry and acknowledges that the mantle is complex and variable in all three dimensions. It will be applied to two separate data sets, one produced by the nearly 500 instruments of the "Hi-Net" array in Japan, the 60-plus seismograph stations of the F-net in and around Japan, and other seismograph stations in eastern China, the Koreas, and southeastern Russia. Targets here include the stagnant Pacific Ocean "slab" in the transition zone of the mantle (the layer between 400 and 700 km depth), evidence of a melt layer atop the transition zone, and mid-mantle reflectors possibly related to past subduction. The second geographic region of study is the SW Pacific and Coral Sea. While station coverage is much more limited there, the abundance and multiple centers of intermediate and deep seismicity adequately compensates. Targets here are similar to Japan. In both cases, the combination of an improved imaging tool and dense data offers the possibility of discovering reflectors without analogs elsewhere in the literature. Broader impacts of the proposal are the support and training of two graduate students, and the utility of this work for understanding mantle flow and perhaps the distribution of water in the mantle.