Characterization of Small-scale Heterogeneity in the Deep Earth

地球深部的三维结构，其尺寸小于100公里，所知甚少。这些小规模的深部构造对了解地球成分和地表构造的历史和未来演化具有重要意义。它们影响地震波的形状和振幅，而地震波的形状和振幅用于预测地震地面运动的大小，以及预测地震和地下核试验的地震特征之间的差异。 这样的小尺度结构不能通过常规地震层析成像，常规地震层析成像用类似于医学CAT扫描的方法处理地震波的行进时间。 相反，该项目采用了一种技术，使用许多紧密间隔的地震仪的地震记录来检索小尺度结构的尺度长度的特征谱。 这种光谱限制了不均匀性的大小、形状和组成。该项目还培训地震数据检索、处理、成像和计算机编程方面的研究生。这些都是资源勘探和受污染地下水补救的重要技能。研究结果将纳入物理科学的本科课程，以加强地球物理研究的学术和工业应用方面的招聘和培训，小规模异质性（100公里）的表征对于了解地球地幔化学的表面取样以及对流和板块构造控制的化学混合的时间历史和性质非常重要。小尺度不均匀性对地震波的方向相关散射会影响粘弹性衰减和各向异性的估计，而粘弹性衰减和各向异性又对估计温度、矿物成分和矿物相很重要。密集地震台站阵列记录的体波振幅和相位相干性将被反演，以反映小尺度非均匀性的统计实现。 这种随机层析成像过程将确定地球小尺度化学和热不均匀性的特征长度尺度和地震速度扰动，这是常规层析成像无法解决的。结果将检验地球动力学模式预测的对流混合的基本假设.

Little is known about three-dimensional structures in the deep earth whose size is less than 100 km. These small-scale deep structures are important to understanding the historical and future evolution of earth's composition and its surface tectonics. They affect the shapes and amplitudes of seismic waves used to forecast the size of earthquake ground motions and to predict the differences between the seismic signatures of earthquakes and underground nuclear tests. Such small-scale structures cannot be imaged by conventiional seismic tomography, which processes travel times of seismic waves with methods similar to medical CAT scanning. Instead, this project employs a technique using seiismic recordings by many, closely spaced, seismometers to retrieve a characterisitic spectrum of scale lengths of small-scale structures. This specturm constrains the sizes, shapes, and composition of the heterogeneities. The project also trains graduate students in seismic data retrieval, processing, imaging, and computer programming. These are skills important in resource exploration and remediation of contaminated groundwater. Results will be incorporated in undergraduate courses in the physical sciences to enhance recruitment and training in both academic and industrial applications of geophysical research.The characterization of small-scale heterogeneity (100 km) is important to understand the surface sampling of Earth's mantle chemistry and the time history and nature of chemical mixing controlled by convection and plate tectonics. Directionally dependent scattering of seismic waves by small-scale heterogeneity can affect estimates of viscoelastic attenuation and anisotropy, which in turn are important for estimating temperature, mineral composition, and mineral phase. Amplitude and phase coherences of body waves recorded by dense arrays of seismic stations will be inverted to image statistical realizations of small-scale heterogeneity. This process of stochastic tomography will determine the characteristic lenth scales and seismic velocity perturbatons of the small-scale chemical and thermal heterogeneity of the earth that cannot be resolved by conventional tomography. The resullts will and test fundamental assumptions of convective miixing predicted from geodynamic models.